Millennial-scale climatic and cultural impacts on vegetation and fire at the southern edge of the Rocky Mountains, USA
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1. Introduction
The societal and ecological importance of mountain ecosystems extends far beyond their regional footprint, especially in arid and semiarid regions of the world. In the southwestern United States (the Southwest), snowmelt from mountain watersheds is the dominant source of water that sustains irrigated agriculture, hydroelectric power, and municipal drinking water for millions of people (Cayan, 1996; Ellis and Sauter, 2017; Woodhouse et al., 2012). Upland ecosystems, including shrublands, woodlands, and coniferous forests have complex interactions with water supplies, providing critical watershed stability that enhances water quality, and affects water yield (Goeking and Tarboton, 2020; Hampton et al., 2022; Penn et al., 2020; Sexstone et al., 2018). Thus, rapid changes in the extent of woody vegetation resulting from wildfire and drought-related mortality compromises water quality and increases the uncertainty in water-yield projections (Dunbar et al., 2022; Penn et al., 2020; Williams et al., 2022b). Mountain ecosystems are also attractive, well-used destinations for recreation, in part due to their higher humidity, productivity, and biodiversity than surrounding lowlands (Sherrouse et al., 2017). Complex topography and elevational gradients produce diverse climatic conditions in mountain landscapes that have sustained biodiversity over millennia of climate change by providing refugia from harsh climatic conditions, which is crucial in a warming climate (Coblentz and Riitters, 2004; Dobrowski, 2011; Gavin et al., 2014). For example, in the Southwest, upland ecosystems range from grasslands and shrublands at lower elevations, to coniferous and deciduous woodlands, dry coniferous forests, subalpine forests, and at the highest elevations, alpine communities. Given their broad societal importance and ecological diversity, maintaining mountain forests and woodlands is a critical task for land managers as climate changes and human populations increase.
Mountain ecosystems in the Southwest are threatened by climatic and culturally driven changes. For example, a warming climate can cause upward displacement of regional vegetation belts, especially at lower treeline where water is limiting, as woodlands, shrublands, or grasslands supplant forests due to increasing fire severity, drought-related mortality and conifer regeneration failure (Allen, 2022; Allen and Breshears, 1998; Breshears et al., 2005; Coop et al., 2020). Land-use changes associated with Spanish and American colonialism after ca. 1600 CE, including the introduction of livestock grazing and fire suppression, altered fuel structure in montane forests, reduced fire frequencies, and contributed to large, intense wildfires during recent decades (Allen et al., 2002; McClure et al., 2024; Swetnam et al., 2016). Climatic conditions that affect fuel availability and aridity are also important determinants of area burned (Henne and Hawbaker, 2023; Margolis et al., 2017; Swetnam and Betancourt, 1990; Williams et al., 2015). Warm, dry conditions during recent decades contributed not only to increases in area burned, but also to drought-related mortality (e.g., bark beetle outbreaks) and regeneration failure following disturbance in woodlands, montane forests, and subalpine forests (Abatzoglou and Williams, 2016; Allen 2014; Haffey et al., 2018; Higuera and Abatzoglou, 2021; van Mantgem et al., 2009; Williams et al., 2013). However, future vegetation changes will be constrained not only by cultural and climatic drivers, but also by current species distributions, standing biomass, soil properties and other ecological properties that were shaped by long-term interactions among climate, disturbance, and human impacts. Therefore, developing long-term management strategies for mountain ecosystems requires understanding the dominant factors that drove past changes.
Forest dynamics in the Southwest are documented on seasonal to annual scales by a dense network of tree-ring archives that provide climate reconstructions for the last 1200+ years and fire histories for the last ca. 500 years (Margolis et al., 2022; Williams et al., 2022a). These data provide critical context for ongoing environmental changes. For example, the period 2000 – 2021 CE was drier than any similar period since 800 CE in the Southwest (Williams et al., 2022a). In contrast, precolonial fire frequencies and area burned in the Southwest far exceeded recent fire activity, which highlights the importance of human impacts on long-term forest dynamics (McClure et al., 2024; Swetnam et al., 2016). However, important gaps remain in long-term understanding of vegetation dynamics in the Southwest. Regional tree-ring archives fade prior to ca. 1500 CE, are primarily available from montane and submontane forests typified by low-severity fire regimes and fire-tolerant trees (e.g., Pinus ponderosa, Pseudotsuga menziesii), and therefore, provide less information about lower-elevation woodlands and upper-elevation subalpine forests.
Sedimentary pollen and charcoal records from subalpine lakes help fill this gap in the Southwest. Pollen data record the upslope expansion of subalpine forests as the climate warmed during the Late Glacial-Holocene transition and document the establishment of subalpine forests during the Holocene (Anderson et al., 2021, 2008b; Briles et al., 2012). Pollen data also demonstrate long-term linkages among forest dynamics, synoptic climate, and precipitation seasonality (Anderson et al., 2015; Jiménez-Moreno et al., 2008). Fire-history reconstructions developed from macroscopic (i.e., > 125 µm) sedimentary charcoal document the recurrence of local fires in subalpine forests during the Holocene. Whereas networks of macroscopic-charcoal-inferred fire reconstructions provide some understanding of millennial-scale, regional trends in fire activity (Anderson et al., 2008a; Calder et al., 2015; Marlon et al., 2012), composite macroscopic charcoal records rely mainly on high-elevation, subalpine records and are not necessarily indicative of fire activity in lower elevation, dry coniferous forests and woodlands that occupy more area and burn more frequently. Therefore, important questions remain about the long-term dynamics of mountain vegetation in the Southwest, especially for periods older than the tree-ring record, which include warmer intervals and periods with rapid warming that affected fire activity and drove major vegetational change (Anderson et al., 2008a, 2008b; Briles et al., 2012; Calder et al., 2015). Furthermore, although tree-ring records document fire regimes back into the late pre-colonial Puebloan era (ca. 1300 – 1600 CE) and include the subsequent dramatic changes resulting from Spanish and Euro-American colonization in northern New Mexico (Liebmann et al., 2016; McClure et al., 2024; Swetnam et al., 2016), interactions among humans, regional fire activity, and upland forests and woodlands before and during Ancestral Puebloan population expansion (ca. 500 – 1300 CE) are less well understood (D’Andrea et al., 2023; Kelly et al., 2025; Kohler, 1992; Kohler and Reese, 2014).
In this paper we present a new multiproxy, paleoecological record from Santa Fe Lake, New Mexico (NM), a subalpine lake at the southern edge of the Rocky Mountains in the Sangre de Cristo Mountains. The surrounding region has experienced intense droughts and exceptionally large and severe wildfires during recent decades that are contributing to the loss of mountain forests and woodlands (Allen, 2014; Guiterman et al., 2022; Rodman et al., 2020). The site and region also have long-term societal importance. Indigenous farming communities have inhabited the surrounding region for centuries (e.g., Tesuque Pueblo since ca. 1200 CE; Snead, 2008), and Santa Fe Lake forms the headwaters of the Santa Fe, NM municipal water supply and the historical source of irrigation water, the Santa Fe River (Margolis et al., 2013). We use pollen and microscopic charcoal to reconstruct the development of forests and regional burning during the Holocene. In contrast to macroscopic charcoal influx peaks, which are used to infer local fire frequencies, trends in microscopic charcoal influx reflect regional burning (i.e., 20 ‒ 100 km) and thus can be indicative of fire activity in lower-elevation woodlands and forests (Clark and Royall, 1995; Conedera et al., 2009; Tinner et al., 1998). We address the development of elevational vegetation belts by differentiating pollen types that are commonly grouped in records from the Rocky Mountains (e.g., Pinus edulis-type, Pinus ponderosa, Pinus aristata) but provide distinct ecological information. We discuss human impacts on regional fire regimes using microscopic charcoal as a proxy for regional fire and Zea mays pollen as an indicator of land-use intensification. Sedimentary geochemical data provide supporting information on glacial activity and erosion in the watershed. We place these results in the context of other paleoecological, paleoclimatic, and archaeological reconstructions from the Southern Rocky Mountains, and the Southwest, which here includes New Mexico, Arizona, Colorado, and Utah. Our results provide a long-term perspective on interactions among climate change, vegetation, fire activity, and society, that is important for understanding mountain forests in a region with rapid and ongoing environmental change.
2. Regional setting.
Santa Fe Lake (35.79°N, 105.78°W, 3532 m a.s.l) is a small (1.4 ha), subalpine lake in the Sangre de Cristo Mountains of the Southern Rocky Mountains (Fig. 1). The southernmost natural lake in the Rocky Mountains, Santa Fe Lake forms the headwaters of the Santa Fe River watershed, which has been closed to the public since 1932 as a measure to protect the municipal water supply of the city of Santa Fe, NM (Margolis et al., 2013). Access to the lake is controlled by the USDA Forest Service as part of Santa Fe National Forest. Santa Fe Lake was glacially formed during the Wisconsin glaciation (Marcott et al., 2019). A small, forested moraine borders the lake to the south and east and a steep slope of granite scree to the north and west (Fig. 1). A small outlet stream feeds wetlands downslope and forms the headwaters of the Santa Fe River.
The climate is highly seasonal, with cold winters and warm summers. Mean temperature is -5.8° C in January, the coldest month, and 10.8° C in July, the warmest month (1991 – 2020 normal; Thornton et al., 2022). Warming during recent decades, which contributed to an intense drought in the Southwest (Williams et al., 2022a; Woodhouse et al., 2016), is evident at Santa Fe Lake where mean annual temperature increased from 1.4° C in 1981 – 2010 to 2.6° C in 1991 – 2020, with warming during all seasons. Mean annual precipitation (1991 – 2020 normal) is 729 mm and has a bimodal distribution. July and August receive the most precipitation due to the North American Monsoon, followed by March, which is the snowiest month (Thornton et al., 2022).
Dense forests dominated by Picea engelmannii (Engelmann spruce) with occasional Abies lasiocarpa (subalpine fir) surround Santa Fe Lake but are interrupted by a steep scree slope. These subalpine trees extend up to the local timberline (~3700 m a.s.l.) where Pinus aristata (Rocky Mountain bristlecone pine) also grows. Alpine tundra forms above timberline with low-growing shrubs and herbs including Artemisia scopulorum and Salix spp. Mixed coniferous forests including Pseudotsuga menziesii (Douglas-fir), Abies concolor (white fir), Populus tremuloides (quaking aspen), Pinus strobiformis (southwestern white pine), and Pinus ponderosa (ponderosa pine) grow below 3100 m a.s.l., with the proportion of P. ponderosa increasing below 2400 m a.s.l. where it can form pure stands and grow with shrubs including Quercus gambelii, Ceanothus fendleri, and Cercocarpus montanus. Pinus edulis (pinyon pine) and Juniperus monosperma (one-seed juniper) increase below 2100 m a.s.l. and form extensive woodlands regionally across widespread plateaus. Landcover is increasingly open below 1900 m a.s.l. where shrublands and grasslands are prevalent (Fig. 1; Larson et al., 2014).
3. Materials and methods
Overlapping sediment cores were taken in September 2020 in the deepest part of Santa Fe Lake in 5.4 m of water from a coring platform with a Livingstone square-rod piston corer, five cm in diameter, in one-m sections. Coring stopped in a sandy layer. Overlapping drives were visually correlated using stratigraphic characteristics to produce a 510 cm, contiguous sampling profile. The upper 78 cm of sediment, including the sediment-water interface were collected through ice in April, 2022 with a freeze-corer containing dry ice and alcohol (Wright, 1991). We were unable to visually correlate the surface sediments with the long core and therefore produced a second chronology for the uppermost sediments.
Cores were split and scanned for elemental composition and magnetic susceptibility at the U.S. Geological Survey (USGS) Florence Bascom Science Center, Reston, VA, with a GeoTek XRF scanner at a resolution of 0.5 cm. We present elemental intensities as a proxy for clastic inputs, erosion into Santa Fe Lake, and aquatic productivity. Specifically, we focus on titanium (Ti), potassium (K), iron (Fe), and silicon (Si). Preliminary investigation demonstrated that these elements are strongly correlated with other elements typically associated with detrital sediment delivery into mountain catchments (e.g., Al, Zr; Arnaud et al., 2016; Davies et al., 2015; Doyen et al., 2016). We converted raw XRF counts to centered natural log ratios (clr) to place the measurements on a constant scale and to correct for physical changes in the sediment and constant-sum effects (Dunlea et al., 2020; Weltje and Tjallingii, 2008). We present Ti as an elemental intensity because it is absent from large sections of the core but provides a robust indicator of terrigenous inputs that are unaffected by biological processes (Davies et al., 2015). Because sedimentary abundance of Si relates to both terrigenous inputs and lacustrine productivity, we included the ratio of Si/K to standardize for terrigenous inputs.
We selected 30, one-cm thick, bulk sediment samples from the surface core for 210Pb dating. Alpha decays were counted at the USGS Coastal and Marine Science Center in Saint Petersburg, FL. We isolated one terrestrial macrofossil from the surface core and 23 terrestrial macrofossils from the long core for AMS 14C dating at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS; Table 1). Macrofossils were picked directly from the split cores where evident or sieved from one-cm increments of sediment. However, we did not undertake a systematic analysis of macrofossils. We developed a Bayesian age-depth model for the surface core with the rplum package (Aquino-López et al., 2018) and the long core with the rbacon package (Blaauw et al., 2024; Blaauw and Christen, 2011) in R (version 3.3.1). Our age-depth model for the 79-cm surface core combines 210Pb counts with one radiocarbon age (Fig. S1; Table S1). Radiocarbon ages from the surface and long cores were converted to calibrated years before 1950 CE (cal yr BP) using the IntCal20 calibration curve (Table 1; Reimer et al., 2020). Rbacon and rplum account for the 2σ errors of calibrated 14C dates and the shape of the age-depth model responds to prior knowledge of sedimentation rates.
Table 1.
Radiocarbon dates and calibrated ages for Santa Fe Lake. Ages not included in final age-depth model are denoted with a *. The age from the surface core is denoted with an (s) and has a separate depth scale (Fig. S1). The modeled age indicates the mean age for each depth from the Bacon model. Single needles were dated for each depth listed.We selected 159 samples for pollen analysis at regular intervals from the core, using 1 cm3 of sediment (sample thickness = 1 cm). Processing followed standard methods for sediment samples including digestion with hydrochloric acid, potassium hydroxide, hydrofluoric acid, and acetolysis (Moore et al., 1991). The samples were sieved through a 147 μm mesh size. Microscopic inspection of the >147 μm fraction of all samples showed that the chosen mesh size was suitable for the separation of all bisaccate pollen types from coarser material. Lycopodium tablets (Batch 710961) were added to calculate pollen concentrations (grains cm-3), pollen influx (grains cm-2 year-1), microscopic charcoal concentrations (particles cm-3), and microscopic charcoal influx (particles cm-2 year-1; Stockmarr, 1971). Pollen identification and nomenclature followed pollen keys (Beug, 2004; Hansen and Cushing, 1973; Kapp et al., 2000; McAndrews et al., 1973), the PalDat online database (PalDat, 2023), and the reference collection of the USGS Geosciences and Environmental Change Science Center. Stomate identification followed MacDonald (2002). We counted a minimum of 300, and an average of 645, terrestrial pollen grains per sample. Pollen percentages for trees, shrubs, and upland herbs were calculated using the terrestrial pollen sum. Percentages of indeterminant pollen, aquatics, and spores used the sum of all pollen and spores. We subdivided the pollen diagrams into local pollen assemblage zones (LPAZ) using optimal partitioning with minimal sum-of-squares and a broken stick model (Bennett, 1996; Birks and Gordon, 1985). To help interpret a period with an anomalous abundance of degraded pollen, Polypodiaceae spores, and Tubiflorae pollen, we calculated Pearson’s correlation coefficient between these grains that may indicate local soil erosion, and Artemisia, a well-dispersed pollen type with a regional source area for pollen samples from 6000 – 3000 cal yr BP. We counted microscopic charcoal particles longer than 10 µm on pollen slides to infer regional burning (Finsinger and Tinner, 2005; Tinner and Hu, 2003). To improve comparison of charcoal data to other proxies, we first rescaled charcoal influx using a minimax transformation, then applied a Box-Cox transformation, and rescaled the values as z-scores (Power et al., 2008).
Pinus pollen is the most abundant taxonomic group in the Santa Fe Lake pollen record, as is common in subalpine lakes of western North America (Anderson et al., 2008b; Minckley et al., 2008). However, separate Pinus species occupy differing portions of the topographic and ecological breadth of forest and woodland communities in the Southern Rocky Mountains and the Southwest. For example, P. edulis is abundant in lower-elevation plateau woodlands, P. ponderosa dominates submontane forests, P. strobiformis is present in montane forests, and P. aristata inhabits treeline near Santa Fe Lake. Therefore, distinguishing among Pinus pollen types provides ecological information that is often overlooked in existing pollen records from the region. We grouped Pinus pollen types into Pinus subgenus Haploxylon and Pinus subgenus Diploxylon (e.g., Kapp et al., 2000). Pinus subgenus Haploxylon is characterized by the presence of verrucae on the distal surface of the pollen grains, whereas verrucae are absent in Pinus subgenus Diploxylon. We further separated Pinus subgenus Haploxylon into P. edulis-t. (t. = type), P. aristata, and P. flexilis-t., and separated Pinus subgenus Diploxylon into P. ponderosa and P. contorta. when possible (Hansen and Cushing, 1973). To avoid overinterpreting trace pollen abundances by taxa that are massive pollen producers and subject to long-distance transport, our pollen diagrams present only Pinus types with samples that exceed 2% of the pollen sum (van der Knaap et al., 2005). Thus, we combined P. flexilis-t. with Pinus subgenus Haploxylon and P. contorta. with Pinus subgenus Diploxylon. However, all differentiation is included in the accompanying data release (Henne et al., 2025). Pinus pollen that was indistinguishable between Pinus subgenus Haploxylon and Pinus subgenus Diploxylon were tallied as Pinus undifferentiated.
4. Results and Interpretation
4.1. Chronology and sediment geochemistry.
Our age-depth model for the surface core indicates that the upper 79 cm spans 350 – -71 cal yr BP (1600 – 2021 cal yr CE; Fig. S1; Table S1). The age-depth model for our 510-cm long core uses 21 of 24 14C dates to produce a continuous chronology spanning 14,600 – 300 cal yr BP (Fig. 2; Table 1). Thus, the two cores have overlapping age ranges. Attempts to isolate terrestrial macrofossils for dating were unsuccessful below 491 cm, where we identified an Abies needle (Table 1). Therefore, chronological uncertainty increases before 13,700 cal yr BP. Our age-depth model suggests the sediments accumulated slowly from 491 – 313 cm (13,700 – 5100 cal yr BP; mean accumulation rate = 48 years cm-1; Fig. 2). Sediment stratigraphy (i.e., light colored bands), overlapping radiocarbon dates, geochemical data indicating abundant terrigenous inputs (i.e., peaks in elemental intensities and magnetic susceptibility), a high proportion of degraded pollen grains, and an overrepresentation of Polypodiaceae spores (see detailed description below) together indicate rapid erosional inputs from 313 – 290 cm (Fig. 2). Therefore, we assumed abrupt accumulation during this interval using the “slump” function in rbacon (Blaauw et al., 2024). The age-depth model assigns an age range of 4971 – 5281 cal yr BP with a mean modeled age of 5100 cal yr BP to the slump. Sediment accumulation returns to slower rates after 290 cm; the mean accumulation rate = 48 yr cm-1 from 290 – 265 cm (5100 – 3900 cal yr BP). Sedimentation increases after 265 cm, with a mean accumulation rate of 21 yr cm-1 from 265 – 156 cm (3900 – 1600 cal yr BP).
Our age-depth model does not pass through three radiocarbon dates from 156 – 124 cm that are older than dates obtained from underlying sediments. Whereas the rejected dates span the range 3437 – 2867 cal yr BP, a date obtained from a Picea cf. engelmannii needle at 178 cm has a calibrated range of 1999 – 1875 cal yr BP (Table 1). There is no obvious reason to reject the three dates due to material dated; two dates are from spruce needles, and one from a small woody twig. Furthermore, there are no indicators of exceptional erosion from the XRF data that may indicate terrigenous inputs from the watershed. However, the rejected dates come from separate, parallel cores and are of similar age, indicating that older macrofossils are not limited to a single core, which eliminates contamination during coring. Preliminary age-depth models that included sediments from 156 – 124 cm resulted in anomalous increases in pollen and charcoal influx that are inconsistent with changes in sedimentary concentrations of these particles. Therefore, we conclude that older sediments were redeposited into the deepest part of the lake from 156 – 124 cm and treat these sediments as a slump at ca. 1600 cal yr BP in our final age model (Fig. 2). It is possible that an earthquake caused sediment redeposition. For example, the timing of the slump in our age-depth model overlaps with radiocarbon-dated seismic activity in the Pajarito fault system of the Rio Grande rift (Crawford et al., 2025). Older, redeposited sediments may extend beyond 156 – 124 cm, but we lack evidence to remove a broader range of depths from our model. Four radiocarbon dates above the slump indicate that sedimentation increased to an average of 15 yr cm-1.
Basal sediments at Santa Fe Lake are sandy clays that transition into banded gyttja above 496 cm (ca. 13,900 cal yr BP). Elemental indicators for detrital inputs that indicate glacial activity or erosion, including Ti, K, and Fe, are abundant in the basal sediments but decline until about 13,300 cal yr BP (Fig. 3). Si follows a similar trend but increases relative to the other detrital elements about 13,300 cal yr BP, possibly indicating an increase in aquatic productivity as detrital inputs declined. Peaks in Ti, K, Fe, and magnetic susceptibility about 13,100 cal yr BP and 12,200 cal yr BP reflect a resurgence of detrital inputs into Santa Fe Lake. Between 11,500 cal yr BP and 9000 cal yr BP, Ti, K, Fe, and magnetic susceptibility values are low, suggesting low detrital inputs from the watershed. Ti intensities are 0 throughout this period, and the sediment is uniform dark gyttja. In contrast, Si and Si/K values are high, which may indicate low turbidity and high aquatic productivity. Erosion indicators including K, Fe, and Ti increase modestly after 9000 cal yr BP, but return to low values from 7600 – 6300 cal yr BP. After 6300 cal yr BP erosion indicators increase. A peak in K, Fe, Si, Ti, and magnetic susceptibility occurs from 315 – 290 cm (ca. 5100 cal yr BP), which suggests major influx of erosional inputs to Santa Fe Lake (Figs. 2, 3). Ti, K, and magnetic susceptibility decline after the erosion event. Fe declines more gradually, but is also generally low after 4000 cal yr BP. Si is more variable, with low Si/K values about 3700, 2700, and 2300 cal yr BP.
4.2. Pollen and vegetation history.
Pollen percentages, concentrations, and influx have similar patterns and are significantly correlated indicating that percentages generally are not affected by calculation effects (Fig. 4). However, high pollen concentrations and influx before 13,900 cal yr BP may mean that our age-depth model underestimates sediment accumulation rates below our oldest radiocarbon date at 491 cm (Fig. 2; Table 1). Very low pollen concentrations and influx ca. 12,200 cal yr BP coincide with geochemical erosion indicators (peaks in magnetic susceptibility and Ti). Pollen influx increases after 4000 cal yr BP and again after 2000 cal yr BP when sedimentation rates increase in our age-depth model (Fig. 4). Whereas four radiocarbon dates in the upper 100 cm document an increase in sedimentation, the timing and rate of this change are affected by uncertainty related to the three rejected radiocarbon dates and our inclusion of a slump in the age-depth model (Figs. 2, 4; Table 1). Nonetheless, a modest increase in pollen concentrations even as sedimentation increases supports our interpretation of increasing pollen influx. Higher pollen influx in the last 4000 years may indicate an increase in biomass and pollen production near Santa Fe Lake and the surrounding region (Knight et al., 2021; Seppä et al., 2009).
The oldest sediments at Santa Fe Lake record the Late Glacial period before 13,800 cal yr BP (Fig. 5; Zone SF1). Low tree pollen and abundant shrub pollen percentages suggest alpine tundra or steppe, dominated by low-growing shrubs and herbs grew near Santa Fe Lake. The sparse plant cover included Selaginella (club moss), a plant typical of dry, rocky or gravelly slopes in the Rocky Mountains. A high proportion of degraded, indeterminant pollen grains in SF1 (up to 36%; Fig. 5) suggest remobilization of pollen into the lake (Fig. 3). High Artemisia percentages (up to 68%) and influx (Figs. 4, 5) indicate Artemisia was probably abundant in the surrounding region. Other important taxa included Juniperus-t., Poaceae, Aster-t., Tubuliflorae, Caryophyllaceae, Cirsium, Fabaceae, and Thalictrum.
Tree-pollen percentages increase and Artemisia decreases in zone SF2 (13,800 – 12,200 cal yr BP). Increasing Abies, Picea, and undifferentiated Pinus pollen indicate the regional expansion of trees. An Abies cf. lasiocarpa needle with a calibration range of 14,010 – 13,600 cal yr BP (Table 1), and conifer stomates ca. 12,600 cal yr BP, may mean that treeline approached the elevation of Santa Fe Lake. However, the continued dominance of non-arboreal pollen types indicates that the lake remained above the timber line (i.e., closed forest). Although Artemisia declines in SF2, it remains the most abundant pollen type. Increasing Poaceae and Cyperaceae pollen probably indicate expansion of shrub tundra communities as indicated by Juniperus-t., Aster-t., Brassicaceae, Caryophyllaceae, Fabaceae, Helianthus-t., and Thalictrum. This expansion and a decrease in degraded pollen is consistent with declining but variable geochemical erosion indicators (Fig. 3) that suggest plant cover expanded in the watershed during SF2 but was variable. Increasing Ambrosia and Amaranthaceae may indicate expansion by herbaceous and steppe shrub communities at lower elevations.
Pollen data in zone SF3 suggest a regional expansion of pine forests into steppe communities (12,200 – 10,300 cal yr BP). Artemisia declines dramatically at the start of the zone as undifferentiated Pinus and P. ponderosa pollen increase to the highest percentages of the record (Fig. 5). Undifferentiated Pinus reaches 53% about 11,400 cal yr BP but declines after 10,900 cal yr BP. Peaks in P. ponderosa pollen at 12,100 cal yr BP (30%) and 10,800 cal yr BP (22%), and a corresponding increase in Pinus subgenus Diploxylon, suggest that the overall increase in Pinus pollen during SF3 resulted from a regional expansion of P. ponderosa into Artemisia steppe. This interpretation relies on the differentiation of Pinus subgenus Haploxylon pollen into P. ponderosa and P. contorta. P. contorta pollen also increases slightly in SF3 (Henne et al. 2026), indicating the possible extra-local presence of P. contorta, a species that today is naturally absent from New Mexico, but forms natural stands > 150 km to the north in the northern Sangre de Cristo Mountains of Colorado (Little Jr, 1971). Given the high-elevation setting, it is unlikely that P. ponderosa ever grew near Santa Fe Lake. Instead, abundant Pinus pollen and trace but increasing percentages of Pseudotsuga pollen suggest the establishment of ponderosa pine and mixed-conifer forests at lower elevations in Sangre de Cristo Mountains and the surrounding region. Pollen of Cercocarpus, a thermophilous shrub, also increases in SF3. Picea declines slightly at the start of SF3 but increases after 11,300 cal yr BP when conifer stomates reappear, indicating the presence of conifers, probably P. engelmannii, in the Santa Fe Lake watershed. Aquatic changes are indicated by the appearance of the green algae Pediastrum boryanum. Percentages of indeterminant pollen grains are generally low in SF3, especially after 11,400 cal yr BP (i.e., 2 – 5%), which together with the geochemical data (i.e., declining then low K, Fe, Ti) indicates a decrease in erosion in the watershed.
Pinus pollen is generally less abundant in SF4 (10,300 – 5100 cal yr BP) due to a decline in undifferentiated Pinus (Fig. 5). However, P. ponderosa remains important, and P. aristata and P. edulis-t. increase, suggesting changes in multiple vegetation belts in the Sangre de Cristo Mountains. Increasing Abies and Picea pollen suggest expansion of subalpine forests. Likewise, abundant conifer stomates and the presence of Picea needles in the sediment after 10,300 cal yr BP (Table 1), document the expansion and continuous presence of subalpine trees in the watershed. Pollen of Arceuthobium (dwarf mistletoe), a parasite on coniferous trees, is common after 10,400 cal yr BP. Whereas increasing Abies pollen may indicate expansion of A. lasiocarpa in subalpine forests, expansion of A. concolor in mixed coniferous forests is also possible. The increase in P. aristata pollen after 8200 cal yr BP probably records P. aristata (Rocky Mountain bristlecone pine) near upper treeline. However, P. aristata is also a component of mixed-coniferous forests in the Sangre de Cristo Mountains. P. flexilis-t., which includes P. strobiformis, also increases in SF4 but remains < 1% of the pollen sum. Therefore, these changes may also indicate upslope expansion or increasing diversity in mixed coniferous forests. Submontane forests may have also included a shrubby understory as suggested by increasing Ceanothus, Quercus, Rhus, and Rosaceae pollen. Alnus also increases in SF4, which may relate to expansion of wetland or riparian shrublands. Pinyon-juniper woodlands expanded during SF4 as indicated by increases of first Juniperus-t. about 10,100 cal yr BP, then P. edulis-t. pollen after 8200 cal yr BP. Today, Juniperus communis grows in alpine tundra and subalpine forest understories near Santa Fe Lake, while Juniperus monosperma is typical of woodlands at lower elevations. Because pollen and stomatal evidence indicate the local presence of subalpine forest at Santa Fe Lake in SF4, increasing Juniperus-t. probably reflects regional expansion of low-elevation J. monosperma. In contrast, open conditions probably supported local J. communis during SF1 and SF2. Peaks in Polypodiaceae spores coincide with increases in Ti, K, Fe, and Si, which may indicate erosion events. Increases in Poaceae and Aster-t. in SF4 may indicate expansion of alpine meadows, an herbaceous understory in submontane forests and woodlands, and/or increasing productivity in low-elevation grasslands. Indeed, low-elevation pollen sources are evident from increases in Ephedra, and Sarcobatus pollen, which may indicate the expansion of dry shrublands, and Amaranthaceae, which is associated with playas (i.e., ephemeral lakes or wetlands) and saline lakes in the Southwest (Rosen et al., 2013).
Zone SF5 consists of eight samples from sediments that were rapidly deposited ca. 5100 cal yr BP. Because this zone resulted from rapid deposition it is not depicted in Fig. 5, which is on an age scale, but is included in Henne et al. (2026). Degraded/indeterminant pollen grains, undifferentiated Pinaceae grains, Polypodiaceae spores (without perine), and Tubuliflorae pollen dominate the pollen assemblages. We selected the period 6000 – 3000 cal yr BP for correlation analysis. This interval includes zone SF5 with abundant erosional indicators and portions of adjacent SF4 and SF6 with limited evidence of erosion. Polypodiaceae, a locally dispersed spore that is often present in reworked sediments (Dirksen et al., 2014) is significantly and positively correlated with indeterminant pollen (r = 0.86; p < 0.001), Tubuliflorae (r = 0.61; p < 0.001), and Selaginella rupestris (clubmoss; r = 0.81; p < 0.001), but significantly and negatively correlated with regionally dispersed pollen types including Artemisia (r = -0.71; p < 0.001), Cercocarpus (r = 0.61; p < 0.001), and Poaceae (r = -0.57; p = 0.002). Thus, samples with overrepresented Polypodiaceae and degraded pollen in SF5 are not representative of regional vegetation and instead probably derive from remobilization from catchment soils.
Picea pollen reaches the highest percentages (up to 30%) in zone SF6 (5100 cal yr BP – present). P. aristata pollen is also important in SF6 (up to 10%). These data and increasing pollen influx after 4000, and especially 2000, cal yr BP (Fig. 4), suggest dense, spruce-dominated forests formed near Santa Fe Lake. Pollen data also suggest the expansion of alpine meadows. Poaceae and Aster-t. are abundant herbaceous taxa, which also include Apiaceae, Anthemis-t., Aquilegia, Tubuliflorae, Cirsium, Erigonum, Fabaceae, and Thalictrum. Notably, several taxa typical of alpine meadows have a more consistent presence in SF6 than other pollen zones, including Brassicaceae, Campanulaceae, Veratrum tenuipetalum, and Saxifraga azoides. Increasing Artemisia percentages and influx during SF6 may also indicate greater inputs from alpine plant communities or alternatively, regional inputs from lower elevations. P. ponderosa and P. menziesii remained important in submontane forests that also supported Cercocarpus. P. edulis-t. increases after 3000 cal yr BP, possibly indicating expansion of pinyon woodlands. The appearance, and presence of Zea mays (maize) pollen, from 800 – 350 cal yr BP (1150 – 1600 cal yr CE) provides unambiguous evidence of human presence and agriculture in the surrounding region.
4.3. Regional fire history
Microscopic charcoal is widely used as an indicator of regional fire activity (i.e., within 20 – 100 km) that is correlated with fire numbers and intensity (Adolf et al., 2018; Clark and Royall, 1995; Conedera et al., 2009; Whitlock and Larson, 2001). Because microscopic charcoal derives from both local and distant fires, and because we did not analyze sediments contiguously for charcoal content, we interpret our charcoal data as indicative of trends in regional burning, not discreet fire events. Relatively high charcoal influx during SF1 (before 13,800 cal yr BP; Fig. 5) may reflect more frequent fires at the start of our record but may also be compromised by elevated erosional inputs and uncertainty in our age-depth model at the base of the core that affect influx calculations. Charcoal influx is relatively stable in SF2 and SF3, with somewhat higher values in SF4 and in SF6 from 5100 – 2000 cal yr BP (Fig. 5). However, charcoal influx is generally less than the Holocene mean (i.e., negative anomalies; Fig 6b) before 2000 cal yr BP. Charcoal influx increases markedly after 2000 cal yr BP and remains greater than the Holocene mean, which indicates a regional increase in burning. Charcoal influx averages 28,833 ± 17,202 particles × cm-2 × yr-1 (mean and standard deviation) after 2000 cal yr BP, which is more than double the mean influx rate before 2000 cal yr BP (10,648 ± 5283). Sediment accumulation rates affect influx calculations and therefore, long-term trends in charcoal influx. For example, decreasing charcoal concentrations after 4000 cal yr BP coincide with a modest increase in charcoal influx (Figs. 4, 5) due to a contemporaneous increase in sediment accumulation rates (Fig. 2). In contrast, both charcoal concentrations and influx increase after 2000 cal yr BP even as sedimentation rates continue a gradual increase. Therefore, the major increase in microscopic charcoal influx after 2000 cal yr BP probably reflects a regional increase in burning, not calculation effects related to our age-depth model.
5. Discussion
5.1. Glacier activity and erosion in the Santa Fe Lake watershed.
Santa Fe Lake formed during the Late Glacial when local evidence from the Sangre de Cristo Mountains, and lowland sites in the surrounding region, indicate a shift to a warmer and drier climate. Glaciers began receding ca. 15,100 ± 400 a. from moraines impounding nearby Lake Katherine (5.5 km northeast of Santa Fe Lake; 3584 m a.s.l.; Fig. 1), which forms the headwaters of Winsor Creek (Leonard et al., 2023; Marcott et al., 2019). At Stewart Bog (ca. 3100 m a.s.l.) downstream of Lake Katherine, a transition from glacial debris to organic sedimentation below a horizon dated to 13,790 – 14,295 cal yr BP (2 σ range of 14C date) marks the termination of (Pinedale) glacial activity in the Winsor Creek watershed (Armour et al., 2002; Jiménez-Moreno et al., 2008). The onset of sediment accumulation at Santa Fe Lake is consistent with this chronology. Our oldest radiocarbon date of an Abies needle at 491 cm of 13,600 – 14,010 cal yr BP (Table 1) overlaps with the glacial termination date from Stewart Bog. Basal sediments from Santa Fe Lake and Stewart Bog are similarly enriched in detrital, and probably glacial, inputs (e.g., high Ti and magnetic susceptibility; Fig 3; Armour et al., 2002; Stansell et al., 2013). Likewise, the decline in MS at both sites, and Ti, K, and Fe at Santa Fe Lake after 14,000 cal yr BP probably reflects the recession of alpine glaciers due to rising temperatures and regional drying during the Bølling-Allerød warm interval. This interpretation of rising temperatures and dryness is consistent with regional evidence from lowland records. For example, a massive decline in water levels at Lake Estancia, 120 km south of Santa Fe Lake, indicates a shift to drier conditions after 14,000 cal yr BP (Menking et al., 2018). Dry conditions were also inferred from a multiproxy lake sediment record from San Luis Lake 200 km to the north (Yuan et al., 2013). Contemporaneous enrichment in 18O in the speleothem record from Fort Stanton Cave, New Mexico, 260 km south of Santa Fe Lake probably indicates a drying climate and reduction in the proportion of precipitation falling during winter (Asmerom et al., 2017, 2010).
Although glacial activity declined after 14,000 cal yr BP, variable delivery of detrital sediments to Santa Fe Lake continued until about 11,500 cal yr BP (Fig. 3). Increased MS and Ti after 13,000 cal yr BP, including a major peak about 12,300 cal yr BP, are consistent with evidence of winter-dominated precipitation and renewed glacial activity during a cooler, wetter Younger Dryas (YD) in the Sangre de Cristo Mountains (Armour et al., 2002; Jiménez-Moreno et al., 2008; Todd et al., 2025). Elsewhere in the Southern Rocky Mountains, glacial activity was intermittent through the end of the YD (Johnson et al., 2011). A regional return to wetter conditions is also recorded by the final high stand in the Estancia Basin (Menking et al., 2018) where cool and wet conditions enabled local peat accumulation from about 12,300 – 11,130 cal yr BP (Hall et al., 2012), and by contemporaneous depletion in 18O at San Luis Lake, and Fort Stanton Cave (Asmerom et al., 2017; Yuan et al., 2013).
Subsequent peaks in MS, Ti, K, and Fe during the Holocene (e.g. from 9000 – 7600 cal yr BP and 6300 – 5100 cal yr BP; Fig. 3) probably postdate glacial activity in the Santa Fe Lake watershed. These geochemical erosion indicators coincide with peaks in Polypodiaceae spores and indeterminant pollen that provide independent evidence for periodic remobilization of terrestrial material to Santa Fe Lake, possibly due to fires, landslides, or other disturbance events in the Santa Fe Lake watershed. However, evaluating the local role of fire as a driver of erosion would require higher-resolution charcoal data than presented here. The erosion event that produced rapid deposition in Santa Fe Lake ca. 5100 cal yr BP is of similar age to the largest Holocene age MS spike at Stewart Bog (4900 uncalibrated 14C yr BP), which may record a comparable erosional event (Armour et al., 2002). It is possible that these events relate to seismic activity in the Rio Grande rift (Crawford et al., 2025) or to a climatically driven increase in erosion, observed elsewhere in the Southern Rocky Mountains (Johnson et al., 2011).
5.2. Climate change impacts on the establishment of subalpine and montane forests at the southern limits of the Rocky Mountains
Forest establishment and dynamics near Santa Fe Lake coincided with dramatic changes in local and regional temperatures and hydroclimate in the Southern Rocky Mountains and the Southwest during the Late Glacial and early Holocene. Pollen evidence from the oldest sediments at Santa Fe Lake (i.e., SF1) including low tree-pollen percentages, very high Artemisia (up to 68%) and high Juniperus-t., indicate a dry steppe environment with few trees. However, chronological uncertainty is high in these sediments, which are unconstrained by a basal radiocarbon date (Fig. 2). Indeed, high pollen influx values before 14,000 cal yr BP (Fig. 4) may indicate our age-depth model underestimates sedimentation rates during this period marked by the possible inflow of glacial debris. Abundant degraded pollen suggests remobilization of pollen from a sparsely vegetated watershed or even from glacial meltwater (Pennington, 1996). Artemisia percentages at Santa Fe Lake before 13,800 cal yr BP far exceed percentages from nearby Stewart Bog (Jiménez-Moreno et al., 2008), which may indicate overrepresentation of Artemisia due to remobilization. However, similar abundances exist in records from Late Glacial sediments in the Southern Rocky Mountains (Briles et al., 2012) and in modern samples from Artemisia steppe (Fall, 1992).
Chronological constraint at Santa Fe Lake improves after 13,800 cal yr BP when a warming climate favored upslope expansion of trees that we infer from major increases in arboreal pollen (e.g., Abies, Picea, and Pinus; Fig. 5). High arboreal pollen percentages alone do not necessarily indicate the local presence of trees in records from high-elevation lakes. Pollen, especially Pinus, can be transported hundreds of kilometers, which obscures local vegetation signals in treeless alpine tundra where pollen production is low (Campbell et al., 1999; Fall, 1992). As a result, Pinus is typically the most abundant pollen in assemblages from high-elevation lakes in the Southwest and Rocky Mountains even when distant from pine-dominated forests (Jackson and Smith, 1994; Minckley et al., 2008). However, because spruce and fir produce large pollen grains that are less dispersible than Pinus, changes in Picea and Abies abundances are indicative of variations in local treeline elevation (Jiménez-Moreno et al., 2008; Jiménez-Moreno and Anderson, 2013; van der Knaap et al., 2001). Thus, the major increase in Picea and continuous presence of Abies after 13,800 cal yr BP suggests upslope expansion and the presence of spruce and fir near Santa Fe Lake (Fig. 5). Macrofossils and stomates provide a more definitive indicator of the local presence of coniferous trees than pollen alone (Ammann et al., 2014; Carrara, 2011; Finsinger and Tinner, 2020; Tinner and Theurillat, 2003). An Abies cf. lasiocarpa needle at ca. 13,726 cal yr BP (2 σ range = 13,600 – 14,010 cal yr BP; Table 1) supports our interpretation and may even indicate that local tree establishment followed recession of glaciers within centuries as regional temperatures rose. Contemporaneous macrofossil evidence demonstrates that Picea reached the elevation of Chihuahueños Bog (2925 m a.s.l.) in the Jemez Mountains by 14,000 cal yr BP (Anderson et al., 2008b). However, abundant pollen of Artemisia and Poaceae, together with short-statured herbs and mosses indicate an open and rather dry environment with few trees at Santa Fe Lake. Similar open vegetation with abundant Artemisia, or Krummholz where trees were present, formed at other high-elevation sites in the Southern Rocky Mountains (Anderson et al., 2021, 2008a; Briles et al., 2012; Jiménez-Moreno et al., 2008). Together these data suggest that whereas warming allowed upslope tree expansion, a dry regional climate limited forest development, and tree cover remained sparse until after 12,200 cal yr BP.
Pinus expansion after 12,200 cal yr BP was a prominent event in the region surrounding Santa Fe Lake (Fig. 5; Anderson et al., 2008a, 2008b; Jiménez-Moreno et al., 2008; Johnson et al., 2013; Reasoner and Jodry, 2000) that provides a possible analogue for understanding the impacts of rapid warming on mountain forests in the Southwest. However, interpreting the vegetational changes underlying this event remains a challenge. Today, P. ponderosa is one of the most widespread and abundant trees in western North America and dominates montane forests in the Southwest (Oliver and Ryker, 1990). However, the distribution of P. ponderosa during the Last Glacial is poorly documented. P. ponderosa macrofossils, which could provide definitive evidence of local populations, are nearly absent from packrat (Neotoma) middens and sedimentary records (Anderson, 1989; Norris et al., 2016). Because of this uncertainty, previous authors concluded that P. ponderosa had a very limited distribution in the Southwest during the Last Glacial, was possibly limited to refugia in southern New Mexico and Arizona, and may not have approached its modern distribution until the middle Holocene (Anderson, 1989; Betancourt and Van Devender, 1981; Van Devender, 1990). However, modern calibration studies demonstrate that the probability of detecting scattered or small tree populations using sedimentary or midden records is low (Lesser and Jackson, 2011; McLachlan and Clark, 2004). Furthermore, sediments at elevations where the climate may have been suitable for P. ponderosa during the Last Glacial and could have preserved macrofossils were likely lost as the climate warmed and low-elevation basins dried up. Therefore, the absence of macrofossils is not evidence that P. ponderosa was absent from refugia near the Southern Rocky Mountains (Anderson, 1989; Birks, 2014; Gavin et al., 2014).
Species distribution models that simulated potential P. ponderosa distributions during the Last Glacial Maximum found high refugial potential in the Rio Grande Basin directly south of Santa Fe Lake and even to the east of the Sangre de Cristo Mountains (Roberts and Hamann, 2016; Shinneman et al., 2016). These hypothesized northern refugia are consistent with the modern geographic patterns of genetic diversity and the distribution of mitochondrial DNA haplotypes of P. ponderosa var. scopulorum (Rocky Mountain ponderosa pine; Potter et al., 2015, 2013). Two haplotypes have been identified in the Southern Rocky Mountains. One ranges from southern Arizona and New Mexico to northern Wyoming, which is consistent with Holocene expansion from known, macrofossil-supported southern refugia (Van Devender, 1990). However, the other ranges from the Sangre de Cristo Mountains in southern Colorado, north to Montana, which may indicate a separate, more northerly refugium near the Southern Rocky Mountains (Potter et al., 2013). Today, disjunct P. ponderosa populations persist in settings that are considerably drier than the montane P. ponderosa zone. For example, in the Great Basin, P. ponderosa stands form on thermally altered soils where low fertility limits competition from desert shrubs (Billings, 1950; DeLucia et al., 1988; Mckee and Knutson, 1987). Disjunct populations also exist in dry interior valleys of the Southern Rocky Mountains below the forest limit where topography may enhance local moisture availability and where the growing season is longer than adjacent highlands (Howard, 2003). Riparian populations of P. ponderosa in the Jemez Mountains survived recent droughts that induced widespread mortality in adjacent upland populations (Allen and Breshears, 1998; Breshears et al., 2005). These scattered, low-elevation and riparian P. ponderosa stands provide a possible analogue for hypothesized refugial populations near the Southern Rocky Mountains during the Last Glacial, perhaps in the Rio Grande valley, that could have spread into the Sangre de Cristo Mountains as temperatures warmed and growing season precipitation increased during the Late Glacial to Holocene transition.
Given the absence of P. ponderosa macrofossils in midden data and low-elevation sedimentary records, pollen records from subalpine lakes provide the best-available fossil evidence for the Late Glacial and early Holocene history of P. ponderosa. Pinus subgenus Diploxylon pollen, which is produced by only P. ponderosa and P. contorta in the Southern Rocky Mountains, is commonly separated from other Pinus pollen (Anderson et al., 2021, 2008b, 2008a; Hansen and Cushing, 1973; Jackson and Smith, 1994; Jacobs, 1985; Jiménez-Moreno et al., 2023). Thus, at a minimum, the major increase in Pinus subgenus Diploxylon pollen after 12,200 cal yr BP at Santa Fe Lake provides strong evidence for expansion of P. ponderosa and/or P. contorta (Figs. 5, 6). Macrofossil evidence from the Colorado Plateau demonstrates that P. ponderosa was present in northern Arizona and southern Utah by 11,000 cal yr BP, following the earlier regional expansion of pine that is recorded by pollen data (Anderson, 1993; Louderback et al., 2020; Weng and Jackson, 1999). However, no similar macrofossil records exist for the Southern Rocky Mountains. We approached this challenge using a pollen key for Southwestern pines (Hansen and Cushing, 1973) to separate not only Pinus subgenera Haploxylon and Diploxylon, but also P. ponderosa and P. contorta pollen. A previous application of this approach in northwestern New Mexico concluded that P. ponderosa grew on the lower slopes of the Chuska Mountains during the Last Glacial (Wright et al., 1973). However, due to an imprecise chronology, this earlier effort provides limited information about P. ponderosa abundance during the Late Glacial.
The major increase in P. ponderosa pollen in our well-constrained record supports the hypothesis that ponderosa pine forests or woodlands established after 12,200 cal yr BP in the Sangre de Cristo Mountains. Pollen percentage thresholds are often used to infer local-regional presence of trees, with separate thresholds for different pollen types based on productivity and dispersibility (Lisitsyna et al., 2011; van der Knaap et al., 2005). For example, MacDonald and Cwynar (1985) used a threshold of 15% to infer the postglacial arrival of Pinus within 30 km of lakes in the Yukon, while Strong and Hills (2013) concluded that a threshold of 5% Pinus pollen is indicative of 1% pine coverage in the same region. At Santa Fe Lake P. ponderosa percentages alone easily exceed even conservative thresholds for local-regional presence after 12,200 cal yr BP (Fig. 5). Whereas Pinus percentages in SF3 are probably high in part because Santa Fe Lake was below treeline, the major increase in P. ponderosa and undifferentiated Pinus, but sustained low abundances of other Pinus types, supports the hypothesis that P. ponderosa expanded into Artemisia steppe in the region surrounding Santa Fe Lake after 12,200 cal yr BP.
Expansion of P. ponderosa during the Holocene is generally attributed to increasing summer precipitation, especially monsoonal precipitation, and/or increasing summer temperatures (Anderson, 1989, 1993; Norris et al., 2016). The initial increase in Pinus pollen at Santa Fe Lake that coincides with declining geochemical indicators of glacier activity (i.e., major declines in MS, Ti, K, Fe; Figs. 3, 6) is consistent with this interpretation. The highest Pinus abundances at Santa Fe Lake and elsewhere in the Sangre de Cristo, Jemez, and San Juan mountains (Figs. 1, 5; Anderson et al., 2008b; Jiménez-Moreno et al., 2008; Johnson et al., 2013) coincide with increases in summer temperatures and the proportion of precipitation falling as rain (Carrara, 2011; Epstein et al., 1999; Friedman et al., 1988; Thompson et al., 1993; Todd et al., 2025; Yuan et al., 2013). These climatic changes may relate to atmospheric teleconnections that affected the hydroclimate of the Southwest. Increasing insolation and summer temperatures probably favored intensification of the North American Monsoon during the early Holocene. (Lachniet et al. 2023; Metcalfe et al., 2015). Changes in the seasonality of precipitation may also relate to atmospheric modes originating in the Pacific Ocean. For example, Todd et al. (2025) concluded that a shift to more positive values in leaf-wax δD at nearby Stewart Bog (Fig. 1) about 11,700 cal yr BP indicates a decline in winter precipitation, and possible increase in summer precipitation that resulted from a teleconnection similar to the negative phase of the Pacific Decadal Oscillation (PDO). Regional Pinus expansion also corresponds to a global increase in atmospheric CO2 concentrations that enhanced water-use efficiency and may have favored P. ponderosa in water-limited environments (Monnin et al., 2001; Rundgren and Björck, 2003; Van de Water et al., 1994).
Continued warming allowed the establishment of spruce forests near Santa Fe Lake. By 11,000 cal yr BP, pollen and stomatal evidence document spruce in the watershed, with continuous presence of stomates and higher pollen abundances after 10,300 cal yr BP (Fig. 5). Macrofossil evidence similarly documents spruce forest establishment further north in the Sangre de Cristo Mountains at Hermit Lake, Colorado (3450 m a.s.l.) by 10,000 cal yr BP (Anderson et al., 2021). Indeed, upper treeline rose throughout the region, reaching elevations above the current limit from 10,400 – 6600 cal yr BP (Carrara, 2011). Increasing temperatures also enhanced aquatic productivity at Santa Fe Lake as reflected by increases in Pediastrum, which is sensitive to growing season temperatures (Xiang et al., 2024) after 12,000 and especially 10,300 cal yr BP (Fig. 5). As summer insolation and regional temperatures rose, monsoonal precipitation probably also continued to intensify (Anderson, 2012; Anderson et al., 2023; Metcalfe et al., 2015; Routson et al., 2022). Increasing summer precipitation is consistent with the expansion of species with higher summer moisture demands; first Quercus and Juniperus then P. edulis in the woodland-shrubland ecotone, grasses, and desert shrubs (Fig. 5).
After the dramatic vegetational changes of the Late Glacial and early Holocene, vegetation dynamics were more subtle near Santa Fe Lake. This probably reflects the relative stability of local vegetation following the establishment and continued presence of spruce forests near the lake. Climate records suggest a general regional shift to lower mean temperatures with increasing moisture availability and a higher proportion of precipitation falling during winter after about 6000 cal yr BP in the Southern Rocky Mountains (Anderson et al., 2015; Shuman and Serravezza, 2017). These hydroclimatic changes may relate to atmospheric modes that brought more winter precipitation to the Southwest during the late Holocene, including teleconnections similar to the positive phase of the PDO and/or more frequent El Niño-like conditions (Todd et al., 2025). The impacts of cooler summers and wetter winters is evident in vegetation records by a lowering of upper treeline and increasing density of subalpine forests (Anderson et al., 2021). Vegetation at Santa Fe Lake is consistent with this interpretation. P. aristata, which today grows at upper treeline near Santa Fe Lake, first expanded after 9000 cal yr BP but was most abundant after 5000 cal yr BP, which may indicate closer proximity of this species to the lake due to a lowering of upper treeline. Likewise, pollen of herbs typical of alpine meadows increases after 4000 cal yr BP (see Results). The last 4000 years is also marked by increasing pollen influx (Fig. 4), perhaps in response to greater cool-season moisture availability that enhanced productivity (Margolis et al., 2017; Swetnam and Betancourt, 1990).
5.3. Interactions among climate, wildfire, and humans
Wildfire reconstructions from the Southern Rocky Mountains suggest that synchronous changes in fire activity occurred in subalpine forests during periods with major climatic and vegetational changes. For example, composite macroscopic charcoal records demonstrate an increase in fire frequencies from ca. 12,000 – 9000 cal yr BP across multiple sites, which was attributed to the establishment of stand-replacing fire regimes as subalpine forests expanded and biomass increased at high elevations (Anderson et al., 2008a; Briles et al., 2012). Periods of spatial variability in subalpine fires also occurred perhaps due to local heterogeneity in fuels (Briles et al., 2012; Gavin et al., 2007). Millennial-scale dynamics among climate, vegetation, and wildfire are less certain for the extensive dry coniferous forests and woodlands of the Southwest. Tree-ring fire scars demonstrate that dry coniferous forests burned at low severity but high frequency (e.g., every 5 – 25 years in ponderosa pine stands) during the last 500 years up until the late 19th century (McClure et al., 2024; McKinney, 2019; Swetnam et al., 2016). However, low-severity fire regimes in dry coniferous forests may predate the tree-ring record. For example, macroscopic charcoal data from northern Arizona linked P. ponderosa expansion during the early Holocene with increasing fire activity (Weng and Jackson, 1999). Major increases in macroscopic charcoal influx after about 5000 cal yr BP at Chihuahueños and Alamo bogs, which are situated in mixed coniferous forests in the Jemez Mountains, may indicate frequent burning during the late Holocene (Anderson et al., 2008a). However, interpretation of these records is complicated by likely inputs of charcoal from burning of the bog surface (Allen et al., 2008). Fire may have also limited the extent of tree cover in lower-elevation pinyon-juniper woodlands and savannas (Margolis, 2014; Romme et al., 2009). However, fire frequencies were probably always lower in coniferous woodlands where generally drier conditions limit fuel availability (Huffman et al., 2008). Ultimately, few Holocene fire records are available from elevations that support dry coniferous forests or woodlands, which limits understanding of long-term regional fire activity during important vegetational changes, including the regional expansion of P. ponderosa that we infer at Santa Fe Lake after 12,200 cal yr BP.
Microscopic charcoal records can provide information about changes in regional fire activity that is not recorded by more spatially constrained analyses of macroscopic charcoal influx peaks. At Santa Fe Lake, the potential source area of microscopic charcoal (e.g., within 20 – 100 km; Adolf et al., 2018; Clark and Royall, 1995; Conedera et al., 2009) includes elevations with vegetation types that are not well represented by sedimentary records in the Southwest. Dry coniferous forests and shrublands, including mixed conifer, ponderosa pine, and pinyon-juniper woodlands comprise 69% of the natural vegetation within 20 km of Santa Fe Lake today (Fig. 1). In contrast, subalpine spruce and fir forests comprise 17%. Therefore, long-term trends in microscopic charcoal influx (Fig. 6) are probably most indicative of changes in fire frequencies in lower-elevation forests and woodlands (Clark and Royall, 1995; Conedera et al., 2009).
Consistent microscopic charcoal influx demonstrates that fire was an important regional, environmental variable throughout the period covered by our record. However, relatively small variation in charcoal influx at Santa Fe Lake after 12,200 cal yr BP may mean that local increases in fire activity identified at subalpine lakes in the Southern Rocky Mountains during the early Holocene (Anderson et al., 2008a; Briles et al., 2012) did not coincide with a regional increase in burning (Fig. 6). It is quite possible that the elevations where fire activity was most frequent shifted upslope as the climate warmed and important fire-tolerant species like P. ponderosa expanded (Allen, 2002; Weng and Jackson, 1999). However, our microscopic charcoal record is unable to resolve possible changes in the location of regional fires or the types of fuels. It is also possible that differences in ignition frequencies or fuel availability constrained fire occurrence and spread before 2000 cal yr BP. Fine fuels such as grasses contribute much of the biomass consumed in low-severity fires in dry coniferous forests and are important for fire spread. In our study region, cool-season precipitation favors the buildup of such fuels, although monsoonal precipitation can also be important. Large fire years tend to follow periods with abundant cool-season precipitation and dry intervals that limit the buildup of fine fuels can limit surface-fire spread (Margolis et al., 2017; Swetnam and Betancourt, 1998). Our results may mean that as increasing summer temperatures and precipitation favored P. ponderosa expansion, declining cool-season moisture (Asmerom et al., 2010; Carrara, 2011; Friedman et al., 1988; Todd et al., 2025; Yuan et al., 2013) limited fine fuel buildup and regional burning relative to the last 2000 years. Indeed, herb pollen is low (both percentages and influx) from 12,200 – 10,300 cal yr BP when pine pollen is most abundant (Figs 4, 5).
Microscopic charcoal influx suggests that regional biomass burning near Santa Fe Lake increased dramatically in the last 2000 years, especially from about 1550 – 1000 cal yr BP (400 – 950 cal yr CE; Fig. 6). Although few comparable microscopic charcoal records are available from the Southwest, this timing coincides with maximum microscopic charcoal influx at nearby Ocate Bog (Fig. 1; Hall, 2020). Increased regional burning is also consistent with composite macroscopic charcoal records from subalpine and mixed conifer sites in Colorado and New Mexico that record an increase in fire frequencies between 1000 and 2000 cal yr BP (Anderson et al. 2008a). It is possible that climatic factors favored an increase in regional burning at this time. For example, prolonged periods of drought were reconstructed from tree-ring archives in New Mexico from 1650 – 1450 BP (300 – 500 CE) and 1150 – 650 BP (800 – 1300 AD; Grissino-Mayer 1996; Roos and Swetnam 2012). Maximum regional fire activity at Santa Fe Lake also overlaps in part with the Medieval Climate Anomaly (MCA; ca. 1150 – 650 cal yr BP) when warmer and drier conditions contributed to increased fire activity in subalpine forests of the Rocky Mountains (Calder and Shuman, 2017; Marlon et al., 2012). However, extended dry intervals may be a more important driver of fire activity in subalpine forests than in the extensive dry coniferous forests and woodlands in the region surrounding Santa Fe Lake. In dry coniferous forests, high-frequency wet-dry oscillations that promote fuel buildup and flammability were linked to regional fire activity during recent centuries (Littell et al., 2018; Margolis, 2014; Margolis et al., 2017; Swetnam et al., 2016). Thus, the long-term trend toward increasing cool-season precipitation during the late Holocene (Anderson, 2012; Anderson et al., 2023; Fall, 1997; Shuman et al., 2009; Todd et al., 2025) may have favored a buildup of fine fuels that when overprinted with atmospheric teleconnections bringing periodic, dry, flammable conditions to the Southwest (e.g., El Niño-Southern Oscillation), contributed to increased regional burning during the last 2000 years (Anderson et al., 2008a; Swetnam and Betancourt, 1990). This rationale implies that intensification of wet-dry oscillations during the last 2000 years drove an increase in regional burning that exceeded the scale of changes during the rest of the Holocene. However, there is no strong evidence for major hydrological or vegetational changes during the last 2000 years at Santa Fe Lake. Our records of magnetic susceptibility and detrital elements do not show major changes during the last 4000 years (Fig. 3). Likewise, there are no statistically significant changes in pollen assemblages during this period (Fig. 5). Therefore additional, non-climatic factors may be needed to understand the late Holocene increase in fire activity.
Cultural change may have been the critical driver of increased regional burning. People occupied the Southwest throughout the Holocene, with archaeological evidence from the last 5000 years in the Pecos, Santa Fe, Nambé, and Pojoaque watersheds that begin in the Sangre de Cristo Mountains surrounding Santa Fe Lake (Damick et al., 2022; McBrinn and Vierra, 2017; Post, 2013). Early (i.e., Archaic Period) sites reflect seasonal and recurrent occupation of lowland and upland sites by mobile societies with a foraging economy reliant on wild plants and game hunting. The duration of occupancy probably increased by 3000 cal yr BP, when maize agriculture is first evident at archaeological sites in the northern Rio Grande basin. Expanding human populations may have contributed to the increase in regional fire that we infer from increasing charcoal influx after 2000 cal yr BP (50 cal yr BCE). However, the major increase in regional burning marked by high microscopic charcoal influx from 1550 – 1000 cal yr BP (400 - 950 cal yr CE) at Santa Fe Lake is more readily attributable to human impacts. This period coincides with a Neolithic Demographic Transition in the Southwest (ca. 500 – 1300 CE) that brought dramatic population growth associated with agricultural innovation including the introduction of dryland maize agriculture (Fig. 6; Kelly et al., 2025; Kohler et al., 2008; Kohler and Reese, 2014; Phillips et al., 2018). Early maize farmers began occupying sites along the Santa Fe River during this period in semisedentary settlements (Post, 2013). The coincident increase in charcoal influx likely reflects diverse uses of fire by these ancestral Puebloan farmers, including to clear land for cultivation and/or to mitigate fire risk (Roos et al., 2022; Swetnam et al., 2016). In the Jemez Mountains, increasing charcoal concentrations in soils and sediments near known settlements after 1500 cal yr BP were attributed to land clearance for agriculture (Roos et al., 2021). Intensifying impacts on forests including the use of fire, tree-cutting, and even deforestation are widely reported in the Southwest as agricultural economies developed (Bocinsky et al., 2016; Kohler, 1992; Kohler and Mathews, 1988; Samuels and Betancourt, 1982; Scheffer et al., 2021). Accordingly, the highest charcoal influx in our record coincides with regional expansion of agriculture, as larger concentrated settlements developed in the northern Rio Grande basin (Fig. 6; Kelly et al. 2025; Ortman, 2016; Post, 2013).
Maize pollen documents local, intense agriculture from 800 – 375 cal yr BP (1150 – 1575 cal yr CE) near Santa Fe Lake (Figs. 5, 6). Whereas the increases in regional burning that we infer from microscopic charcoal may result from cultural and/or climatic factors, maize pollen is an unambiguous cultural indicator. Maize produces large, wind-dispersed grains that are poorly dispersed. Field experiments with modern cultivars showed that up to 99% of maize pollen is deposited within 30 m of the source (Jarosz et al., 2003). However, under convective conditions that typically produce thunderstorms during midsummer in the Sangre de Cristo Mountains, and when maize pollination occurs, maize pollen is readily transported hundreds of meters into the atmosphere (Barker Schaaf et al., 1988; Boehm et al., 2008). Maize pollen also appears in precisely dated pollen records from glaciers in the European Alps shortly after introduction of maize agriculture, which demonstrates the relevance of maize pollen as a regional cultural indicator in alpine archives (Brugger et al., 2021). The appearance of maize pollen at Santa Fe Lake about 800 cal yr BP (1150 cal yr CE) coincides with dramatic population increases in the Tewa Basin (Fig. 6) that likely corresponded to the expansion of maize agriculture to larger areas and higher elevations (i.e., up to 2300 m a.s.l) near Santa Fe Lake (Bocinsky and Kohler, 2014; Post, 2013; Schillaci and Lakatos, 2016). Although the largest inferred increase in regional burning at Santa Fe Lake precedes the first appearance of maize pollen by 750 years, charcoal influx remains generally higher during the 450-year period when maize pollen is present than earlier in the record when regional land use was less intense (Fig. 6). This may mean that the high charcoal influx beginning about 1550 cal yr BP reflects an initial use of fire to gain land for agriculture, while later burning was used to maintain open environments and limit fuel loads (Roos et al., 2022; Swetnam et al., 2016). The absence of maize pollen after 375 cal yr BP (1575 cal yr CE) marks the onset of Spanish colonialism in the Santa Fe region that brought cultural upheaval and major fire-regime and ecological changes that are well-documented by indigenous accounts, historical records, and tree-ring archives (Liebmann et al., 2016; Ortman, 2016; Roos et al., 2021; Swetnam et al., 2016; Wilcox, 2009).
6. Conclusions
Vegetation dynamics at Santa Fe Lake were driven by climatic change during the Late Glacial to early Holocene transition. A warming climate after 14,000 cal yr BP brought the termination of glaciation in the Sangre de Cristo Mountains, with a possible return of glacier activity during the Younger Dryas interval. Subalpine forests dominated by P. engelmannii expanded into alpine communities near Santa Fe Lake by 10,300 cal yr BP and persisted for the remainder of the Holocene. Our pollen data support the hypothesis that warming temperatures and increasing growing season precipitation triggered the regional establishment of ponderosa pine forests after 12,200 cal yr BP. Additional pollen records that distinguish P. ponderosa and P. contorta pollen, or new macrofossil evidence from elevations where P. ponderosa may have grown, are needed to support this conclusion. Our combined pollen and microscopic charcoal data suggest that expansion of fire-tolerant P. ponderosa did not coincide with a regional increase in burning. Instead, regional fire activity remained relatively consistent until the last 2000 years, with a major increase after 1550 cal yr BP. The timing of this increase in regional burning coincides with the expansion of agriculture, major human population increases in the Southwest, and the establishment of increasingly permanent settlements by Puebloan societies in the northern Rio Grande region (Kelly et al., 2025; Kohler and Reese, 2014; Ortman, 2016). However, increasing cool-season precipitation that favored the buildup of fine fuels, and periodic droughts that enhanced flammability, may have also been important factors.
Our findings support previous evidence of cultural control over fire frequencies and fuel loads in some locations and time periods prior to Spanish colonization of the Southwest. Whereas prehistorical human impacts on regional fire regimes are increasingly well documented by tree-ring inferred fire histories (Allen, 2002; Roos et al., 2022; Swetnam et al., 2016), our data add important millennial-scale context. Average microscopic charcoal influx at Santa Fe Lake more than doubles after 2000 cal yr BP, which suggests regional burning at this time far exceeded the range of fire activity during earlier periods of the Holocene, and that the regional increase in fire was massive. However, the major increase in charcoal influx may primarily reflect land-use change in the northern Rio Grande region, such as the use of fire to clear woodlands and maintain lands for agriculture. Therefore, the broader implications of our results are uncertain, especially for the expansive lower-elevation woodlands, shrublands, and grasslands in mountain ranges throughout the Southwest where the availability of continuous long-term data is limited. Our approach combining well-dated pollen percentage and microscopic charcoal influx data to understand regional burning is novel for the Southwest. New microscopic charcoal records from subalpine lakes in variable proximity to prehistoric agricultural settlements are needed to better understand regional changes in fire activity, and links to humans, climate, and vegetation. Such microscopic records can complement new or existing high-elevation macroscopic charcoal records and can also be bolstered by new macroscopic charcoal records from lower-elevation sites adjacent to dry coniferous forests (e.g., D’Andrea et al., 2023). Approaches that differentiate among fuel types and combustion intensity using charcoal reflectance or sedimentary biomarkers may also provide understanding of regional fire-regime change (Hudspith et al., 2015; Kirchgeorg et al., 2014). Although our microscopic charcoal record has striking consistency with the timing of societal changes reconstructed from the archaeological record, definitively attributing fire-regime changes to human activity would benefit from additional proxies for human presence and regional burning (Argiriadis et al., 2018; Zennaro et al., 2015). Such data are critical for understanding interactions between dry coniferous forests and wildfire and are needed to inform management practices that maintain forest cover in a warming climate.
Figures
Left: Map showing the location of Santa Fe Lake, NM (red star) in the Sangre de Cristo Mountains of the Southern Rocky Mountains (green outline). Study sites mentioned in the text include the Estancia Basin (EB; Menking et al., 2018), Chihuahueños Bog (CB; Anderson et al., 2008b), San Luis Lake (SLL; Yuan et al., 2013), and Ocate Bog (OB; Hall, 2020). The San Juan Mountains and Jemez Mountains are mentioned in the text and are labeled in the map. Right: vegetation types (Long et al., 2023) and topography near Santa Fe Lake (red star). Locations mentioned in the text include Lake Katherine (LK; Leonard et al., 2023), Stewart Bog (SB; Jiménez-Moreno et al., 2008), Tesuque Pueblo (TP), Nambé Pueblo (NP), Pecos Pueblo (PP), and Santa Fe (SF). Bottom: Photo of Santa Fe Lake during fieldwork, September 2020 (photo credit: Paul Henne, U.S. Geological Survey). Note steep scree slope and surrounding Engelmann spruce (Picea engelmannii) forest.
Left: age-depth model for Santa Fe Lake calculated with rbacon 3.1.1 (Blaauw et al., 2024). Blue histograms show probability distributions for calibrated radiocarbon dates. Probability distributions of dates that were omitted from the model are crossed out in red. Grey stippled lines show the 95% confidence intervals, darker greys indicate higher probability ages, and red stippled line shows the mean ages for each depth that were used to plot proxies in Figs. 3-6. Grey bands denote (1) an interval interpreted as an erosion event and (2) within lake sediment redeposition (i.e., a slump). Middle: x-ray fluorescence (XRF) counts of titanium (Ti), an element associated with detrital inputs to the lake. Right: percentages of Polypodiaceae spores, interpreted as an erosion indicator, relative to the sum of all pollen and spores.
Geochemical and pollen indicators of erosion and glacial activity from Santa Fe Lake. From left: (a) magnetic susceptibility; (b) x-ray fluorescence (XRF) counts of titanium (Ti); (c) XRF counts of potassium (K, black), iron (Fe, red), and silicon (Si, blue), transformed with centered log ratios (clr); (d) XRF counts (clr) of Si, standardized with K; and (e) percentages of Polypodiaceae spores (pink) and indeterminant, mostly degraded pollen (black). Grey lines denote local pollen assemblage zones.
Comparison among pollen percentages (%), concentrations (C), and influx (I) from selected pollen sub-sums (trees, steppe shrubs, and upland herbs) from Santa Fe Lake. Grey lines denote local pollen assemblage zones. Uncalibrated radiocarbon dates are shown on the y axis. Grey bars show the 2σ calibration range.
Selected percentages of pollen, spores, non-pollen palynomorphs, charcoal concentrations, and charcoal influx from Santa Fe Lake. Grey lines denote local pollen assemblage zones. Empty curves show 10 × exaggerations. Pollen and charcoal analyst: Susann Stolze, Grana Consulting, LLC.
Comparison of proxies for vegetation, regional burning, and alpine glacier activity from Santa Fe Lake with reconstructions of human populations. (a) Dark green shows Pinus pollen as a percentage of the terrestrial pollen sum. Light green shows the percentage of Pinus ponderosa-type pollen. The grey line marks the regional expansion of ponderosa pine. Plus symbols (+) denote the presence of conifer stomates, a proxy for the local presence of trees. (b) Transformed microscopic charcoal influx. Positive values show above average and negative values, below average, regional burning. (c) Brown line shows x-ray fluorescence (XRF) counts of titanium (Ti) before 11,000 cal yr BP, which are indicative of alpine glacier activity in the Santa Fe Lake watershed. (d) Summed probability distribution of 4167 AMS 14C dates from the Rio Grande watershed in New Mexico, USA. Dates were extracted from dataset 2 in Kelly et al. (2025): only dates “identified as AMS and entries known to be normalized.” Blue dashed line is a 200-year smoothing. (e) Population estimates from known settlements in the Tewa Basin in the northern Rio Grande region of New Mexico, which is situated between the Sangre de Cristo and Jemez Mountains, west of Santa Fe Lake. Black lines show population estimates and grey lines uncertainty ranges (redrawn from Ortman, 2016). (f) Zea mays (maize) pollen percentages from Santa Fe Lake.
Age-depth model for surface sediments from Santa Fe Lake calculated with rplum package version 0.5.1 in R (Aquino-López et al., 2018). Grey stippled lines show the 95% confidence intervals, darker greys indicate higher probability ages, and red stippled line shows the mean ages for each depth that were used to plot proxies in Figs. 3-6. Blue bar shows the 2σ calibration range and probabilities for a radiocarbon date of a Picea needle.
Acknowledgements
This research was funded by the U.S. Geological Survey, Land Change Science Program in the Ecosystems Mission Area. We thank Ellis Margolis, Manuel Lopez, Kara Fox, Jens Stevens and Jill Baron for help with coring in a challenging setting. Ellis Margolis, Robert Thompson, and three anonymous reviewers contributed thoughtful comments on an early draft of this manuscript. Christoph Schwörer provided R code to calculate pollen zones. Jeremy Havens and Richard Pelltier improved the figures. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Additional Information
Data availability: All data presented in this manuscript are available in Henne et al. (2026), https://doi:10.5066/P9GDOLI1.
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Supporting Information
Table S1.
Depths, bulk densities, and 210Pb activities of bulk sediment samples from Santa Fe Lake used to produce an age-depth model for the surface core.Authors
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Suggested Citation
Henne, P., Stolze, S., Kehrwald, N., Brice, R.L., Allen, C., 2026, Millennial-scale climatic and cultural impacts on vegetation and fire at the southern edge of the Rocky Mountains, USA: Quaternary Science Reviews, v. 376, 109821, 18 p.; Data Release, https://doi.org/10.1016/j.quascirev.2026.109821.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Millennial-scale climatic and cultural impacts on vegetation and fire at the southern edge of the Rocky Mountains, USA |
| Series title | Quaternary Science Reviews |
| DOI | 10.1016/j.quascirev.2026.109821 |
| Volume | 376 |
| Publication Date | January 28, 2026 |
| Year Published | 2026 |
| Language | English |
| Publisher | Elsevier |
| Contributing office(s) | Geosciences and Environmental Change Science Center |
| Description | 109821, 18 p.; Data Release |
| Country | United States |
| State | New Mexico |
| Other Geospatial | Santa Fe Lake |