Endangered Mexican Pine Held Its Climate Niche for 21,000 Years

An endangered pine confined to a single mountain range in western Mexico has clung to essentially the same climatic niche for roughly 21,000 years, according to a new modeling study published in Discover Life. Pinus rzedowskii, a relict species found only in the Sierra de Coalcomán within the Sierra Madre del Sur, shows what the researchers describe as climatic niche stasis: across the Last Glacial Maximum, the present day, and two future scenarios for 2071–2100, the modeled ecological niche of the species barely moved. Niche overlap between past and future projections reached values of 0.867 to 0.936 on a similarity index that runs from 0 to 1, and the geographic center of the niche shifted by no more than 5.4 kilometers across the entire span of time examined.

The finding is striking because the species’ own history is precarious. Pinus rzedowskii survives in 17 fragmented populations whose sizes range from roughly 3,000 reproductive individuals down to just 13. It occupies slopes between 1,700 and 2,300 meters above sea level on poorly developed cambisol soils, and it reproduces poorly, with only 17.1 percent viable seeds and 5.0 percent germination recorded in earlier work. Despite carrying high genetic variation for its group, the tree is classified as endangered, and its extreme restriction to one mountain range made it, in the authors’ view, an ideal test case for the hypothesis that climate change drives habitat loss and local extinction over different time scales.

To reconstruct the species’ climatic history, the team built ecological niche models using three algorithms in parallel: a generalized linear model, a generalized additive model, and a maximum entropy method. From an initial set of 331 presence records drawn from specialized literature and field surveys, they filtered duplicates and points closer than one kilometer apart, leaving 27 unique records for training. Pseudoabsences were generated at a 1:10 ratio and replicated five times, and models were calibrated with K-fold cross-validation using five partitions and ten replicates. Only individual models scoring a True Skill Statistic of at least 0.7 entered the final weighted-mean consensus, which itself performed strongly, with a TSS of 0.950, a receiver operating characteristic score of 0.990, and a Kappa coefficient of 0.724.

The environmental backbone of the models came from four variables that survived screening for multicollinearity: Temperature Seasonality, the mean daily minimum temperature of the coldest month, Precipitation Seasonality, and the De Martonne Aridity Index, a composite of annual precipitation and mean annual temperature. Precipitation Seasonality contributed most to the niche, with a score of 41.02, followed by the Aridity Index at 25.63 and Temperature Seasonality at 22.84. The authors note that precipitation seasonality recurs as the dominant niche variable in other Mexican conifers, including firs, junipers, and several pines, and even in the species’ close relictual relatives within the pinyon pine subsection, suggesting a broad pattern in which moisture rhythms, not simply temperature averages, define where these trees can live.

The calibration area was deliberately constrained to the Michoacán district of the Sierra Madre del Sur subprovince, the region historically accessible to the species. Climate layers came from the CHELSA database for the present, defined as 1981–2010, and for the future window of 2071–2100, while the Last Glacial Maximum reconstruction, about 21,000 years before present, drew on the PaleoClim database. One problematic variable, mean monthly precipitation of the coldest quarter, was excluded after artifacts appeared in the past and future layers. For the glacial reconstruction the team used the NCAR CCSM4 global circulation model, chosen because its simulations match palynological and geomorphological evidence for central Mexico, and for the future they used the Max Planck Institute Earth System Model under two contrasting shared socioeconomic pathways: SSP1-2.6, a sustainability scenario with sharply reduced emissions, and SSP5-8.5, a high-emissions scenario in which carbon dioxide output doubles by mid-century.

The projections traced a clear trajectory. Suitable area, classified with a minimum training presence threshold, was largest during the Last Glacial Maximum, covering 19.7 percent of the projected area, but almost entirely of low quality; the glacial niche sat in the southern portion of the calibration zone. From that past maximum the suitable area contracted by more than 12.5 percent to the present, when the three suitability categories together covered 81,000 hectares, or 7.2 percent of the Sierra Madre del Sur, concentrated in the central Sierra de Coalcomán. Under the future scenarios the trend reverses: the low-emissions model projected 12.2 percent suitable area and the high-emissions model 9.5 percent, with the consensus average showing a slight expansion of more than 5 percent relative to today. Crucially, habitat quality, defined as the combined area of high and moderate suitability, was lowest in the glacial period and highest in the future average, meaning the species traded a broad but marginal glacial footprint, about 221,300 hectares, for a smaller but ecologically richer modern one.

The strongest evidence for stasis came from the geometry of the niche itself. Weighted by environmental suitability, the niche centroid moved 5.4 kilometers to the northwest, mainly latitudinally, between the glacial maximum and the present, and is projected to shift only 0.5 kilometers toward lower latitudes by the end of the century. Schoener’s overlap index registered 0.869 between past and present, 0.936 between present and future, and 0.867 between past and future, all with non-significant P values above 0.05. The spatial configuration of suitable conditions in the future projections is nearly identical to the current distribution, with the best areas concentrated in the Sierra de Coalcomán and small extensions west of Coalcomán and east of Aguililla. Together, the authors conclude, these measures support the interpretation that the Sierra Madre del Sur, particularly its Michoacán subprovince, has experienced climatic stasis and functioned as a potential climatic refuge in which the species persisted through glacial oscillations with only moderate altitudinal movement.

This scenario contrasts with the fate of other Mexican conifers that track cold conditions uphill. Species such as Pinus hartwegii and the firs require temperatures below 16 degrees Celsius and elevations above 2,500 meters, making them, the authors argue, clearly vulnerable to extinction as climates warm. Pinus rzedowskii, by comparison, tolerates temperatures between 16 and 26 degrees Celsius below 2,500 meters, and its refuge apparently buffered it against the fluctuations that displaced cold-adapted relatives. The team suggests the pattern may extend beyond a single species: the Sierra de Coalcomán, a Cretaceous-era range recognized as a conservation priority for its endemism, may harbor a broader community of species sharing this climatic stability, and related rare pines such as Pinus maximartinezii and Pinus nelsonii appear, from prior modeling, to show similar precipitation-driven niche stasis.

The study’s authors are careful about limits. The models consider climate only; soil variables such as available nitrogen, topographic attributes like surface rugosity and stoniness, and biological data on seed production and seedling establishment were unavailable for the region and would refine the niche characterization. They recommend caution before treating the projections as the sole basis for management decisions, and they point to genetic compensation models that incorporate genomic information on local adaptation as a next step. For conservation, however, the message is concrete: the central and northern zones of the species’ distribution contribute most to the niche centroid and show the highest overlap across all three time periods, and the central zone already holds the largest population with the best regeneration, seed viability, and genetic variability. Prioritizing those zones, alongside land-use regulation, local seed production areas, nursery-based reforestation with SEMARNAT and educational institutions, and ex situ establishment of new populations in moderately to highly suitable future habitat, offers a grounded path for keeping this 21,000-year refuge occupied.

Subject of Research: Climatic niche stability of the endangered relict pine Pinus rzedowskii across past, present, and future climate scenarios

Article Title: Climatic niche stasis of Pinus rzedowskii (Pinaceae), a relictual and endangered species

Article References: Molina-Sánchez, A., Moreno-Letelier, A., González, C., González-Rodríguez, A., Piñero, D., Hernández-Guzmán, R., & Delgado, P. (2026). Climatic niche stasis of Pinus rzedowskii (Pinaceae), a relictual and endangered species. Discover Life, 56(1), Article 36. https://doi.org/10.1007/s11084-026-09759-z

Image Credits: AI Generated

DOI: 10.1007/s11084-026-09759-z

Keywords: Pinus rzedowskii, ecological niche modeling, climatic niche stasis, Sierra Madre del Sur, Last Glacial Maximum, climate refugia, endangered conifers, Mexico, species distribution models, conservation, precipitation seasonality, climate change