Late Quaternary range dynamics of Pinus remota and Pinus cembroides (Pinaceae): contrasting climatic stability and habitat persistence

The fragmented distribution of many desert and montane species in North America has frequently been interpreted as a legacy of Late Quaternary climatic fluctuations. Among pinyon pines, Pinus remota exhibits a markedly discontinuous distribution in northeastern Mexico and southern Texas, raising the question of whether this pattern represents the remnant of a formerly broader range. To evaluate this hypothesis, we reconstructed the potential distributions of P. remota and P. cembroides from the Last Glacial Maximum (~20 ka) to the present using species distribution models calibrated with Random Forest and palaeoclimatic reconstructions derived from CHELSA-TraCE21k. Both species experienced substantial distributional changes during the Late Quaternary, but their responses differed markedly. Pinus remota showed pronounced contractions and expansions of suitable habitat, with potential distributions ranging from 51% to 149% of its present area. In contrast, P. cembroides maintained consistently broader distributions, ranging from 77% to 200% of its current area. Analyses of temporal stability and habitat persistence revealed extensive climatically stable areas for P. cembroides, whereas P. remota retained only small and fragmented zones of long-term suitability. Comparisons with fossil occurrences from packrat (Neotoma spp.) middens showed variable agreement among periods, although several records coincided with projected suitable areas. These results indicate contrasting biogeographic responses to Late Quaternary climatic oscillations and support the interpretation that the present disjunct distribution of P. remota represents a relict pattern associated with long-term environmental change, whereas P. cembroides persisted across a broader network of climatically stable habitats.