Climatic factors as drivers of elevational shifts in the montane forests-paramo boundary over the last 15,000 years in the northwest Andes

In this study, conducted in the Belmira paramo in the northwestern Andes of Colombia, we used pollen records to track vegetation changes over the past 15 calibrated thousand years before AD 1950 (cal kyr BP). Employing ordination (NMDS), species indicator, and wavelet analysis, we found a pattern of ecosystem change that shifted from a paramo to a tree-dominated community, before shifting to a forest/paramo transitional ecosystem. At the whole pollen community level, our results revealed temporal synchronous changes between floristic composition, arboreal pollen abundance (as a proxy of mean annual temperature - MAT) and Fe concentrations (as a proxy of catchment-scale terrigenous input and runoff variability). Independent univariate wavelet analyses showed similar 1,000 years periodicities for MAT and the orthogonal compositional NMDS axes (NMDS I and NMDS II), while Fe exhibited significant variance at longer periodicities, ranging from 2,000 to 4,000 years. The strong and significant covariation between NMDS II and Fe further confirmed the role of precipitation in shaping tree species turnover on cycles of approximately 1,000 years. The cross-spectral phase relationships hint at potential temporal offsets between environmental proxies and compositional adjustments, however, rather than a calculable response time, these offsets underscore the inherent difficulties in disentangling immediate versus lagged ecosystem responses, which highlights the need for adaptive frameworks in nature-based conservation strategies under rapid global change.