Temperature and Humidity 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 15,000 years before present (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, which became a forest/paramo transitional ecosystem again. At the whole pollen community level, our results revealed spatially synchronous processes (i.e., temporal co-evolution) at regional scales between changes in pollen composition and mean annual temperature (MAT) and Fe concentrations (proxy of precipitation). Independent univariate wavelet analyses showed similar periodicities between 500 and 1000 years for MAT and the orthogonal compositional NMDS axes, while Fe exhibited significant variance at longer periodicities, ranging from 2000 to 4000 years. The strong and significant covariation assessed using wavelet coherence between NMDS II and Fe further confirmed the role of precipitation in shaping tree species turnover on cycles of approximately 1,000-500 years. However, our study points to the existence of a lag in vegetation tracking to climate change of centuries, which could constitute a major challenge for the implementation of effective nature-based strategies of conservation to ameliorate the ongoing global change.