Three millennia upper forest line changes in northern Ecuador: Pollen records and altitudinal vegetation distributions

New pollen records from a peat bog and a soil profile in the Guandera Reserve (0°36′N, 77°42′E) document the altitudinal position and dynamics of the natural upper forest line (UFL) in the deforested landscape of northern Ecuador during the last ~ 3000 yr. We tested the hypothesis that páramo vegetation between 3600 and 4100 m developed during the last centuries as a consequence of anthropogenic deforestation. Analysis of pollen and non-pollen palynomorphs in 170 cm long peat core G8 at 3810 m, some 200 m above the current UFL, shows five periods of forest dynamics: (1) from 2880 to 1370 cal yr BP the UFL was at ~ 3500 m and patches with asteraceous trees and shrub in the páramo were close to the site; (2) from 1370 to ~ 500 cal yr BP the UFL lowered to ~ 3350 m; (3) from ~ 500 to ~ 300 cal yr BP upper montane rainforest (UMRF) expanded rapidly and the UFL shifted to ~ 3550 m while relatively wet climatic conditions prevailed; (4) from ~ 300 to ~ 150 cal yr the UFL reached ~ 3600 m and (5) from ~ 150 cal yr BP to present high proportions of Rumex indicate an increase of agricultural fields. The UFL continued at ~ 3600 m. Pollen analysis of the 70 cm deep soil monolith G7 shows during the last three millennia a continuous presence of páramo at 3820 m elevation but did not allow to estimate altitudinal shifts of the UFL. We conclude that during the last three millennia the natural UFL was maximally at 3700 m elevation. This is in support of previous palynological studies by Wille et al. (2002) and Bakker et al. (2008). The hypothesis assuming an UFL around 4000 m is rejected which implicates páramo vegetation above 3650 m reflects a natural ecosystem. There is now compelling evidence that planting forest in the frame of the Kyoto Protocol is unjustified above 3650 m elevation.