Patterns of Mountain Vegetation Dynamics and their Responses to Environmental Changes in the South Ecuadorian Andes

Abstract

The South Ecuadorian Andes harbour an outstandingly high species-richness. Many different environmental factors influence one another in a most limited space and create unique and complex ecosystems. This area is highly endangered because of growing human impact through the intensification of land-use and global change. Only little is known about palaeoecological history and landscape dynamics of this area. The information about why and how ecosystems changed in the past is crucial for the development of innovative strategies for conservation and future climate predictions. In this study, we present palynological analyses carried out in the southern Ecuadorian Andes region that help to shed light on patterns and processes in present and past ecosystems. A palaeoecological study of the Quimsacocha volcanic basin on the eastern ridge of the western Andean Cordillera reveals climate, vegetation and fire regime changes since the early Holocene period. The mid-Holocene was a period of severe environmental change due to a drier and supposedly warmer climate in this area. During the late Holocene, several warm and cool phases are indicated in the record. Fire was present in the area since the early Holocene and may be a first sign of human impact. Combined multivariate analysis with other cores in the south Ecuadorian Andes revealed partly contrasting developments, which are supposedly due to the environmental heterogeneity of the different sites. Furthermore, a three year study of the modern pollen rain – vegetation relationship was carried out in the Podocarpus National Park region, in order to understand the pollen dispersal patterns of the different vegetation types of premontane forest, lower montane forest, upper montane forest and páramo to create a better basis for interpretation of fossil pollen data. A comparison of abundance and presence-absence data at family level for pollen and vegetation showed that diversity, distribution and abundance patterns correspond well to one another in both datasets. However, varying amounts of long-distance transported pollen, uneven pollen productivity of different taxa and heterogeneous wind systems impact the patterns. Analyses of pollen accumulation rates indicated low inter-annual but high spatial variation in the pollen data. The assessment of two different pollen trap types frequently used in tropical palynological studies, the modified Oldfield trap and the Behling trap, in comparison with surface soil samples and a reference trap, showed that in soil samples, taxa with a fragile exine are represented to a lesser extent than in the traps. Furthermore, it indicated that whereas in the forest, all trap types provide similar results, the Behling trap should be preferred in the páramo, as it better withstands high radiation and dry periods. All analyses add to a precise and comprehensive understanding of vegetation dynamics of the tropical Andes hotspot in space and time.