Relationship between fragmentation, degradation and native and exotic species richness in an Andean temperate forest of Chile

Human impact such as forest fragmentation and degradation may have strong effects on native and exotic plant communities. In addition, these human-caused disturbances occur mostly in lowlands producing greater fragmentation and degradation there than in higher elevations. Plant invasion should be greater in more fragmented and degraded forests and hence lowlands should be more invaded than higher elevations. In turn, native species richness should be negatively related to fragmentation and degradation and hence greater in higher elevations within a forest type or elevation belt. We assessed these hypotheses in an Andean temperate forest of southern Chile, Araucania Region. We recorded the vascular plant composition in twelve fragments of different size, perimeter/area, elevation level and evidence of human degradation (loping, fire, cattle faeces). Based on these variables we performed a fragmentation and a degradation index. Pearson correlations were used to analyze the relationship between all these variables. We found that fragmentation and degradation were positively correlated, and each of them decreased with altitude. Furthermore, fragmentation and degradation affected native and exotic species richness in different ways. Invasion was enhanced by both fragmentation and degradation, and as consequence of the altitudinal patterns of these human-caused disturbances, invasion seems to occur mainly in lowlands. In turn, native species richness decreased with fragmentation, and it was not related to degradation nor altitude.