Tropical montane forests are rich repositories of biodiversity and endemism and provide essential ecosystem services to downstream human settlements. Given that topography-climate interactions create a multitude of microhabitats over short distances and that species with restricted habitat requirements typically are most vulnerable to extinction, it can be understood why tropical montane forests are among the most vulnerable ecosystems on earth. Considering that they also have tangible economic value, these areas have importance beyond that of biological conservation. The forest along the Manu National Park treeline responds strongly the temperature and precipitation regimes. Predicted climate change in the Andes will require plant species to migrate upslope to avoid extinction. The existence of potential ecological barriers to forces driving altitudinal shift of tree species could contribute to increased extinction rates. We contend that cattle grazing and fire are among the human activities that can have a significant impact on this process. Here we reevaluate the question of tree migration into highland grasslands in the light of microenvironmental and microbiotic information. For this purpose we used an Andean tree line (3650 m) setting where we evaluated 16 plots over a period of 3 years, monitoring recruitment and survival of seedlings and saplings in dry and rainy seasons and recording climatic variables and soil microbiotic profiles.
Results/Conclusions
Most current reports suggest that Andean mountain treelines are not moving, and that they function as hard barriers to species migrations. Other studies point to historical patterns of human activity as the cause for lack of treeline mobility. Our observations suggest a high rate of natural replacement and we propose a model to explain successional dynamics based on nursery species. Preliminary results indicate that in drier plots the predominant pioneer vegetation is Escallonia resinosa. This hardy species grows both in brush and tree form and can be seen as isolated individuals within grassland plots. Escallonia sheltered the highest numbers of saplings of its own and other tree species. However, more humid plots showed a different pattern. In these, Diplostephium sp. was the pioneer species having this role, suggesting differing successional patterns based on water regimes. We consider that our results have direct application to protected area management strategies.