5. Conclusions
This study demonstrated how native forest restoration in formerEucalyptus plantations affected streamflow over a nine-year post-treatment period in the Valdivian Coastal Reserve, south-central Chile. To our knowledge this study is the first to test streamflow response to native forest restoration in former fast-growingEucalyptus forest plantations. Clear-cutting of Eucalyptusplantations and replacement with young planted and naturally regenerating native forest species increased streamflow and enhanced water provision, a key ecosystem service. An aging Eucalyptusplantation (7 to 20 years) continued to have high rates of transpiration that apparently prevented the recovery of base flow, whereas base flow gradually increased in the catchments under restoration, confirming predictions that native forest has lower evapotranspiration rates than intensively managed fast-growing plantations. A very dry year, early in the restoration period, revealed that the catchments were still prone to drought-induced streamflow reductions, whereas later increases in base flow indicated that restoration of base flow after removal of forest plantations may require a decade or more.
This catchment forest restoration study is a long-term effort. The native forests under restoration are very young (8 years old) and will continue to change and affect streamflow as they grow. The development of a fully stocked, multi-tier forest is expected to take 50 to 70 years, and conditions comparable to old-growth Valdivian rainforest will require 130 to 180 or more years (Lara et al., 2013). Continued monitoring of these experimental catchments is essential to understand how native forest succession influences streamflow in the long term.
Differences in streamflow response among catchments under restoration of native forests could not be attributed to specific differences in native stand density or basal area, nor to differences in the area in native forest riparian buffers. Instead, other factors controlling catchment hydrology, such as geomorphology and geology that determined water transfer and differences in groundwater storage capacity, influenced streamflow response to forest restoration.
This long-term forest hydrology research and monitoring program has been possible due to a diverse institutional arrangement involving academic, NGO, and forest industry partners, and a sequence of grants from various agencies throughout this period. Maintaining long-term catchment studies is a major challenge in Chile, which like many countries in Latin America lacks a national funding program for long-term catchment or ecosystem research. The basic research findings about hydrology and forest succession and their relevance to key policy decisions about water and forest ecosystems in the context of climate change, as shown by this study, underscore the importance of continuation and expansion of long-term catchment forest hydrology studies in Chile and elsewhere in the global South.