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.