Abstract
This study presents the results of a long-term paired catchment
experiment in south central Chile (mean annual precipitation = 2,500 mm,
5% falling in summer, mean annual temperature = 10 °C) in which
fast-growing plantations of exotic Eucalyptus spp. were clearcut
and replaced with native temperate rainforest species as part of an
ecological restoration project. Precipitation, streamflow, and
vegetation were measured starting in 2006 in four small (3 to 5 ha)
catchments with Eucalyptus globulus plantations and native
riparian buffers in the Valdivian Coastal Reserve. In 2011, the
12-yr-old Eucalyptus plantations were harvested in three
catchments, and the clearcut area was planted with native trees
(Nothofagus dombeyi), and diverse native forest species
regenerated vigorously. In the restoration period (2011 to 2019), annual
streamflow increased in average by 21 – 73% compared to the 2006-2010
pre-treatment period, and as much as 100% in wet years and by more than
150% in fall and summer of some years. Streamflow was 50 to 100% lower
than before treatment in two dry summers (2014-2015. Base flow increased
by 28 to 87% during the restoration period (2011 to 2019) compared to
the pre-treatment period, and remained elevated in later years despite
low summer precipitation. Streamflow increases persisted through the
first decade of restoration. Overall, these findings indicate that
removal of Eucalyptus plantations immediately increased
streamflow, and native forest restoration gradually restored deep soil
moisture reservoirs that sustain base flow during dry periods, and these
flows showed steady positive values in the last three years contributing
to water provision ecosystem services. The results of this study are
relevant to efforts to restore native forest ecosystems on land
currently intensively managed fast-growing forest plantations. They also
provide useful information to inform policy and decision-making related
to options for climate change mitigation under a drying trend in
South-central Chile. To our knowledge this study is the first to test
streamflow response to native forest restoration in former fast-growing
Eucalyptus forest plantations.