The Impacts of Native Forests and Forest Plantations on Water Supply in Chile

Abstract

Over the past 40 years, south-central Chile has experienced important land-use-induced land cover changes, with massive conversion from native forests (NF) to Pinus radiata D.Don and Eucalyptus spp. exotic forest plantations (FP). Several case studies have related this conversion to a reduction in water supply within small catchments (<100 ha). In this work, we explore the impacts of NF and FP on streamflow by using a large-sample catchment dataset recently developed for Chile. We select 25 large forested catchments (>20,000 ha) in south-central Chile (35° S–41° S), analyze their land cover and precipitation spatial distributions, and fit a regression model to quantify the influence of NF, FP, grassland (GRA) and shrubland (SHR) partitions on annual runoff. To assess potential effects of land cover changes on water supply, we use the fitted model (R2 = 0.84) in synthetic experiments where NF, GRA and SHR covers within the catchments are replaced by patches of FP. We show that annual runoff consistently decreases with increments of FP, although the magnitude of the change (ranging from 2.2% to 7.2% mean annual runoff decrease for 10,000 ha increment in FP) depends on several factors, including the initial land cover partition within the basin, the replaced land cover class, the area of the catchment, and the type of catchment (drier or humid). Finally, in the context of the mitigation strategies pledged in the Chilean NDC (Nationally Determined Contributions defined after the Paris Agreement), which include the afforestation of 100,000 ha (mainly native forest) by 2030, we quantify the impacts on water supply due to the afforestation of 100,000 ha with different combinations of NF and FP. We show that annual runoff is highly sensitive to the relative area of FP to NF: ratios of FP to NF areas of 10%, 50% and 90% would lead to 3%, −18% and −40% changes in mean annual runoff, respectively. Our results can be used in the discussion of public policies and decision-making involving forests and land cover changes, as they provide scientifically-based tools to quantify expected impacts on water resources. In particular, this knowledge is relevant for decision making regarding mitigation strategies pledged in the Chilean NDC.

Inversión estatal en investigación y desarrollo forestal frente a la COP-25: ¿Libres de elegir entre bosques nativos y plantaciones exóticas?

“…Los bosques entregan múltiples beneficios además de secuestro de carbono, por lo que debieran ser el foco de los esfuerzos privados y públicos (Chazdon & Brancalion, 2019). La evidencia científica en Chile muestra que los bosques -si es que se les permite crecer-ayudan a regular los caudales, controlar la erosión y mantienen la biodiversidad (Alvarez-Garreton, Lara, Boisier & Galleguillos, 2019;Banfield, Braun, Barra, Castillo & Vogt, 2018;Braun et al, 2017;Iroumé, Mayen & Huber, 2006;Little, Lara, McPhee & Urrutia, 2009;C. Oyarzún, Campos & Huber, 1997;Oyarzún & Huber, 2003).…”

Effect of Land Use/Cover Change on the Hydrological Response of a Southern Center Basin of Chile

“…The increase in the forest area was higher than 16% of the total basin area. Additionally, Alvarez-Garreton et al [78] demonstrated that annual runoff always decreases with the increase of forest plantation area. However, the magnitude of the changes depends on several factors, including the initial percentage of the land covered within the basin, the land use/cover type replacement, and the basin area and its type (dry or wet basins).…”

Large-sample hydrology: recent progress, guidelines for new datasets and grand challenges

“…Wehren et al 2010), and changes in land cover influence the distribution of streamflow, specifically baseflow volumes and flashiness of runoff (e.g. Vertessy 2000, Brown et al 2005, Alvarez-Garreton et al 2019. Consequently, providing information on such alterations is critical to assess the magnitude of human impacts on hydrological behaviour (e.g.…”