Revealing the impact of forest exotic plantations on water yield in large scale watersheds in South-Central Chile

Little, C., et al., 2009. Journal of Hydrology

Original research (primary data)
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Land-use and forest cover change play important roles in socio-economic processes and have been linked with water supply and other ecosystem services in various regions of the world. Water yield from water- sheds is a major ecosystem service for human activities but has been dramatically altered by landscape management superimposed on climatic variability and change. Many studies from different regions of the world have documented that in small watersheds (<100 ha) fast-growing forest plantations reduce water yield. Nevertheless, these effects have not been adequately documented in large watersheds >10,000 ha. In this paper, we examine the temporal variation of the residuals between best-fit precipitation–runoff relationships and instrumental streamflow records for two large watersheds (Purapel en Nirivilo, PNN and Cauquenes en el Arrayaجپn, CQA) located in the Mediterranean-climate coastal range of South-Central Chile. In these watersheds, high resolution satellite imagery shows a decline in native forest cover from 52.3% to 14.2% for PPN and 36.1% to 8.1% in CQA, between 1975 and 2000. Conversely, in the same period the percentage area covered by forest plantations, mainly Pinus radiata, increased from 12% to 55% in PPN, and 4.7% to 42% in CQA. We observed a decreasing trend in summer runoff residuals regressed against annual precipitation in the same period, with slopes significantly different from zero for PPN (p = 0.035) and CQA (p = 0.008). We interpreted this pattern as an evidence of change in the hydrological regime in these watersheds as a consequence of forest cover and land-use changes. From a reanalysis of the observed data we estimate a decrease in runoff from 13.1 to 7.5 mm/summer for PPN and from 7.3 to 5 mm/summer for CQA, refer to the period 1991–2000 compared to 1981–1990. Multiple regression anal- yses of annual and seasonal flows show that besides precipitation, percentage-cover of forest plantations is a statistically significant predictor of summer flow with a partial negative correlation of 0.45 and 0.44 for PPN and CQA, respectively, p < 0.05. This study clearly shows the important effect that land- use change can have on water yield and to our knowledge this is the first study documenting the decrease in summer runoff in a landscape where native forest cover has dramatically declined and forest exotic plantations have expanded. Similar methods could be used elsewhere to inform policy and decision- making regarding forest and land-use planning.

Case studies

Basic information

  • Case ID: INT-169-1
  • Intervention type: Created habitats
  • Intervention description:

    the conversion of deciduous Nothofagus spp. native forests to exotic P. radiata plantations in the Coastal Range of South-Central Chile. Forest exotic plantations, mainly Pinus radiata with different age classes managed with a 20-year rotation ... This category included young exotic plantations (under 3–4 years) and recent clearcuts (<2 years after the image date);

  • Landscape/sea scape ecosystem management: Yes
  • Climate change impacts Effect of Nbs on CCI Effect measures
    Reduced water availability  Negative change in annual and seasonal runoff flows (mm/ year or season)
  • Approach implemented in the field: Yes
  • Specific location:

    two watersheds defined by the Purapel en Nirivilo (PPN) (35°340 S, 72°120 W) and Cauquenes en El Arrayán (CQA) (35°570 S, 72°270 W) in the Coastal Range of South-Central Chile.

  • Country: Chile
  • Habitat/Biome type: Created forest |
  • Issue specific term: Natural infrastructure


  • Notes on intervention effectivness: Effectiveness determined by assessing % of land covered by exotic plantations (vs native forest) and changes in precip/temperature over time then performing a multiple regression to determine the contribution of plantations to changes in runoff: "Finally, we applied the multiple regression model following the forward stepwise technique, in order to estimate a functional rela- tionship between seasonal runoff as the dependent variable, and precipitation and land-use cover as independent variables" "The residual analysis used here permit- ted the assessment of the decrease in summer runoff as a response to the increase in P. radiata plantations area, at the expense of na- tive forests in the 1975–2000 in South-Central Chile. "
  • Is the assessment original?: Yes
  • Broadtype of intervention considered: Not applicable
  • Compare effectivness?: No
  • Compared to the non-NBS approach: Not applicable
  • Report greenhouse gas mitigation?: No
  • Impacts on GHG: Not applicable
  • Assess outcomes of the intervention on natural ecosystems: No
  • Impacts for the ecosystem: Not reported
  • Ecosystem measures:
  • Assess outcomes of the intervention on people: No
  • Impacts for people: Not reported
  • People measures:
  • Considers economic costs: No
  • Economic appraisal conducted: No
  • Economic appraisal described:
  • Economic costs of alternative considered: No
  • Compared to an alternative: Not reported

Evaluation methodology

  • Type of data: Quantitative
  • Is it experimental: No
  • Experimental evalution done: Not applicable
  • Non-experimental evalution done: Empirical case study
  • Study is systematic: