Partial river flow recovery with forest age is rare in the decades following establishment.
Global change biology
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Bentley, L., & Coomes, D. (2020). Partial river flow recovery with forest age is rare in the decades following establishment.. Global change biology, 26 (3), 1458-1473. https://doi.org/10.1111/gcb.14954
Forest regeneration and expansion is occurring in many countries, with 80 million ha established from 2000-2012 under the Bonn accord and 17.5 million ha established from 1990-2005 according to the Food and Agriculture Organisation. Multiple reviews have linked increasing forest cover with reduced river flow and potentially detrimental effects downstream. Previous reviews have investigated trends in river flow response over time, but the influence of forest age remains uncertain. Partial river flow recovery (towards non-forested conditions) has been reported in decades following forest establishment, but the role of climate in driving these trends has not been explored. Here, we evaluate river flow trends in 43 studies following forest establishment, which provide sufficient information to distinguish the effects of aging forests from variable climate. Our meta-analysis supports previous findings showing that forestation reduces annual river flow (by 23 percent after 5 years and 38 percent after 25 years) with greater reductions in catchments with higher mean annual precipitation, larger increases in forest cover, and which were idle, rather than agricultural land, prior to forestation. The impact of forests on river flow is sensitive to annual precipitation and potential evapotranspiration, but responses are highly variable. Forests affect river flow less when annual precipitation is low, and sensitivity to precipitation decreases as catchment aridity increases. The majority of catchments demonstrated persistent river flow declines after forest establishment. However, nine catchments showed partial flow recovery after an initial decrease, with peak flow reductions at an average age of 15, and across a range of tree species. The mean rate of recovery was 34 mm per year over five years. Partial flow recovery with forest age cannot be commonly expected however, and forestation programs should take in to account that changes to annual river flow are likely to persist for up to five decades.
Climate, Rivers, Agriculture, Climate Change, Forests
This work was funded by a grant from IUCN (International Union for the Conservation of Nature) through the KNOWFOR project (grant number: GB-1-203034)
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External DOI: https://doi.org/10.1111/gcb.14954
This record's URL: https://www.repository.cam.ac.uk/handle/1810/299426
Attribution 4.0 International
Licence URL: https://creativecommons.org/licenses/by/4.0/