In the tropics, there are vast areas of degraded land, which can be restored back into higher and sustainable production with tree planting. In this way previously degraded lands could play a key role for improved food security and at the same time offer various other benefits.
Water is crucial for food security and climate change adaptation. Under the last decades the popular view that trees are beneficial for water availability has lost credibility since paired-catchment studies show the contrary: afforestation decreases water yields globally. Thus, the general science based view is that trees always reduce water availability. This has raised numerous concerns about tree planting in water limited regions, undermining support for widespread forestation and reforestation projects. Notably, tree planting – whether for local livelihood or environmental purposes – has often lacked support.
It is rarely recognized that this trade-off theory in which more trees mean less water is based almost entirely on studies of forest plantations of exotic eucalyptus and pines outside the tropics. We lack empirical evidence from widespread areas of forests, woodlands and agroforests with open tree cover on easily degradable tropical soils. This strongly limits the applicability of the trade-off theory, since it is on degraded soils where tree planting could theoretically improve water availability through improved soil hydraulic properties. Recently a number of case studies in relevant contexts indicate a more positive effect of trees on water, and demonstrate the need for a more diversified view for good policies and land use decisions.
In addition, the trade-off theory has repeatedly been criticized for only considering trees as water consumer – neglecting their role as contributors to rains. New analyses suggest that this might indeed be more important than previously known.
The workshop will be convened 4-5 November, 2014 in Uppsala. The first day will be devoted to sharing knowledge between scientists and practitioners from the policy and management community. This feedback will then be taken further during the second day by a smaller group that will draft a concise “opinion/perspectives paper” targeted to a multidisciplinary policy and management audience. We will also explore tools to visualize spatial relationships between trees and the water budget to improve understanding and communication of the complex hydrological processes to decision makers. Participation in the workshop is by invitation only, and limited to a small group. Contact Ulrik Ilstedt if you are interested in the workshop. Further background and information can be found here…