Resource Details

Hydrological functions of tropical forests: not seeing the soil for the trees?

Literature: Journal Articles Available at NO COST

Bruijnzeel, L. A. 2004. "Hydrological functions of tropical forests: not seeing the soil for the trees?", Agriculture, Ecosystems & Environment, vol. 104, no. 1, pp. 185-228.

Contact Info

Corresponding Author: sampurno.bruijnzeel@geo.falw.vu.nl

Affiliations

Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085-1087, 1081 HV Amsterdam, The Netherlands

Link(s)

Located at Science Direct

Available free of charge at CATIE

Description

  • This literature review provides a summary of hydrological functions in tropical forests, and includes differences in the hydrology of disturbed areas, secondary forests, and mature forests.
  • Climate:
    • Reforestation is usually too small to have an effect on climate (local temperature and rainfall), but in some situations such as montane cloud forest, the forests rely significantly on fog drip, so reforestation could have an impact on total soil water (water from fog drip averages 5-20% of total water but sometimes much higher).  
  • Water use:
    • Conventional wisdom is that forests act as a sponge by soaking up the surface water during rainy season and releasing it slowly during the dry season, but this hasn't really been demonstrated (and it is hard to study because of confounding factors like geology, natural climatic variation, and lag time for the reforested site to have a measureable effect). 
    • Crops will consume less water than natural forests and increase runoff, while exotic tree plantations (Eucalyptus) can consume even more water than natural forests (cause a “mining” of soil water reserves).  
  • Flow regimes:
    • Forest clearing will result in greater surface runoff but reduced infiltration capability. Net effects on the flow regime will depend on the depth of the soil and the size of the underground water reservoir.  
    • Reforestation will reduce the peak runoff flow and reduce flood damage, but we are unsure about the maintenance of low flows. Natural regrowth and reforestation in a cleared watershed can also restore hydrologic functioning in 3-5 years (measured by evapotranspiration found to be very similar to that of a mature forest).   
    • Reforesting with rapidly growing timber trees can be risky because they will have a high water demand, and their water demand will peak in years 5-10 of their growth (before soil infiltration properties have been restored).  
  • Erosion:
    • Clearing of forests will result in greater sediment loads (erosion), but properly managed grazing or agriculture can have low rates of erosion.  
    • Large scale erosion events (landslides) are more dependent on geology (because they are deep) and surface vegetation doesn't matter.  
    • Litterfall is an important determinant of reduction in erosion, and restored forests often lag in their accumulation of litter, so reforestation can take several years (or decades) to reduce erosion. Modifications like check dams and sand traps may be more effective in reducing runoff than can reforestation.

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