Saturday, 15 July 2006
166-4

The Effect of Forest Clearance and Subsequent Land Use on Erosion Losses and Soil Properties in the Golestan National Park, Iran.

Ali Reza Zahirnia, Soil and Watershed Managment Research Institute, Agriculture Faculty of Tehran Univ, Karaj, Terhan, Iran and Toraj Asadi, Islamic Azad Univ, Bandar Abbas Branch, P.O. Box 79145/1311, Bandar Abbas, Iran.

As pressure on land and forest resources increases, there is a growing need to assess and improve the sustainability of slash-and-burn agriculture in Hyrcanian uplands. On steep-hillslopes (24–32o) in the forest buffer zone of the Golestan National Park , following clearance of natural forest the relative impact on surface runoff, soil erosion and soil properties of three land-use treatments: maintained weed-free without cultivation (bare); cultivated with herbaceous crops (agriculture); and cultivated with herbaceous crops and intercropped with Olive trees (Olea europea L.) and White mulberry trees (Morus alba L.) contour hedges (agroforestry) were assessed over a 5-year period and compared with an uncleared secondary forest (control). The forest provided good protection against surface runoff (which was consistently less than 0.2% of rainfall) and soil erosion losses (<500 kg.ha-1.yr-1); agriculture caused a seven-fold increase in surface runoff and 21-fold increase in soil erosion. However, agroforestry was effective in conservation of water (45% reduction in runoff compared with agriculture) and soil (erosion reduced by 35%). The clearance of the secondary forest led to large changes in most measured soil properties. Over 5 years concentrations of organic matter declined by 31%, total N by 38%, exchangeable K by 47%, Ca by 43% and Mg by 56%; over the same period bulk density increased by 48%. Of the soil properties more subject to year-to-year fluctuations, after 5 years the concentration of available P was 36% less in cleared plots than in forest, exchangeable Na was 50% less and moisture content 43% less. Only total P concentration and pH were unaffected. Five years after forest clearance there was no good evidence that these changes had stabilized and very little difference in soil properties was found amongst the three land-use treatments. However, within the agroforestry plots, exchangeable K, Na and sand concentrations became higher under the hedgerows than between them (by 14, 9 and 8%, respectively), whilst clay concentration became higher between them (by 9%). The results indicate that this low-input, contour-tree-hedgerow technology is effective at soil and water conservation through the sieve-barrier effect and increased water infiltration (respectively) and has the potential to enhance the sustainability of this land-use system at a plot scale. Key words: Slash and burn agriculture, Surface runoff, Soil erosion, Soil fertility, Forest buffer zone, Agroforestry, Contour hedgerow, Pyrus boissieriana, Golestan National Park.


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