The effect of plant litter on ecosystem properties in a patchy Mediterranean semi-arid shrubland
We studied the distribution of litter in a shrubland of the Negev with a semi-arid Mediterranean climate of less than 200 mm of rainfall per year. Our focus was on the effects of litter on properties of landscape patches relevant to ecosystem processes (water runoff and soil erosion), annual plant community responses (seedling density, biomass production and species richness), and animal activity (soil disturbance by termites). Three 60-m transects, extending across a pair of opposing north- and south-facing slopes and their drainage channel, showed that litter accumulates not only under shrubs, but to a lesser extent also on the crusted inter-shrub open areas.
We used 35 experimental units (‘cells’, 0.5 m ¥ 1 m), each containing a crust and a shrub patch. Because runoff flows from crusted patches and is intercepted by shrub patches, the latter were in the lower third of the cells. Leaf litter was added in single and double amounts providing ca. 0.5 and 1.0 cm litter depth, to either, both, or none of the patches. Litter addition significantly decreased the amount of runoff, regardless of the location and amount of litter applied. Litter on the crust increased species number and seedling density of species with low abundance. Adding a double litter layer increased annual plant biomass production, while a single amount had no effect. Litter addition to the shrub patch affected neither biomass nor species richness. Litter addition to both patches at both quantities caused a large increase in termite activity. Termites caused disturbance by disrupting the crust, which may contribute to the reduction in runoff amounts.
In the open, flat crust patches, annual plant communities are limited in their productivity and species richness, as there are few structures stopping the outflow of water, soil and seeds. Litter adds such structures, but affects the plant communities only when added to litter-free crust. Litter accumulation and its patchy distribution have large impacts on landscape patch properties affecting resource distribution, plant productivity and diversity, and animal activity. Therefore, understanding litter distribution in relation to the patchy structure of the landscape of semi-arid shrubland should be viewed as an important component of shrubland management.
pp. 825-832
doi:
Published 01 December 2001
Boeken, B. & Orenstein, D.
Keywords: Annual plant; Biomass production; Crust patch; Desertification; Runoff; Shrub patch; Soil disturbance; Species richness; Termite; Water retention.
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