Inputs of particulate organic matter to streams with different riparian vegetation

To test whether afforestation with eucalyptus affects the amount, quality, and timing of litter inputs, we evaluated the inputs of coarse particulate organic matter (CPOM) to 2 headwater streams, one flowing through a mixed deciduous forest and one through a plantation of Eucalyptus globulus. Vertical and lateral traps were sampled at least monthly, and the material collected was sorted into 4 main categories: fallen leaves (several species), fruits and flowers, twigs and bark, and debris. The eucalyptus plantation resulted in a reduction of 32% of total litter inputs, and 73% of lateral inputs, compared to the mixed deciduous forest. It also had a less marked seasonal pattern of inputs, and different timing of peak litterfall, the peak in the deciduous forest occurring in autumn, whereas in the eucalyptus plantation the peak occurred in summer. Similarly, leaf diversity was greatly reduced under the eucalyptus, with 98% of the leaf litter mass from 1 species, resulting in broad changes in litter quality. Litter inputs in the eucalyptus plantations contributed 67% less nitrogen and 65% less phosphorus to the stream than in the deciduous forest. Although eucalyptus plantations result in broad changes in organic inputs, no drastic impacts on the structure or function of benthic communities are evident so far in the Aguera stream. Nevertheless, caution suggests maintaining the quantity and timing of allochthonous inputs by keeping buffer strips of native riparian forest.