Original paper

Effects of eucalyptus plantations on CPOM dynamics in headwater streams: a manipulative approach

Bañuelos, R. Larrañaga

Abstract

There is concern about the ecological impacts that vast eucalyptus plantations in the Iberian Peninsula could have on streams, but the evidence so far gathered is far from conclusive. In an attempt to check the effects of eucalyptus plantations while reducing inter-stream variability, we performed a manipulative experiment. In each of two small headwater streams, two 50-m long reaches were covered with 1-mm mesh net in order to exclude terrestrial inputs. We periodically added deciduous litter to the upstream reaches (deciduous treatments), and eucalyptus litter to the downstream ones (eucalyptus treatments), simulating the amount, composition and timing of inputs under both types of forest, and followed litter dynamics in the stream (inputs, storage and outputs). Two reaches further upstream were used as controls to evaluate the effect produced by the exclusion mesh. Inputs in eucalyptus plantations were more abundant but less diverse than deciduous ones, and were more evenly distributed throughout the year. Most deciduous inputs occurred in a single autumn pulse. Benthic litter storage was also higher in the eucalyptus treatments, but differences in litter export were small. Although leaf-litter decayed more slowly at eucalyptus reaches, net processing outputs were greater than at deciduous ones since eucalyptus leaves stayed in place for longer, because a larger fraction entered the stream during low flows. As a result, ecosystem efficiency in input use was higher in the eucalyptus treatments. In conclusion, our results confirmed previous findings that afforestation with eucalyptus produces noticeable changes in stream litter budgets.

Keywords

litter breakdownlitter retentiondeciduous vs eucalyptusbenthic litter storageparticulate organic matter