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Impact of timber harvesting on litterfall inputs and benthic coarse particulate organic matter (CPOM) storage in a small stream draining a eucalyptus plantation

Abstract:

Eucalyptus plantations have a short rotation cycle and harvesting occurs every 12-15years, with the potential to modify the ecological integrity of the small streams draining the harvested areas through the reduction of litterfall inputs. We studied litterfall inputs and benthic coarse particulate organic matter (CPOM) storage in a small headwater stream draining a eucalyptus (Eucalyptus globulus Labill.) plantation before and after clear felling of the plantation. We hypothesized that wood harvesting will result in a reduction of CPOM inputs and storage in the stream. Litterfall inputs ranged 530-700gm-2y-1 and were approximately halved (200-320gm-2y-1) after the harvesting of the eucalyptus trees. Bark and woody materials showed the largest reduction. Leaf inputs were initially reduced sharply, but, during the second year after the harvest, they recovered to about 90% of the values observed before the harvesting. Harvesting of the eucalyptus plantation caused an increase of benthic CPOM storage to 535gm-2, but this was a temporary effect and these materials were washed downstream of the study reach. One year after the harvesting, benthic CPOM was reduced below 15gm-2. Bark, twigs and other woody residues generated during the preparation of the logs for transportation were retained within the study site and represented the main component (>90%) of the benthic CPOM after timber harvesting. However, 2years after the harvesting, low inputs of these materials caused an overall reduction of in-stream retention and residence time of benthic CPOM. Amount and composition of benthic CPOM changed quickly in response to alterations of the riparian forest, so we propose the use of CPOM as an indicator of the impact of forestry activities on the ecological functioning of small streams. © 2011 Elsevier B.V.