| I studied the effects of six levels of dispersed green tree retention harvesting (2%, 10%, 20%, 50%, and 75%, and unharvested control) on understory plant communities in the 8th growing season post-harvest in the mixedwood boreal forest in northwestern Alberta. Sample plots were located in the partially harvested (retention) strips as well as in corridors used by the harvesting equipment. As the amount of retention decreased, the difference, as compared to unharvested control, increased. In lower retention levels the cover of understory vegetation, especially graminoids, was higher but species richness was unaffected. Lower retention lead to increased abundance of early successional, shade-intolerant species. The results suggest a possible threshold in response between the 10% and 20% retention. In terms of understory cover and composition machine corridors resembled clearcuts within partially harvested forests. |
