With a field experiment, we studied nitrogen deposition and climate warming impacts on planted tree seedlings and associated understory plants in clear-cuts and forest edges. Microenvironments were assessed, including soil properties and edge effects. Microenvironmental effects on plants were habitat dependent. Moderate climate warming may enhance tree seedling performance and plant cover in a clear-cuts of Pacific Northwest coastal ecosystems.
Abstract
Questions
Do nitrogen deposition and climate warming affect tree seedlings and plant communities in different habitats? In these habitats, how do microenvironments, including soil properties and, when applicable, edge effects relate to plant performance?
Location
The University of British Columbia Malcolm Knapp Research Forest, Maple Ridge, British Columbia, Canada.
Methods
We assessed performance of Pseudotsuga menziesii (Mirb.) Franco, Thuja plicata Donn ex D. Don and Tsuga heterophylla (Raf.) Sarg. planted tree seedlings and associated vascular plant communities. Performance of tree seedlings (height) and under vascular plant communities (percent cover) were examined in an experiment with warming (open-top chambers) and nitrogen deposition (ammonium nitrate applied at 10 kg N ha−1 year−1) treatments applied to subplots in six forest edges and six clear-cuts (N = 298 total subplots).
Results
In clear-cuts, tree seedling height increased with experimental warming and differed among species, and vascular plant cover increased with warming. In clear-cuts, species identity, not soil variables, was a strong predictor of height, and plant cover was negatively related to pH. In forest edges, edge position and some soil variables were related to height, but not plant cover. There were no interaction effects found between experimental nitrogen deposition and warming.
Conclusions
Our results suggest that moderate warming can enhance tree seedling height and understorey vascular plant cover in clear-cuts in Pacific Northwest coastal ecosystems, but low nitrogen deposition may not have an effect alone or synergistically with warming.