Experimental warming and nitrogen deposition in clear-cuts and forest edges: Assessing impacts on plant communities and tree seedling performance

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.