Modeled Vegetation Community Trajectories: Effects from Climate Change, Atmospheric Nitrogen Deposition, and Soil...

Area of Science:

• Ecology
• Environmental Science
• Conservation Biology

Background:

• Forest understory plant communities are vital for biodiversity and sensitive to climate change and nitrogen (N) deposition.
• Rising temperatures and soil recovery from sulfur (S) and N deposition create uncertainty for these ecosystems.

Purpose of the Study:

• To evaluate the impacts of atmospheric N deposition and climate change on plant species occurrence probability in the Great Smoky Mountains National Park (GRSM).
• To establish regional critical loads (CLs) for N deposition and assess their attainability under future scenarios.

Main Methods:

• Utilized the US-PROPS model with species response functions for over 1,500 species.
• Simulated six future scenarios combining soil pH recovery (no change, +0.5 units) and climate change (+1.5°C, +3.0°C).
• Determined species N critical loads and projected occurrence probabilities under various conditions.

Main Results:

• N critical loads (< 2 kg N/ha/yr) were low and exceeded across large areas of GRSM under most scenarios.
• Northern hardwood, yellow pine, and chestnut oak forests were identified as highly N-sensitive.
• Increased temperatures generally decreased species occurrence probability, rendering CLs unattainable.
• Most species benefited from increased soil pH, though some showed decreased occurrence probability.

Conclusions:

• Current and future N deposition levels pose a significant threat to GRSM's understory plant communities.
• The developed methodology for establishing regional CLs and evaluating future impacts is transferable to other protected areas.
• Urgent management strategies are needed to mitigate N deposition and address climate change impacts on forest biodiversity.