Deer slow down litter decomposition by reducing litter quality in a temperate forest

Area of Science:

• Ecology
• Forestry
• Biogeochemistry

Background:

• Litter decomposition is vital for nutrient cycling in temperate forests.
• The influence of large herbivores on this process is not well understood.
• Sitka black-tailed deer (Odocoileus hemionus sitkensis) were introduced to Haida Gwaii, creating a unique study system.

Purpose of the Study:

• To investigate how Sitka black-tailed deer affect litter decomposition.
• To determine if deer alter litter quality or decomposer communities.
• To quantify the impact on carbon and nitrogen cycling.

Main Methods:

• Utilized two litterbag experiments on islands with and without deer.
• Assessed changes in litter mass loss, carbon, and nitrogen content.
• Evaluated the impact of deer feces on decomposition rates.

Main Results:

• Deer presence significantly reduced litter mass loss by 30% (carbon) and 28% (nitrogen) after one year.
• Reduced litter quality was the primary driver, outweighing direct effects on decomposer activity.
• Decomposer ability to break down carbon decreased by 5% in the presence of deer.
• Minor but significant effects of deer feces deposition were observed.

Conclusions:

• Sitka black-tailed deer significantly inhibit litter decomposition and alter carbon and nitrogen cycling.
• Changes in litter quality are the main mechanism through which deer impact decomposition.
• Increasing deer populations may have substantial effects on ecosystem nutrient dynamics.