Multiple Browsers Structure Tree Recruitment in Logged Temperate Forests.

Area of Science:

• Forest ecology
• Wildlife management
• Herbivore-plant interactions

Background:

• Historical extirpations have led to simplified large herbivore communities in northern forests.
• White-tailed deer (Odocoileus virginianus) impacts on forest regeneration are well-studied, but moose (Alces americanus) recolonization introduces complexity.
• Differences in size and foraging between deer and moose suggest a lack of functional redundancy.

Purpose of the Study:

• To investigate how low densities of deer + moose affect forest community structure compared to low densities of deer alone.
• To assess the impact of sympatric large herbivores on forest regeneration in recently logged areas.

Main Methods:

• Established randomized block experiments with three herbivore treatments: no ungulates, deer only, and deer + moose.
• Monitored forest regeneration, stem densities, basal area, and species richness over 6-7 years.
• Used remote camera traps to assess herbivore usage of experimental plots.

Main Results:

• Deer + moose significantly reduced stem densities and basal area (2-3 fold) and tree recruitment (3-6 fold).
• Combined browsing by deer and moose decreased species richness by 19% (1.7 species).
• Deer alone significantly reduced species richness by 28% (2.5 species) but had non-significant effects on other vegetation metrics.

Conclusions:

• Sympatric large herbivores, particularly moose due to their biomass, exert significant and complex browsing effects.
• A lack of functional redundancy in foraging behavior between deer and moose leads to amplified impacts on forest communities.
• Understanding herbivore species interactions is crucial for predicting forest dynamics in areas with returning large ungulates.