Ungulate browsers promote herbaceous layer diversity in logged temperate forests

Area of Science:

• Ecology
• Forestry
• Wildlife Management

Background:

• Ungulates significantly influence plant communities globally.
• Multiple ungulate species co-occur in many ecosystems, but their combined impacts are understudied.
• Understanding additive vs. compensatory effects of multiple browsers is crucial for ecosystem management.

Purpose of the Study:

• To investigate the combined effects of moose (Alces americanus) and white-tailed deer (Odocoileus virginianus) on herbaceous layer composition and diversity.
• To determine if these ungulate browsers exert additive or compensatory effects.
• To assess impacts 5-6 years post-timber harvest in Massachusetts, USA.

Main Methods:

• Utilized fenced exclosures with three ungulate treatments: none, deer only, and deer + moose.
• Established six replicated blocks in a post-timber harvest forest landscape.
• Analyzed changes in herbaceous layer composition and species richness at plot (169 m²) and subplot (1 m²) scales.

Main Results:

• Species composition diverged significantly among browser treatments, with generally additive effects observed.
• Moose and white-tailed deer browsing led to decreased abundance of forest-associated plant assemblages and increased abundance of open/disturbed habitat assemblages.
• Combined browsing by deer and moose resulted in higher herbaceous species richness at the plot scale and woody species richness at the subplot scale compared to exclusion or deer-only plots.

Conclusions:

• Browsing by moose and white-tailed deer significantly altered forest herbaceous layer composition, structure, and diversity.
• Moderate browsing by these ungulates can enhance both herbaceous and woody plant diversity in forest openings.
• Findings support the grazing-species richness curve concept in forest ecosystems, a phenomenon rarely documented previously.