Fire versus herbivory for oak woodland restoration: burning achieves short-term structural and compositional objectives whereas browsing alone fails to reduce stem densities and promote ground flora

Abstract

Background Declines in ecologically beneficial fire, coincident with alterations to native herbivory and intensive land use, have led to dynamic changes in woodland structure and composition, leading to midstory densification and reductions in ground flora abundance and diversity. Frequent, low intensity fire is key to achieving woodland restoration objectives and prescribed burns are often used to meet management goals. For a variety of reasons, the use of prescribed fire is often limited. Further, growing season prescribed burning is often suggested to have a greater impact on woody stems than dormant season applications, but its implementation is difficult. Targeted herbivory may emulate many aspects of prescribed fire holding the potential to diversify management strategies for restoration. We designed a replicated, experimental study to evaluate targeted browsing and prescribed burning for achieving restoration objectives, specifically, a two layered oak woodland with a diverse and abundant native ground flora. The six treatments included: (1) spring browsing, (2) fall browsing, (3) dormant-season and fall browsing, (4) dormant-season prescribed fire, (5) spring browsing plus dormant-season prescribed fire, and (6) an untreated control. Results Results suggest that fire had an overriding effect on the reduction of midstory stems that was not comparable to the browsing treatments. Burning reduced leaf litter, increased bare soil exposure and forb coverage. Browsing may reduce the accumulation of woody stems when compared to the control, but this effect was not statistically meaningful. Differences in browsing seasonality and frequent browsing were also not statistically important but trends suggest a greater influence of spring browsing for meeting woodland objectives. Browsing may also exert compositional changes to woodlands because of forage preferences by goats. Conclusions To achieve woodland objectives in the short-term, fire is necessary to quickly reduce midstory densities, increase light availability, consume leaf litter, and thereby promote native ground flora abundance and diversity which may not be achieved with targeted browsing alone. Further, the interaction of fire and herbivory suggest that browsing preferences may influence structural and compositional outcomes associated with pyric herbivory regimes in woodlands that require further investigation.