The long‐term impacts of deer herbivory in determining temperate forest stand and canopy structural complexity

Abstract

Ungulates place immense consumptive pressure on forest vegetation globally, leaving legacies of reduced biodiversity and simplified vegetative structure. However, what remains unresolved is whether browse‐induced changes occurring early in succession ultimately manifest themselves in the developed forest canopy. Understanding the development and persistence of these legacies is critical as canopy structure is an important determinant of forest ecosystem functions such as carbon sequestration and wildlife habitat. We measured how white‐tailed deer Odocoileus virginianus browse during stand initiation affected canopy structure, tree species richness, diversity, stem density, and basal area on Pennsylvania's Allegheny Plateau using a portable canopy LiDAR system. We capitalized on an historic deer enclosure experiment where forests were subjected to four deer densities (4, 8, 15, and 25 deer/km2) for 10 years following stand initiation. Deer browsing impacts on the forest canopy are apparent nearly four decades since stand initiation. The highest deer density treatment experienced a significant reduction in tree species diversity, density, and basal area with stands becoming dominated by black cherry Prunus serotina. Reductions in overstorey diversity and tree density resulted in a more open canopy with low leaf area and high horizontal leaf variability. Canopies were tallest at the lowest and highest deer densities. Synthesis and applications. Using a portable canopy LiDAR system and a former deer enclosure experiment, we show that high deer browsing pressure during stand initiation can have a decades‐long impact on stand and canopy structure. High deer densities led to stands with lower species diversity and tree density, which resulted in canopies that were taller and less dense. As remote sensing of the canopy becomes more prevalent, considering the legacy of ungulate herbivory on canopy structure may inform both land management and our understanding of ecological function, such as forest carbon sequestration, maintenance of diverse understory communities, and creation of wildlife habitat

Chronic browsing by an introduced mammalian herbivore in a tropical island alters species composition and functional traits of forest understory plant communities

“…Our data demonstrate a significant decrease in species richness and a slight decrease in plant abundance in understory communities along a gradient of chital habitat use (Figure 3). These results align with previously reported effects of introduced chital on understory plant communities in the Andaman Islands (Ali, 2004) and with studies from other ecosystems with introduced herbivores (Camargo- Sanabria et al, 2014;Martin et al, 2011;Reed et al, 2022;Royo & Carson, 2022;Simberloff et al, 2013;Stephan et al, 2017). Although it is possible that both vegetation and chital habitat use are simultaneously responding to underlying environmental factors, similarity in rainfall, topography and bedrock among our sites leads us to expect low environmentally driven covariation.…”

“…Persistent effects of ungulate browsers on communities within browse height can indirectly affect vegetation in adult size classes by affecting recruitment probabilities and composition of recruits (Bellingham & Allen 2003, Coomes et al, 2003; Reed et al, 2022; Royo & Carson, 2022). Decreased abundances and altered composition in smaller stems over long timescales can reduce overall recruitment and alter adult tree composition (Ramirez, 2021).…”

Regeneration in European beech forests after drought: the effects of microclimate, deadwood and browsing

“…Our findings of a positive relationship between browsing and diversity in species and structures and no effect of browsing on regeneration density are somewhat unexpected, particularly considering the high browsing intensity observed on our plots. This result is challenged by a number of studies suggesting negative impacts of browsing on regeneration (Ammer 1996 ; Gill and Beardall 2001 ; Schulze et al 2014 ; Reed et al 2021 ). It is important to note that the relationships found here do not necessarily imply a causal effect of browsing.…”

The importance of natural forest stewardship in adaptation planning in the United States

“…As one example, low density regeneration reduces the severity of reburns, facilitating forest recovery (Cansler et al, 2022; Harvey et al, 2016). Heterogeneity of natural regeneration also avoids structural uniformity that occurs with planting and can extend the duration of early successional patches and gaps, there by accelerating the development of spatial and structural complexity (Donato et al, 2012; Reed et al, 2022; Swanson et al, 2011).…”