Deer herbivory affects the functional diversity of forest floor plants via changes in competition‐mediated assembly rules

Abstract

Distorted plant diversity patterns due to ungulate herbivory could be explained by changes in community assembly processes, but the effects of ungulate herbivory on plant community assembly remain unclear. Here, we examined the role of deer herbivory in the regulation of the assembly processes of a forest floor plant community by assessing species and functional diversity in over-and no-grazing plots (control and exclosure plots, respectively) in Shiretoko National Park in Japan. Compared with the exclosure plot, vegetation coverage was considerably lower, and species richness and diversity were higher in the control plot. Functional traits associated with competitive ability (leaf area and chlorophyll content) were significantly higher in the exclosure plot. The pattern of functional diversity changed from overdispersion to clustering with an increase in local crowdedness. This trait clustering indicates that the local communities that were free from ungulate disturbance gradually became dominated by some competitively superior plant species, which led to low species diversity and biotic homogenization. In contrast, the reduction in vegetation due to overgrazing by deer resulted in an increase in the relative importance of stochastic assembly processes, which enabled the coexistence of various species, including less competitive ones. Our results emphasize that although deer overabundance is of concern, their complete exclusion has a negative consequence from an ecological perspective.Because deer herbivory is an inherent process that affects the biodiversity of plants on the forest floor, the establishment of fences requires careful consideration to ensure the conservation of ecological processes and their associated biodiversity.

Ungulates increase forest plant species richness to the benefit of non‐forest specialists

“…It is striking that deer emerged as a moderator for the plant cover of this species group, not only in other parts of Europe (Kirby & Thomas, 2000;Perrin, Mitchell, & Kelly, 2011), but also for Rubus spp. species in the United States (Faison et al, 2016;Horsley, Stout, & deCalesta, 2003;Murray et al, 2016;Royo et al, 2010 (Faison et al, 2016;Murray et al, 2016;Nishizawa et al, 2016;Perrin et al, 2011). After 10 years of fencing, the lower species richness of the herbaceous layer inside the exclosures of our 82-site network, along with the gradual response to deer abundances provide a large-scale support for this grazing curve.…”

“…The classic grazing response curve, based on the intermediate disturbance hypothesis, predicting an increase in plant species richness from low to moderate browsing pressure, has been already locally documented (Faison et al., ; Murray et al., ; Nishizawa et al., ; Perrin et al., ). After 10 years of fencing, the lower species richness of the herbaceous layer inside the exclosures of our 82‐site network, along with the gradual response to deer abundances provide a large‐scale support for this grazing curve.…”

“…These ungulate-induced modifications of plant-plant interactions may involve particular species, namely by reducing the dominance of palatable species with high competitive abilities and, in turn, enhancing plant species richness (Nishizawa, Tatsumi, Kitagawa, & Mori, 2016). Among the recovering plant species, bramble (Rubus fruticosus agg.)…”

Study on the Timely Adjustment of the Grazing Prohibition Policy: Ban or Lift? Empirical Research from Local Government Managers

“…Therefore, moderate grazing is beneficial to the benign cycle of grassland ecology. Grazing had been banned for a long time, the biodiversity and biomass of grassland had declined [25,26] and the natural degradation gradually appeared. It is generally believed that five years was a suitable grazing ban period in Yanchi County, Ningxia [27,28].…”

Different trends in phylogenetic and functional structure of plant communities along an elevation gradient

“…To calculate functional distance, we used 10 functional traits that have been widely used in previous studies: two binary traits (clonality and deciduous/evergreen), three categorical traits (dispersal type: unassisted dispersal, wind dispersal, internal animal transport, external animal transport, dispersal by hoarding, dispersal by water, and dispersal by launching; Raunkiaer life form: phanerophytes, chamaephytes, hemicryptophytes, geophytes, therophytes, and biennial; and growth form: short basal, semi-basal, erect leafy, cushions, tussocks, dwarf shrubs, shrubs, trees, and climbers), and five numerical traits (seed mass, maximum height, width of leaf, specific leaf area [SLA], and leaf carbon:nitrogen ratio [leaf C/N]). Except for SLA and leaf C/N, all of the traits were collected from various pictorial books of Japanese flora (the same sources used by Nishizawa et al 2016), which covered all of the species in our inventory. For SLA, mean values were calculated for each species from five mature leaves sampled from five individuals of each species.…”