Effects of Domestic and Wild Ungulate Management on Young Oak Size and Architecture

Scattered oaks in traditional silvopastoral systems (i.e., “dehesas”) provide important ecological services. However, livestock intensification applied to these systems over the last century has affected the architecture of young oak plants. This unsuitable rangeland management practice jeopardizes the long-term system sustainability. Here we examine the alterations in architecture of regenerating oak plants in Mediterranean dehesas under three representative management regimes: (1) traditional management with extensive sheep grazing; (2) commercially driven management with extensive cattle grazing, and (3) native deer grazing at moderate stocking rates (<0.11 livestock units × ha-1). Plant architecture was considerably altered in cattle-grazed “dehesas”, finding a 50% reduction in plant height–diameter ratios, compared to sheep-grazed dehesas where plants with higher height–diameter ratios predominated. Young oak plants, however, showed less altered architecture and less probability of damage on shoot apex (0.20-fold difference) in areas with deer grazing at moderate stocking rates. In addition, those young oak plants with multi-stemmed individual architecture were more stunted (lower values of crown height–diameter ratio) in areas with livestock grazing than wildlife areas (0.78-fold difference). Shrub presence, under all management schemes, helped to increase in plant height, except when shrubs were located under tree canopies. Conversely, plants without shrub protection showed stunted architecture with well-developed basal diameters but short stature. Appropriate sustainable practices should include cattle stocking rate reduction, traditional sheep grazing promotion, nurse shrub preservation and fencing stunted individuals along with pruning basal sprouts. Our study indicates that management may have important consequences on dehesa regeneration via alterations of plant architecture and therefore on system sustainability.

Plant community recovery from intense deer grazing depends on reduction of graminoids and the time after exclosure installation in a semi-natural grassland

Exclosures that exclude large herbivores are effective tools for the protection and restoration of grazed plant communities. However, previous studies have shown that the installation of an exclosure does not ensure plant community recovery. Our study aimed to determine the effects of the domination of unpalatable plants and the timing of exclosure installation on the plant community recovery process in montane grassland overgrazed by sika deer (Cervus nippon) in Japan. In this study we compared plant species composition and their cover with inside and outside exclosures installed at different times. Furthermore, we also compared them with those in 1981, when density of sika deer was very low. We used quadrats inside and outside fenced areas established in 2010 and 2011 to record both the cover and the height of species in each quadrat between 2011 and 2015. Plant cover, with the exception of graminoid species, increased in later years in all treatments. Non-metric multidimensional scaling (NMDS) plots showed significantly differentiated treatment trends. The species composition within the 2010 fenced area gradually shifted to greater similarity with the species composition reported in 1981. The plant community in the 2011 fenced area was slower to recover. Compositions of plant communities outside the fenced areas hardly changed from 2011 to 2015. Chao’s dissimilarity index decreased over time between the plant community surveyed between 2011 and 2015 and the past plant community in 1981 within the exclosures, and was higher in the 2011 fenced area than in the 2010 fenced area. In conclusion, we show that the reduction of graminoids and the time after exclosure installation were important for plant community recovery from deer grazing damage. A delay in exclosure installation of one year could result in a delay in plant community recovery of more than one year.

Suitability of Eight Northeastern U.S. Native Shrubs as Replacements for Invasive Plants in a Difficult Landscape Site with White-tailed Deer Pressure

Nursery and landscape professionals are interested in white-tailed deer (Odocoileus virginianus)–resistant native plants to replace invasive species used in difficult landscape sites, such as parking lot islands, which are dry, nutrient-poor, and exposed to sun and heat. Eight native shrubs [creeping sand cherry (Prunus pumila var. depressa), elderberry (Sambucus canadensis), gray dogwood (Cornus racemosa), highbush blueberry (Vaccinium corymbosum), round leaf dogwood (Cornus rugosa), northern spicebush (Lindera benzoin), sweetbells (Eubotrys racemosa), and virginia rose (Rosa virginiana)] were planted in a large commuter parking lot on the University of Connecticut campus to evaluate their suitability for use in difficult landscapes. The non-native, invasive shrubs ‘Compactus’ winged euonymus (Euonymus alatus) and ‘Crimson Pygmy’ japanese barberry (Berberis thunbergii) were also planted as controls representing non-native species typically planted in such sites. Aesthetic quality ratings for sweetbells matched the controls (rating of 4.5 out of 5.0) and plants exhibited a high level of white-tailed deer resistance. Virgina rose and creeping sand cherry had similar aesthetic quality to controls, despite light grazing of plants by white-tailed deer. Elderberry was damaged by moderate white-tailed deer grazing and snow load, but plants regenerated to 485% of initial size in one growing season with white-tailed deer exclusion. Gray dogwood, round leaf dogwood, and northern spicebush exhibited the least resistance to white-tailed deer grazing. Both dogwood species had lower aesthetic quality than the controls, and round leaf dogwood had the lowest survival rate (68%) after 2 years. However, several individuals of gray dogwood, round leaf dogwood, and northern spicebush that were less heavily damaged by white-tailed deer grew into attractive shrubs after white-tailed deer exclusion. Highbush blueberry had significantly lower aesthetic quality than controls and only 75% survival after 2 years, indicating that this species is an unsuitable replacement for invasives in difficult landscape sites. This study identified the underused native shrubs sweetbells, virginia rose, and creeping sand cherry as suitable replacements for invasives in difficult landscape sites with white-tailed deer pressure.

Effects of Deer Grazing on Vegetation and Ground-Dwelling Insects in a Larch Forest in Okutama, Western Tokyo

Sika deer (Cervus nippon) have experienced a rapid increase in the Japanese archipelago. Although the effects of deer grazing have been widely studied, the indirect effects have received little attention. Using an eight-year-old deer exclosure in western Tokyo (Japan), we studied the direct effects on plants and the indirect effects on insects and microenvironments. Plant biomass was 14 times higher inside the exclosure than outside. Shrubs (e.g.,Aralia elataandHydrangea paniculata) and trees (e.g.,Symplocos sawafutagiandClethra barbinervis) were more abundant inside, whereas only unpalatable trees in poor condition grew outside (e.g.,Pterostyrax hispidaandCynanchum caudatum). In the summer months, the maximum temperature was 8–10°C higher outside the exclosure and humidity was lower. Soil movement was 80 times more pronounced outside than inside. These results suggest that the abiotic environment became less stable for ground-dwelling insects. Carabid beetles were less abundant outside than inside, suggesting that deer grazing reduced plants and subsequently lowered habitat quality for these beetles. In contrast, carrion beetles, dung beetles, and camel crickets were more abundant outside. The increase in these insects is attributed to the availability of deer feces and carcasses and is a direct effect of deer presence.