Ungulate Herbivory Research Articles

Seedling Response to Simulated Browsing and Reduced Water Availability: Insights for Assisted Migration Plantations

To facilitate forest transition to future climate conditions, managers can use adaptive silvicultural tools, for example the assisted translocation of tree species and genotypes to areas with suitable future climate conditions (i.e., assisted migration). Like traditional plantations, however, assisted migration plantations are at risk of failure because of browsing by ungulate herbivores. The ability of seedlings to tolerate browsing could also be hampered by low water availability, as is expected under climate change. Using a greenhouse experiment with five eastern North American tree species, we evaluated the effects of simulated winter browsing and reduced water availability on the growth (total biomass, shoot:root ratio), survival, and chemical composition (nitrogen, total phenolics, flavonoids) of seedlings. We compared seedlings from three geographic provenances representing three climate analogues, i.e., locations with a current climate similar to the climate predicted at the plantation site at a specific time (here: current, mid-century and end of the century). We hypothesized that seedlings would allocate resources to the system (shoots or roots) affected by the most limiting treatment (simulated browsing or reduced water availability). Additionally, we evaluated whether the combination of treatments would have an additive or non-additive effect on the growth, survival and chemical composition of the seedlings. Quercus rubra seedlings reacted only to the water reduction treatment (changes in biomass and N concentration, dependent on geographic provenance) while Pinus strobus reacted only to the simulated browsing treatment (biomass and chemical composition). We also observed non-additive effects of reduced water availability and simulated browsing on Prunus serotina, Acer saccharum and Thuja occidentalis. In general, shoot:root ratio and investment in chemical defense did not vary in response to treatments. The regrowth response observed in Q. rubra and A. saccharum suggests that these species could tolerate periodic browsing events, even when water availability is reduced. More information is required to understand their long-term tolerance to repeated browsing events and to harsher and more frequent water stress. We highlight the importance of species-specific growth and allocation responses that vary with geographic provenance, which should be considered by managers when planning climate-adapted strategies, such as assisted migration.

Positive impacts of livestock and wild ungulate routes on functioning of dryland ecosystems.

Livestock grazing is often perceived as being detrimental to the quality and functioning of dryland ecosystems. For example, a study in a semiarid Kenyan savanna proposed that cattle form bare spaces throughout the landscape, which indicate ecosystem degradation. Other studies, conducted in north‐eastern Spain, where climatic conditions range between semiarid and Mediterranean subhumid, reported that sheep and goat trails have increased the emergence of rill erosion processes. Sometimes, this negative perception is extended to include wild, large ungulate herbivores as well. Here, we challenge this perception by highlighting the generally nonadverse and even ameliorative impacts of moderate animal rate on geoecosystem functioning of hilly drylands. Specifically, trampling routes (also known as treading paths, livestock terracettes, cattle trails, migration tracks, cowtours, etc.) formed across hillslopes by grazing animals—being either domesticated livestock or native large herbivores—transform the original two‐phase vegetation mosaic of shrubby patches and interpatch spaces into a three‐phase mosaic. The animal routes increase the complexity of ecosystem, by strengthening the spatial redistribution of water and soil resources at the patch scale and decreasing hydrological connectivity at the hillslope scale. As a consequence, the animal routes improve functioning of hilly drylands and increase their resilience to long‐term droughts and climatic change. Therefore, instead of viewing the animal routes as degraded spots, they should be perceived at a wider perspective that allows to properly understand their overall role in sustaining dryland geoecosystems.

Influence of deer herbivory on regeneration dynamics and gap capture in experimental gaps, 18 years post-harvest

Declines in species diversity have been linked to shifting disturbance regimes and increases in ungulate herbivory. Successful forest regeneration depends on silvicultural methods that can address stand-specific recruitment limitations. This study revisits a long-term experimental gap study in a hemlock-hardwood forest. Our objective was to determine if the treatment effects of deer exclosures and gap size would alter regeneration trajectories. We examined cohort development using permanent plots and gap-wide surveys of likely gap-capture trees. After 18 years, deer herbivory was a strong filter for tree regeneration and appeared to pose an insurmountable bottleneck to the recruitment of some species. Overall, 90% of unprotected stems >0.5 to ≤2 m showed evidence of being browsed by white-tailed deer (Odocoileus virginianus Zimmerman). Our results indicate that browse sensitive species were unable to recruit even in resource-rich gap environments. Eastern hemlock (Tsuga canadensis L.) and yellow birch (Betula alleghaniensis Britton) were particularly sensitive to herbivory and absent in heights >1 m outside exclosures. However, inside exclosures in larger gaps, yellow birch saplings often co-dominated the tallest cohorts and eastern hemlock was well established at heights >1 m. Sugar maple (Acer saccharum Marsh.) was the dominant tree species across all treatments and ironwood (Ostrya virginiana Mill.) was frequently among the tallest trees in gaps outside of deer exclosures. Gap size only impacted unprotected seedlings which suggests regeneration is more sensitive to gap size when deer are present. The installation of relatively small (∼3.5% of total gap area) deer exclosures, at year two post-harvest, provided opportunities for the recruitment of browse-sensitive species. Collectively, our results highlight the pervasive role of ungulates in structuring forest composition.

Junipers enable heavily browsed rowan saplings to escape ungulates in boreal forest

Recent increases in ungulate herbivore populations have intensified browsing pressure in northern forest ecosystems. High browsing pressure affects recruitment into tree populations and saplings are among the most impacted and critical tree stages. This calls for research on factors that enhance sapling survival and promote recovery of herbivore preferred species. One understudied factor in ungulate dominated boreal forests is the ability of young trees to escape large herbivores by utilising “nurse plants”. First, we examined the impact of ungulate browsing on the abundance and size of rowan (Sorbus aucuparia), a functionally important tree species in an old-growth boreal pine forest, western Norway. The responses were compared between exclosures and ungulate-access plots over ten years (2001–2011) combined with investigations along a browsing intensity gradient (Exp. A). In a second experiment we investigated whether rowan saplings escape browsing and enhance growth and survival by growing within nurse plants. Consequently, we planted rowan saplings in ungulate browsing areas, inside and outside coniferous juniper (Juniper communis) bushes, and analysed the treatment effect on browsing, growth, and survival of rowan saplings across five years (2013–2018; Exp B). Excluding large herbivores resulted in a large increase in rowan saplings which were six times more abundant in exclosures (0.44 ind./m2) compared to ungulate-access plots (0.07 ind./m2) after ten years (Exp. A). The abundance of rowan saplings also decreased with higher browsing intensity. Moreover, the rowans in exclosures grew to almost twice the height of the ungulate-access rowans. The protected rowan saplings experienced significantly less browsing damage, and only 25% of the protected plants experienced heavy browsing or died after the first winter, compared to 70% of the unprotected plants (Exp. B). After five years, 50% more unprotected than protected plants experienced heavy browsing or mortality, and growth in protected plants was nearly 50% greater over the period. The negative impact of ungulate browsing on abundance and growth of rowans can be counteracted by positive plant-plant interactions. Rowan saplings growing within nurse plants showed significantly less browsing and better performance indicating high functional importance of the forest understorey. Forest managed with multi-layered and multi-species understoreys may therefore also be beneficial for tree recruitment in browsed boreal forest landscapes.

Herbivory and Soil Water Availability Induce Changes in Arbuscular Mycorrhizal Fungal Abundance and Composition.

We tested the prediction that abundance and composition of arbuscular mycorrhizal fungi (AMF) in Ipomopsis aggregata roots and soils are influenced by ungulate herbivory and drought conditions by examining the effects in a field setting over two years. We used a multi-metric approach to quantify AMF root colonization, AMF reproduction, and AMF community composition in roots and soils. We incorporated complimentary community characterization assays by morphologically identifying spores from trap cultures and the use of terminal restriction fragment length polymorphism (T-RFLP) fingerprinting. Herbivory caused a twofold increase in spore production, an increase in AMF taxa diversity in roots, and a shift in AMF species composition in rhizosphere soils. The impact of herbivory was dependent on water availability, which differed in the two contrasting years. This study demonstrates that both soil water availability and herbivory shape arbuscular mycorrhizal fungi communities. The changes to mycorrhizal communities may help in understanding mycorrhizal function in changing climates.

Do early‐successional weeds facilitate or compete with seedlings in forest restoration? Disentangling abiotic versus biotic factors

Abstract Semi‐arid forests need cost‐effective restoration strategies to address their severe degradation. Tree shelters are often used to minimize abiotic and biotic stress during seedling establishment. We asked if early‐successional weeds act as a natural shelter by facilitating native seedlings, contingent on abiotic and biotic stressors and seedling ecological strategy. We conducted a manipulative weed exclusion experiment at a semi‐arid site in South Texas targeted for large‐scale forest restoration to discern the net effect of weeds on the growth and survival of target thornscrub tree and shrub seedlings. We assessed the roles of contrasting seedling ecological strategies (fast vs. slow growth habit), temporal variation in abiotic stress, microclimate and mammalian herbivory in modulating weed–seedling interactions. Ungulate herbivory on seedlings was common, of similar frequency across most species, but not diminished by the presence of weed neighbours. On average, seedlings growing adjacent to weed neighbours experienced modest but non‐significant increases in both height and mortality after 6 months, relative to weed‐excluded areas. However, seedlings without significant herbivory and adjacent to weed neighbours grew more vigorously (increased height and branching) during hot and dry periods, particularly those species with a fast growth habit. Although seedling light‐saturated photosynthetic capacity (Asat) and air temperature were unaffected by weed presence during hot and dry periods, afternoon light levels were reduced by approximately 50%, possibly indicative of lower leaf temperatures and improved seedling water status. Our results show that realizing the facilitative potential of weeds in semi‐arid forest restoration requires minimizing mammalian herbivory and temporally separating competition for resources. Managing for intermediate but not excessive levels of forb canopy cover is likely required to reduce high radiation loads and reduce transpiration without adverse competitive effects. Longer‐term experiments manipulating cover crop identity, cover and mammalian herbivory will inform whether forbs can be effectively exploited to enhance restoration success at large scales.

Ungulate herbivory reduces abundance and fluctuations of herbivorous insects in a boreal old-growth forest

Ecological theory predicts the strongest ecosystem effects of herbivory when dominant and ecologically important species are consumed. Bilberry, Vaccinium myrtillus, is such a key plant species, attractive to many other species in the boreal forests, for example ungulate and invertebrate herbivores. Large herbivores may remove substantial biomass and alter plant quality and therefore affect abundance and populations of invertebrate animals sharing the same food plant. We combined experimental exclusion of ungulates with a browsing intensity gradient to investigate the 15-year effect of ungulate (Cervus elaphus and Ovis aries) browsing on bilberry plant size and on bilberry-feeding herbivorous larvae (Lepidoptera and Symphyta), in a Norwegian old growth boreal forest ecosystem. Bilberry ramets in exclosure plots had nearly nine times higher dry mass and three times higher abundance of invertebrates feeding on them than in ungulate-access plots. Sweep-netting data verified these findings as larval numbers were twice as high in exclosure plots. The pattern in the large herbivore effects on bilberry size and abundance of herbivorous larvae were identical along the browsing gradient. Differences in larval abundance between treatments, as indicated by leaf-chewing, increased during the 15-year study period, and the community fluctuations were larger when ungulate herbivores were excluded. The browsing effect was moderated by plant quality as larval densities were lowest on both heavily-browsed and non-browsed plants, and highest on ramets that had 50–74% of annual shoots browsed. Our study supports previous findings in that bilberry is relatively disturbance tolerant and may recover quickly, but that ungulates may compete with herbivorous larvae for food biomass. Additionally, our results strongly indicates that population insect community peaks and fluctuations are dampened by ungulate consumption. Our findings add to the understanding on how ungulates may structure forest ecosystems directly and indirectly.

Effects of Elk and Bison Herbivory on Narrowleaf Cottonwood

Ungulate browsing influences the structure and composition of woody plant communities, including species composition and biomass production as well as age distribution, recruitment, and mortality. We evaluated effects of elk and bison herbivory on narrowleaf cottonwood (Populus angustifolia) communities in a semiarid ecosystem in southern Colorado. Cottonwoods in this ecosystem have been aged at ≥300 years old and are among the oldest cottonwood trees in North America. We compared browsing intensity and structural and productivity responses of cottonwood to ungulate herbivory. We compared responses in sites with elk and bison, sites with elk but no bison, and sites where both ungulates were excluded. We found that the majority of browsing on cottonwood occurred during summer in this high desert ecosystem. Areas with both elk and bison had higher browse utilization than areas with only elk, but diet data indicated that elk consumed a much greater proportion of cottonwood than bison. Overall, browse utilization observed in this study was low to moderate compared to other studies, and our results may not be representative of sites experiencing intense year-round herbivory. Removal of all ungulate herbivory led to taller and denser cottonwood suckers; however, other environmental factors, in addition to herbivory, still strongly limit cottonwood growth and recruitment in this ecosystem.

Rainfall, fire and large‐mammal‐induced drivers of Vachellia drepanolobium establishment: Implications for woody plant encroachment in Maswa, Tanzania

AbstractWorldwide, open grass areas of savannah ecosystems are being transformed into shrubland. This woody plant encroachment is likely a result of factors such as rainfall, fire and secondary dispersal by ungulate herbivory. However, few experiments have been conducted to disentangle and quantify the role of these factors for seed germination in savannahs. We assessed in situ germination success of Vachellia drepanolobium seeds under simulated rainfall variability patterns, fire treatments and dung experiments in Maswa Game Reserve, Tanzania. Fire reduced seed germination by more than 13%, whereas germination in buffalo and elephant dung increased by 1% and 3% respectively. Additionally, intermediate simulated rainfall was more beneficial for seedling emergence success than large, infrequent simulated rainfall amounts, while shoot growth was twice as high under frequent and intermediate simulated rainfall treatments than under large infrequent simulated rainfall. Our results provide insights that bush fires, drought stress, and large rainfall events can suppress V. drepanolobium seedling emergence and growth. Hence, bush encroachment may be linked to management practices such as fire regimes and climatic conditions, i.e., frequent low rainfall conditions. Our results can help predict future patterns of encroachment under varying rainfall and fire events.

Determination of Sex in Ungulate Herbivores via near Infrared Spectroscopy of Hair: Growing Cattle as a Surrogate Model

Abstract Near infrared spectroscopy (NIRS) has been used in a variety of medical and veterinary science applications. In particular, NIRS calibrations have been developed in livestock for steroid content in cattle hair, and wound age or stage of healing in hot iron cattle brands. These NIRS applications also have potential utility in forensic science. Portable NIRS instruments facilitate measurements on live animals and or animal samples in the field. The objective of this study was to evaluate the efficacy of determining sex in growing cattle via NIRS of hair utilizing a portable spectrometer. In two consecutive years, log 1/R spectra (350–2500 nm) were collected using an ASD Field Spec fitted with a contact probe. Experimental subjects were Bos taurus cross calves (n = 12, yr 1; n = 14, yr 2) born to cows grazing central Arizona rangeland. Calf age was approximately 60, 90 and 210 d at branding, estrus synchronization, and weaning, respectively. As cattle were gathered for these routine working events, a total of 7 M and 19 F calves were scanned 3 times each over the left ribcage. A linear discriminant function was applied to spectral data in order to determine sample membership in M or F groups at each collection date. Chi-square procedures were used to determine differences (P < 0.05) in proportion of correct identifications per group and collection date. Overall, 86% of F and 72% of M were correctly (P < 0.05) identified. Corresponding values were 82% for F and 71% for M at branding, 100% for F and 89% for M at estrus synchronization, and 86% for F and 64% for M at weaning. Calf sex was successfully determined using portable NIRS in this proof of concept study. Efficacy of this method should be evaluated for different ungulate herbivores and under additional collection scenarios.

Cumulative effects of spruce budworm and moose herbivory on boreal forest ecosystems

Abstract Ungulate herbivory is a key natural disturbance in many ecosystems. In forest ecosystems, ungulate herbivory often co‐occurs with other disturbances yet there are few studies looking at the cumulative impacts of ungulates and other natural disturbances on forest dynamics. We report on an 18‐year experiment to investigate the combined effects of introduced, non‐native moose and native spruce budworm herbivory on balsam fir forest recruitment and regeneration. Specifically, we measured inputs into early life‐history components of balsam fir dominant boreal forest ecosystems such as seed density, seedbed quality, seedling and sapling height and density, as well as adult density in eight paired moose exclosure and control sites across a spruce budworm disturbance gradient (i.e. no outbreak, recent outbreak, old outbreak) that resulted in closed, partially open and open canopies. Piecewise structural equation models (SEMs) revealed a strong negative effect of spruce budworm disturbance on balsam fir adult density and indirect effects of this budworm disturbance on balsam fir seedling and sapling density mediated through adult density. We observed a similar pattern of budworm disturbance effects on balsam fir seed density with the lowest densities in sites with open canopy, then partially open and closed canopies. As expected, the SEM showed a positive effect of bryophyte seedbed cover on balsam fir seedling density. The SEM showed support for a positive effect of moose exclusion on balsam fir sapling height and density. Specifically, saplings were on average taller and denser in exclosure than control plots and these differences are most pronounced at sites with partially open canopies created by spruce budworm disturbance and undisturbed or closed canopy sites. Overall, we show evidence for cumulative and interactive effects of spruce budworm and moose herbivory on all life stages of balsam fir and such effects are negatively affecting regeneration of balsam fir forests. Human activities are creating conditions that facilitate the expansion and increased impacts of herbivores on boreal ecosystem functioning. A greater understanding of how ungulate herbivory interacts with other disturbances is needed to improve our predictions of forest ecosystem dynamics under global change. A free Plain Language Summary can be found within the Supporting Information of this article.

Species‐specific responses of a marsh‐forest ecotone plant community responding to climate change

Ecotones are responsive to environmental change and pave a path for succession as they move across the landscape. We investigated the biotic and abiotic filters to species establishment on opposite ends of a tidal marsh-forest ecotone that is moving inland in response to sea level rise. We transplanted four plant species common to the ecotone to the leading or trailing edge of the migrating ecotone, with and without caging to protect them from ungulate herbivores. We found that species exhibited an individualistic response to abiotic and biotic pressures in this ecotone; three species performed better at the leading edge of the ecotone in the coastal forest, whereas one performed better at the trailing edge in the marsh. Specifically, grass species Phragmites australis and Panicum virgatum grew more in the low light and low salinity conditions of the leading edge of the ecotone (forest), whereas the shrub Iva frutescens grew better in the high light, high salinity conditions of the trailing edge of the ecotone (marsh). Furthermore, of the four species, only P. australis was affected by the biotic pressure of herbivory by an introduced ungulate, Cervus nippon, which greatly reduced its biomass and survival at the leading edge (forest). P. australis is an aggressive invasive species and has been observed to dominate in the wake of migrating marsh-forest ecotones. Our findings detail the role of lower salinity stress to promote and herbivory pressure to inhibit the establishment of P. australis during shifts of this ecotone, and also highlight an interaction between two non-native species, P. australis and C. nippon. Understanding migration of the marsh-forest ecotone and the factors controlling P. australis establishment are critical for marsh conservation in the face of sea level rise. More generally, our findings support the conclusion that the abiotic and biotic filters of a migrating ecotone shape the resulting community.

Contrasting responses of nitrogen: Phosphorus stoichiometry in plants and soils under grazing: A global meta‐analysis

Abstract Grazing by ungulate herbivores can greatly alter nitrogen ([N]) and phosphorus ([P]) concentrations in plants and soils. It is not clear, however, how grazing might affect N:P co‐limitation in grasslands depending on soil N and P availability. Here we selected 173 peer‐reviewed studies, which measured 12 key variables associated with changes in [N], [P] and N:P ratios (i.e. N:P stoichiometry) in soils and plants in the presence or absence of herbivore grazing. Subsequently, we addressed the magnitude and direction of grazing effects on these variables using a meta‐analysis approach. Grazing increased leaf [N] and [P] but decreased total and available soil [N] and [P]. Grazing also increased leaf N:P ratios while decreasing root and total soil N:P ratios. The response ratio (RR) of leaf N:P was negatively correlated with RR of plant‐available soil [P] and positively correlated with RR of available soil N:P ratio (rather than with RR of total soil N:P). Intensive grazing (e.g. heavy grazing or long‐term grazing) had in general more positive effects on plant N:P stoichiometry and negative effects on soil N:P stoichiometry than light grazing. Responses of plant‐soil N:P stoichiometry to grazing greatly varied depending on plant functional group identity, plant organizational level (i.e. species and community) and grassland type. Synthesis and applications. Our study suggests that understanding changes in available soil N:P stoichiometry (rather than total soil N:P) in response to grazing is crucial to predict nutrient co‐limitation in grassland biomes. Our findings show that P is more important for plant growth than generally thought due to greater reduction of plant‐available soil [P] under grazing. A better mechanistic understanding of the relationships between plant and available soil N:P stoichiometry under grazing will greatly help improve the sustainability of natural and semi‐natural grassland ecosystems.

Deer Exclusion Changes Vegetation Structure and Hunting Guilds of Spiders, but Not Multitrophic Understory Biodiversity

Ungulate herbivores modify plant community compositions, which can modulate biodiversity at higher trophic levels. However, these cascading effects on herbivorous and predatory arthropods in forest ecosystems remain poorly understood. We compared plant and arthropod communities between fenced exclosures and unfenced control plots in a permanent forest in Germany. After five years of deer exclusion, we quantified plant diversity and vegetation structure as well as the diversity of insects and spiders in 32 pair-wise plots. In addition, we compared spider communities with respect to different hunting guilds because they are expected to have different requirements for vegetation structure. Although we did not find differences in plant communities, vegetation height and heterogeneity were higher in exclosures compared to control plots. The diversity of insects and spiders was not affected by deer presence. However, the abundance of sheet-web weavers and ambush hunters was lower in exclosures whereas ground hunters were more common in exclosure plots. Structural changes in the vegetation changed predator hunting guilds even though mere abundance and biodiversity indices were not affected. We therefore suggest that monitoring of vegetation structure and associated functional groups seems more sensitive to assess the impact of ungulate herbivores compared to taxonomic metrics.

Interacting effects of insect and ungulate herbivory on Scots pine growth

Most plants are subjected to damage from multiple species of herbivores, and the combined impact on plant growth can be non-additive. Since plant response to herbivores tends to be species specific, and change with repeated damage, the outcome likely depend on the sequence and number of attacks. There is a high likelihood of non-additive effects on plant growth by damage from mammals and insects, as mammalian herbivory can alter insect herbivore damage levels, yet few studies have explored this. We report the growth response of young Scots pine trees to sequential mammal and insect herbivory, varying the sequence and number of damage events, using an ungulate-pine-sawfly system. Combined sawfly and ungulate herbivory had both additive and non-additive effects on pine growth—the growth response depended on the combination of ungulate browsing and sawfly defoliation (significant interaction effect). Repeated sawfly herbivory reduced growth (compared to single defoliation) on un-browsed trees. However, on browsed trees, depending on when sawfly defoliation was combined with browsing, trees exposed to repeated sawfly herbivory had both higher, lower and the same growth as trees exposed to a single defoliation event. We conclude that the sequence of attacks by multiple herbivores determine plant growth response.

Analyzing long-term impacts of ungulate herbivory on forest-recruitment dynamics at community and species level contrasting tree densities versus maximum heights

Herbivores are constitutive elements of most terrestrial ecosystems. Understanding effects of herbivory on ecosystem dynamics is thus a major, albeit challenging task in community ecology. Effects of mammals on plant communities are typically explored by comparing plant densities or diversity in exclosure experiments. This might over-estimate long-term herbivore effects at community levels as early life stage mortality is driven by a multitude of factors. Addressing these challenges, we established a set of 100 pairs of ungulate exclosures and unfenced control plots (25 m2) in mixed montane forests in the Alps in 1989 covering a forest area of 90 km2. Investigations ran until 2013. Analogous to the gap-maker–gap-filler approach, dynamically recording the height of the largest trees per tree species in paired plots with and without exclosures might allow for assessing herbivore impacts on those individuals with a high probability of attaining reproductive stages. We thus tested if recording maximum heights of regenerating trees would better reflect effects of ungulate herbivory on long-term dynamics of tree regeneration than recording of stem density, and if species dominance patterns would shift over time. For quantifying the effects of ungulate herbivory simultaneously at community and species level we used principle response curves (PRC). PRCs yielded traceable results both at community and species level. Trajectories of maximum heights yielded significant results contrary to trajectories of total stem density. Response patterns of tree species were not uniform over time: e.g., both Norway spruce and European larch switched in their response to fencing. Fencing explained about 3% of the variance of maximum tree heights after nine years but increased to about 10% after 24 years thus confirming the importance of long-term surveys. Maximum height dynamics of tree species, addressed in our study, can thus reflect local dominance of tree species via asymmetric plant competition. Such effects, both within and among forest patches, can accrue over time shaping forest structure and composition.

Mitigation of Deer Herbivory in Temperate Hardwood Forest Regeneration: A Meta-Analysis of Research Literature

Ungulate herbivory poses global challenges to forest regeneration. Deer, in combination with other biotic and abiotic factors, threaten to shift forest composition away from palatable hardwoods, such as oaks (Quercus spp.), and cause regeneration failure in some cases. Many studies have assessed methods to reduce or manage browse, but comprehensive analyses of the relative effectiveness of these techniques among published experiments are lacking. We synthesized the literature describing the results of methods to reduce deer browsing impacts, and assessed the effectiveness of deer browse management methods in controlling damage to hardwood forest regeneration. Specifically, we systematically analyzed results from 99 studies that used repellents, physical barriers, lethal population control, timber harvests, facilitation by neighboring plants, or fertilizer to affect browse, survival, or height growth of hardwood seedlings. Across studies, browse was reduced (mean effect size and confidence intervals) with the following: Fencing −3.17 (CI: −4.00–−1.31), shelters −1.28 (CI: −2.02–−0.67), cages −1.48 (CI: −3.14–−0.62), facilitation from neighboring plants −0.58 (CI: −1.11–−0.13), repellents −0.45 (CI: −0.56–−0.21), hunting −0.99 (CI: −1.51–−0.26). These methods each had positive effects on seedling height growth (except for repellents), and cages, timber harvests, fences, and mesh sleeves had positive effects on survival. Logging slash had no effect on browse incidence (−0.05, CI: −0.97–0.19). Fertilizer applied during seedling establishment increased browse (0.13, CI: 0.11–0.21), and did not affect height growth. We conclude that fences or other physical barriers best control for the effects of deer, but facilitation by surrounding vegetation, logging slash, hunting, habitat management through timber harvest, and certain repellents may also be moderately effective. Discrepancies between browse effectiveness and relative costs suggest that economic analyses should be developed to help to guide prescriptions for management.

Natural and anthropogenic correlates of habitat use by wild ungulates in Shuklaphanta National Park, Nepal

Wild ungulate herbivores are crucial for maintaining terrestrial ecosystems and restoring population of top predators like tiger. Thus, it is essential to understand wild ungulates-habitat relationships to devise an effective strategy to conserve their population and top predators like tiger that depend on them. We have limited understanding about the ungulates and their habitat in sub-tropical lowlands. In this study, we conducted transect based occupancy surveys in December 2016 across 30 geographic grid cells of 3 km × 3 km spanning 270 km2. We used the occupancy modelling approach that accounts for the imperfect detection to test multiple hypotheses concerning ecological and anthropogenic correlates of site use pattern of five wild ungulate species in Shuklaphanta National Park, Nepal. The model-average estimates showed that proportion of site use was highest for spotted deer (0.83 ± SE 0.29) followed by blue bull (0.53 ± SE 0.22), hog deer (0.37 ± SE 0.12), swamp deer (0.23 ± SE 0.17), and lowest for barking deer (0.14 ± SE 0.05). While the proportion of forest had a positive influence on blue bull and barking deer, the proportion of grassland had a positive influence on spotted deer and swamp deer. Water availability positively influenced site use of barking deer. Human disturbance had a strong negative influence on the distribution of hog deer but blue bull had a positive association with human activities. Similarly, fire had a strong positive influence only on the habitat use of swamp deer. Overall, our results showed that these five wild ungulate species vary in their site use responses to natural habitat and anthropogenic factors suggesting that the consideration of species-specific habitat requirements is important for their conservation and management.

High silicon concentrations in grasses are linked to environmental conditions and not associated with C4 photosynthesis.

The uptake and deposition of silicon (Si) as silica phytoliths is common among land plants and is associated with a variety of functions. Among these, herbivore defense has received significant attention, particularly with regard to grasses and grasslands. Grasses are well known for their high silica content, a trait which has important implications ranging from defense to global Si cycling. Here, we test the classic hypothesis that C4 grasses evolved stronger mechanical defenses than C3 grasses through increased phytolith deposition, in response to extensive ungulate herbivory ("C4 -grazer hypothesis"). Despite mixed support, this hypothesis has received broad attention, even outside the realm of plant biology. Because C3 and C4 grasses typically dominate in different climates, with the latter more abundant in hot, dry regions, we also investigated the effects of water availability and temperature on Si deposition. We compiled a large dataset of grasses grown under controlled environmental conditions. Using phylogenetically informed generalized linear mixed models and character evolution models, we evaluated whether photosynthetic pathway or growth condition influenced Si concentration. We found that C4 grasses did not show consistently elevated Si concentrations compared with C3 grasses. High temperature treatments were associated with increased concentration, especially in taxa adapted to warm regions. Although the effect was less pronounced, reduced water treatment also promoted silica deposition, with slightly stronger response in dry habitat species. The evidence presented here rejects the "C4 -grazer hypothesis." Instead, we propose that the tendency for C4 grasses to outcompete C3 species under hot, dry conditions explains previous observations supporting this hypothesis. These findings also suggest a mechanism via which anthropogenic climate change may influence silica deposition in grasses and, by extension, alter the important ecological and geochemical processes it affects.

Ungulate herbivores reduce fruit production of shrubs in dry conifer forests of the interior Pacific Northwest, USA

Ungulate herbivores can affect food webs by reducing fruit production of browsed plants. In this study, we evaluated the effects of herbivory by large mammalian herbivores (cattle, elk, and mule deer) on fruit production of three common, widely distributed shrub species, Amelanchier alnifolia, Ribes cereum and Rosa woodsii that produce fleshy fruit consumed by wildlife in dry conifer forests of eastern Oregon, U.S.A. Specifically, we evaluated herbivory effects on fruit count, shrub height and fruit density in stands exposed to ungulates and in adjacent stands where ungulates have been excluded for 15 years. We measured shrub height, density and fruit production within each herbivore treatment using belt transects. Data was collected for two years for A. alnifolia, and one year for R. cereum and R. woodsii. For A. alnifolia, herbivory decreased the probability that an individual shrub would produce fruit by 80%. Herbivory reduced overall fruit set of A. alnifolia by ~90%; there was weak evidence of a decline in R. woodsii fruit set by ~31%; and we found no significant herbivore effect on R. cereum. Reduced fruit production in combination with herbivore impacts on shrub density resulted in large differences in estimated fruit density across treatments, with the greatest effects found for A. alnifolia; estimated fruit production per hectare was 97–99% lower when exposed to herbivores as compared to the control treatment. Results support the hypothesis that ungulate herbivores influence standing fruit crops of at least some browsed shrubs within this forest ecosystem. This has implications for food webs because forest understory shrubs are a primary provider of fleshy fruits that are consumed by a wide range of insects, mammals, and birds in these forest systems.