Ungulate Herbivory Research Articles

Growth in three Karoo shrub species under various grazing treatments: the tracking of marked individuals over 25 years

Growth studies of long-lived shrubs are uncommon. In semi-arid rangelands, livestock and wildlife grazing influence growth processes and may interact with changing climate. Tierberg-LTER, excluded from livestock since 1987, and two adjacent ranches allowed for a comparative growth study of three shrub species (Osteospermum sinuatum – palatable, Pteronia empetrifolia – moderately palatable, and P. pallens – unpalatable) across contrasting present ungulate herbivory (none in exclosures, wildlife only, or livestock and wildlife combined) and past livestock herbivory (moderate and overgrazed). Marked individuals were measured at irregular intervals over 25 years. Stem basal diameter (mm), height (m) and two canopy diameters (m) were measured at the onset of the study and in 2014. Mean basal diameter growth (mm y−1) varied between species and treatments. Change in mean attribute values was influenced by interactions with grazing history and treatments. Some historical and grazing treatments had a negative effect on the palatable O. sinuatum and no significant effect on moderately palatable P. empetrifolia or unpalatable P. pallens. The age of the originally marked individuals are unknown but >70% of these individuals survived over the 25-year period. Our results support previous findings that dwarf shrubs in deserts are slow growing and long lived, and that grazing regime affects plant growth.

Pervasive moose browsing in boreal forests alters successional trajectories by severely suppressing keystone species

AbstractLarge herbivores can shape young forest stands and determine the successional trajectory of forested ecosystems by selectively browsing palatable species at the sapling stage. Moose (Alces alces) is the dominant vertebrate herbivore in Fennoscandian boreal forests, and high population densities have raised concerns about potential negative effects on ecosystem functioning and properties including biological diversity and timber production. We used 31 herbivore exclosures in Norway to investigate how forests developed after clear‐cutting with or without moose present. We tested how tree demography, abundances of understory plant functional groups, community composition, and plant diversity (including bryophytes) across multiple scales varied with moose exclusion. After seven years, the exclosures were dominated by deciduous trees, including many large rowan (Sorbus aucuparia) individuals, a functionally important keystone species. In contrast, the open plots subject to moose impacts (browsing, trampling, defecation) were dominated by economically important coniferous trees and there was next to no rowan recruitment to taller height classes. The biomass of large herbs and ferns was much greater inside exclosures. This study emphasizes the large immediate effect of moose on early successional boreal forest stands. Landscape‐level alterations caused by reduced deciduous dominance, and a reduction in large flowering herbs is likely to lead to cascading effects on ecosystem functioning. The management of boreal production forests needs to account for the combined effects of silvicultural practices and ungulate herbivory to ensure ecosystem functioning, but this management goal may be jeopardized in our study regions due to drastically reduced abundance of keystone species.

Temporal patterns of ungulate herbivory and phenology of aspen regeneration and defense.

Ungulate herbivory can create strong top-down effects on forest recruitment, especially after fire. Defense strategies of tree species against ungulate herbivory include escape through vertical growth and resistance through the production of defense compounds. Using afour-way fence design and camera traps we characterized the differential impacts of ungulate herbivores (deer, elk, cattle) on aspen forest recruitment and plant defense responses and how they vary depending on the timing of herbivory. Aspen height growth was greatest between June and August and ungulate use of aspen was highest in July and August. Threeyears after fire, height of aspendiffered among fence treatments with full ungulate exclusion > deer-only plots > native ungulate plots > fenceless plots: 108 ± 4cm, 94 ± 4cm, 89 ± 4cm, and 65 ± 4cm, respectively. Fenceless plots had the highest rates of removal of apical meristems by the end of 2014 and 2015 (61% and 53%, respectively). Native ungulate plots, and deer-only plots both had similar removal of apical meristems in 2014 (37% and 39%, respectively). The highest phenolic glycoside concentrations were associated with an 80% reduction in meristem removal and four-fold greater aspen height by the end of summer. Low nitrogen was associated with an 86% reduction in apical meristem removal and threefold greater aspen height. In conclusion, our study suggests that high ungulate abundance can have detrimental impacts on forest recruitment and that high aspen defense chemistry and lower leaf N deters ungulate herbivory, especially in the late summer.

The Neogene Record of Northern South American Native Ungulates

South America was isolated during most of the Cenozoic, and it was home to an endemic fauna. The South American Native Ungulates (SANUs) exhibited high taxonomical, morphological, and ecological diversity and were widely distributed on the continent. However, most SANU fossil records come from high latitudes. This sampling bias challenges the study of their diversity dynamics and biogeography during important tectonic and biotic events, such as the Great American Biotic Interchange, the faunal exchange between North and South America after the formation of the Isthmus of Panama. We describe new SANU remains from the Neogene of the Cocinetas (northern Colombia) and Falcon (northwestern Venezuela) Basins. In the Cocinetas Basin, the middle Miocene fauna of the Castilletes Formation includes Hilarcotherium miyou sp. nov. (Astrapotheriidae), cf. Huilatherium (Leontiniidae), and Lambdaconus cf. L. colombianus (Proterotheriidae). The late Pliocene fauna of the Ware Formation includes a Toxodontinae indet. and the putative oldest record of Camelidae in South America. In the Falcon Basin, the Pliocene/Pleistocene faunas of the Codore and San Gregorio Formations include Falcontoxodon aguilerai gen. et sp. nov. and Proterotheriidae indet. We provide a phylogenetic analysis for Astrapotheriidae and Toxodontidae. The new data document a low-latitude provinciality within some SANU clades (e.g., Astrapotheriidae, Leontiniidae) during the middle Miocene. This contrasts with the wide latitudinal distribution of clades of other mammals recorded in the fauna, including the sparassodont Lycopsis padillai, the sloth Hyperleptus?, and the proterotheriid Lambdaconus cf. L. colombianus. The Pliocene/Pleistocene tropical faunas from northern South America are characterized by the predominance of native taxa despite their proximity to the Isthmus of Panama (fully emerged by that time). Only one North American ungulate herbivore immigrant is present, a cf. Camelidae indet. The Pliocene and early Pleistocene faunas suggest that environmental changes and biotic interactions affected the diversity dynamics and biogeographic patterns of SANUs during the Great American Biotic Interchange.

Timing and mode of simulated ungulate herbivory alter aspen defense strategies.

Timing of herbivory or selection of specific plant tissues (mode of herbivory) by different ungulate herbivore species are likely to have important influences on plant defense strategies. In this study, we devised two different modes of simulated herbivory, representing a selective ungulate feeding strategy (defoliation: leaf tissue removal only) and a bulk feeding strategy (clipping: leaves, twigs and meristems taken together). We applied these contrasting herbivory treatments to juvenile aspen suckers (Populus tremuloides Michx.) regenerating underneath aspen stands in early summer (June), late summer (August) or at both times to determine the effects of herbivory mode, timing and frequency on regenerating aspen. In response to the simulated herbivory treatments, we measured traits related to three plant defense strategies: tolerance (aboveground biomass and stem diameter), resistance (foliar phenolic glycosides) and vertical escape (sucker height and average leader length). There was no evidence that mode, timing or frequency of simulated herbivory induced or repressed phenolic glycoside production. Early summer herbivory was more detrimental than late summer herbivory on aspen tolerance and escape. Repeat herbivory in late summer did not amplify the negative effects of early summer herbivory. Clipping and defoliation tended to have similar effects on tolerance but clipping was more detrimental than defoliation on vertical escape. These results suggest that different ungulate herbivore species may have disparate impacts on the plant communities by selecting different tissues of the same plant, or browsing the plant at different times in the growing season.

An invasive plant provides refuge to native plant species in an intensely grazed ecosystem

Invasion by exotic plant species and herbivory can individually alter native plant species diversity, but their interactive effects in structuring native plant communities remain little studied. Many exotic plant species escape from their co-evolved specialized herbivores in their native range (in accordance with the enemy release hypothesis). When these invasive plants are relatively unpalatable, they may act as nurse plants by reducing herbivore damage on co-occurring native plants, thereby structuring native plant communities. However, the potential for unpalatable invasive plants to structure native plant communities has been little investigated. Here, we tested whether presence of an unpalatable exotic invader Opuntia ficus-indica was associated with the structure of native plant communities in an ecosystem with a long history of grazing by ungulate herbivores. Along 17 transects (each 1000 m long), we conducted a native vegetation survey in paired invaded and uninvaded plots. Plots that harboured O. ficus-indica had higher native plant species richness and Shannon–Wiener diversity H′ than uninvaded plots. However, mean species evenness J was similar between invaded and uninvaded plots. There was no significant correlation between native plant diversity and percentage plot cover by O. ficus-indica. Presence of O. ficus-indica was associated with a compositional change in native community assemblages between paired invaded and uninvaded plots. Although these results are only correlative, they suggest that unpalatable exotic plants may play an important ecological role as refugia for maintenance of native plant diversity in intensely grazed ecosystems.

Conservation lessons from large-mammal manipulations in East African savannas: the KLEE, UHURU, and GLADE experiments.

African savannas support an iconic fauna, but they are undergoing large-scale population declines and extinctions of large (>5kg) mammals. Long-term, controlled, replicated experiments that explore the consequences of this defaunation (and its replacement with livestock) are rare. The Mpala Research Centre in Laikipia County, Kenya, hosts three such experiments, spanning two adjacent ecosystems and environmental gradients within them: the Kenya Long-Term Exclosure Experiment (KLEE; since 1995), the Glade Legacies and Defaunation Experiment (GLADE; since 1999), and the Ungulate Herbivory Under Rainfall Uncertainty experiment (UHURU; since 2008). Common themes unifying these experiments are (1) evidence of profound effects of large mammalian herbivores on herbaceous and woody plant communities; (2) competition and compensation across herbivore guilds, including rodents; and (3) trophic cascades and other indirect effects. We synthesize findings from the past two decades to highlight generalities and idiosyncrasies among these experiments, and highlight six lessons that we believe are pertinent for conservation. The removal of large mammalian herbivores has dramatic effects on the ecology of these ecosystems; their ability to rebound from these changes (after possible refaunation) remains unexplored.

Optimizing silviculture in mixed uneven-aged forests to increase the recruitment of browse-sensitive tree species without intervening in ungulate population

An increase in ungulate abundance in Europe in recent decades has raised concerns for the survival of browse-sensitive tree species in its early life history stages. A possible strategy for mitigating the browsing-induced mortality of natural regeneration is to optimize silviculture. We used matrix population models parameterized for three types of Abies alba - Picea abies - Fagus sylvatica forests (3,183 permanent sample plots from three study areas in Slovenia, 39,717 ha), and a non-linear optimization to: (i) schedule optimal timing and intensity of logging in the next 100 years to increase the recruitment of Abies alba without intervening in the population of ungulates; and (ii) examine the influence of different natural recruitment rates on the potential for mitigating recruitment failure through silviculture optimization. The optimal management has required species-, growth- and diameter-specific logging, including intensive logging of large-diameter Abies alba in the first decades and strict conservation of recruits. The potential for mitigating recruitment failure through optimization increased progressively with natural recruitment rate and progressively at a decreasing rate with time. Optimizing silviculture was effective for maintaining Abies alba in stands exposed to low or moderate browsing pressures. Faced with chronic ungulate herbivory, forest managers should primarily focus on the reduction of herbivory and to a lesser extent on optimizing silviculture.

Differential effects of cattle, mule deer, and elk herbivory on aspen forest regeneration and recruitment

The abundance and composition of ungulate herbivore communities are changing globally, which can impact the resilience and function of Earth’s ecosystems. Impacts from herbivory are compounded in areas where multiple ungulates overlap, which is common in forest ecosystems. The objective of this study was to examine the differential and combined effects of ungulate communities (deer, elk, and cattle) on aspen forest recruitment after fires that occurred in 2012. Eight sets of differential ungulate exclosures, monitored by camera traps, were established across three National Forests in Utah. We identified the differential effect of each of three ungulate species using fencing that allowed for deer-only, native ungulate only (deer and elk), all ungulates and a complete ungulate exclosure. Over a three year period (2013–2016) we quantified ungulate species impacts on aspen height, density, and browse rates using camera trap photos. Ungulate activity was nearly 10-fold higher in two National Forests compared to the third, and gradually decreased over time. Meristem removal by ungulates in unfenced plots across sites averaged 60% which we identified as a critical threshold point for aspen recruitment failure. All three ungulate species had significant and similar effects on aspen regeneration success, but when adjusted for differences in estimated forage intake (animal unit months), differential impacts became apparent (deer > elk > cattle). We estimated that 4 cattle per camera−1 day−1 and 2.5 deer or elk per camera−1 day−1 was sufficient to reach the critical recruitment threshold of 60% removal of apical meristems. We conclude that ungulates species differentially influence aspen regeneration and recruitment, and that ungulate browsing above 30% meristem removal impairs aspen recruitment with recruitment failure occurring above 60% meristem loss.

Red deer structure the ground-dwelling beetle community in boreal forest

Changes in large herbivore distribution and abundance can have effects that potentially cascade throughout the trophic structure of an ecosystem. Little is known about these indirect trophic effects of ungulate herbivory, so the aim of this study was to investigate the role of red deer (Cervus elaphus) in determining the distribution and diversity of ground-dwelling beetles. We collected > 9000 beetles belonging to 149 species in a Western Norway boreal forest by pitfall trapping inside and outside red-deer exclosures placed along a gradient in herbivory intensity. Our study showed that red deer herbivory had a significant effect on structuring ground beetle communities in this boreal ecosystem. Key findings were that: (1) out of 17 beetle species represented by more than 100 specimens, four species benefited from red deer herbivory and associated impacts, while two were detrimentally affected; 2) red deer herbivory did not affect beetle abundance or alpha diversity, but increased local variation in beetle community structure (higher beta diversity); and 3) red deer browsing is important for the composition of the ground-beetle fauna. Herbivory improved the explanation of variation in beetle species composition on the forest floor by 40%. Given that herbivory is an indirect but central predictor of ground-dwelling beetle communities, it should be included in future studies or monitoring programs of red listed or keystone ground-dwelling beetles.

Spatial variation in herbivory, climate and isolation predicts plant height and fruit phenotype in Plectritis congesta populations on islands

Abstract Climate and herbivory can each drive natural selection on plant traits but may interact to give rise to different patterns in trait distributions when surveyed across island populations. These different patterns may arise because the occurrence of ungulate herbivores often varies across archipelagos, potentially leading to strong and abrupt spatial heterogeneity in the direction or intensity of natural selection. In contrast, climate tends to vary gradually and thus is more likely to lead to gradual clines in trait values. Population isolation may also affect trait values, given that random genetic drift may fix alleles or traits in the absence of gene flow or because gene flow between populations with similar or opposing selection pressures may augment or swamp the effects of selection. Here, we estimate the independent and interactive effects of deer, climate and isolation on fruit phenotype and plant height in 285 Plectritis congesta populations at 77 island and 44 mainland sites in western North America. Plectritis congesta is a palatable winter annual with two fruit phenotypes based on a simple Mendelian locus with clear dominance and heritable variation in height as a polygenic trait. Fruit phenotype and plant height were well predicted by deer occurrence; plants in populations with resident deer were short (15.0 ± 1.1 cm) and mainly expressed wingless fruits (73.0 ± 4.0%), whereas plants in populations without deer were 2.6 times taller (38.9 ± 5.3 cm) and only 9.0 ± 1.6% expressed wingless fruits. Wingless fruits were less common in populations experiencing wetter conditions with more seasonal variability in temperatures, particularly in the absence of deer. In contrast, population isolation was unrelated to fruit phenotype, except in populations rarely exposed to deer, where plants expressed phenotypes more like those in populations without deer as isolation increased. Our results are consistent with the hypothesis that spatial variation in browsing by deer or other factors correlated with it contributes to population‐level variation in fruit phenotype and plant height in P. congesta and that climate leads to a modest spatial gradient in plant height. Synthesis. The occurrence of deer at 285 island and mainland populations of Plectritis congesta predicted plant height and fruit phenotype, supporting the hypothesis that spatial variation in herbivory is a key factor affecting population‐level variation in the distribution of these heritable traits.

Functional composition of temperate forest trees under chronic ungulate herbivory

AbstractQuestionFunctional plant traits often express consistent changes along ecological gradients and, hence, are often used as indicators of environmental change (e.g. nutrient availability, temperature changes). Besides being driven by edaphic conditions, functional plant composition is filtered by herbivory, and traits responsive to nutrient availability often coincide with those related to palatability or resistance to browsing. We hypothesized that herbivory may distort the ways in which traits are expressed along environmental gradients.LocationBiałowieża National Park, Poland.MethodsWe used a long‐term controlled, exclosure experiment in the Białowieża National Park to study tree functional trait expression and plant indicator values, with and without large ungulate browsing, along a natural soil fertility gradient.ResultsBrowsing largely reduced the functional diversity of regenerating trees, indicated by multivariate analysis and Rao's Quadratic Entropy (RQE), and altered how several traits change with increasing fertility. Browsing led to an increase in specific leaf area (SLA) on poorer sites. RQE showed a hump‐backed trend along the fertility gradient, indicating the largest functional diversity at intermediate fertility. However, this pattern was not affected by browsing. Unlike the morphological tree traits, trends of light and N plant indicator values along the gradient were unaffected by browsing.ConclusionsThese results highlight how the expression of plant traits resulting from one driver (soil fertility) can be modified by another driver (herbivory,) and stress the importance of taking herbivory into account when using plant traits as indicators of large‐scale processes (e.g. climate change). Furthermore, the results suggest that plant indicator values may be more robust towards these effects, while compiled indices such as RQE could mask considerable functional turnover. Several traits (e.g. SLA) are strongly connected to nutrient cycling. The development, driven by browsing, towards higher SLA on poorer sites may thus cause a positive feedback effect on site fertility that drives an increase in nutrient availability. This may in turn have implications for ecosystem functionality. Hence, the large reduction in functional diversity revealed at the scale of this study may in the long term have implications on multiple ecosystem processes.

Interpreting Feral Goat (Capra hircus) Movement to Guide Management in a Mesic Watershed on Oʻahu, Hawaiʻi

Author(s): Char, Jared; Leary, J. J. K.; Litton, C. M. | Abstract: Endemic Hawaiian ecosystems evolved without ungulate herbivores. Feral goats, a common nonnative ungulate on Pacific Islands, browse and trample vegetation which can denude watersheds and expose them to soil erosion. Since 1993, the Hawaiʻi Division of Forestry and Wildlife has actively suppressed feral goat populations to protect critical watersheds in a 1600-ha management area on Mount Kaʻala in the leeward Waiʻanae mountain range of Oʻahu. Despite these ongoing efforts, total eradication has not been achieved to date. This study examined the movement patterns of one male and one female feral goat in this management area over one year in 2015-16 with GPS collars. The primary objective was to determine if feral goat movements are related to seasonality, moon phase and precipitation to inform future management efforts. The male goat exhibited a large range, extending out 2.5 km from its starting point and over an 800m elevation range within the year, traveling to lower elevations during the summer months. The female goat, in turn, had a much smaller range and stayed relatively close to its initial starting point. The male goat exhibited greater movement at night than during the day, and this was particularly evident during full moon phases; animals also exhibited aversion to movement during precipitation events. Hot spot analyses showed that the female was largely confined to one location throughout the course of the study, while the male moved to multiple locations but displayed a strong affinity to the eastern portion of the management area in the Fall season. These initial findings help build knowledge on local patterns of feral goat movement within this managed area that can be used for control efforts. GPS collars provided useful high-resolution data to support further adoption of this technology to better inform management decisions. Future management strategies should incorporate longer-term movement data sets from multiple individuals to better understand habituation (e.g., return to favored locations), patterns of sexual segregation and rutting. This would allow a more demographic approach for maintaining populations below levels that are considered detrimental to this critical habitat.

A stoichiometric perspective of the effect of herbivore dung on ecosystem functioning.

Ungulate herbivores play a prominent role in maintaining the tree–grass balance in African savannas. Their top‐down role through selective feeding on either trees or grasses is well studied, but their bottom‐up role through deposition of nutrients in dung and urine has been overlooked. Here, we propose a novel concept of savanna ecosystem functioning in which the balance between trees and grasses is maintained through stoichiometric differences in dung of herbivores that feed on them. We describe a framework in which N2‐fixing trees and grasses, as well as ungulate browsing and grazing herbivores, occupy opposite positions in an interconnected cycle of processes. The framework makes the testable assumption that the differences in dung N:P ratio among browsers and grazers are large enough to influence competitive interactions between N2‐fixing trees and grasses. Other key elements of our concept are supported with field data from a Kenyan savanna.

Elk nutritional resources: Herbicides, herbivory and forest succession at Mount St. Helens

Concern exists about the effects that silvicultural herbicides, past herbivory, and forest succession may have on the carrying capacity for ungulates in the vicinity of Mount St. Helens in southwest Washington. We independently evaluated the effects of both operational herbicides and ungulate herbivory on biomass and available digestible energy of forages in a chronosequence of early-succession (ES) forest stands using a retrospective, paired-site design. We distinguished between trends in biomass by classifying species as avoided (used less than available) or accepted (used equal or more than available) forages for elk based on recent research involving foraging trials of hand-raised, tractable elk in western Oregon and Washington. Herbicide application reduced biomass of accepted forages (kg/ha) for only two years, whereas the initial reduction in avoided biomass persisted throughout the 13-year ES period that we evaluated. The reduction in avoided species was not associated with an increase in accepted species, which may be related to herbivory. We observed that forest canopy closure even at 10–13years was similar in stands treated and untreated with herbicides, suggesting herbicides did not shorten the seral window when palatable forages were abundant. Because dry matter digestibility of accepted species was generally higher than avoided species, digestible energy (DE, kcal/ha) available to elk was similar to trends in accepted and avoided biomass. An initial 2-year increase in modelled estimates of dietary DE in herbicide-treated stands in years 1–2 resulted from a rapid recovery of plants with high digestibility. In contrast to herbicide treatments, effects of ungulate herbivory on ES communities increased with stand age with a reduction of deciduous shrub height but not densities, reduced biomass of accepted but not avoided species, and reduced standing DE of accepted species outside exclosures. Despite the influence of herbicide applications, herbivory, or their interactions, nutritional resources for elk were equal or more available in ES stands than in mid- and late-succession stands, highlighting the importance of maintaining ES stands for elk in this region.

Herbivory impacts of elk, deer and cattle on aspen forest recruitment along gradients of stand composition, topography and climate

The abundance and composition of large ungulate communities are changing dramatically across terrestrial ecosystems due to human activities. This has resulted in novel herbivory regimes that create strong top-down effects on biological communities, and can reduce ecosystem resilience. Biotic and abiotic conditions that influence the population structure and behavior of ungulate herbivores are highly variable across space and time, making it difficult to predict ungulate impacts across complex landscapes. Where multiple ungulate species co-exist, it can be challenging to differentiate species impacts on plant communities. We examined the effects of cattle, American elk, and mule deer on aspen regeneration and recruitment along gradients of forest composition and physiographic conditions in 3 National Forests of Utah, USA. Aspen regeneration and recruitment increased with winter precipitation, elevation and higher abundance of overstory aspen. Binned fecal count densities of elk, mule deer, and cattle showed strong inverse correlations with aspen height (elk: r2=0.83; deer: r2=0.92; cattle: r2=0.35) and aspen recruitment (elk: r2=0.51; deer: r2=0.59). Aspen stem density was negatively correlated with elk (r2=0.35) and cattle fecal densities (r2=0.71). We found that 60% of the sites we surveyed had low ungulate activity and good aspen regeneration, 32% were intermediate use sites that warrant additional monitoring, and 8% of sites showed high ungulate use that exhibited aspen regeneration failure and lack of recruitment where targeted management is recommended. We conclude that ungulate impacts in aspen forests should be considered on a site by site basis and should primarily be evaluated based on the total abundance of the ungulate community with precipitation, elevation and stand composition as secondary factors.

Ungulate grazing drives higher ramet turnover in sodium‐adapted Serengeti grasses

AbstractQuestionsUngulate grazers requiring sodium (Na) will preferentially graze in areas with Na‐accumulating forage grasses (i.e. many saline soils with high NaCl). Given that high‐Na conditions necessitate specific adaptations in plants, the mechanisms allowing plants to persist under combined herbivory and Na stress are unclear. Has adaptation to soil salinity in East African grasses modified the evolution of grazing tolerance, leading to plants that are susceptible to defoliation? Does grazing differentially impact the survivorship of plants with different tolerances to Na? Finally, can species traits that confer salinity and herbivory tolerances help to explain the presence of mosaic structure in high salinity regions?LocationShort‐grass plains of Serengeti National Park, Tanzania, East Africa.MethodsWe tracked the fate of 836 individuals of 26 grass species, over an entire growing season, in the short‐grass plains using a network of 41 quadrats (0.25 m2). We investigated the impact of soil properties (e.g., electrical conductivity [EC], bulk density, clay), ungulate herbivory and grass species identity on patterns of composition and turnover. Finally, we linked plant leaf Na and leaf palatability data to species environmental responses.ResultsUnder comparable levels of grazing pressure, grass species known to accumulate Na have much higher levels of turnover compared to low‐Na species. These Na accumulators were generally short, highly palatable and clonal species.ConclusionsHerbivory most affects turnover (of ‘ramets’) of species with the highest tolerance to Na, suggesting that Na tolerance ability interacts with defoliation response in Serengeti grasses. As a result, spatial heterogeneity in soil EC produces high‐turnover communities that overlay high‐EC soil adjacent to more stable communities composed of Na‐intolerant species. While Na‐intolerant grasses in Serengeti range from short and palatable to taller and less palatable species, grasses that accumulate Na tend to be short and palatable, a likely result of the grazing pressure they experience.

Wild ungulate herbivory suppresses deciduous woody plant establishment following salmonid stream restoration

Domestic and wild ungulates can exert strong influences on riparian woody vegetation establishment, yet little is known about how wild ungulate herbivory affects riparian restoration in the absence of cattle. We evaluated elk (Cervus elaphus) and mule deer (Odocoileus hemionus) impacts on the establishment of deciduous woody riparian plantings along 11km of Meadow Creek, a steelhead (Oncorhynchus mykiss) and Chinook (Oncorhynchus tshawytscha) salmon stream in northeastern Oregon, USA. We compared survival and growth between protected and unprotected plantings (from wild ungulates), and assessed the contribution of the plantings to the total deciduous woody cover after two growing seasons. Riparian use by wild ungulates was estimated by tracking a subset of the deer and elk populations using global positioning system telemetry collars. Elk riparian use was 11 times greater than deer, and in contrast to elk, deer were functionally absent from greater than 50% of the restored reach. Wild ungulate herbivory decreased planting survival by 30%, and growth by 73%, and was most detrimental to cottonwood (Populus balsamifera; increased likelihood of mortality by 5 times and suppressed growth by more than 90%). Herbivory impacts resulted in survival rates below regional criteria (50%) for restoration success after only two growing seasons. Naturally recovering shrubs accounted for 99% of the deciduous woody cover, and were mostly composed of the same species or genera as those planted. Our results suggest that wild ungulate herbivory can impede riparian restoration along salmonid streams by suppressing woody plant establishment and recovery.

Simulating ungulate herbivory across forest landscapes: A browsing extension for LANDIS-II

Browsing ungulates alter forest productivity and vegetation succession through selective foraging on species that often dominate early succession. However, the long-term and large-scale effects of browsing on forest succession are not possible to project without the use of simulation models. To explore the effects of ungulates on succession in a spatially explicit manner, we developed a Browse Extension that simulates the effects of browsing ungulates on the growth and survival of plant species cohorts within the LANDIS-II spatially dynamic forest landscape simulation model framework. We demonstrate the capabilities of the new extension and explore the spatial effects of ungulates on forest composition and dynamics using two case studies. The first case study examined the long-term effects of persistently high white-tailed deer browsing rates in the northern hardwood forests of the Allegheny National Forest, USA. In the second case study, we incorporated a dynamic ungulate population model to simulate interactions between the moose population and boreal forest landscape of Isle Royale National Park, USA. In both model applications, browsing reduced total aboveground live biomass and caused shifts in forest composition. Simulations that included effects of browsing resulted in successional patterns that were more similar to those observed in the study regions compared to simulations that did not incorporate browsing effects. Further, model estimates of moose population density and available forage biomass were similar to previously published field estimates at Isle Royale and in other moose-boreal forest systems. Our simulations suggest that neglecting effects of browsing when modeling forest succession in ecosystems known to be influenced by ungulates may result in flawed predictions of aboveground biomass and tree species composition.

OUP accepted manuscript

Herbivory by ungulates can affect forest regeneration success, but its long-term impacts on tree function and recruitment are less studied. We evaluated strategies of resistance, tolerance and vertical escape against ungulate herbivory by evaluating leaf traits (photosynthesis, morphology and chemistry) and growth rates of aspen in the presence and absence of ungulate herbivores 1, 2, 3 and 26 years after fires initiated aspen suckering. Over the initial 3-year period, ~60% of aspen stems in unfenced plots showed evidence of being browsed by ungulates. After 3 years, aspen in unfenced plots had smaller leaves, were 50% shorter, and had 33% lower nonstructural carbohydrate concentrations and 33% greater concentrations of condensed tannins, when compared with fenced aspen. Aspen exposed to ungulate herbivory over a 26-year period maintained smaller leaves, had lower annual radial growth rates and were still below the critical height threshold of 2 m required to escape ungulate herbivory for successful recruitment. In contrast, the average height of aspen protected from ungulates was approaching 6 m. Over the 26-year period leaves in unfenced plots had 41% lower nonstructural carbohydrate concentrations and greater expression of defense compounds-condensed tannins (63%) and phenolic glycosides (102%)-than leaves in fenced plots. Photosynthetic rates were slightly higher in aspen that experienced ungulate browsing, suggesting that changes in leaf anatomy and chemistry due to ungulate herbivory did not interfere with photosynthesis. Our data suggest that ungulate browsing increases investment in chemical defense, lowers nonstructural carbohydrate concentrations and reduces leaf area, which decreases the recruitment potential of regenerating aspen.