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1. Increasing ungulate populations are affecting vegetation negatively in many areas, but few studies have assessed the long-term effects of overbrowsing on individual life-history traits of ungulates. 2. Using an insular population of white-tailed deer (Odocoileus virginianus Zimmermann; Anticosti, Québec, Canada) introduced in 1896, and whose density has remained high since the first evidence of severe browsing in the 1930s, we investigated potential feedbacks of long-term and heavy browsing on deer life-history traits. 3. We assessed whether chronic browsing contributed to a decline of the quality of deer diet in early autumn during the last 25 years, and evaluated the impacts of reduced diet quality on deer body condition and reproduction. 4. Rumen nitrogen content declined 22% between two time periods, 1977-79 and 2002-04, indicating a reduction in diet quality. 5. After accounting for the effects of year within the time period, age and date of harvest in autumn, peak body mass of both sexes declined between the two time periods. At the end of November, males were on average 12% heavier and adult does 6% heavier in 1977-79 than in 2002-04. Hind foot length did not vary between time periods. 6. The probability of conception increased 15% between the two time periods, but litter size at ovulation declined 7%, resulting in a similar total number of ovulations in 2002-04 and in 1977-79. 7. Our results suggest that following a decline in diet quality, white-tailed deer females modified their life-history strategies to maintain reproduction at the expense of growth. 8. Deer appear to tolerate drastic reductions in diet quality by modifying their life history traits, such as body mass and reproduction, before a reduction in density is observed. Such modifications may contribute to maintain high population density of large herbivores following population irruption.

During winter, ungulates in boreal forests must cope with high energetic costs related to locomotion in deep snow and reduced forage abundance and quality. At high density, ungulates face additional constraints, because heavy browsing reduces availability of woody browse, the main source of forage during winter. Under these severe conditions, large herbivores might forage on alternative food sources likely independent of browsing pressure, such as litterfall or windblown trees. We investigated the influence of alternative food sources on winter habitat selection, by studying female white-tailed deer (Odocoileus virginianus) living in 2 landscapes with contrasted browse abundance, recently logged and regenerated landscapes, in a population at high density and on a large island free of predators. We fitted 21 female whitetailed deer with Global Positioning System (GPS) collars and delineated winter home ranges and core areas. We measured snow conditions in different habitat categories and sampled vegetation in the core areas and in the rest of the home ranges to determine how forage abundance, protective cover, and snow conditions influenced habitat selection within the home range. In both landscapes, deer were less likely to use open habitat categories as snow accumulated on the ground. At a finer scale, deer inhabiting the regenerated landscape intensively used areas where balsam fir cover was intermediate with greater balsam fir browse density than in the rest of the home range. In the recently logged landscape, deer were more likely to be found near edges between clear-cuts and balsam fir stands and in areas where windblown balsam fir trees were present; the latter being the most influential variable. Although balsam fir browse was sparse and mainly out of reach in this landscape, deer increased the use of areas where it was present. Our results offer novel insights into the resource selection processes of northern ungulates, as we showed that access to winter forage, such as woody browse and alternative food sources, depends on climatic conditions and stochastic events, such as abundant compacted snow or windthrows. To compensate for these scarce and unpredictable food supplies, deer selected habitat categories, but mostly areas within those habitat categories, where the likelihood of finding browse, litterfall, and windblown trees was greatest.

Management of tree cover, either to curb bush encroachment or to mitigate losses of woody cover to over-browsing, is a major concern in savanna ecosystems. Once established, trees are often “trapped” as saplings, since interactions among disturbance, plant competition, and precipitation delay sapling recruitment into adult size classes. Saplings can be directly suppressed by wildlife browsing and competition from adjacent plants, and indirectly facilitated by grazers, such as cattle, which feed on neighboring grasses. Yet few experimental studies have simultaneously quantified the effects of cattle and wildlife on sapling growth, particularly over long time scales. We used a series of replicated 4-ha herbivore-manipulation plots to investigate the net effects of wildlife and moderate cattle grazing on Acacia drepanolobium sapling growth over 10 years that encompassed extended wet and dry periods. We also simulated more intense cattle grazing using grass removal treatments (0.5-m radius around saplings), and we quantified the role of intraspecific tree competition using neighborhood tree surveys (trees within a 3-m radius). Wildlife, which included elephants, had a positive effect on sapling growth. Wildlife also reduced neighbor tree density during the 10-yr study, which likely caused the positive effect of wildlife on saplings. Although moderate cattle grazing did not affect sapling growth, grass removal treatments simulating heavy grazing increased sapling growth. Both grass removal and neighbor tree effects on saplings were strongest during above-average rainfall years following drought. This highlights that livestock-driven reductions in grass cover and catastrophic wildlife damage to trees during droughts present a need, or an opportunity, for targeted management of sapling growth and woody plant cover during ensuing wet periods.

Diverse communities of large mammalian herbivores (LMH), once widespread, are now rare. LMH exert strong direct and indirect effects on community structure and ecosystem functions, and measuring these effects is important for testing ecological theory and for understanding past, current, and future environmental change. This in turn requires long-termexperimental manipulations, owing to the slow and often nonlinear responses of populations and assemblages to LMH removal. Moreover, the effects of particular species or body-size classes within diverse LMH guilds are difficult to pinpoint, and the magnitude and even direction of these effects often depends on environmental context. Since 2008, we have maintained the Ungulate Herbivory Under Rainfall Uncertainty (UHURU) experiment, a series of size-selective LMH exclosures replicated across a rainfall/productivity gradient in a semiarid Kenyan savanna. The goals of the UHURU experiment are to measure the effects of removing successively smaller size classes of LMH (mimicking the process of size-biased extirpation) and to establish how these effects are shaped by spatial and temporal variation in rainfall. The UHURU experiment comprises three LMH-exclusion treatments and an unfenced control, applied to nine randomized blocks of contiguous 1-ha plots (n = 36). The fenced treatments are MEGA (exclusion of megaherbivores, elephant and giraffe), MESO (exclusion of herbivores ≥40 kg), and TOTAL (exclusion of herbivores ≥5 kg). Each block is replicated three times at three sites across the 20-km rainfall gradient, which has fluctuated over the course of the experiment. The first 5 years of data were published previously (Ecological Archives E095-064) and have been used in numerous studies. Since that publication, we have (1) continued to collect data following the original protocols, (2) improved the taxonomic resolution and accuracy of plant and small-mammal identifications, and (3) begun collecting several new data sets. Here, we present updated and extended raw data from the first 12 years of the UHURU experiment (2008–2019). Data include daily rainfall data throughout the experiment; annual surveys of understory plant communities; annual censuses of woody-plant communities; annual measurements of individually tagged woody plants; monthly monitoring of flowering and fruiting phenology; every-other-month small-mammal mark–recapture data; and quarterly largemammal dung surveys. There are no copyright restrictions; notification of when and how data are used is appreciated and users of UHURU data should cite this data paper when using the data.

Questions: Ungulate herbivory and formation of large termite mounds occur over different time scales, but both can affect plant community composition in savannas. Human-managed savanna systems are increasingly dominated by domesticated grazing herbivores. These have replaced a mix of indigenous browsers and grazers, leading to changes in plant communities such as increased bush encroachment. We compared the relative impacts of five decades of different types of ungulate herbivory (cattle grazing, browsing and grazing by wild herbivores, and exclusion of all larger herbivores) on woody plant assemblages in two habitats, namely, large termite mounds, which may be thousands of years old, and the surrounding matrix. Location: Miombo woodland savanna, Zimbabwe. Methods: To determine the influence of termite mounds and herbivory on spatial distribution and composition of woody assemblages, we compared 40 paired mound-matrix plots from the three herbivory treatments using PERMANOVA. We assessed whether mound plots were more similar to each other than matrix plots were to each other, and whether herbivory influenced similarity. We used SIMPER analysis to identify changes in abundance of indicator species for each habitat (i.e. mound or matrix). Results: Species composition differed significantly between mound and matrix and also between herbivory treatments. Woody plant assemblages on mounds were more similar to each other than woody plant assemblages in matrix plots were to each other, regardless of type of herbivory, but herbivory reduced the mound/matrix contrast. Sample location (i.e. on mound or in matrix) explained 23% of the variation in woody species composition, compared to 12% explained by herbivory. Woody plant abundance was lowest where there were both grazers and browsers. Conclusions: The influence of large termite mounds on plant assemblages was roughly double that of herbivory, which has occurred over five decades. Type of herbivory emerged as relatively influential on woody plant species composition, given that the time periods involved were short by comparison to the slow formation of termite mounds. Type of herbivory also influenced species composition and vegetation structure, with a diversity of herbivores necessary to reduce encroachment by woody species.

Questions What is the long‐term impact of deer browsing on the diversity of the herbaceous layer and tree species regeneration? Which parameters of regeneration of the tree species regeneration and the herbaceous layer best indicate browsing impact? Study site Dinaric Mountains, Slovenia. Methods We studied the long‐term impact of red deer on mixed temperate forests by comparing the tree species regeneration and herbaceous layer vegetation under two treatments: deer present, no deer. We analyzed the regeneration of trees older than one year up to a diameter at breast height of 10 cm (categorized into five height classes) and the cover abundance of plant species in the herbaceous layer (<50 cm). Results There were no significant differences between the treatments in the number of tree species regeneration. Browsing impact on the most abundant tree species—European beech, silver fir and sycamore—varied, indicating differences in palatability. When deer were present, the number of silver fir regenerating was significantly lower in all height classes, and regeneration of European beech specimens shorter than 50 cm was more abundant, while for sycamore shorter seedlings (<20 cm) were more abundant, and regeneration of taller specimens (≥50 cm) was significantly less abundant. The reduction of tree species diversity during natural regeneration is evident. There were no significant differences between the treatments in the number and diversity of plant species in the herbaceous layer; however, the abundance of 13 plant species differed significantly between the treatments. Deer reduce the density of tree species saplings due to long‐term browsing and thus indirectly increase tree species diversity in the regeneration up to 20 cm in height and plant species diversity in the herbaceous layer. Conclusions We documented the direct and indirect impact of deer on the diversity of tree species regeneration, but only found an indirect influence on the diversity of the herbaceous layer. The height structure of palatable tree species regeneration appears to be the most appropriate indicator of browsing impact. The observed browsing impact leads to the complete dominance of European beech in the tree species composition of forest stands. Naturally regenerating tree species showed different, size‐dependent responses to the impact of red deer. Deer prevented recruitment of palatable tree species above the browse layer. No plant species in the herbaceous layer went locally extinct because of deer; however, deer influenced the abundance of some plant species. Deer indirectly increased plant species diversity in the herbaceous layer by reducing the density of tree saplings.

European yew (Taxus baccata) is an endangered long-lived tree species. The species is facing a regeneration failure in a large part of its natural distribution, likely due to interplay of climate change and browsing by herbivores. Forest management approaches that support inter-specific complementarity can help the species mitigate these negative effects. However, a lack of long-term records has prevented an adequate answer to the facilitation hypothesis. Therefore, we compiled unique data from eleven long-term plots established on three sites in the western Carpathian Mountains in 1972, 1989 and 1995. During the past 30–50 years, forest stands were treated by various management alternatives, and the development of stands and regeneration were monitored in 5–12-year intervals. In this study, we tested the hypothesis that an increase in tree species diversity positively correlates with abundance of yew regeneration. Additionally, we compared the relationships between management and no-management alternatives. Our results revealed the positive correlation of tree species diversity and the quantity of yew regeneration. Moreover, an increase in the proportion of maple seedling at the expense of beech supported the establishment of yew seedlings at increased abundance. However, recently (since 1982) the growth of yew saplings did not exceed 20 cm in height, mostly because of heavy damage caused by deer browsing. We conclude that forest managers and conservationists can support the regeneration of yew using the treatments that increase tree species diversity.

Achieving an optimal density of trees is essential for the final yield in commercial forestry. Soil scarification is commonly used in Scandinavia in order to produce successful regenerations of Scots pine (Pinus sylvestris L.), especially in areas with risk of browsing damage by moose (Alces alces L.). The research presented in this paper provides knowledge on how increased intensity of soil scarification affects the regeneration of pine and birch (Betula spp. L.). A total of 67 stands were treated with different intensities of soil scarification. Tree seedling density and current annual growth (CAG) were measured one to five years after scarification. Results showed that the density of pine and birch seedlings increased with soil scarification intensity. CAG of pine decreased with scarification intensity. CAG of downy birch decreased with proportion of exposed mineral soil, but increased with proportion of exposed humus. The effect of soil scarification intensity on CAG of both tree species was relatively weak. Results suggest that although increased scarification intensity had a positive effect on seedling establishment, the effect on early growth may be unfavourable. Further research is needed in order to evaluate the long-term effects of soil scarification intensity on growth.

Treelines are expected to expand into alpine ecosystems with global warming, but herbivory may delay this expansion. This study quantifies long-term effects of temporally varying sheep densities on birch recruitment and growth in the treeline ecotone. We examined treeline ecotone successional trajectories and legacy effects in a replicated experimental setup, where enclosures were present for 14 years with three different sheep densities (0, 25, 80 sheep km⁻²). Before and after the enclosures were present, the site had an ambient sheep density of 20–25 km⁻². We sampled field data 4 years after enclosure removal and compared these to data sampled 8 and 9 years after enclosure erection. We sampled data on birch browsing pressure, birch distribution across life-stages (recruits, saplings, and mature trees), and birch annual radial growth. Fourteen years of increased or decreased sheep density had observable legacy effects depending on birch life-stage. Birch recruit prevalence decreased in areas, where sheep were reintroduced after being absent for 14 years. For the same areas, sapling and mature tree prevalence increased, indicating that these areas have entered alternative successional trajectories compared to areas, where sheep were present the whole time. Birch annual radial growth showed a lag effect of 2 years after enclosure removal, with growth decreasing in areas where sheep had been absent for 14 years and increasing where sheep densities were high. Thus, decadal-scale absences of herbivores can leave legacy effects due to increased numbers of trees that have high resistance to later-introduced herbivore browsing.

Although disturbance theory has been recognized as a useful framework in examining the stability of ant–plant mutualisms, very few studies have examined the effects of fire disturbance on these mutualisms. In myrmecophyte-dominated savannas, fire and herbivory are key drivers that could influence ant–plant mutualisms by causing complete colony mortality and/or decreasing colony size, which potentially could alter dominance hierarchies if subordinate species are more fire resilient. We used a large-scale, replicated fire experiment to examine long-term effects of fire on acacia–ant community composition. To determine if fire shifted ant occupancy from a competitive dominant to a subordinate ant species, we surveyed the acacia–ant community in 6–7 yr old burn sites and examined how the spatial scale of these burns influenced ant community responses. We then used two short-term fire experiments to explore possible mechanisms for the shifts in community patterns observed. Because survival of ant colonies is largely dependent on their ability to detect and escape an approaching fire, we first tested the evacuation response of all four ant species when exposed to smoke (fire signal). Then to better understand how fire and its interaction with large mammal herbivory affect the density of ants per tree, we quantified ant worker density in small prescribed burns within herbivore exclusion plots. We found clear evidence suggesting that fire disturbance favored the subordinate ant Crematogaster nigriceps more than the dominant and strong mutualist ant C. mimosae, whereby C. nigriceps (1) was the only species to occupy a greater proportion of trees in 6–7 yr old burn sites compared to unburned sites, (2) had higher burn/unburn tree ratios with increasing burn size, and (3) evacuated significantly faster than C. mimosae in the presence of smoke. Fire and herbivory had opposite effects on ant density per meter of branch for both C. nigriceps and C. mimosae, with fire decreasing ant densities per meter of branch and the presence of large herbivores increasing ant density. Taken together, these experiments suggest that major ecosystem disturbances like fire can disrupt mutualistic associations and maintain diversity in partner quality and identity despite a clear dominance hierarchy.