Unfenced Plots Research Articles

Using photography to estimate above-ground biomass of small trees

AbstractQuantifying tree biomass is an important research and management goal across many disciplines. For species that exhibit predictable relationships between structural metrics (e.g. diameter, height, crown breadth) and total weight, allometric calculations produce accurate estimates of above-ground biomass. However, such methods may be insufficient where inter-individual variation is large relative to individual biomass and is itself of interest (for example, variation due to herbivory). In an East African savanna bushland, we analysed photographs of small (<5 m) trees from perpendicular angles and fixed distances to estimate above-ground biomass. Pixel area of trees in photos and diameter were more strongly related to measured, above-ground biomass of destructively sampled trees than biomass estimated using a published allometric relation based on diameter alone (R2 = 0.86 versus R2 = 0.68). When tested on trees in herbivore-exclusion plots versus unfenced (open) plots, our predictive equation based on photos confirmed higher above-ground biomass in the exclusion plots than in unfenced (open) plots (P < 0.001), in contrast to no significant difference based on the allometric equation (P = 0.43). As such, our new technique based on photographs offers an accurate and cost-effective complement to existing methods for tree biomass estimation at small scales with potential application across a wide variety of settings.

Initial Survival and Development of Planted European Beech (Fagus sylvatica L.) and Small-Leaved Lime (Tilia cordata Mill.) Seedlings Competing with Black Cherry (Prunus serotina Ehrh.).

Black cherry (Prunus serotina Ehrh.) is considered one of the most invasive tree species in central Europe and causes problems for both nature conservation and silviculture. Besides mechanical control treatments, a suggested control method to prevent its ongoing spread is to underplant shade-tolerant native tree species. Therefore, we combined two mechanical treatments, with underplanting of European beech (Fagus sylvatica L.) or small-leaved lime (Tilia cordata Mill.) on fenced and unfenced plots. After the first growing season, survival rates were evaluated, and selected seedlings were destructively harvested to analyze their growth performance and leaf morphology in association with the different light regimes resulting from mechanical treatments Survival rates for both seedlings were very high (>95%). Survival rates were higher on fenced plots than on unfenced plots, most likely as result of browsing. The mortality of F. sylvatica decreased with increasing light availability on fenced plots. The mortality of T. cordata did not change along the light gradient. After one vegetation period no differences with respect to biomass allocation could be detected along the light gradient. However, the specific leaf areas of both species responded similarly, decreasing with increasing light availability. In summary, both species were able to establish and survive in the dense P. serotina understory and might have the potential to outcompete the invasive alien species in the long run.

Above- and Below-ground Cascading Effects of Wild Ungulates in Temperate Forests

Ungulates have become abundant in many temperate forests, shifting tree species composition by browsing and altering soil physical conditions by trampling. Whether these effects cascade down to other trophic levels and ecosystem processes is poorly understood. Here, we assess the paths through which ungulates have cascading effects on other trophic levels (regeneration, litter, invertebrates, rodents and organic matter decomposition). We compared ungulate effects by comparing 15 response variables related to different trophic levels between paired fenced and unfenced plots in twelve temperate forest sites across the Netherlands, and used pathway analysis model to identify the (in)direct pathways through which ungulates have influenced these variables. We found that plots with ungulates (that is, unfenced) compared to plots without (that is, fenced) had lower litter depth, sapling diversity, sapling density, rodent activity, macro-invertebrate biomass, decomposition rate of tea bags, pine and birch litter and higher soil compaction. These findings were used in a path analysis to establish potential causal relationships, which showed that ungulate presence: decreased sapling density, which indirectly decreased rodent activity; decreased litter depth, which indirectly reduced invertebrate diversity; increased soil compaction, which also decreased invertebrate diversity. Soil pH decreased invertebrate biomass, which also increased nitrogen mineralization. Yet, we did not find cascading effects of ungulates on decomposition rates. Importantly, an increase in ungulate abundance strengthens the cascading effects in this system. Our results suggest that ungulates can trigger cascading effects on lower trophic levels, yet decomposition and mineralization rates are resilient to ungulate browsing and trampling. Therefore, temperate forests conservation could benefit by limiting ungulate abundance.

Long‐Term Elimination of Grazing Reverses the Effects of Shrub Encroachment on Soil and Vegetation on the Ordos Plateau

AbstractConversion from grasslands to shrublands resulting from overgrazing occurs worldwide and is reinforced by the global climatic change. The functioning, biogeochemical cycles (e.g., carbon and water), and the stability of grassland ecosystems are significantly affected by the conversion. To best manage and use those grassland ecosystems, it is imperative to examine how the shrub‐encroached grasslands can be restored to native grassland ecosystems. In this study, aboveground biomass of all species, root biomass, soil water content, and soil texture in a set of fenced and unfenced plots were observed every three years from 1992 to 2011 in a semishrub encroached grassland on the Ordos Plateau of China. In the fenced plots, aboveground biomass increased for grass species and decreased for semishrub species. Root biomass and soil water content in the 0–10‐cm soil layer increased, but decreased in the 10–30‐cm soil layers. The fraction of soil particle sizes less than 0.01 mm increased in the 0–10‐cm soil layer. In contrast, these variables remained constant in the unfenced plots over the experimental period. The semishrub encroached grassland dominated by Artemisia ordosica was replaced with a native perennial grass, Stipa bungeana, when grazing was eliminated in the fenced plots. Changes in soil texture and moisture after fencing were correlated with the native grassland restoration from semishrub encroached grasslands. This study suggests that, to restore the native grassland, grazing should be eliminated in the study region.

The function of open-field farming – managing time, work and space

ABSTRACT Open fields were a dominant agricultural feature in Central, Western and Northern Europe for nearly a millennium. The spatial organisation of villages and the degree of communal management of common resources varied, but the basic characteristics and common features of the open-field system were that individual holdings were fragmented into several small unfenced plots and intermingled in one or more fields. Research on the subject is extensive, and several explanations for its cause(s) have been presented; however, the answer regarding the question of its rationale and persistence over time is still up for debate. The overarching aim of this article is to present new findings concerning open-field farming from a functional and practical perspective. What were the farming practices and how was the spatial organisation in open fields integrated in those practices? This article shows that the common practice in Skaraborg County, Sweden, was diversification by using different crops. In the village of Kleva, the preparation of plots and the planting of different crops was carried out in a sequence. Sources indicate that the scattered plots in open fields were integrated into that sequence and that certain plots were designated for certain crops to be sown at a certain moment in time. In the village of Kleva, open fields were used to cater to precision farming as a way to manage time, work and space.

Effects of white-tailed deer (Odocoileus virginianus) exclusion on plant recovery in overwash fans after a severe coastal storm.

We documented the impacts of an abundant deer population on dune vegetation recovering from severe storm surge on a barrier island through use of permanent plots and a repeated measures analysis. Three years after landfall of the storm, vegetation cover was dominated by American beachgrass, Ammophila breviligulata, though we observed 12 plant species among plots surveyed. We documented significantly greater vegetation cover in fenced than unfenced plots in overwash fans in two consecutive years. The difference in species richness between fenced and unfenced plots was significant, though richness was consistently low (≤4 species per plot) and we did not detect a statistically significant difference between years. Both deer trampling and foraging effects were captured in this study, though separation between these effects was not possible. Because trampling effects are often exacerbated on sandy soils, trampling and foraging effects should be isolated and investigated in future assessments of deer impacts on coastal vegetation. Managing deer to lower abundance may enhance coastal resilience if vegetation is allowed to recover unimpeded by foraging and trampling, though a better understanding of the precise nature of deer impacts on dune vegetation is necessary.

Effect of twin-lead type electric fence for deterring scansorial animals

Electric fences are usually effective in deterring terrestrial wild animals. However, they can prove inefficient in case of scansorial animals such as martens and raccoons, which can touch the electric fence without being grounded, thus not experiencing the electric shock. To overcome this limitation, we developed a twin-lead type electric wire fence comprising two parallel conductor wires spaced by a polyethylene ribbon containing two wire lines: one connected to the power source and the other connected to the earth. We then investigated whether the twin-lead type electric wire fence could effectively deter scansorial animals using two species: the Japanese marten and raccoon. A feeder was installed on the top of a pole at a height of 1.5 m above the ground. Three test plots were set up: (1) the twin-lead wire wound around the pole: an electric wire fence plot (“EF plot”), (2) a commercially available barbed iron plate plot (“BP plot”), and (3) no countermeasures against scansorial animals: control, unfenced plot (“CT plot”). The behavior of the scansorial animals attracted to each feeder was recorded using remote video cameras. Variable voltage appliances were attached to the electric fence and the deterring effect of scansorial animals was compared among test plots. The experiment comprised six experimental stages, which differed by the use of electric voltage in the twin-lead fence. We observed that the Japanese marten experienced an electrical shock from the fence at a voltage of approximately 2 kV and avoided the EF plot in further experimental stages with higher voltages. The raccoon began experiencing an electric shock at a voltage of approximately 0.5 kV and avoided EF plots in experimental stages at > 2.8 kV voltages. Conversely, the effects of the barbed iron plate could not be confirmed against both the species. These results show that the twin-lead type electric wire fence can effectively deter scansorial animals from climbing, when energized with voltages > 2.8 kV.

Limited evidence of compositional convergence of restored vegetation with reference states after 20 years of livestock exclusion

AbstractNative pastures and rangelands may become degraded by intensive pastoral use through clearing of woody components, loss of sensitive native species, invasion of opportunistic exotics and soil erosion, compaction and nutrient imbalance. Livestock exclusion is commonly a first management step to restore ecosystems degraded by overgrazing. However, few studies evaluate the outcomes of livestock exclusion on plant species composition and soil chemistry, while those that do are inconclusive due partly to highly variable responses and to inexplicit performance criteria. We adopted a conceptual model that characterised responses to fencing in terms of divergence from initial states and convergence with targeted states that represent restoration goals. We used the model to design an investigation of fencing effects on grassy woodlands within livestock production landscapes in subhumid southeastern Australia. First, we asked whether fencing initiated divergence from continually grazed vegetation and convergence with reference states with respect to plant species composition and soil properties. Secondly, we asked how responses depend on livestock exclusion time, degradation of the initial state, and soil conditions. Compositional trajectories based on a 17‐year chronosequence showed that livestock exclusion initiated some divergence from unfenced controls but convergence with reference states was limited, variable among sites and unrelated to time‐since‐livestock‐exclusion. Fencing initiated the development of novel communities comprising exotic taxa and a subset of native taxa from the reference species pool. Initial state offered limited explanation for the variability in compositional divergence from unfenced controls. Soil properties did not converge with reference states over time, and initial state did not explain the degree divergence of fenced from unfenced plots. The findings suggest site selection is crucial to successful restoration and reinforce the need to consider supplementary management actions, such as planting, scalping, direct seeding and weed control, in addition to livestock grazing exclusion, to restore woodlands towards desired states.

Direct and indirect effects of ungulates on forest birds’ nesting failure? An experimental test with artificial nests

Increasing deer and wild boar populations in North America and Western Europe are suspected of threatening low-nesting forest birds. Ungulates may directly affect these birds by predating eggs or chicks, or indirectly attract other mammalian or avian predators or reduce nesting site availability and habitat quality. To test some of these various mechanisms in two French forests, 528 artificial nests, 77 of which (14.6%) were monitored with camera traps, were set up in 44 plots which were either unfenced or fenced to respectively include or exclude ungulates. We used generalized linear mixed models to relate the nest failure rate to indices of plot frequentation by ungulates and other nest predators, to vegetation structure and to local bird community richness indices. Nest failure rate was significantly higher in the unfenced plots (39%) than in the fenced plots (32%) but this was related neither to red deer nor to wild boar frequentation of the plots. Furthermore, levels of frequentation for other mammalian and avian predators tended to be positively correlated to ungulate presence but not to nest failure rate. Nest failure rate depended on both nest height and shrub cover: nests on the ground (31% failure rate) were less predated or disturbed than nests in low shrubs (41% failure rate). Nests surrounded by low shrub cover experienced a slightly higher predation risk. We conclude that ungulates have a limited influence on nest failure for low-nesting forest birds; in particular, they seem to contribute very little to egg predation compared to other predators.

Short-term recovery of native vegetation and threatened species after restoration of a remnant forest in a small oceanic island of the South Pacific

ABSTRACTBackground: Invasive alien species have transformed many natural ecosystems, especially on islands where endemic species are critically endangered, and where habitat restoration is a challenge.Aims: We set up an experimental protocol to aid the restoration of a native remnant forest by excluding feral ungulates and suppressing an invasive tree.Methods: Sixteen plots of 144 m2 were delimited in a dry-mesic forest located on the small oceanic island of Rapa Iti (South Pacific) and half of them were fenced. The invasive tree Psidium cattleianum was manually cut in four fenced and four unfenced plots. We monitored understorey species diversity and abundance every 6 months for a period of 30 months in twenty-four 4-m2 quadrats randomly selected in each plot.Results: A significant increase of native species richness occurred in the fenced plots where the invasive tree was suppressed, and a decrease of alien species diversity in the fenced plots. The abundance of native and alien species was significantly reduced in the fenced plots, where recruitment of endemic threatened species was observed.Conclusion: Rapid vegetation change occurred in 30 months. The understorey plant community response to ungulate exclusion and invasive tree removal strongly differed between native and alien species, with the recovery of native vegetation.

Long-term effects of wild ungulates on the structure, composition and succession of temperate forests

Ungulates in temperate regions are increasing in range and abundance, leading to concerns that browsing and trampling reach levels that hamper tree recruitment and forest regeneration. However, studies that actually quantify the long-term effects of ungulates on forest succession are scarce. Here, we use a chronosequence of ungulate exclosures (fenced) and control (unfenced) plots to assess the long-term effects of ungulates on forest structure, diversity and litter depth in forests on poor sandy soils at the Veluwe, the Netherlands, which have moderate ungulate densities (x¯ = 13.6 ungulates km−2). We surveyed the vegetation in 27 paired fenced and unfenced plots that ranged from 1 to 33 years old, and measured seven variables to characterize forest structure (stem density, canopy cover and understory vegetation cover), composition (Shannon diversity, species richness and conifer proportion) and leaf litter depth. We found on average that fencing compared to unfencing reduced understory vegetation cover (fenced = 64.3 ± 20.2%, unfenced = 80.3 ± 19.4%), increased canopy cover (fenced = 47.4 ± 30.1%, unfenced = 29.3 ± 21.1%), tree species richness (fenced = 4.5 ± 1.3 spp., unfenced = 2.7 ± 1.2 spp.), tree Shannon diversity (fenced = 1.1 ± 0.3 index, unfenced = 0.7 ± 0.3 index) and litter layer depth (fenced = 4.4 ± 1.4 cm, unfenced = 2.4 ± 1.1 cm). While fenced plots developed woody vegetation with palatable broadleaved species such as Betula pendula, Betula pubescens, Prunus serotina, and Quercus robur, unfenced plots were not associated with any particular tree species. Our results show that current ungulate densities in this system have pronounced long-term effects on forest structure, composition and litter depth, implying that ungulates can slow down natural succession of temperate forest, from light demanding to shade tolerant species, by keeping the system in an arrested state consisting of light demanding species.

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.

The effects of introduced ungulates on native and alien plant species in an island ecosystem: Implications for change in a diverse mesic forest in the Hawaiian Islands

Abstract In island ecosystems, where endemic species have long been viewed as competitively inferior and more susceptible to herbivory relative to continental species, the impacts of invasive species may be especially pronounced. The sensitivity of island species to invasive species may lead to threshold effects causing irreversible changes in these ecosystems. Predictions that native, mostly endemic plant species are more adversely affected by ungulates than introduced alien plant species, and that competitive interactions between understory native and alien plant species are more severe when ungulates are removed were examined in a 15 year longitudinal study in a diverse mesic forest on Kaua‘i (Hawaiian Islands). Over this time period the density of both native and alien overstory canopy trees declined more in unfenced control plots than in plots fenced to exclude ungulates; alien and native trees in the canopy responded similarly to ungulate exclusion via fencing. A differential effect of ungulates on native vs. alien plant species was pronounced in the understory, where the density of small individuals of native canopy species declined sharply in unfenced relative to fenced plots. In contrast, the density of small individuals of alien canopy species was less affected over time by ungulate exclusion. Native herbaceous and understory shrub species also decreased in density over time in unfenced plots relative to fenced plots, while alien understory species increased greatly in some fenced plots relative to unfenced plots. Despite the increase in alien understory plants, no evidence for competition between these alien species and small individuals of native canopy species in the understory could be detected, as numbers of plants in these two understory categories covaried similarly in the presence or absence of ungulates. The contrast between large numbers of native species in the canopy and the severe disruption of the understory in this forest suggests that ungulate removal implemented now or in the near future might prevent loss of the canopy and lead to regeneration of these species. The near absence of recruitment of any endangered species not already present in protected plots indicates that active restoration will be essential to prevent loss of many of the characteristic species of these forests.

Vegetation cover density and disturbance affected arbuscular mycorrhiza fungi spore density and root colonization in a dry Afromontane forest, northern Ethiopia

Arbuscular mycorrhiza fungi (AMF) are vital in the regeneration of vegetation in disturbed ecosystems due to their numerous ecological advantages and therefore are good indicators of soil and ecosystem health at large. This study was aimed at determining how the seasonal, vegetation cover density, edaphic and anthropogenic factors affect AMF root colonization (RC) and spore density (SD) in Desa’a dry Afromontane forest. AMF RC and SD in the rhizosphere of five dominant woody species, Juniperus procera, Olea europaea, Maytenus arbutifolia, Carissa spinarum and Dodonaea angustifolia growing in Desa’a forest were studied during the rainy and the dry seasons in three permanent study vegetation cover density plots (dense, medium, and poor). Each plot (160 × 40 m2) has two management practices (fenced and unfenced plots) of area. A 100 g sample of rhizosphere soil from moisture-free composite soil was used to determine spore density. Spore density ranged from 50 to 4467 spores/100 g soil, and all species were colonized by AMF within a range of 4–95%. Glomus was the dominant genus in the rhizosphere of all species. Vegetation cover density strongly affected SD and RC. The SD was significantly higher (p 0.05) except for total nitrogen. Disturbance, vegetation cover density, season and total nitrogen are significant factors that control the dynamics and management interventions to maintain the forest health of dry Afromontane forests.

Are Native Tree Seedlings Facilitated by an Invasive Shrub Where White-Tailed Deer Are Abundant?

Positive interactions (facilitation) between plant species have been documented, particularly in stressful environments. We investigated whether an invasive shrub enhances growth or survival of native tree seedlings in forests where white-tailed deer (Odocoileus virginianus) are abundant. Seedlings of four tree species were planted under, or 0.5 m outside of, the canopy of Amur honeysuckle (Lonicera maackii) shrubs in plots unfenced or fenced to exclude deer in two stands in southwestern Ohio, USA, and monitored for 1 y. One species succumbed to transplant shock, but browse was extensive on the other three species in unfenced plots. Facilitation was evident on sugar maple (Acer saccharum), as seedlings under shrub cover had higher survival and final leaf count in unfenced plots, but not where deer were excluded. However, there was no significant facilitation by L. maackii of seedling growth or survival for white oak (Quercus alba) or shagbark hickory (Carya ovata), indicating this shrub's branches do not deter deer browse on highly preferred species or the effect is too modest to emerge in a one-year study. In at least some cases, the negative effects of L. maackii on tree seedlings that have been documented previously are offset by mitigation of the negative effects of deer herbivory. This suggests that where browsing impacts are problematic, deer abundance should be reduced before this, and perhaps other invasive shrubs, are managed.

Recovery of the Herb Layer in a Southern Appalachian Forest Following Chronic Herbivory by Deer (Odocoileus virginianus)

ABSTRACT The high abundance of ungulates in temperate zone forests is affecting biodiversity and ecosystem functions worldwide. A randomized, replicated experiment excluded white-tailed deer, Odocoileus virginianus, from six 10 × 10 m fenced plots for 10 years; six unfenced plots were maintained as controls. The effects of chronic herbivory were assayed by comparisons using the mean responses of ground-level vegetation in nine subplots within each of the 12 plots. Deer had a small effect on species richness but a strong effect on species prevalence, cover, and biomass, with repeatable differences in the responses of taxa to the treatments. Graminoids were favored in control plots, many other monocots and several dicots were favored in fenced plots, and parasitic plants and chemically defended herbs showed few detectable responses to fencing. The height of the vegetation represented by the shrub Vaccinium erythrocarpum and the herb Medeola virginiana was significantly taller in fenced than in control plot...

Effects of an invasive shrub, Lonicera maackii, and a generalist herbivore, white-tailed deer, on forest floor plant community composition

Both overabundant ungulates and invasive shrubs negatively impact forest floor plants, but few studies have investigated their interaction. We tested for direct effects and interactions of white-tailed deer, Odocoileus virginianus, and the invasive shrub, Lonicera maackii, on forest floor plant richness and composition in five sites in southwest Ohio. In each site a deer exclosure and an unfenced plot (each 20×20m) were established in 2010; in half of each plot all L. maackii was removed. Each spring and summer, 2011–2014, percent cover of each plant species in 50×20cm subplots was recorded.Herb layer species richness was greater where L. maackii was removed, and this effect tended to be stronger where deer were excluded. Species composition in the spring was not affected by treatments, whereas summer species composition (in one year) was affected by L. maackii treatment. Cover of graminoids, spring herbs, and vines were lower where L. maackii was intact, whereas cover of shrubs and tree seedlings were lower, and cover of bare ground higher, where deer had access.Our findings reveal that deer and L. maackii negatively impact different components of the forest herb layer. However, the combined effects on species richness tended to be antagonistic (less than additive), possibly due to deer browse reducing the cover of this invasive shrub. This suggests that the diversity of the herb layer will be enhanced more by both removal of invasive shrubs and reduction of the deer population than by either management action alone.

The impact of wintering geese on crop yields in Bulgarian Dobrudzha: implications for agri-environment schemes

Wintering wildfowl are widely perceived to damage agricultural crops, resulting in economic losses and conflict between farmers and conservationists. However, examinations of the nature and extent of the damage show very variable outcomes, ranging from no detectable impact to yield losses exceeding 50%; this makes it hard to infer losses in unstudied systems. In Bulgarian Dobrudzha, a large wintering goose population almost exclusively consumes winter wheat, but the impact on wheat yields is poorly understood. We used crop exclosures and dropping counts to manipulate and measure goose grazing intensity, and estimated crop yield and its components (grain mass, grains per stem, stem density). Crop yield was 13.2% lower in unfenced control plots than in exclosures in one winter during which goose grazing intensity was high but mainly occurred relatively early in the season, but there was no effect of goose exclusion in an earlier winter when goose grazing intensity was relatively low but occurred late in the season. A negative relationship between grazing intensity and crop yield was found, mainly driven by a lower stem density in heavily grazed plots. We use this relationship to infer total yield loss and calculate the economic impact for the study area to be in the order of €15,000–100,000. However, the generality of these results remains unclear because the impact of a given grazing intensity appears likely to vary according to factors such as timing of grazing, weather, stage of crop development and soil conditions. We discuss the results in light of a new agri-environment scheme that has been launched in the area with the aim of securing appropriate forage conditions for wintering geese whilst compensating farmers for losses and reducing conflict.

Deer browsing promotes Norway spruce at the expense of silver fir in the forest regeneration phase

Deer populations have dramatically increased over the last decades in Western Europe and their browsing has affected forest vegetation, especially plant community composition. High deer browsing pressure may threaten forest ecosystems and needs to be assessed over the long run. However, few studies to date have addressed the long-term impact of deer on forest regeneration.During one regeneration phase, we assessed the impact of deer (Cervus elaphus L. and Capreolus capreolus L.) browsing on mixed silver fir (Abies alba Mill.)/Norway spruce (Picea abies L. H. Karst.) stands in the Vosges Mountains in North-eastern France. For both tree species, we measured seedling and sapling density, height and diameter in 28 paired fenced – unfenced plots distributed over two sites that had been fenced 27years ago, for 10 and 23years respectively.We demonstrated that the presence of deer decreased the density, height and diameter of silver fir saplings, while it increased the height of Norway spruce saplings. We also noticed that the effect of fencing was very different depending on fencing duration, and that even 10years of fencing led to changes that were still visible 17years later.Our results confirm that deer browsing has a long-term impact on the regeneration of silver fir. Furthermore, they suggest that deer browsing may cause a species substitution, with Norway spruce gradually replacing silver fir. Such a trend would have an impact on the ecological and economical value of these forests. How browsing impacts the forest’s ability to adapt to global warming should also be considered, since browsing might impede the implementation of management policies designed to address this issue.

Evaluation of an unpalatable species ( Anthemis arvensis L.) as an alternative cover crop in olive groves under high grazing pressure by rabbits

Abstract Sustainability is a key attribute for the future of the olive grove. Cover crops can be considered as an effective tool to achieve sustainability of olive orchards to reduce soil erosion, improve soil fertility and increase biodiversity. However, wild herbivores may forage on cover crops when natural food resources are scarce. In this study we assessed the impact of European rabbit grazing on the implantation of herbaceous cover crops of two native plant species, one palatable (Bromus rubens L.) and the other unpalatable (Anthemis arvensis L.) in two olive orchards with very scarce vegetation cover in Andalusia, Southern Spain. Eight rabbit exclusion plots, close to eight other unfenced plots, were planted where the aboveground biomass, height and the ground covered by each species were measured. The results showed that the biomass, height and the ground cover by B. rubens were higher in the rabbit exclusion areas (ground cover: 36.5 ± 3.3%; height: 30.3 ± 3.9 cm, averaged over the entire measuring period; and biomass: 158 ± 36 g/m2, in April) than in unfenced areas (ground cover: 1.9 ± 0.2%; height: 5.6 ± 0.7 cm; biomass: ≅0), while A. arvensis showed no difference in biomass, height or ground cover between the two treatments (ground cover: 11.3 ± 6.3%; height: 12.2 ± 7.9 cm, averaged over the entire measuring period; and biomass: 49.5 ± 10 g/m2, in April). The results further showed that the damage by rabbits was caused from the early stages of development of B. rubens, which avoid its growth; notwithstanding the plant biomass consumption was minimal, the damage caused was critical. These findings suggest that unpalatable species such as A. arvensis could be a suitable tool for establishing herbaceous cover crops in olive groves at high rabbit densities, where other palatable species (e.g., B. rubens) are strongly consumed, thus contributing to soil conservation and improvement in olive groves with soils already degraded by erosion.