Rabbit Grazing Research Articles

Do Woody Plants Facilitate Herbaceous Plants in Dryland New Zealand?

Aims: Woody plants are postulated to facilitate understory herbaceous plants in arid and semi-arid environments worldwide, the so-called ‘nurse plant’ effect, but this mechanism. has been little studied in the drylands of New Zealand. Indigenous dryland plants postulated to have grown under woody shrubs in New Zealand before European settlement may benefit from their recovery, or even their replacement by exotic substitutes. The aim of this study was to investigate woody pant facilitation of understory herbaceous plants in dryland New Zealand.
 Study Design: In this study I investigated the effects of canopies of four shrub species – Kunzea serotina, Discaria toumatou, Rosa rubiginosa and Coprosma propinqua – on herbaceous plant species richness, in the presence and absence of rabbit grazing (for K. serotina).
 Place and Duration of Study: The study was conducted in the drylands of Central Otago, New Zealand, from August 2007 to January 2009.
 Results: Herbaceous plant species richness was lower under canopies of K. serotina, possibly because the dense canopy shaded the understorey plants. It was higher under C. propinqua, D. toumatou and R. rubiginosa canopies than in their adjacent open grasslands, but for all three species this effect was seen only in winter. Woody plant canopy protection of understorey herbaceous plants against winter frost may explain the effects. Grazing significantly decreased herbaceous plant species richness. Since D. toumatou, R. rubiginosa and C. propinqua showed facilitative effects on herbaceous plant species richness they are possible agents for the restoration of dryland vegetation.
 Conclusion: I conclude that control of grazing and the protection of these three woody species could be a good management strategy for the maintenance of a predominantly indigenous dryland mixed herbaceous and woody vegetation in Central Otago.

Lagomorph grazing alters suitability of hillside grassland for Orthoptera

The effects of lagomorph grazing on the Orthoptera of a small hill at Lound Lakes (Suffolk, UK) were studied during the summer of 2020. The transect counts of Orthoptera revealed low sward height due to high rabbit Oryctolagus cuniculus (Linnaeus, 1758) grazing on the high slopes which led to the general absence of tall grass species such as the Common Green Grasshopper Omocestus viridulus (Linnaeus, 1758) and Roesel's Bush-cricket Roeseliana roeselii (Hagenbach, 1822). Only nymphs and Field Grasshopper Chorthippus brunneus (Thunberg, 1815) adults were found in any number on the higher slopes, perhaps utilising the short swards and bare earth as basking habitat. The lower slopes and pastures supported tall-grass Orthoptera due to the absence of rabbit grazing and tussocky grassland.

The Self-Seeding of Anthemis arvensis L. for Cover Crop in Olive Groves under Intense Rabbit Grazing

Cover crops can be an effective means to protect soil and reduce risks of erosion in olive groves. However, for this protection to be significant, the vegetation must attain a significant amount of ground cover, which is estimated to be at least 30% during the rainy season. In olive groves on degraded soils, which occupy large surface areas in the olive-growing areas of the Mediterranean region, the establishment of cover crops may be an arduous challenge, particularly in areas with a high density of rabbits. In this study, we have selected two olive orchards with scarce natural vegetation located in Andalusia (southern Spain), in which rabbit populations intensively forage the cover crops, to test whether the self-seeding of an unpalatable species corn chamomile (Anthemis arvensis L.; A. arvensis for short) could achieve sufficient coverage for soil protection, in the year following that in which the broadcast-seeding was carried out for the implementation of cover crops. The hand broadcast-seeding of A. arvensis was carried out on sixteen elementary plots in the lanes of the two olive orchards in the autumn of 2015, and seed germination in the subsequent self-seeding took place in the autumn of 2016. The plant height and A. arvensis ground cover in these plots were measured throughout the two growth cycles, and aerial biomass was measured at maturity. The results showed that there were no significant differences in the maximum plant height between the two growth cycles (mean ± SD of 21.2 ± 1.6 cm), while the ground cover was significantly greater in the case of self-seeding, especially during the winter (37.2 ± 8.1 and 9.3 ± 6.7% for self-seeding and broadcast-seeding, respectively), and aerial biomass at maturity had more than doubled (99.7 and 43.9 g m−2, respectively). These data suggest that this unpalatable species could establish an effective herbaceous cover by means of self-seeding in olive groves on degraded soils that are being overgrazed owing to the high pressure of rabbits. Despite the poor establishment in the broadcast-seeding year, our findings indicate that A. arvensis might be an alternative cover crop that could help the sustainability of these threatened olive groves. Its high seed production (2000 to 4000 seeds per plant), and an early emergence just after the first autumn rains, should result in an increased ground cover by A. arvensis during the rainy season in the subsequent years of self-seeding. This, therefore, could contribute to soil conservation, in addition to providing other benefits of increased biodiversity and improvement for agricultural landscapes.

Grazing and productivity alter individual grass size dynamics in semi‐arid woodlands

The spatial arrangement of perennial vegetation is critical for ecosystem function in drylands. While much is known about how vegetation patches respond to grazing and abiotic conditions, the size dynamics of individual plants is mostly limited to theoretical studies. We measured the size distribution (mean, variance, skewness) and density of individual grasses, and grass species composition at 451 sites spanning a range of grazing intensities across three broad vegetation communities in semi‐arid eastern Australia. We assessed the relative role of grazing by livestock (cattle and sheep), native (kangaroos) and introduced (rabbits) free ranging herbivores, and several environmental measures (productivity, diversity, composition and groundstorey plant cover) on the size distribution and density of individual grasses. We found mean grass size and density were more sensitive to shifts in grazing intensity and environmental conditions than size variance or the frequency of the smallest individuals (skewness), and shifts were mostly driven by site productivity and cattle and kangaroo grazing. Sheep grazing only reduced mean grass size, and rabbit grazing had no consistent effects. Importantly, we found that site productivity and species composition altered the impacts of grazing on grass density and size distribution. For example, increasing cattle grazing led to larger grasses in low productivity sites. It also led to larger, denser, more variable‐sized grasses among grass species from sites with finer soil texture. Increasing kangaroo grazing led to smaller, denser individuals among grass species from sites with coarse soil texture. At high diversity sites kangaroo grazing led to denser, more homogenised grass sizes with a lower frequency of small individuals. Understanding the in situ response of individual plant sizes gives us insights into the processes driving shifts in perennial vegetation patchiness, improving our ability to predict how the spatial arrangement of ecosystems might change under global change scenarios.

Is livestock grazing a key factor for changing vegetation patterns in lime rich coastal dunes in the Netherlands?

In 1990, livestock grazing was introduced in Meijendel, a 1800 ha lime-rich coastal dune area, at a density of 0.06–0.07 LLU.ha-1.year−1 (1:12–18 ha) to counteract encroachment of tall grasses and shrubland on dune grassland and increase the bare sand area. Monitoring was based on four digital orthophotos (1975–1990–2001-2009) with a high spatial resolution (pixel size 25 × 25 cm). The changes were tested using Generalized Estimating Equations. Habitat changes occurred, but contradicting our hypothesis, there was no significant impact from the grazing on bare sand, grassland or shrubland within 11 and 19 years post livestock introduction. (1) After several decennia of decreasing bare sand, there was a significant increase between 2001 and 2009, irrespective of livestock presence. (2) The changes in grasslands and shrublands are independent of the livestock, but dependent on distance to the coast. (3) Bare sand and shrub cover determine the space left for the dune grasslands. It appears other factors than livestock grazing must have induced the changes. Changes in climate conditions and nitrogen load might have stimulated bare sand. An interaction with the end of Marram planting in 1990 cannot be concluded from available data. The disease-led reduction of rabbit grazing from the mid-1950s led to an expansion of the dominant shrub Hippophae rhamnoides. However, Hippophae shrubland typically regresses to grasslands on its collapse after 25–40 years. Tree species like Crataegus, Betula and Quercus will gradually dominate the landscape for far longer. Active removal of these indigenous species is necessary to prevent future loss of dune grasslands.

Limited evidence for the use of livestock for the conservation management of exotic plant cover

Livestock grazing has been used for conservation management in some situations to reduce exotic plant cover, but supporting empirical evidence is scant. This is particularly true for eastern Australian semiarid woodlands and forests. We surveyed 451 sites across three broad semiarid vegetation communities (cypress pine, black box, red gum) in eastern Australia to examine the effects of recent and longer-term (historic) grazing by livestock on exotic (and native) plant cover. Because our focus was the use of domestic livestock for conservation management, our sites were mostly located in conservation reserves, travelling stock routes and native production forests where domestic grazing is approved via permit. We also included recent grazing by kangaroos and rabbits, which occur widely with livestock across the study sites. Structural equation modelling revealed that recent sheep and cattle grazing was associated with increased exotic plant cover in two of the three communities (cypress pine, black box), and historic grazing was associated with lower exotic (and native) plant cover across all communities. Recent cattle grazing-induced reductions in exotic plant cover in the red gum community resulted from declines in the palatable exotic annual grass Ehrharta longiflora. Higher intensity grazing by rabbits, sheep and cattle in the cypress pine community increased exotic plant cover by suppressing the negative effect of native cover on exotic cover. Higher intensity rabbit grazing reinforced the negative effect of nitrogen on native plant cover, resulting in increases in exotic cover. Overall, we found strong evidence that domestic livestock grazing reduces native plant cover either directly or indirectly in all three communities, but limited evidence that it would be a useful conservation management strategy to reduce exotic plant cover in these communities.

Interactions between plant genome size, nutrients and herbivory by rabbits, molluscs and insects on a temperate grassland.

Angiosperm genome sizes (GS) vary ca 2400-fold. Recent research has shown that GS influences plant abundance, and plant competition. There are also tantalizing reports that herbivores may select plants as food dependent on their GS. To test the hypothesis that GS plays a role in shaping plant communities under herbivore pressure, we exploit a grassland experiment that has experimentally excluded herbivores and applied nutrient over 8 years. Using phylogenetically informed statistical models and path analyses, we show that under rabbit grazing, plant species with small GS generated the most biomass. By contrast, on mollusc and insect-grazed plots, it was the plant species with larger GS that increased in biomass. GS was also shown to influence plant community properties (e.g. competitive strategy, total biomass) although the impact varied between different herbivore guilds (i.e. rabbits versus invertebrates) and nutrient inputs. Overall, we demonstrate that GS plays a role in influencing plant-herbivore interactions, and suggest potential reasons for this response, which include the impact of GS on a plant's response to different herbivore guilds, and on a plant's nutrient quality. The inclusion of GS in ecological models has the potential to expand our understanding of plant productivity and community ecology under nutrient and herbivore stress.

Rabbits and livestock grazing alter the structure and composition of mid-storey plants in a wooded dryland

Woody plants are critical for supporting wildlife and maintaining ecosystem structure and function in drylands. Grazing has the potential to alter woody plant community structure by affecting the size and survival of shrubs and saplings. We assessed the role of recent and historic grazing by livestock, and recent grazing by kangaroos and rabbits, on woody plant structure and composition. We measured the density and species occurrence of saplings and shrubs within three plant communities across 0.5 M km2 of eastern Australia and used generalised linear mixed models to examine how grazing, soil texture and the basal area of mature trees altered the structure and composition of mid-storey woody plants. Due to co-evolution, we expected a stronger negative effect of grazing on shrub and sapling density and species occurrence by introduced herbivores than native herbivores and that shorter individuals would be more susceptible to recent grazing activity. We found that the density and occurrence of shrubs and saplings generally responded more negatively to introduced herbivores irrespective of their height. Sapling density was strongly reduced by recent rabbit and livestock grazing but increased in density at sites with greater kangaroo and historic livestock grazing. Recent livestock grazing also reduced the occurrence of sapling species. There were no strong effects of any grazing on shrub density, but rabbit grazing strongly reduced shrub species occurrence, with few strong responses among individual species. Our data provide strong evidence that recent grazing by livestock and rabbits can reduce sapling density and alter woody plant occurrence. This has the potential to induce long-term changes in ecosystem structure by limiting shrub and sapling establishment which could lead to aging and contracting woody plant populations.

Combined Grazing and Drought Stress Alter the Outcome of Nurse: Beneficiary Interactions in a Semi-arid Ecosystem

Positive interspecific plant–plant interactions in (semi-)arid ecosystems are crucial for supporting ecosystem diversity and stability, but how interactions respond to grazing combined with temporal variation in drought is poorly understood. In a semi-arid area in south-eastern Spain (Murcia region), we planted 1280 saplings of the palatable shrub Anthyllis cytisoides (beneficiary) under the canopy of the unpalatable shrub Artemisia herba-alba (nurse) or in open microsites between shrub patches. We applied four grazing treatments (no grazing, low goat grazing pressure, high goat grazing pressure and rabbit grazing) and two watering treatments. Sapling height and survival were followed for two consecutive years, during which one extreme drought event occurred. We analysed how grazing, watering and their combination affected nurse effects throughout the course of the study. Grazing and the drought event, but not watering, significantly altered the nurse effects. Under ungrazed conditions prior to the extreme drought event, nurse effects on sapling survival were neutral, whereas they were positive at rabbit-grazed plots. At low goat grazing, sapling growth was higher under nurse shrubs than in open microsites. However, after the extreme drought event, sapling survival was higher in open microsites at ungrazed plots, whereas at rabbit-grazed plots, nurse effects shifted from positive to neutral. Our findings highlight the importance of rabbit grazing in determining the direction of plant–plant interactions in arid ecosystems. Moreover, our findings support the idea that positive plant–plant interactions may wane under the combination of high grazing and drought stress.

Functional groups of soil fungi decline under grazing

Fungi play vital roles in organic matter decomposition, and mineralisation of phosphorus and nitrogen, are significant plant and animal pathogens, and major mutualistic symbionts with the roots of higher plants. Despite their importance, relatively little is known about the effects of livestock grazing on different functional groups of fungi. We used structural equation modelling to examine how grazing by domestic livestock and native herbivores, and aridity, plant cover and soil carbon influenced four functional groups of soil fungi (ectomycorrhizal fungi, arbuscular mycorrhizal fungi, dung saprobes, plant pathogens) from three microsites (tree, shrub, grass) at 54 woodland sites across 0.4 million km2 of dryland in eastern Australia. Structural equation modelling showed that aridity influenced fungi indirectly by affecting different herbivores and by changing plant cover, which had different effects on different fungal groups. Rabbit grazing had a direct negative effect on ectomycorrhizal and arbuscular mycorrhizal fungi, most likely by disrupting hyphal networks through soil disturbance. Increased cattle grazing was directly positively associated with fungal dung saprobe abundance, and indirectly, negatively associated with dung saprobes by suppressing the positive effects of soil carbon. Sheep had direct and indirect negative effects on the abundance of plant pathogens. Grazing was always an important predictor of the relative abundance of all fungal groups, either directly or indirectly. Thus, overgrazing is likely to have substantial effects on a range of important soil processes controlled by these microorganisms. Overall, our work indicates that increasing grazing, linked to on-going land use intensification to support a growing global population, will have major impacts on fungal functional groups.

Introduced and native herbivores have different effects on plant composition in low productivity ecosystems

AbstractQuestionsUnderstanding how livestock grazing alters plant composition in low productivity environments is critical to managing livestock sustainably alongside native and introduced wild herbivore populations. We asked four questions: (1) does recent livestock and rabbit grazing reduce some plant attributes more strongly than others; (2) does grazing by introduced herbivores (i.e. livestock and rabbits) affect plants more strongly than native herbivores (i.e. kangaroos); (3) do the effects of recent livestock grazing differ from the legacy effects of livestock grazing; and (4) does the probability of occurrence of exotic plants increase with increasing net primary productivity (NPP)?LocationSouth‐eastern Australia.MethodsWe measured the recent grazing activity of co‐occurring livestock (cattle, sheep, goats), rabbits and kangaroos by counting faecal pellets; historic grazing activity by measuring livestock tracks; and derived NPP from satellite imagery. We used a hierarchical GLMM to simultaneously model the presence or absence (i.e. probability of occurrence) of all plant species as a function of their attributes (growth form, lifespan and origin) to assess their average response to recent grazing, historic grazing and productivity in a broad‐scale regional study.ResultsRecent and historic livestock grazing, rabbit grazing and increasing NPP reduced the average probability of occurrence of plant species, although responses varied among plant attributes. Both recent and historic livestock grazing strongly reduced the average probability of occurrence of native species, and forbs and geophytes, but differed in their relative effects on other growth forms. Recent livestock grazing, rabbit grazing and NPP had similar effects, strongly reducing native species and forbs, geophytes, shrubs and sub‐shrubs. The overall effects of recent kangaroo grazing were relatively weak, with no clear trends for any given plant attribute.ConclusionOur results highlight the complex nature of grazing by introduced herbivores compared with native herbivores on different plant attributes. Land managers need to be aware that domestic European livestock, rabbits and other free‐ranging introduced livestock such as goats have detrimental impacts on native plant communities. Our results also show that kangaroo grazing has a relatively benign effect on plant occurrence.

Long-term belowground effects of grassland management: the key role of liming.

The functioning of human-managed grassland ecosystems strongly depends on how common management practices will affect grassland "belowground compartment" including soil biogeochemistry and plant roots. Key questions remain about how animal grazing, liming (e.g., the addition of CaCO3 to soils), and nutrient fertilization might affect, in the long-term, soil nutrient cycling and multiple root traits. Here we focus on a mesotrophic grassland located in Berkshire, UK, where contrasting levels of rabbit grazing, liming, and different inorganic fertilizers have been applied since 1991. We ask how (1) soil nitrogen (N) availability and cycling, (2) total root mass, (3) root mass decomposition, and (4) arbuscular mycorrhizal fungal (AMF) root colonization might respond to 22years of very different management. We found that liming strongly affected total root mass, root decomposition, root AMF colonization as well as soil N availability and cycling and that these effects were mainly driven by liming-induced increases in soil pH. Increases in soil pH were associated with significant (1) decreases in root mass, (2) increases in root mass decomposability and in the mineralization of N in decomposing root detritus, and (3) increases in AMF infection. Soil pH was also significantly related to greater N availability (i.e., soil NO3 levels) and to lower δ15 N natural abundance, which suggests more efficient N uptake by plants in limed soils as we found in our study. The application of multiple nutrients (N, P, K, Mg) also reduced total root mass, while N-only fertilization was associated with greater AMF infection. Surprisingly the long-term impact of grazing was generally weak and not significant on most plant and soil parameters. Despite soil pH affecting most belowground variables, changes in soil pH were not associated with any change in soil C and N stocks. Because liming can improve nutrient cycling (and benefits soil pH and grass yields) without negatively affecting soil C sequestration, we suggest that regular liming applications may provide management solutions for increasing the long-term sustainability of permanent grassland.

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.

Impact of European wild rabbits foraging in different habitat and vegetation types in an insular environment

Abstract European wild rabbits (Oryctolagus cuniculus) are prolific herbivores, affecting natural and agricultural ecosystems. We installed 10 experimental units, each consisting of two fenced plots, one excluding all herbivores and one allowing rabbit access only, to estimate the impact of rabbit grazing in three vegetation types occurring in two dominant habitat types on Lemnos Island, Greece. Plant productivity was significantly higher in barley crops than on both fallow land and Mediterranean scrublands. Rabbit grazing caused significant reduction of productivity in barley crops and Mediterranean scrublands, but not on fallow land. Selective feeding and seasonal food availability may have shaped patterns of rabbit impact.

Change in the distribution of the indigenous grass Poa litorosa on sub-Antarctic Macquarie Island following the eradication of rabbits.

The recent eradication of rabbits, rats and mice from Macquarie Island has resulted in unprecedented changes to the vegetation. One unforeseen outcome is the expansion in the known distribution of the indigenous grass, Poa litorosa (L.) which was known from only four restricted populations on Macquarie Island prior to 2014. An increase in abundance of P. litorosa was observed in 2014 and so we undertook surveys to document changes in the known distribution of the species and established fixed transects in the new and previously recorded populations to monitor future changes. Monitoring of an exclosure and control plot over a 24-year period gave insights into past effects of rabbit grazing on the species. Our surveys documented a dramatic increase in the known distribution of the species. Existing populations have expanded and new populations have been recorded. Monitoring of the exclosure and control plot revealed suppression of P. litorosa plants in control plots in comparison to fenced plots during peak rabbit numbers, and so we attribute the population expansion to the recent eradication of rabbits and subsequent release of grazing pressure. This research contributes to the increasing bank of knowledge of changes occurring on Macquarie Island post-eradication and highlights the importance of monitoring to detect unforeseen changes.

Barking up the wrong tree? Are livestock or rabbits the greater threat to rangeland biodiversity in southern Australia?

Increasing provision of permanent water points has put most Australian pastoral rangelands within grazing distance of sheep, cattle, kangaroos and large feral herbivores, and there is concern that grazing-sensitive native plants will be lost as a result. Proposals have been developed to conserve plant biodiversity by permanently excluding livestock from any areas that are remote from permanent water, or to buy back pastoral properties and remove existing water points to create large reserves. There is, however, little evidence that water-remote areas provide refuge for grazing-sensitive plants, nor consistent evidence of plant biodiversity loss along gradients of increasing livestock grazing pressure in proximity to water. One of the reasons why that evidence might be lacking is that most livestock studies have not considered the grazing impact of sympatric European rabbits, the most widespread and abundant wild herbivore in southern Australia. Numerous studies have shown that rabbit grazing has a major impact on rangeland vegetation and can prevent regeneration at densities which may be too low to be thought important. Plant biodiversity gradients are readily discernible along gradients of rabbit density in livestock-free reserves. Rabbits are therefore likely to be a significant confounding factor when assessing livestock impacts, or possibly the primary cause of observed patterns of plant diversity. If so, attempts to preserve plant biodiversity by removing livestock are destined to fail in rabbit-grazed areas. Public funds for biodiversity conservation in the pastoral zone might be better spent on co-investment with pastoralists for rabbit control on conservatively stocked properties, rather than on restricting pastoral use of land in livestock-free, rabbit-infested reserves.

Change in the distribution of the indigenous grass Poa litorosa on sub-Antarctic Macquarie Island following the eradication of rabbits

The recent eradication of rabbits, rats and mice from Macquarie Island has resulted in unprecedented changes to the vegetation. One unforeseen outcome is the expansion in the known distribution of the indigenous grass, Poa litorosa (L.) which was known from only four restricted populations on Macquarie Island prior to 2014. An increase in abundance of P. litorosa was observed in 2014 and so we undertook surveys to document changes in the known distribution of the species and established fixed transects in the new and previously-recorded populations to monitor future changes. Monitoring of an exclosure and control plot over a 24-year period gave insights into past effects of rabbit grazing on the species. Our surveys documented a dramatic increase in the known distribution of the species. Existing populations have expanded and new populations have been recorded. Monitoring of the exclosure and control plot revealed suppression of P. litorosa plants in control plots in comparison to fenced plots during peak rabbit numbers, and so we attribute the population expansion to the recent eradication of rabbits and subsequent release of grazing pressure. This research contributes to the increasing bank of knowledge of changes occurring on Macquarie Island post-eradication and highlights the importance of monitoring to detect unforeseen changes.

Short communication. The role of rabbit density and the diversity of weeds in the development of cover crops in olive groves

Cover crops are an effective means to reduce soil erosion and to provide food and shelter for wildlife. However, in areas of intensive farming, which are characterised by the scarcity of weed communities, wild herbivores may focus their grazing on cover crops, which could make their implementation difficult. In this work, we test whether rabbit grazing can prevent the growth of herbaceous cover crops in olive groves in Southern Spain in addition to assessing the role of rabbit abundance and diversity of weeds in the development of cover crops. This question has been addressed by sowing Bromus rubens between the rows of five olive groves in Cordoba province (Spain). We then monitored the surface covered by B. rubens, along with both diversity of weed communities and rabbit abundance. Two rabbit exclusion areas were also placed in each olive grove in order to assess the impact of rabbits on the development of cover crops. Our results showed that the surface occupied by B. rubens was considerably higher in the rabbit exclusion areas (mean 56.8 ± 5.65 %) than in those areas in which they could feed (mean 35.6 ± 4.32 %). The coverage occupied by cover crops was higher in areas with lower rabbit density, although this relationship was modulated by the weed diversity index, since in areas with the same rabbit abundance the coverage was higher in those with a richer weed community. These findings suggest that high rabbit abundances can prevent the development of herbaceous cover crops in olive groves, particularly in areas in which alternative food resources (measured as weed diversity) are scarce.

The impact of 36 years of grazing management on soil nitrogen (N) supply rate and Salix repens N status and internal cycling in dune slacks

To determine the impact of long-term rabbit and sheep grazing on Salix repens N status (green and abscised leaf N content and C:N ratio), internal N dynamics and soil N supply rate in dune slacks. Herbivore exclosures were erected in dune slacks at Ainsdale Sand Dunes NNR, creating three grazing treatments: rabbit grazing; rabbits excluded for 36 years; rabbit grazing followed by sheep and rabbit grazing for 18 years. Soil N supply rate was analysed using ion exchange membranes; leaf N dynamics of S. repens were measured over one summer. Soil N supply rate was higher in ungrazed plots. There was no difference in green leaf NMASS or C:N ratio between treatments, but N dynamics differed. Adding sheep to existing rabbit grazing reduced S. repens N resorption efficiency (REFF) from 67 to 37 %; excluding rabbits had no impact. Litter NMASS was lower and C:N ratio higher in ungrazed plots. Grazing can impact significantly on leaf N resorption, but this impact depends on the grazing regime.

Spatial and temporal variation in damage and dieback in a threatened subantarctic cushion species

A decline was observed in the subantarctic Macquarie Island endemic cushion, Azorella macquariensis, during the summer of 2008–2009, resulting in the listing of the species as critically endangered in 2010. Photographs of A. macquariensis in the period 2009–2013 were used to (1) identify types of damage, (2) determine the likely causes of three distinct types of damage, (3) establish whether dieback was spreading from affected to unaffected sites and (4) find out whether dieback was associated with the expansion of Agrostis magellanica. Grey damage occurred on the most wind-exposed parts of cushions and on the most wind-exposed sites. Speck damage occurred in the opposite situations and was consistent in its location, attributes and timing with rabbit grazing. Yellow dieback was sporadic in its occurrence. Its symptoms were consistent with those of a pathogen. Yellow damage expanded between spring 2009 and autumn 2010, with neither grey nor speck damage increasing. Yellow damage was associated with a marked decline in live cushion cover in plots between 2010 and 2013. The cushion was not eliminated from any plots, despite increased cover of A. magellanica in plots with dead cushions. Only one site not affected by yellow damage in 2010 had become affected by 2013. Given these results, and given that yellow damage has been observed in the past, 2008–2010 may have been an infrequent extreme outbreak of a pathogen and/or a response of a pathogen to ongoing climatic change.