Unpalatable Plant Species Research Articles

The dynamics of vegetation grazed by a food‐limited population of Soay sheep on St Kilda

Abstract The population of Soay sheep on the island of Hirta in the Outer Hebrides has been the subject of continuous study for more than 35 years. This paper focuses on the botanical aspects of the plant–herbivore interaction, showing how the vegetation affects and is affected by the sheep. Grazing impacts on biomass and spatial structure varied across plant communities, with Holcus/Agrostis grasslands affected most and Wet Heath least, consistent with the hypothesis that herbivore impacts are proportional to plant productivity. Within plant communities, the negative relationships between sheep numbers and plant abundance (sward height, gap/tussock cover and biomass) were significant in March but not significant in August, as expected if sheep numbers are limited by food supply in winter. In most species, flower stem density declined with increasing sheep numbers. There were no examples where unpalatable plants showed increased flowering (e.g. from competitor release under selective grazing). Plant production in temporary grazing exclosures (above‐ground net primary production) was greatest in Holcus/Agrostis grassland (12.6 t ha−1 dry matter year−1), lower in Nardus grassland (5.1 t ha−1 year−1) and least in Plantago sward (1.3 t ha−1 year−1) associated with differences in historical nutrient supply and microclimate. The net effect of grazing on plant species richness was positive: A few highly palatable species were excluded, but small‐scale coexistence of grazing‐tolerant species was enhanced by defoliation. The Soay sheep population fluctuated from 908 (in 1988) to 2,208 (in 2009), increasing by an average of 39 extra animals per year over the period 1985–2011. Between 2011 and 2020, the population fluctuated less widely and showed no trend. Population change (ln(N(t + 1)/N(t))) was inversely density dependent but positively correlated with plant production in Holcus/Agrostis grassland which increased during the study. This plant–herbivore interaction is highly resilient, and though some species (Festuca rubra and Ranunculus acris) declined in the Holcus/Agrostis grassland, there was no significant upward trend in the abundance of unpalatable plant species. Synthesis. Implications for future studies and analyses of plant–herbivore data. Concentrating on estimating primary productivity and herbivore offtake, rather than simply measuring change in plant biomass, is likely to provide greatly improved explanatory power for understanding herbivore population dynamics.

Population structures and spatial patterns of two unpalatable Arisaema species (Araceae) with and without clonal reproduction in a riparian forest intensively grazed by Sika deer

General decline of understory cover can result from increased abundance of and foraging pressure by deer. But population size and degree of aggregation can increase for unpalatable understory plants that escape foraging pressure. Clonal reproduction can enable unpalatable plant species to increase their population sizes while trending toward spatially aggregated distributions. However, the details of the relationship between clonal reproduction in unpalatable plants and their dynamics under intensive deer herbivory are not clear. We compared the population structures and spatial patterns of two coexisting unpalatable plant species, Arisaema ovale (with clonal reproduction) and A. peninsulae (without clonal reproduction) in a riparian forest intensively grazed by Sika deer, and examined the null hypothesis that the extent of spatial aggregation and local population size would not differ between the clonal and non-clonal Arisaema species. In a 0.36-ha plot, A. ovale had a larger population size (1087 individuals) with a higher abundance ratio of small plants (p < 0.01) than A. peninsulae (84 individuals). Analyses of spatial point processes showed that both populations were spatially aggregated (p < 0.05). The spatial aggregation of A. peninsulae, however, became weaker than that of A. ovale, when we excluded one dense patch originating from irregular seed dispersion. These results, excluding the aggregated distribution observed in A. peninsulae, suggested a substantial contribution of clonal reproduction to the expansion of the local A. ovale population following intensive grazing by Sika deer.

Carbon, nitrogen and phosphorus stocks differ among vegetation patch types in a degraded alpine steppe

Degradation of grassland creates diverse vegetation patch types with plant species with different palatabilities, potentially affecting ecosystem productivity and soil organic carbon (SOC) sequestration. This study investigated variations in SOC densities and carbon/nitrogen/phosphorus (C/N/P) ratios among vegetation patch types in a degraded alpine steppe on the Qinghai-Tibetan Plateau. We examined soil, shoot and root C, N and P densities, and C/N/P ratios in a growing season for five vegetation patch types dominated by palatable plant species Stipa purpurea, S. purpurea and Poa litwinowiana, and unpalatable plant species Leontopodium nanum, Artemisia nanschanica, and Oxytropis glacialis. Soil C and N as well as shoot and root densities varied among patch types, but not soil C/N. Patches dominated by unpalatable plant species had a lower SOC density, lower soil and plant N/P ratios, and greater plant nutrient densities than those dominated by palatable plant species. Vegetation patch type strongly influenced nutrient densities and ratios in soil-plant systems, and sampling only areas dominated by palatable plant species may overestimate the C sequestration rate at the ecosystem scale. Even though patch-level plant biomass and nutrient density may increase with increasing degradation, the decrease in palatability and SOC storage at the ecosystem scale would impair grassland sustainability as alpine grassland degradation proceeds. The palatability of plants should thus be considered for improving regional SOC stock estimate in future research.

Intraspecific variation in litter palatability to macroarthropods in response to grazing and soil fertility

Abstract Clarifying the functional consequences of intraspecific trait variability in response to interacting trophic levels would provide a significant improvement in our understanding of above‐ground–below‐ground linkages. In particular, the effects of grazing on plant traits may translate into altered litter quality, with potentially important consequences for litter‐feeding decomposers. Plant and litter variability in response to grazing is expected to depend on soil fertility levels, with tolerance and defensive strategies more commonly expressed on fertile and poorer soils, respectively. However, how grazing and fertility interactively alter litter quality and palatability to detritivores has not been explored yet. We conducted a cafeteria experiment with three common millipede (Diplopoda) species feeding on leaf litter from two plant species, the grass Bromopsis erecta and the forb Potentilla verna. Each millipede was offered a binary choice between litter types produced by the same plant species, but sampled in plots with distinct herbivory and fertilization status: litter originating from grazed areas or from 1‐year sheep exclosures, both in native areas and in adjacent paddocks that received chemical N and P fertilization, as well as litter from a 25‐year sheep exclosures in the native area. We found that fertilization and herbivore exclusion interactively affected Bromopsis litter quality and palatability, whereas Potentilla was much less affected. Bromopsis litter palatability was not affected by grazing when litter was collected in native plots, except for the long‐term exclosure which led to low palatability. In contrast, and in line with our expectations, herbivory was associated with much higher palatability in fertilized plots. The changes in palatability were associated with important alterations of litter quality. Overall, our study demonstrates that intraspecific variation in litter can have profound consequences for soil functioning. It emphasizes the role of grazing as a key, but plant species‐specific factor controlling litter intraspecific variability, and its complex interaction with soil fertility level. Moreover, our results advocate for a better understanding of the response of the different organisms involved in the decomposition process, in particular litter‐feeding macro‐detritivores. We encourage future studies aiming at disentangling the various and complex relationships between above‐ground processes such as herbivory and soil functioning.

Characterization of Piospheres in Northern Liddar Valley of Kashmir Himalaya

Grazing in pastures results in the formation of degraded patches called piospheres. It alters soil composition and vegetation in the vicinity of the watering points, shade, mineral licks and sheepfolds. A comparative approach was adopted in Liddar valley of Himalaya to study soil and vegetation composition of piosphere patches using various techniques. Pasture soils were investigated for nitrogen (N), organic matter (OM), pH, electrical conductivity (EC), total phosphorus (P2O5), total potassium (K2O), total calcium (CaO), total magnesium (MgO) and total sulfur (S) using energy dispersive X-ray florescence and physical properties like soil texture and bulk density were also studied using respective techniques. Importance value index and plant species compositions were studied using transect method along the weakening effect radiating outward from center of piosphere. The change in their spatial extent was also studied using remote sensing technique. The results indicate that there is an enrichment of nutrients in piospheres such as N (0.02%), P (0.30%), K (0.04%), S (0.04%), and reduction of others like Ca (0.30%) and Mg (0.38%). Soil fractions like clay decreased by (17.62%) coupled with increase of sand and silt portion by 9.83% and 7.78% respectively, which eventually resulted in increase of bulk density by 0.08%. Furthermore, number of species have decreased to half (31) in the piospheres as compared to non piospheres (64). Paired samples t test was performed to determine the differences existed between two grazing intensities. The enrichment of some nutrients especially P results in terrestrial eutrophication which becomes suitable for the encroachment of weedy and unpalatable plant species. Remote sensing data also indicates that the total area under these degraded patches increased from 2.07% in 1992 to 2.69% in 2010. The management perspectives degradation of pasturelands by piosphere formation needs an immediate attention which otherwise shall reduce the grazing area and economic value of grazing lands in Himalayas.

Effect of Senna obtusifolia (L.) invasion on herbaceous vegetation and soil properties of rangelands in the western Tigray, northern Ethiopia

IntroductionInvasion of exotic plant species is a well-known threat to native ecosystems since it directly affects native plant communities by altering their composition and diversity. Moreover, exotic plant species displace native species through competition, changes in ecosystem processes, or allelopathic effects. Senna obtusifolia (L.) invasion has affected the growth and productivity of herbaceous vegetation in semi-arid regions of northern Ethiopia. Here, we investigated the species composition, species diversity, aboveground biomass, and basal cover of herbaceous vegetation, as well as soil properties of rangelands along three S. obtusifolia invasion levels.MethodsHerbaceous vegetation and soil properties were studied at two locations, Kafta Humera and Tsegede districts, in the western Tigray region of northern Ethiopia under three levels of S. obtusifolia invasion, i.e., non-invaded, lightly invaded, and heavily invaded. Herbaceous plant species composition and their abundance were assessed using a 1-m2 quadrat during the flowering stage of most herbaceous species from mid-August to September 2015. Native species were classified into different functional groups and palatability classes, which can be useful in understanding mechanisms underlying the differential responses of native plants to invasion. The percentage of basal cover for S. obtusifolia and native species and that of bare ground were estimated in each quadrat. Similar to sampling of the herbaceous species, soil samples at a depth of 0–20 cm were taken for analyzing soil physical and chemical properties.ResultsHighly palatable grasses and legumes based on the frequency of occurrence were 1.9 and 3.8 times higher in non-invaded sites than in lightly and heavily invaded sites, respectively. Furthermore, unpalatable plant species were 4.0 times higher in the heavily invaded sites than in the lightly invaded sites. Aboveground biomass, basal cover, and species diversity of the herbaceous vegetation were significantly (P < 0.01) lower in the heavily invaded sites compared to the non-invaded sites. However, most soil properties were not affected by S. obtusifolia invasion compared with non-invaded sites in our study.ConclusionsOur findings contribute towards better understanding of how S. obtusifolia invasion affects the community structure and composition of native herbaceous vegetation in semi-arid rangelands in northern Ethiopia. Further long-term studies are required to understand the mechanisms of how S. obtusifolia invasion influences soil properties for better control and eradication of its invasion in the semi-arid rangelands of northern Ethiopia.

Vegetation gradients around cattleposts in the eastern mountains of Lesotho

The grasslands of the mountains in eastern Lesotho support large numbers of sheep, angora goats and other livestock during the summer, during which they are corralled nightly by herders at cattleposts. Few studies, however, have quantified the impact of grazing on the composition and structure of the mountain grasslands. Gradients of grazing and trampling intensity related to distance from 23 cattleposts in the subalpine and alpine belts (2 650–3 175 m above sea level) were examined to describe the long-term effects of livestock on unpalatable dwarf shrubs, bare area and plant species composition. The potential for shrub invasion and bare areas (low herbaceous cover) to develop was highest near cattleposts. Species composition also changed significantly along the grazing gradient, accompanied by a shift in dominants from grazing-sensitive to grazing-resistant grasses and shrubs. Species either decreased or increased monotonically along the grazing gradient or had an intermediate, unimodal response. The relative positions of species’ centroids along the grazing gradient were used to quantify their grazing sensitivity on a scale from 10 (most sensitive) to 0 (most resistant), which confirmed and contradicted previous classifications of their grazing responses. Basic ecological research on this important mountain grazing and catchment system is recommended.

Potential of Tannin Ferrous Plants to Improve Efficiency of Sheep Production in Dry Areas

ABSTRACTKeywords: Acacia saligna – Cassava – Economic efficiency- Growing SheepINTRODUCTIONFeed resources deficiency considers one of the basic constraints to improve animal production in arid and semi-arid regions of Egypt. Improving nutritional status of livestock graze in desert (sheep, camels and goats), particularly during the prolonged dry seasons, could increase the average annual animal production by approximately 27%. Attention directed towards the necessity of utilizing the marginal resources, i.e. saline soils and underground water for producing unconventional animal feeds. The native natural rangelands constitute the principal feed resources in the Egyptian deserts. They are widely distributed throughout several regions of Egypt due to presence of numerous salines along the Mediterranean and Red Seas shores and inlands). Halophytes represent a major part of the natural range, particularly perennials and shrubby ones. The less and unpalatable plant species represent approximately 70% of the total coverage. Several attempts made towards utilization of such low value or unpalatable halophytic plants through proper processing methods to improve their palatability and nutritional utilization. Under semi-arid area condition, small ruminant fed on trees and shrubs such as Cassava and Acacia to solve the attendant problems of low productivity (El ShaerThis research was performed to study the effect of feeding ammoniated wheat straw and its mixture with Cassava or/and Acacia Saligna on methane emission and growth performance of Barki lambs under semi-arid condition. The study conducted at Animal Production Research Station, Borg El Arab, belonging to Animal Production Research Institute, Agricultural Research Center, Egypt. A total number of twenty five Barki lambs were randomly allocated into six groups. These animals often depend on low quality crop residues and limited feed supplement. Egyptian desert consider a source of tannin-ferrous plants (TFP) along the year. These plants had lot of nutritive problems need to solve before depending on them as a fodder. In vitro experiments conducted to evaluate the effect of several mixtures of TFP with urea treated wheat straw (TWS) on dry matter degradation, ammonia-N and methane production. Six treatments were examined(G1) CFM+ Acacia Saligna (A): TW Sat (50:50), (G2) CFM+ Prosopis Juliflora (P): TWS at (50:50), (G3) CFM+ Cassava (C): TWS at (50:50), (G4) CFM+ A: P: TWS at (25: 25: 50), (G5) CFM+ A: C: TWS at (25: 25: 50) and (G6) CFM+ P: C: TWS at (25: 25: 50), respectively. Samples of each forage type collected after 0, 3, 6, 12 and 24 h of incubation for determination of cumulative gas production. In addition, thirty growing male Barki lambs, aged average 3 months were used to study the effect of the tested rations on growth performance. The results showed that the condensed tannin (CT) content ranged from 20 (A: C: TWS –G5) to 30 g/kg DM (Acacia saligna). Methane production per unit of fermented DM was inversely related to protein solubility. G1showed a lower (P<0.01) ruminal NH3-N concentration which associated with the decrease (P<0.01) in rumen protein degradability. After 24 h of in vitro incubation, CH4 production was17, 18, 17, 15, 13 and 14 ml, for all groups, respectively. Daily body gains were significantly affected by tested rations. The highest values recorded with G 5. Consequently, consumption of combination of TFP containing various classes of secondary components with resource of NPN leads to reduce CH4 emission from ruminants and improve lamb growth performance.

Alterations in photosynthetic pigments, protein, and carbohydrate metabolism in a wild plant Coronopus didymus L. (Brassicaceae) under lead stress

Coronopus didymus has been emerged as a promising wild, unpalatable plant species to alleviate lead (Pb) from the contaminated soils. This work investigated the hypothesis regarding various metabolic adaptations of C. didymus under lead (Pb) stress. In pot experiments, we assessed the effect of Pb at varied concentrations (500–2900 mg kg−1) on growth, photosynthetic pigments, alteration of macromolecular (protein and carbohydrate) content, and activities of enzymes like protease, α-and β-amylase, peroxidase (POX), and polyphenol oxidase (PPO) in C. didymus for 6 weeks. Results revealed that Pb exposure enhanced the growth, protein, and carbohydrate level, but decreased the leaf pigment concentration and activities of hydrolytic enzymes. The activities of POX and PPO in roots increased progressively by ~337 and 675%, respectively, over the control, at 2900 mg kg−1 Pb treatment. Likewise, contemporaneous findings were noticed in shoots of C. didymus, strongly indicating its inherent potential to cope Pb-induced stress. Furthermore, the altered plant biochemical status and upregulated metabolic activities of POX and PPO indulged in polyphenol peroxidation elucidate their role in allocating protection and conferring resistance against Pb instigated stress. The current work suggests that stress induced by Pb in C. didymus stimulated the POX and PPO activities which impart a decisive role in detoxification of peaked Pb levels, perhaps, by forming physical barrier or lignifications.

Vegetation shift from deciduous to evergreen dwarf shrubs in response to selective herbivory offsets carbon losses: evidence from 19years of warming and simulated herbivory in the subarctic tundra.

Selective herbivory of palatable plant species provides a competitive advantage for unpalatable plant species, which often have slow growth rates and produce slowly decomposable litter. We hypothesized that through a shift in the vegetation community from palatable, deciduous dwarf shrubs to unpalatable, evergreen dwarf shrubs, selective herbivory may counteract the increased shrub abundance that is otherwise found in tundra ecosystems, in turn interacting with the responses of ecosystem carbon (C) stocks and CO2 balance to climatic warming. We tested this hypothesis in a 19-year field experiment with factorial treatments of warming and simulated herbivory on the dominant deciduous dwarf shrub Vacciniummyrtillus. Warming was associated with a significantly increased vegetation abundance, with the strongest effect on deciduous dwarf shrubs, resulting in greater rates of both gross ecosystem production (GEP) and ecosystem respiration (ER) as well as increased C stocks. Simulated herbivory increased the abundance of evergreen dwarf shrubs, most importantly Empetrum nigrum ssp. hermaphroditum, which led to a recent shift in the dominant vegetation from deciduous to evergreen dwarf shrubs. Simulated herbivory caused no effect on GEP and ER or the total ecosystem C stocks, indicating that the vegetation shift counteracted the herbivore-induced C loss from the system. A larger proportion of the total ecosystem C stock was found aboveground, rather than belowground, in plots treated with simulated herbivory. We conclude that by providing a competitive advantage to unpalatable plant species with slow growth rates and long life spans, selective herbivory may promote aboveground C stocks in a warming tundra ecosystem and, through this mechanism, counteract C losses that result from plant biomass consumption.

Unexpected consequences of reintroductions: competition between reintroduced red deer and Apennine chamois

Reintroductions are commonly used to restore the local biological diversity and/or save threatened taxa. In human-altered landscapes, we may expect that reintroduced species affect taxa already present. In Abruzzo, Lazio and Molise National Park (central Apennines, Italy), a 30% decline in the abundance of ‘vulnerable’ Apennine chamois (2005: c. 650 individuals, 2010: c. 450 individuals) has been recorded, whereas red deer (reintroduced in 1972–1987: 81 individuals) have greatly increased (2010: > 2500 individuals). We investigated space and diet overlaps between red deer and Apennine chamois, and their effects on foraging behaviour of the latter. We also compared the composition of grasslands with that recorded when the former were absent. In 2010–2011, we found out: (1) a great space (> 75%) and diet (> 90%) overlap between deer and chamois; (2) a significant increase of unpalatable plant species and a decreasing trend of the nutritious, most grazed species by chamois, in respect to when deer were absent; (3) irrespective from vegetation type, a significantly reduced bite rate of adult female chamois in patches used also by deer, compared with areas without deer. Our results suggest a negative effect of red deer on the availability of nutritious plant species in summer–autumn, possibly because of grazing and physical damage on the grassland caused by trampling. Environmental conditions and access to high-quality forage in the warm season influence the winter survival of offspring of mountain ungulates. Our results indicate that interspecific overlap in resource use with an increasing, reintroduced population can threaten rare taxa. Reintroductions of potentially competing species should be avoided in areas where populations of threatened taxa exist.

Long-term stability of grazing lawns in a small protected area, the Mountain Zebra National Park

We examined a heavily grazed plant community dominated by creeping grass species with the aim of, (1) determining its response to the exclusion of grazing and (2) its long-term persistence. This plant community was particularly favoured by wild ungulate species that prefer short grasses – blesbok (Damaliscus dorcas phillipsi), springbok (Antidorcas marsupialis) and black wildebeest (Connochaetes gnou). Exclusion of grazing by large herbivores by means of fencing resulted in the virtual disappearance of the creeping grasses and their replacement by tall tufted species. On plots that remained unfenced, the plant species composition was found to be little changed after an interval of more than 20 years. The number large stock unit equivalents (LSU) per ha carried by the plant community was used as a proxy for grazing intensity. Monitored for approximately 2 years at the start of the study, LSU per ha was found to greatly exceed levels recommended for commercial livestock production. This plant community conforms to a recently published definition of a grazing lawn, in that intense grazing promotes palatable, grazing-tolerant grass species.Conservation implications: The positive association between grazers and grazing-tolerant grass species evidently persisted for more than 20 years and there was no evidence of an increase in abundance of unpalatable plant species. Despite the small size of the park, which limited the extent of large herbivore movements, localised heavy grazing did not lead to range degradation.

Refuge effect of an unpalatable forb on community structure and grass morphology in a temperate grassland

The role of unpalatable plant species as biological antiherbivore refuges for palatable species is well-documented at community level particularly in harsh environments. In productive sub-humid temperate grassland subjected to domestic grazing, we examined the protective effect of Eryngium horridum on plant community structure and floristic composition, and evaluated whether these changes impacted on a number of morphological traits of grasses, related to grazing resistance. We also investigated, for a palatable grass species (Stipa neesiana) the existence of morphological differences between protected and unprotected plants and if this eventual variation was either plastic or genetic. The study consisted of a field survey where we compared paired patches, with and without E. horridum, and a greenhouse experiment where we evaluated individuals of S. neesiana coming from both patch types over a 11 months period. Patches dominated by E. horridum had lower richness and cover of forbs than patches without the forb, and similar richness but greater cover of cool-season tussock palatable grasses, which suggests a protective role on the latter. Grasses in these patches also had longer blades and sheaths and lower specific leaf area. The morphological differences of S. neesiana individuals collected from both patch types disappeared after 11 months growth in a common environment which revealed significant phenotypic plasticity in this species. These results suggest the existence of plant-to-plant facilitation in a productive ecosystem not only at community level, through changes in species richness and the promotion of palatable grasses, but also at population level, through plastic changes in aboveground morphological traits. Both facilitation and plasticity, would contribute to the persistence of threatened palatable grasses in the heavy grazed productive ecosystems.

Influências de Atta spp. (Hymenoptera: Formicidae) na recuperação da vegetação pós-fogo em floresta de transição amazônica

Este estudo investigou o papel das saúvas na recuperação da vegetação pós-fogo. Foi hipotetizado que a perturbação do fogo aumenta a abundância de ninhos de saúva (1) e as atividades de remoção de sementes (2) e desfolha (3), especialmente no ambiente de borda. Os ninhos de saúva foram inventariados e mapeados e após 17 meses, checados para o registro de sua atividade e de novas colônias emergindo na área. Realizou-se experimentos comparativos de remoção de sementes e desfolha de plântulas em duas parcelas de 50 ha, uma submetida a fogo anual (tratamento) e outra sem fogo (controle). A abundância de ninhos de saúva foi maior na parcela tratamento que na parcela controle, especialmente na borda da floresta. As espécies encontradas foram: Atta cephalotes, A. laevigata e A. sexdens , sendo esta última a espécie mais abundante e que mostrou aumento em número de colônias ativas após 17 meses. O aumento na abundância de ninhos na parcela tratamento foi acompanhado por um aumento na atividade dessas formigas. Enquanto mais de duas folhas foram arrancadas por plântula nessa parcela, menos de uma foi registrada na parcela controle. Também a abundância média de galhos desfolhados e de sementes removidas por saúvas foi maior na parcela tratamento que na parcela controle. As saúvas tanto podem diminuir ou retardar o processo de regeneração florestal pós-fogo, quanto acelerá-lo, devido à elevada predação seletiva que favorece as espécies menos palatáveis. Desta forma, suas atividades podem modificador apenas a composição da vegetação recuperando-se do fogo.

Refuge effects of Juncus effusus in grazed, subtropical wetland plant communities

Unpalatable plant species often act as biotic refuges by protecting neighboring plants from herbivores. This positive interaction can increase functional diversity in grazed ecosystems by protecting species sensitive to grazing. While many studies investigate pair-wise interactions between benefactors and beneficiaries, few show that these interactions result in community composition effects. We studied the effect of an unpalatable plant, Juncus effusus, on wetland plant communities in grazed and ungrazed plots. We tested the following predictions: (1) Juncus would increase plant functional diversity in grazed wetlands; (2) Juncus would have significant effects on community composition; and (3) the effects of Juncus on other species would change across the grazing gradient. We found that Juncus preserved functional diversity in grazed wetland communities by protecting species that decrease with grazing pressure. In multivariate analyses, grazing was the strongest driver of species composition but we found significant effects of Juncus on both vegetation change and species composition in grazed plots. Interactions with Juncus were facilitative in grazed plots and competitive in ungrazed plots, but did not vary along the grazing gradient (0.15–1.7 cows/ha). These results indicate that Juncus has significant community composition effects in grazed wetland plant communities. Understanding the effects of plant interactions such as these at the community level is essential to applying plant interactions to restoration or management.

Nonconsumptive effects of a generalist ungulate herbivore drive decline of unpalatable forest herbs

High herbivore pressure is expected to benefit unpalatable species that co-occur with palatable browsed species. However, for five unpalatable understory species we found no evidence of benefit from deer browse. Detailed studies of one species in natural populations, Arisaema triphyllum, revealed surprising changes in its population structure and demography: deer browse level on a palatable species significantly correlates with reduced plant size and seed rain and male-biased sex ratios of co-occurring Arisaema populations. Analyses of individual size in five unpalatable forest plant species in long-term experimental paired deer exclosure/deer access plots corroborate the natural site results; all five species were smaller in deer access plots. Analyses of abiotic variables in natural and experimental sites suggest one potential mechanism for indirect effects of deer. Deer-mediated soil quality declines included increased soil penetration resistance and decreased leaf litter depth, which are known to hinder plant growth. Our results are likely applicable to other unpalatable forest species and have clear consequences for understory biodiversity. Unpalatable plant species in forests experiencing high deer numbers may be in decline along with their palatable neighbors. Our study implicates deer overabundance in the cascade of forest species decline and the urgency of this conservation issue in North America.

Vegetation Responses to Prescribed Burning of Grazed Shortgrass Steppe

Over the past century, fire has been widely suppressed in the western Great Plains, in part because of the potential negative effects on forage production for livestock. More recently, interest in the use of prescribed fire in shortgrass steppe has increased because of the potential applications for wildlife management, control of unpalatable plant species, and restoration of historic disturbance regimes. We studied the effects of prescribed burns conducted during late winter on herbaceous production, forage nitrogen content, and plant species composition of shortgrass steppe on the Pawnee National Grassland in northeastern Colorado. Late-winter burns conducted in moderately grazed sites under a wide range of precipitation conditions during 1997–2001 did not negatively affect herbaceous production in either the first or the second postburn growing season. Burning followed by a severe drought in 2002 reduced production by 19% in the second postburn growing season of 2003. Burns temporarily suppressed the abundance of broom snakeweed (Gutierrezia sarothrae) and prickly pear cactus (Opuntia polyacantha) and enhanced forage nitrogen content during May and June of the first postburn growing season. These findings suggest that, except following severe drought, prescribed burns conducted during late winter in grazed shortgrass steppe for objectives unrelated to livestock production can also have neutral or positive consequences for livestock.

Sheep foraging behavior in response to interactions among alkaloids, tannins and saponins

AbstractBACKGROUND: A mixture of plant species adds biochemical diversity to pastures that may enhance productivity while decreasing reliance on herbicides and insecticides. All plants contain secondary metabolites (PSMs) that interact in plant communities in a variety of ways. Our objective was to determine if PSM diversity enhanced food intake when sheep were allowed to select from foods that varied in concentrations of tannins, saponins, and alkaloids. We hypothesized that intake of foods containing alkaloids would increase when sheep were offered supplemental foods with tannins and saponins. The alkaloid gramine is proteinaceous in nature, tannins bind to proteins in the gut, which enhances excretion of proteins, so we hypothesized tannins would bind to gramine and enhance its excretion from the body. The alkaloid ergotamine is steroidal, saponins have a high affinity for binding to lipid and steroidal compounds in the gut and then being excreted, so we hypothesized saponins would bind to ergotamine and enhance its excretion from the body.RESULTS: We found that sheep fed either gramine or ergotamine in combination with tannin‐ or saponin‐containing foods had higher intakes of food than sheep offered only foods with gramine or ergotamine.CONCLUSION: These findings are consistent with the hypothesis that animals can neutralize the negative effects of alkaloids by ingesting tannins and saponins. Our results show that PSMs can complement one another to increase a herbivore's intake of unpalatable plant species, with the potential to maintain healthy animals and bio‐diverse landscapes. Copyright © 2008 Society of Chemical Industry

Contrasting effects of rabbit exclusion on nutrient availability and primary production in grasslands at different time scales

Herbivores influence nutrient cycling and primary production in terrestrial plant communities. However, both empirical and theoretical studies have indicated that the mechanisms by which herbivores influence nutrient availability, and thus their net effects on primary production, might differ between time scales. For a grassland in southeast England, we show that the effects of rabbits on primary production change over time in a set of grazed plots paired with exclosures ranging from 0 to 14 years in age. Herbivore exclusion decreased net aboveground primary production (APP) in the short term, but increased APP in the long term. APP was closely correlated with N mineralization rates in both grazed and ungrazed treatments, and accumulation of litter within the grazing exclosures led to higher N mineralization rates in exclosures in the long run. Rabbit grazing did not influence litter quality. The low contrast in palatability between species and the presence of grazing-tolerant plants might prevent rabbits from favoring unpalatable plant species that decompose slowly, in contrast to results from other ecosystems. Our results indicate that it is essential to understand the effects on N cycling in order to predict the effect of rabbit grazing on APP. Rabbits might decrease N mineralization and APP in the long term by increasing losses of N from grasslands.

Effects of Key deer herbivory on forest communities in the lower Florida Keys

Ungulate herbivory can have strong impacts on plant communities, but these impacts are rarely considered in recovery plans of endangered species. This study examined the effects of the endangered Key deer ( Odocoileus virginianus clavium) on its environment in the lower Florida Keys. The Key deer population has increased to over 700 deer from approximately 50 deer in the 1950s; however, approximately 75% of the population resides on only a few islands (Big Pine, No Name, Big Munson) where Key deer herbivory on forest communities may be substantial. Effects of deer herbivory on plant densities were estimated on these islands using vegetation quadrats in hardwood hammock, buttonwood transition, and mangrove wetlands and compared to nine other islands with intermediate or low deer densities. On islands with high deer density, densities of preferred woody plant species <1.2 m tall (within Key deer reach) were significantly lower than islands with lower deer densities, while densities of some nonpreferred species were significantly higher. Deer exclosures established in hardwood hammock on a high-density deer island revealed a mean increase in abundance/height of preferred woody species inside exclosures, while nonpreferred species significantly increased in open plots. We conclude that on high deer density islands, highly preferred plant species might eventually fail to regenerate and unpalatable plant species may become dominant. Careful criteria need to be developed to maintain Key deer numbers above an endangered species status yet below levels that are destructive to local forest species.