Long-term effects of prescribed early fire, grazing and selective tree cutting on seedling populations in the Sudanian savanna of Burkina Faso

Annual early fire, selective tree cutting and exclusion of grazing are currently used as management tools in the Sudanian savanna of Burkina Faso although their long-term effects on seedling recruitment are poorly documented. A factorial experiment involving fire, grazing and cutting, each with two levels, was established in 1992 to study the effects of these management regimes and their interactions on the regeneration of woody species, and examine whether their effects varied temporally. Species richness, density and the morphology of seedlings were assessed in 1997 and 2002, and their relative changes were determined. The change in species richness of multi-stemmed individuals was significantly higher ( P  = 0.018) on plots that received fire × cutting treatment than the control plots. Significantly more species with single-stem were found on unburnt than on burnt plots ( P  < 0.001). Grazing tended to reduce the change in total density while fire ( P  < 0.001) and grazing ( P  = 0.029) significantly reduced the change in density of single-stemmed individuals. Selective cutting did not affect the total seedling density, but tended to reduce the change in single-stemmed seedling density. Principal component analysis revealed species-specific responses to treatments, particularly the relatively high abundance of lianas compared with other species.     

Before Cattle: A Comparative Floristic Study of Eucalyptus Savanna Grazed by Macropods and Cattle in North Queensland,Australia1

Floristic differences between cattle-grazed and macropod-grazed sites (protected from domestic stock by enclosure within a Holocene lava flow) were examined in Eucalyptus savanna in north Queensland, Australia. While macropod-grazed sites have had a lower incidence of fire than the cattle-grazed sites, it seems probable that grazing impacts per se are the major differences between these treatments. One dominant (Capillipedium parviflorum) and another common (Sehima nervosa) native perennial grass in the macropod-grazed treatment were not recorded within the cattle-grazed treatment. There was generally a lower species richness and Shannon-Weaver diversity of perennial forbs in the cattle-grazed treatment compared to the macropod-grazed treatment. There was higher richness, diversity, and abundance of annual grasses in the cattle-grazed treatment compared to the macropod-grazed treatment. The relative richness of native and exotic species was not significantly affected by cattle grazing.     

Effect of fire regime on plant abundance in a tropical eucalypt savanna of north‐eastern Australia

Abstract Changes in plant abundance within a eucalypt savanna of north‐eastern Australia were studied using a manipulative fire experiment. Three fire regimes were compared between 1997 and 2001: (i) control, savanna burnt in the mid‐dry season (July) 1997 only; (ii) early burnt, savanna burnt in the mid‐dry season 1997 and early dry season (May) 1999; and (iii) late burnt, savanna burnt in the mid‐dry season 1997 and late dry season (October) 1999. Five annual surveys of permanent plots detected stability in the abundance of most species, irrespective of fire regime. However, a significant increase in the abundance of several subshrubs, ephemeral and twining perennial forbs, and grasses occurred in the first year after fire, particularly after late dry season fires. The abundance of these species declined toward prefire levels in the second year after fire. The dominant grass Heteropogon triticeus significantly declined in abundance with fire intervals of 4 years. The density of trees (>2 m tall) significantly increased in the absence of fire for 4 years, because of the growth of saplings; and the basal area of the dominant tree Corymbia clarksoniana significantly increased over the 5‐year study, irrespective of fire regime. Conservation management of these savannas will need to balance the role of regular fires in maintaining the diversity of herbaceous species with the requirement of fire intervals of at least 4‐years for allowing the growth of saplings >2 m in height. Whereas late dry season fires may cause some tree mortality, the use of occasional late fires may help maintain sustainable populations of many grasses and forbs.     

Herbaceous phytomass and nutrient concentrations of four grass species in Sudanian savanna woodland subjected to recurrent early fire

Fire is an integral ecological factor in African savanna ecosystems, but its effects on savanna productivity are highly variable and less understood. We conducted a field experiment to quantify changes in herbaceous phytomass and nutrient composition in a Sudanian savanna woodland subjected to annual early fire from 1993 to 2004. Fire effects were also assessed on two perennial and two annual grass species during the following growing season. Early fire significantly reduced above‐ground phytomass of the studied species (P = 0.03), their crude protein (P = 0.022), neutral detergent insoluble crude protein (P = 0.016) and concentrations of Ca, Fe and Mn (P < 0.05). Perennial grasses had higher above‐ground phytomass but lower total crude protein and fat than annual grasses. Nonstructural carbohydrates tended to be higher for annuals, while fibre and lignin contents were high for perennials. Except Na and Fe, the concentration of mineral elements varied between species. Fire did not affect measures of digestibility and metabolizable energy, but its effect differed significantly among species. In conclusion, the results illustrate that long‐term frequent fire will counterbalance the short‐term increase in soil fertility and plant nutrient concentrations claimed to be accrued from single or less frequent fire.     

Savannas after afforestation: Assessment of herbaceous community responses to wildfire versus native tree planting

Afforestation and fire exclusion are pervasive threats to tropical savannas. In Brazil, laws limiting prescribed burning hinder the study of fire in the restoration of Cerrado plant communities. We took advantage of a 2017 wildfire to evaluate the potential for tree cutting and fire to promote the passive restoration of savanna herbaceous plant communities after destruction by exotic tree plantations. We sampled a burned pine plantation (Burned Plantation); a former plantation that was harvested and burned (Harvested & Burned); an unburned former plantation that was harvested, planted with native trees, and treated with herbicide to control invasive grasses (Native Tree Planting); and two old-growth savannas which served as reference communities. Our results confirm that herbaceous plant communities on post-afforestation sites are very different from old-growth savannas. Among post-afforestation sites, Harvested & Burned herbaceous communities were modestly more similar in composition to old-growth savannas, had slightly higher richness of savanna plants (3.8 species per 50-m²), and supported the greatest cover of native herbaceous plants (56%). These positive trends in herbaceous community recovery would be missed in assessments of tree cover: whereas canopy cover in the Harvested & Burned site was 6% (less than typical of savannas of the Cerrado), the Burned Plantation and Native Tree Planting supported 34% and 19% cover, respectively. By focusing on savanna herbaceous plants, these results highlight that tree cutting and fire, not simply tree planting and fire exclusion, should receive greater attention in efforts to restore savannas of the Cerrado.     

Influence of Grazing on Soil Seed Banks Determines the Restoration Potential of Aboveground Vegetation in a Semi‐arid Savanna of Ethiopia

Species composition, number of emerging seedlings, species diversity and functional group of the soil seed banks, and the influence of grazing on the similarity between the soil seed banks and aboveground vegetation, were studied in 2008 and 2009 in a semi‐arid savanna of Ethiopia. We tested whether the availability of persistent seeds in the soil could drive the transition from a degraded system under heavy grazing to healthy vegetation with ample perennial grasses. A total of 77 species emerged from the soil seed bank samples: 21 annual grasses, 12 perennial grasses, 4 herbaceous legumes, 39 forbs, and 1 woody species. Perennial grass species dominated the lightly grazed sites, whereas the heavily grazed sites were dominated by annual forbs. Heavy grazing reduced the number of seeds that can germinate in the seed bank. Species richness in the seed bank was, however, not affected by grazing. With increasing soil depth, the seed density and its species richness declined. There was a higher similarity in species composition between the soil seed bank and aboveground vegetation at the lightly grazed sites compared with the heavily grazed sites. The mean similarity between the seed banks and aboveground vegetation was relatively low, indicating the effect of heavy grazing. Moreover, seeds of perennial grasses were less abundant in the soil seed banks under heavy grazing. We concluded that restoration of grass and woody species from the soil seed banks in the heavily grazed areas could not be successful in semi‐arid savannas of Ethiopia.     

Short‐term effects of herbicides and a prescribed fire on restoration of a shrub‐encroached pine savanna

Shrub encroachment occurring worldwide in savannas and grasslands has commonly been hypothesized to result from anthropogenically altered environments. Two disturbance‐based approaches to restoration have involved: (1) application of selective herbicides to reduce density/cover of shrubs; (2) reinstatement of natural fire regimes to generate environmental conditions favoring herbaceous species. We studied short‐term responses of native shrubs, vines, and grasses in a Louisiana pine savanna to herbicides followed by a prescribed fire and fire alone. Plots established in the summer, 2013, were hand‐sprayed in the fall with Imazapyr and Triclopyr, Triclopyr alone, or no herbicide, then prescribed burned the following spring. Numbers of species of shrubs and vines at scales of 1 and 100 m², numbers of stems and regrowth of stems produced by six common species of shrubs, and the number of flowering culms of perennial C₄ grasses were assessed postfire in 2014. Compared with fire alone, herbicides followed by fire resulted in (1) small reductions in species richness of shrubs and no effects on vines, (2) fewer stems comprising shrub genets, but similar postfire regrowth of resprouting shrub stems, and (3) fewer flowering culms of C₄ grasses. Underground storage organs of savanna shrubs and vines survived both aboveground disturbances. Thus, single applications of herbicides followed by fires reduced, but did not reverse shrub encroachment and negatively affected grasses. Because effects of herbicides overrode those of prescribed fires, these disturbances did not act synergistically, suggesting that reinstating natural fire regimes should be a priority in restoration of savannas and grasslands.     

Land use and drought interactively affect interspecific competition and species diversity at the local scale in a semiarid steppe ecosystem

Few studies have considered interactive effects of grazing and drought on species composition and the relative contribution of species to total biomass, although it is important to understand the short-term dynamics and community succession in grazed ecosystems. We monitored species diversity and relative biomass contribution at one site protected from grazing since 1979 (UG79), and at winter grazing (WG) and heavily grazed (HG) sites. Continuous heavy grazing resulted in lower plant height and more but small individuals (tillers or stolons). Drought significantly reduced total plant density on all sites. Grazing affected species diversity more than drought. Species richness at site UG79 was significantly higher than at sites WG and HG, while drought only tended to reduce species diversity. Drought stress and grazing disturbance interactively controlled species competition and functional groups. Both perennial grasses and forbs had greater contribution to total biomass at site UG79, and perennial grasses contributed more than 97% of total biomass at site WG. The contribution to total biomass of annual forbs and semi-shrubs significantly increased at site HG after two dry years. The significant decrease in Potentilla acaulis and a substantial increase in annual species at this site indicate that the perennial vegetation of this ecosystem is in great danger of extinction under conditions of prolonged drought.     

Grazing effects on plant functional group diversity in Mediterranean shrublands

Grazing is one of the prevalent human activities that even today are taking place inside protected areas with direct or indirect effects on ecosystems. In this study we analyzed the effects of grazing on plant species diversity, plant functional group (PFG) diversity and community composition of shrublands. We analyzed plant diversity data from 582 sampling plots located in 66 protected areas of the Greek Natura 2000 network, containing in total 1102 plant species and subspecies. We also classified a priori all plant species in seven PFGs: annual forbs, annual grasses/sedges, legumes, perennial forbs, perennial grasses/sedges, small shrubs and tall shrubs. For each site, grazing intensity was estimated in four classes (no grazing, low, medium and high grazing intensity). We found that, at the spatial and temporal scale of this study, as grazing intensity increased, so did total species richness. However, each PFG displayed a different response to grazing. Short-lived species (annual grasses or forbs and legumes) benefited from grazing and their species richness and proportion in the community increased with grazing. Perennial grasses and forbs species richness increased with grazing intensity, but their dominance decreased, since their proportion in the community declined. Short shrub species richness remained unaffected by grazing, while tall shrub diversity decreased. Finally, in sites without grazing the spatial pattern of species richness of the different PFGs was not congruent with each other, while in grazed sites they were significantly positively correlated (with the exception of tall shrubs). This finding may imply that grazing is a selective pressure organizing the community structure, and imposing a certain contribution of each PFG. So, in Mediterranean shrublands in protected areas with a long historical record of grazing, it seems that grazing promotes species diversity and its continuation on a portion of the landscape may be a necessary part of an effective management plan.     

Long-term vegetation dynamics mediated by herbivores,weather and fire in a Juniperus-Quercus savanna

Abstract. Long-term (45-yr) basal area dynamics of dominant graminoid species were analyzed across three grazing intensity treatments (heavily grazed, moderately grazed and ungrazed) at the Texas A&M University Agricultural Research Station on the Edwards Plateau, Texas. Grazing intensity was identified as the primary influence on long-term variations in species composition. Periodic weather events, including a severe drought (1951–1956), had little direct influence on composition dynamics. However, the drought interacted with grazing intensity in the heavily grazed treatment to exacerbate directional changes caused by grazing intensity. Species response to grazing was individualistic and noisy. Three response groups were identified. Taller, more productive mid-grasses were most abundant under moderate or no grazing. Short grasses were most abundant under heavy grazing. Intermediate species were most abundant under moderate grazing and opportunistic to weather patterns. Graminoid diversity increased with the removal or reduction of grazing intensity. The moderately and ungrazed treatments appeared most resistant to short-term weather fluctuations, while the heavily grazed treatment demonstrated significant resilience when grazing intensity was reduced after over 110 yr of overgrazing. Identification of a ‘climax’ state is difficult. Significant directional change, which took nearly 20 yr, appears to continue in the ungrazed treatment after 45 yr of succession. The observed, relatively linear patterns of perennial grass composition within the herbaceous patches of this savanna were generally explained by traditional Clementsian succession. However, when dynamics of the herbaceous community are combined with the woody component of this savanna, the frequency and intensity of fire becomes more important. Across the landscape, successional changes follow several pathways. When vegetation change is influenced by several factors, a multi-scale model is necessary to demonstrate interactions and feedbacks and accurately describe successional patterns. Absence of fires, with or without grazing, leads ultimately to a Juniperus/Quercus woodland with grazing intensity primarily influencing the fuel load and hence fire intensity.     

Abundance of trees and grasses in a woodland savanna in relation to environmental factors

The relationships of plant species associations and underlying environmental factors in a woodland savanna in South Africa were investigated. 40 plots were included with 25 tree and 17 grass species dominating the arboreal and ground cover. Correspondence Analysis described the relationships between soil moisture retention, soil nutrients and the abundance of trees and grasses. Dry matter indices represented the accumulated effects of rainfall, fire and grazing of the herbaceous layer. Variations in the abundance of plants corresponded to well-defined gradients of soil nutrients. The distribution of grass and tree species along the ordination axes indicated that soils with high water retention capacity and high nutrient contents provided a suitable substrate for many of the tree species sampled. However, grass species abundance was high in plots with porous soils and poor nutrient availability.     

Loss of a large grazer impacts savanna grassland plant communities similarly in North America and South Africa

Large herbivore grazing is a widespread disturbance in mesic savanna grasslands which increases herbaceous plant community richness and diversity. However, humans are modifying the impacts of grazing on these ecosystems by removing grazers. A more general understanding of how grazer loss will impact these ecosystems is hampered by differences in the diversity of large herbivore assemblages among savanna grasslands, which can affect the way that grazing influences plant communities. To avoid this we used two unique enclosures each containing a single, functionally similar large herbivore species. Specifically, we studied a bison (Bos bison) enclosure at Konza Prairie Biological Station, USA and an African buffalo (Syncerus caffer) enclosure in Kruger National Park, South Africa. Within these enclosures we erected exclosures in annually burned and unburned sites to determine how grazer loss would impact herbaceous plant communities, while controlling for potential fire-grazing interactions. At both sites, removal of the only grazer decreased grass and forb richness, evenness and diversity, over time. However, in Kruger these changes only occurred with burning. At both sites, changes in plant communities were driven by increased dominance with herbivore exclusion. At Konza, this was caused by increased abundance of one grass species, Andropogon gerardii, while at Kruger, three grasses, Themeda triandra, Panicum coloratum, and Digitaria eriantha increased in abundance.     

Examination of multiple disturbances effects on herbaceous vegetation communities in the Sudanian savanna-woodland of West Africa

In West Africa, policies for prescribed early fire, grazing and selective tree cutting in the savanna-woodlands are rarely based on long-term experimental studies. The purpose of this study was to provide scientific evidence based on field data from two case studies for an informed discussion on the long-term response of herbaceous abundance both at the community and individual species levels to fire, grazing, selective cutting and their interactions. A long-term factorial experiment was established in two State forest reserves in Burkina Faso that mainly differ in their soil attributes. Community abundance data recorded from line intercept sampling over 13 years were analyzed using a multivariate ordination technique known as principal response curves (PRC).     

Influence of grazing and fire frequency on small-scale plant community structure and resource variability in native tallgrass prairie

In grasslands worldwide, grazing by ungulates and periodic fires are important forces affecting resource availability and plant community structure. It is not clear, however, whether changes in community structure are the direct effects of the disturbance (i.e. fire and grazing) or are mediated indirectly through changes in resource abundance and availability. In North American tallgrass prairies, fire and grazing often have disparate effects on plant resources and plant diversity, yet, little is known about the individual and interactive effects of fire and grazing on resource variability and how that variability relates to heterogeneity in plant community structure, particularly at small scales. We conducted a field study to determine the interactive effects of different long-term fire regimes (annual vs four-year fire frequency) and grazing by native ungulates ( Bos bison ) on small-scale plant community structure and resource variability (N and light) in native tallgrass prairie. Grazing enhanced light and nitrogen availability, but did not affect small-scale resource variability. In addition, grazing reduced the dominance of C₄ grasses which enhanced species richness, diversity and community heterogeneity. In contrast, annual fire increased community dominance and reduced species richness and diversity, particularly in the absence of grazing, but had no effect on community heterogeneity, resource availability and resource variability. Variability in the abundance of resources showed no relationship with community heterogeneity at the scale measured in this study, however we found a relationship between community dominance and heterogeneity. Therefore, we conclude that grazing generated small-scale community heterogeneity in this mesic grassland by directly affecting plant community dominance, rather than indirectly through changes in resource variability.     

Strategies for Savanna Restoration in the Southern Great Plains: Effects of Fire and Herbicides

Woody plant encroachment has degraded grassland and savanna ecosystems worldwide by decreasing herbaceous production and diversity, and altering these physiognomies toward woodlands. This study evaluated the long-term efficacy of fire and herbicide restoration strategies used in the southern Great Plains to reduce Honey mesquite ( Prosopis glandulosa ) dominance, restore a grassland/savanna physiognomy, and increase herbaceous production and diversity. Three treatments were evaluated: high-intensity winter fire, aerial spray of clopyralid + triclopyr (C + T), and aerial spray of clopyralid and were compared to untreated mesquite woodland (control). Post-treatment mesquite stand physiognomy was different between fire (low mortality, high basal sprouting), C + T (high mortality, high basal sprouting of surviving plants), and clopyralid (moderate mortality, low basal sprouting of surviving plants) treatments. From 6 to 8 years post-treatment, herbaceous production was increased in C + T and clopyralid treatments but not in the fire treatment. Mesquite regrowth in the fire treatment exerted a competitive influence that limited herbaceous production. Herbaceous functional group diversity was increased in fire and C + T treatments due to a decrease in C₃ perennial grass dominance and an increase in C₄ perennial grasses and/or C₃ forbs. Treatments that maintained mesquite overstory (control and clopyralid) had lower herbaceous diversity due to C₃ perennial grass dominance and lower C₄ perennial grass cover. The clopyralid treatment demonstrated greatest potential for long-term restoration of southern Great Plains savanna by reducing mesquite canopy cover to historic levels, limiting mesquite basal regrowth and increasing grass production.     

Composition of grazed and cleared temperate grassy woodlands in eastern Australia: patterns in space and inferences in time

Abstract. A regional vegetation survey of the temperate grassy woodlands (temperate savanna) in Australia was designed to assess the effects of clearing and grazing on the composition of vegetation remnants and the adjacent pasture matrix. Vegetation was sampled across a range of habitats using 77 0.1024‐ha quadrats; the relative abundance of species was recorded. Classification analysis clustered the sites into three main groups that corresponded to intensity of grazing/clearing followed by groups based on underlying lithology (basalt, metasediment, granites). Using Canonical Correspondence Analysis, exogenous disturbance and environmental variables were related to the relative abundance of species; grazing intensity had the highest eigenvalue (0.27) followed by tree canopy cover (0.25), lithology (0.18), altitude (0.17) and slope (0.10). Based on two‐dimensional ordination scores, six species response groups were defined relating to intensity of pastoralism and nutrient status of the landscape. Abundance and dominance of native shrubs, sub‐shrubs, twiners and geophytes were strongly associated with areas of less‐intense pastoralism on low‐nutrient soils. The strongest effects on species richness were grazing followed by canopy cover. Continuously grazed sites had lower native species richness across all growth forms except native grasses. There was no indication that intermediate grazing intensities enhanced forb richness as a result of competitive release. Species richness for all native plants was lowest where trees were absent especially under grazed conditions. Canopy cover in ungrazed sites appeared to promote the co‐existence of shrubs with the herbaceous layer. Predicted declines in forb richness in treeless, ungrazed, sites were not detected. The lack of a disturbance‐mediated enhancement of the herbaceous layer was attributed to habitat heterogeneity at 0.1 ha sampling scale.     

Fire frequency and tree canopy structure influence plant species diversity in a forest-grassland ecotone

Disturbances and environmental heterogeneity are two factors thought to influence plant species diversity, but their effects are still poorly understood in many ecosystems. We surveyed understory vegetation and measured tree canopy cover on permanent plots spanning an experimental fire frequency gradient to test fire frequency and tree canopy effects on plant species richness and community heterogeneity within a mosaic of grassland, oak savanna, oak woodland, and forest communities. Species richness was assessed for all vascular plant species and for three plant functional groups: grasses, forbs, and woody plants. Understory species richness and community heterogeneity were maximized at biennial fire frequencies, consistent with predictions of the intermediate disturbance hypothesis. However, overstory tree species richness was highest in unburned units and declined with increasing fire frequency. Maximum species richness was observed in unburned units for woody species, with biennial fires for forbs, and with near-annual fires for grasses. Savannas and woodlands with intermediate and spatially variable tree canopy cover had greater species richness and community heterogeneity than old-field grasslands or closed-canopy forests. Functional group species richness was positively correlated with functional group cover. Our results suggest that annual to biennial fire frequencies prevent shrubs and trees from competitively excluding grasses and prairie forbs, while spatially variable shading from overstory trees reduces grass dominance and provides a wider range of habitat conditions. Hence, high species richness in savannas is due to both high sample point species richness and high community heterogeneity among sample points, which are maintained by intermediate fire frequencies and variable tree canopy cover.     

Influence of grazing and fire on breeding birds and perennial plants in Cyprus scrub and forest systems

Grazing and browsing by sheep and goats has been an important anthropogenic influence on ecosystems in the Mediterranean region for centuries. This influence has changed significantly in recent decades, with a general shift from range grazing to the penning of animals. The intermediate disturbance hypothesis (IDH) proposes that perturbation - including anthropogenic disturbance - is the norm for Mediterranean ecosystems, and that higher species diversity is found under conditions of continuous, moderate disturbance. Here we test the IDH as it relates to grazing of scrub and open forest habitats in Cyprus, while also testing for the effects of fire. We carried out surveys of breeding birds and vegetation at 48 study sites in scrub and open woodland across Cyprus. We estimated relative grazing pressure (past and present) and fire history at these sites, and tested for associations between these factors, breeding bird species richness and perennial vegetation diversity. We found moderate current grazing reduces density of lower and middle level scrub, and a higher level of diversity of perennial vegetation at moderately over intensively grazed sites. We found that moderate historical grazing pressure had a positive influence on richness of breeding bird species in lower scrub habitat such as phrygana, but that this effect was weaker the taller and denser the habitat. By contrast, current grazing pressure had a negative effect on species richness in lower scrub, but species richness in grazed habitats was higher in denser, taller scrub habitat such as garrigue and maquis. Our study suggests grazing plays an important role in maintaining habitat heterogeneity but the impact on avian species richness depends on the density and height of the vegetation.     

Emergence and survival of herbaceous seedlings in temperate grassy woodlands: Recruitment limitations and regeneration niche

Abstract Field experiments examined herbaceous seedling emergence and survival in temperate grassy woodlands on the New England Tablelands of New South Wales. Effects of intensity of previous grazing, removal of ground cover by fire or clearing, burial of seeds, grazing and seed theft by ants on seedling emergence and survival were studied in two field experiments. Thirteen species with a range of traits were used in the experiments and their cumulative emergence was compared with laboratory germination studies. Field emergence correlated to laboratory germination but all species had lower emergence in the field. Little natural emergence of native species was observed in the field in unsown treatments. Short‐lived forbs had the highest emergence, followed by perennial grasses; rhizomatous graminoids and perennial forbs had the lowest emergence. Soil surface and cover treatments did not markedly enhance emergence suggesting that intertussock spaces were not prerequisites for forb emergence. No consistent pattern of enhanced emergence was found for any treatment combination across all species. Seedling survival varied among species, with perennial grasses and short‐lived forbs having the highest seedling mortality. Low mortality rates in the graminoids and rhizomatous forbs appeared partially to compensate for lower seedling emergence. All perennial grasses and some short‐lived forbs showed increased risk of mortality with grazing. Differences in emergence and survival of species were related to ground cover heterogeneity, soil surfaces and, to some extent, herbivory. The complexity of these patterns when superimposed on temporal variability suggests that no generalizations can be made about the regeneration niche of herbaceous species groups. Strong recruitment limitation and partitioning of resources in the regeneration niche may reduce competition among native species and explain the high species richness of the herbaceous layer in the temperate grassy communities of eastern Australia.     

The effect of shrub clearing and grazing on the composition of a Mediterranean plant community: functional groups versus species

Abstract. Fuel-breaks to impede the spread of fires in Mediterranean woody vegetation are created by clearing of shrubs, followed by very intensive cattle grazing before the fire season. The present research analysed the effects of these two disturbance types on herbaceous community composition at the functional group and the species level, by using canonical discriminant ordination analysis and by categorical modeling methods. Grazing caused an increase in the abundance of small species, geophytes, and species with an early flowering period that ends before the grazing period. The abundance of many different species increased as a result of clearing. However, no association was found between positive or negative response to clearing and any species attribute tested. Several a priori functional groups defined by life form and family showed responses to either grazing or clearing. Links between these responses and individual species attributes are discussed. The results emphasize the different nature of the two disturbances: grazing as a selective agent, and shrub clearing as a generalized one. It also stresses the importance of the plant architecture and the morphological and phenological niche in determining community composition under extremely intensive grazing conditions.