The effects of herbivory by a mega- and mesoherbivore on tree recruitment in sand forest, South Africa

Herbivory by megaherbivores on woody vegetation in general is well documented; however studies focusing on the individual browsing effects of both mega- and mesoherbivore species on recruitment are scarce. We determined these effects for elephant Loxodonta africana and nyala Tragelaphus angasii in the critically endangered Sand Forest, which is restricted to east southern Africa, and is conserved mainly in small reserves with high herbivore densities. Replicated experimental treatments (400 m(2)) in a single forest patch were used to exclude elephant, or both elephant and nyala. In each treatment, all woody individuals were identified to species and number of stems, diameter and height were recorded. Results of changes after two years are presented. Individual tree and stem densities had increased in absence of nyala and elephant. Seedling recruitment (based on height and diameter) was inhibited by nyala, and by elephant and nyala in combination, thereby preventing recruitment into the sapling stage. Neither nyala or elephant significantly reduced sapling densities. Excluding both elephant and nyala in combination enhanced recruitment of woody species, as seedling densities increased, indicating that forest regeneration is impacted by both mega- and mesoherbivores. The Sand Forest tree community approached an inverse J-shaped curve, with the highest abundance in the smaller size classes. However, the larger characteristic tree species in particular, such as Newtonia hildebrandtii, were missing cohorts in the middle size classes. When setting management goals to conserve habitats of key importance, conservation management plans need to consider the total herbivore assemblage present and the resulting browsing effects on vegetation. Especially in Africa, where the broadest suite of megaherbivores still persists, and which is currently dealing with the 'elephant problem', the individual effects of different herbivore species on recruitment and dynamics of forests and woodlands are important issues which need conclusive answers.     

Changes in structure of savanna woodlands in northern Botswana following the impacts of elephants and fire

Fluctuations in densities of woody plant species were monitored in plots within three northern Botswana woodland types subjected to elephant damage and burning. Woodlands dominated by Baikiaea plurijuga and Colophospermum mopane sustained significant changes occurring on an annual basis, whereas Acacia erioloba plots maintained a typical structure. The structure of A. erioloba woodlands appeared to be influenced by factors other than elephants and the occurrence of fire. Woodlands dominated by C. mopane plants were subjected to obtrusive elephant damage, although the densities of tall trees remained largely unchanged. The effects of fire were most prominent in B. plurijuga woodlands. Tree densities declined consistently and plants of lower height classes, such as shrubs and seedlings increased in densities in areas subjected to a high occurrence of fire.     

Elephant herbivory in Majete Wildlife Reserve,Malawi

Elephants have a major influence on vegetation structure, composition and ecosystem processes, and are primary agents of habitat change in Africa. At moderate‐to‐high population densities, elephants can damage vegetation, especially when enclosed in protected areas. This study examines the effects of elephant browsing on woody trees in Majete Wildlife Reserve (WR), south‐western Malawi. Regression analysis is used to assess the associations of six factors known to drive elephant browsing in other areas and determine which ones have the most influence on browsing at Majete WR. Twenty‐four per cent of tagged trees had been subject to elephant browsing. The model with vegetation type, stem diameter and distance from permanent water correctly predicted browsing for 80% of the observations. Elephants mostly favoured riparian woodlands, followed by Acacia‐dominated woodland and Brachystegia‐dominated woodland. Browsing occurrence was negatively related to distance from permanent water and diameter at breast height(DBH). A larger number of trees, sampled at random and covering a larger portion of the reserve would provide more reliable estimates of browsing and related factors. Knowledge of time‐ and site‐specific factors affecting elephant browsing can be used to forecast future habitat transformations and manipulate the range of the elephants within the reserve.     

Carbon dioxide and the uneasy interactions of trees and savannah grasses

Savannahs are a mixture of trees and grasses often occurring as alternate states to closed forests. Savannah fires are frequent where grass productivity is high in the wet season. Fires help maintain grassy vegetation where the climate is suitable for woodlands or forests. Saplings in savannahs are particularly vulnerable to topkill of above-ground biomass. Larger trees are more fire-resistant and suffer little damage when burnt. Recruitment to large mature tree size classes depends on sapling growth rates to fire-resistant sizes and the time between fires. Carbon dioxide (CO(2)) can influence the growth rate of juvenile plants, thereby affecting tree recruitment and the conversion of open savannahs to woodlands. Trees have increased in many savannahs throughout the world, whereas some humid savannahs are being invaded by forests. CO(2) has been implicated in this woody increase but attribution to global drivers has been controversial where changes in grazing and fire have also occurred. We report on diverse tests of the magnitude of CO(2) effects on both ancient and modern ecosystems with a particular focus on African savannahs. Large increases in trees of mesic savannahs in the region cannot easily be explained by land use change but are consistent with experimental and simulation studies of CO(2) effects. Changes in arid savannahs seem less obviously linked to CO(2) effects and may be driven more by overgrazing. Large-scale shifts in the tree-grass balance in the past and the future need to be better understood. They not only have major impacts on the ecology of grassy ecosystems but also on Earth-atmosphere linkages and the global carbon cycle in ways that are still being discovered.     

Responses of woody vegetation to exclusion of large herbivores in semi‐arid savannas

The Nkuhlu large‐scale long‐term exclusion experiment in Kruger National Park was designed to study the long‐term effects of large herbivores on vegetation. One treatment excludes elephants, another excludes all herbivores larger than hares and another one comprises an open, control area. Vegetation monitoring was implemented in 2002 when a baseline survey was conducted prior to exclusion. Monitoring was repeated 5 years after exclusion. Data from the surveys were analysed to establish how structure and composition of woody vegetation had changed 5 years after herbivore exclusion. The analysis showed that neither plant assemblage nor mean vegetation height had changed significantly since exclusion. However, both species richness and density of woody plants increased 5 years after exclusion of all large herbivores, but not after the exclusion of elephants alone. One already common species, Dichrostachys cinerea, became more common after excluding all large herbivores compared with either no exclusion or elephant exclusion, possibly leading to competitive suppression of other species. Species other than D. cinerea tended to either increase or decrease in density, but the changes were insufficient to induce significant shifts in the overall assemblage of woody plants. The results indicate that after 5 years of exclusion, the combined assemblage of large herbivores, and not elephants alone, could induce changes in species richness and abundances of woody plants, but the effect was so far insufficient to induce measureable shifts in the assemblages of woody plants. It is possible that assemblages will change with time and increasing elephant numbers may amplify future changes.     

How widespread is woody plant encroachment in temperate Australia? Changes in woody vegetation cover in lowland woodland and coastal ecosystems in Victoria from 1989 to 2005

Aim Encroachment or densification by woody plants affects natural ecosystems around the world. Many studies have reported encroachment in temperate Australia, particularly in coastal ecosystems and grassy woodlands. However, the degree to which published studies reflect broad-scale changes is unknown because most studies intentionally sampled areas with conspicuous densification. We aimed to estimate changes in woody vegetation cover within lowland grassy woodland and coastal ecosystems in Victoria from 1989 to 2005 to determine whether published reports of recent encroachment are representative of broad-scale ecosystem changes. Location All lowland grassy woodland and coastal ecosystems (c. 6.11 × 10⁵ ha) in Victoria, Australia. Four major ecosystems were analysed: Plains woodlands, Herb-rich woodlands, Riverine woodlands and Coastal vegetation. Methods Changes in woody vegetation cover from 1989 to 2005 were assessed based on state-wide vegetation maps and Landsat analyses of woody vegetation cover conducted by the Australian Greenhouse Office’s National Carbon Accounting System. The results show changes in woody cover within mapped patches of native vegetation, rather than changes in the extent of woody vegetation resulting from clearing and revegetation. Results When pooled across all ecosystems, woody vegetation increased by 18,730 ha from 1989 to 2005. Woody cover within Riverine woodlands and within Plains woodlands each increased by >7000 ha. At the patch scale, the mean percentage cover of woody vegetation in each polygon increased by >5% in all four ecosystems: Riverine woodlands (+9.2% on average), Herb-rich woodlands (+7.6%), Plains woodlands (+6.7%) and Coastal vegetation (+5.9%). Regression models relating degree of encroachment to geographic and climatic variables were extremely weak (r² ≤ 0.026), indicating that most variation occurred at local scales rather than across broad geographic gradients. Main conclusions At the scale of observation, woody vegetation cover increased in all lowland woodland and coastal ecosystems over the 16-year period. Thus, published examples of encroachment in selected coastal and woodland patches do appear to reflect widespread increases in woody vegetation cover in these ecosystems. This densification appears to be associated with changes in land management rather than with post-fire vegetation recovery and is likely to be ongoing and long-lasting, with substantial implications for biodiversity conservation and ecosystem services.     

Effect of vegetation density, height, and connectivity on the oviposition pattern of the leaf beetle Galeruca tanaceti

Vegetation structure can profoundly influence patterns of abundance, distribution, and reproduction of herbivorous insects and their susceptibility to natural enemies. The three main structural traits of herbaceous vegetation are density, height, and connectivity. This study determined the herbivore response to each of these three parameters by analysing oviposition patterns in the field and studying the underlying mechanisms in laboratory bioassays. The generalist leaf beetle, Galeruca tanaceti L. (Coleoptera: Chrysomelidae), preferentially deposits its egg clutches on non‐host plants such as grasses. Earlier studies revealed that oviposition within structurally complex vegetation reduces the risk of egg parasitism. Consequently, leaf beetle females should prefer patches with dense, tall, or connected vegetation for oviposition in order to increase their reproductive success. In the present study, we tested the following three hypotheses on the effect of stem density, height, and connectivity on oviposition: (1) Within habitats, the number of egg clutches in areas with high stem densities is disproportionately higher than in low‐density areas. The number of egg clutches on (2) tall stems or (3) in vegetation with high connectivity is higher than expected for a random distribution. In the field, stem density and height were positively correlated with egg clutch presence. Moreover, a disproportionately high presence of egg clutches was determined in patches with high stem densities. Stem height had a positive influence on oviposition, also in a laboratory two‐choice bioassay, whereas stem density and connectivity did not affect oviposition preferences in the laboratory. Therefore, stem height and, potentially, density, but not connectivity, seem to trigger oviposition site selection of the herbivore. This study made evident that certain, but not all traits of the vegetation structure can impose a strong influence on oviposition patterns of herbivorous insects. The results were finally compared with data on the movement patterns of the specialised egg parasitoid of the herbivore in comparable types of vegetation structure.     

The hard lives of trees in African savanna—Even without elephants

The ongoing loss of large trees and densification of shrubs are two prevalent processes that take place in African savannas, with profound consequences for their structure and function. We evaluated herbivore impacts on savanna woody communities using a long-term exclosure experiment in the Kruger National Park, South Africa, with three treatments: the exclusion of large mammals only (i.e. elephant and giraffe), exclusion of all herbivores larger than a hare, and areas open to all herbivores. We asked three questions: (1) How did variable exclusion of herbivores affect woody density and structure across the catena (i.e. riparian, sodic and crest vegetation)? (2) Did the exclusion of herbivores result in unique woody species composition? (3) Did herbivore exclusion result in a higher proportion of palatable species? After 17 years, we found that herbivores mainly affected the heights and densities of existing species, rather than leading to turnover of woody species assemblages. Although densities of individuals increased in the full exclosure (350 ha⁻¹), the change was more moderate than expected. By contrast, mixed mega-and meso-herbivores decreased the number of trees and shrubs (decreases of 780 ha⁻¹) via a variety of physical impacts. Meso-herbivores alone, on the other hand, had less impact on individual density (i.e. no change), but limited average height growth and canopy dimensions in certain habitat types. Where elephants are present, they are effective at reducing the density of woody stems to the point of counteracting woody encroachment, but at the same time are actively preventing the persistence of large trees (>5 m) as well as preventing trees from recruiting to larger size classes. However, the lack of massive recruitment and woody cover increases with elephant exclusion, especially for more preferred species, suggests that factors beyond elephants, such as dispersal limitation, seed predation, and drought, are also acting upon species.     

Ecological succession following forest decline in a xeric oak forest of south-central United States

Aims The loss of canopy trees associated with forest decline can greatly influence the species composition and structure of a forest and have major impacts on the ecosystem. We studied the changes in forest composition and structure 1 and 5 years following nearly total canopy mortality on several hundreds of hectares of xeric oak forests in south-central United States. Because the forests were within an ecotonal vegetation type composed of a mosaic of forest, savanna and grassland, we sought to learn whether forest decline areas would recover to forest or change to more open savanna and grassland conditions in the landscape pattern of vegetation. Because low intensity fire shaped the vegetation type, we sought to learn whether fire would keep the decline areas open.Methods The study was conducted in a xeric oak forest in east-central Oklahoma, USA. Randomly located vegetation and regeneration surveys were conducted in decline and non-decline stands 1 and 5 years following nearly total canopy mortality. Diameter at breast height (DBH), regeneration and sprout origin were recorded for all woody species.Important findings The major canopy species post oak (Quercus stellata Wangenh.), blackjack oak (Quercus marilandica Muenchh.) and black hickory (Carya texana Buckl.) suffered 85–92% mortality; however, minor canopy components experienced limited mortality. Mortality affected all size classes of canopy trees except those below 5cm breast height diameter. There was abundant regeneration of all species and fire seemed to maintain a high level of sprouting. Decline appeared to decrease the relative importance of stump sprouting and increase other types including root sprouts. Decline areas had abundant true seedlings, with stem origin from a root with the same diameter as the stem, which is very unusual for xeric oak forests. Regeneration height in decline areas was twice that of non-decline forests. Our findings suggest that forest decline may lead to: (i) reduced oak dominance and species change in the canopy, (ii) change in reproduction type to increase success of true seedlings and maintain genetic diversity of oaks.     

Addressing regional relationships between white‐tailed deer densities and land classes

White‐tailed deer (Odocoileus virginianus) populations have recovered to about 30 million animals in the United States, but land cover has changed during the interval of recovery. To address the relationship between deer densities and current land cover at regional scales, I applied random forests and extreme gradient boosting classifiers to model low and high deer density classes, at two different thresholds (5.8 and 11.6 deer/km²), and land classes in three regions during approximately 2003. For low and high deer density classes divided at 5.8 deer/km², deciduous broadleaf forest overall was the most influential and positive variable in the central east and central regions and crop and pasture were the most influential and negative variables in the southeast region. Deer density increased with area of deciduous and mixed forests, woody wetlands, and shrub in all regions. Deer density decreased with area of crop, developed open space, and developed low and medium residential density in all regions. For density classes divided at 11.6 deer/km², deer density had the strongest relationship with woody wetlands in the central east region, mixed and deciduous forest in the southeast region, and woody wetlands and herbaceous vegetation in the central region. Deer density increased with deciduous and mixed forests, woody wetlands, and shrub in all regions. Conversely, deer density decreased with herbaceous vegetation, crop, and developed low residential densities in all regions. Therefore, at regional scales, deer overall occurred at greater densities in forests and woody wetlands and lower densities in agricultural and residential development, which did not appear to support more deer. Deer preference for forests does result in damage to forest products, but alternatively, some may consider that deer provide important socioeconomic and ecological services by reducing number of small trees, particularly in the absence of other disturbances that historically controlled tree biomass.     

Post‐fire development of faunal habitat depends on plant regeneration traits

The concept that vegetation structure (and faunal habitat) develops predictably with time since fire has been central to understanding the relationship between fire and fauna. However, because plants regenerate after fire in different ways (e.g. resprouting from above‐ground stems vs. underground lignotubers), use of simple categories based on time since fire might not adequately represent post‐fire habitat development in all ecosystems. We tested the hypothesis that the post‐fire development of faunal habitat structure differs between ecosystems, depending on fire regeneration traits of the dominant canopy trees. We measured 12 habitat components at sites in foothill forests (n = 38), heathy woodlands (n = 38) and mallee woodlands (n = 98) in Victoria, Australia, and used generalised additive models to predict changes in each variable with time since fire. A greater percentage of faunal habitat variables responded significantly to time since fire in mallee woodlands, where fires typically are stand‐replacing, than in foothill forests and heathy woodlands, where canopy tree stems generally persist through fire. In the ecosystem with the highest proportion of epicormic resprouters (foothill forests), only ground cover and understorey vegetation responded significantly to time since fire, compared with all but one variable in the ecosystem dominated by basal resprouters (mallee woodlands). These differences between ecosystems in the post‐fire development of key habitat components suggest there may also be fundamental differences in the role of fire in shaping the distribution of fauna. If so, this challenges the way in which many fire‐prone ecosystems currently are categorised and managed, especially the level of dependence on time since fire and other temporal surrogates such as age‐classes and successional states. Where time since fire is a poor surrogate for habitat structural development, additional complexity (e.g. fire severity, topography and prior land‐use history) could better capture processes that determine faunal occurrence in fire‐prone ecosystems.     

Structure of the woody vegetation in disturbed and undisturbed arid savanna,Botswana

The structure of woody vegetation was studied in little disturbed arid savanna and in adjacent over-grazed vegetation. In the over-grazed areas density and cover of woody plants were higher than in the less disturbed vegetation. The difference was accounted for by one species, Acacia mellifera, which was strongly dominant in the overgrazed vegetation. In the open savanna, the woody species varied in height from small shrubs to trees, while the dense shrub vegetation was of uniformly low stature.It is suggested that, while the differences in total abundance of woody species depend on differences in the amount of soil water available for woody growth, differences in species composition and height distribution are governed by the spatial and temporal distribution of water in the soil profile.     

The effect of herbivores and humans on the Sand Forest species of Maputaland,northern KwaZulu-Natal,South Africa

Sand Forest in the Maputaland region of KwaZulu-Natal in South Africa is deemed the most valuable, but also probably the most complex vegetation type of this part of the Maputaland–Pondoland–Albany hotspot of biodiversity. However, Sand Forest is under threat from the current human population growth in that region as well as from uncontrolled increases in wild herbivore numbers in conservation areas. The present study compares the impacts of herbivores and humans on the state of woody resources between two sites under differing utilisation regimes. Sand Forest was found to be a complex association of tree assemblages defined by different canopy and subcanopy properties. Although marked differences in the abundance of selected species were noted at the two sites, the Sand Forest remained dominated by fine-grained species under both utilisation regimes. The fine-grained nature of Sand Forest implies that regeneration depends on the creation of small canopy gaps either by natural processes, humans or elephants, while the creation of large gaps could transform it into woodland. Management of conservation areas where Sand Forest occurs should therefore concentrate efforts on regulating animal populations to levels that provide gap properties that favour forest regeneration.     

河南白云山温带落叶阔叶林萌生特征及萌生个体空间分布格局

以河南省白云山自然保护区温带落叶阔叶林5 hm2样地群落为研究对象,分析该样地木本植物的特征,同时利用点分布格局对样地内萌生能力较强的个体进行空间格局分析.结果显示:该样地内共有木本植物91种17369株;发生萌生现象的有62种2082株,萌生物种占总物种数的68.13％,萌生个体占总个体数的11.99％.样地内所有发...     

Genetic variation in resistance and tolerance to insect herbivory in Salix cordata

1. This study investigated whether sand-dune willow Salix cordata , exhibits genetic variation in resistance and tolerance to herbivory.
2. A field experiment using cuttings from nine willow clones demonstrated genetic variation in resistance to the specialist herbivore Altica subplicata , as measured by beetle densities. Willow clones differed significantly in both total biomass and leaf trichome densities, and herbivore densities were marginally correlated with both of these parameters.
3. Tolerance to herbivory was measured in a greenhouse experiment by comparing growth response of plants experiencing 50% artificial defoliation and plants experiencing no defoliation. Clones showed significant differences in tolerance to herbivory for some growth measures (changes in height and number of leaves), but not for other growth measures (stem diameter growth and final biomass).
4. Despite the significant genetic variation in both resistance and tolerance, no trade-off was found between resistance and tolerance to herbivory.     

Change in Mesoherbivore Browsing Is Mediated by Elephant and Hillslope Position

Elephant are considered major drivers of ecosystems, but their effects within small-scale landscape features and on other herbivores still remain unclear. Elephant impact on vegetation has been widely studied in areas where elephant have been present for many years. We therefore examined the combined effect of short-term elephant presence (< 4 years) and hillslope position on tree species assemblages, resource availability, browsing intensity and soil properties. Short-term elephant presence did not affect woody species assemblages, but did affect height distribution, with greater sapling densities in elephant access areas. Overall tree and stem densities were also not affected by elephant. By contrast, slope position affected woody species assemblages, but not height distributions and densities. Variation in species assemblages was statistically best explained by levels of total cations, Zinc, sand and clay. Although elephant and mesoherbivore browsing intensities were unaffected by slope position, we found lower mesoherbivore browsing intensity on crests with high elephant browsing intensity. Thus, elephant appear to indirectly facilitate the survival of saplings, via the displacement of mesoherbivores, providing a window of opportunity for saplings to grow into taller trees. In the short-term, effects of elephant can be minor and in the opposite direction of expectation. In addition, such behavioural displacement promotes recruitment of saplings into larger height classes. The interaction between slope position and elephant effect found here is in contrast with other studies, and illustrates the importance of examining ecosystem complexity as a function of variation in species presence and topography. The absence of a direct effect of elephant on vegetation, but the presence of an effect on mesoherbivore browsing, is relevant for conservation areas especially where both herbivore groups are actively managed.     

Remnant Trees Affect Species Composition but Not Structure of Tropical Second-Growth Forest

Remnant trees, spared from cutting when tropical forests are cleared for agriculture or grazing, act as nuclei of forest regeneration following field abandonment. Previous studies on remnant trees were primarily conducted in active pasture or old fields abandoned in the previous 2–3 years, and focused on structure and species richness of regenerating forest, but not species composition. Our study is among the first to investigate the effects of remnant trees on neighborhood forest structure, biodiversity, and species composition 20 years post-abandonment. We compared the woody vegetation around individual remnant trees to nearby plots without remnant trees in the same second-growth forests (“control plots”). Forest structure beneath remnant trees did not differ significantly from control plots. Species richness and species diversity were significantly higher around remnant trees. The species composition around remnant trees differed significantly from control plots and more closely resembled the species composition of nearby old-growth forest. The proportion of old-growth specialists and generalists around remnant trees was significantly greater than in control plots. Although previous studies show that remnant trees may initially accelerate secondary forest growth, we found no evidence that they locally affect stem density, basal area, and seedling density at later stages of regrowth. Remnant trees do, however, have a clear effect on the species diversity, composition, and ecological groups of the surrounding woody vegetation, even after 20 years of forest regeneration. To accelerate the return of diversity and old-growth forest species into regrowing forest on abandoned land, landowners should be encouraged to retain remnant trees in agricultural or pastoral fields.     

Stem diameter changes before bud opening in <Emphasis Type="Italic">Zelkova serrata</Emphasis> saplings

It is well known that stems of woody plants shrink and swell diurnally. These fluctuations of stem diameter are induced mainly by the changes of water contents in plants, which are caused by the combination of leaf transpiration and root absorption of water. This implies that dormant-like deciduous broadleaved trees in a leafless state should show no or less changes in stem diameter. However, some physiological activities in woody plants are also known to precede their winter bud opening. Whether and how diameter changes occur in deciduous tree stems during winter was investigated using Zelkova serrata saplings in a leafless state. Measurements of stem diameter changes were done for more than 4 months continuously. The saplings showed distinct diameter changes with periodicities from diurnal to a few weeks, and these changes were initiated 2 months before winter bud opening. These results indicate that some physiological and/or developmental activities occur in the stem of deciduous trees before winter bud opening, and do not correspond to changes in water relations as a result of leaf transpiration. These internal activities cause fluctuations in stem diameter prior to winter bud opening in deciduous trees. Electronic Publication     

Contrasting effects of large herbivore grazing on smaller herbivores

Assemblages of large herbivores may compete for food or facilitate one another. However, small vertebrate herbivore species co-occurring with large herbivores may be affected by large herbivore grazing through changes in plant species composition, nutrient content and vegetation structure. These changes can be either positive or negative for the smaller herbivores, but this may depend on the species of small herbivores. We experimentally tested the impact of cattle grazing on habitat choice of European rabbits (Oryctolagus cuniculus) and common voles (Microtus arvalis). We excluded cattle for 7 years and measured changes in vegetation parameters, and the response of rabbits and voles. Rabbits were facilitated by cattle, whereas voles strongly preferred vegetation without cattle. The facilitation effect was stronger at low rabbit densities. Vegetation biomass and nitrogen concentration were not affected by cattle grazing, but vegetation height increased significantly where cattle were excluded. Plant species composition also changed following cattle exclusion; however, the main food plants of rabbits and voles remained abundant in each grazing treatment. We conclude that the response of both rabbits and voles predominantly reflect the differences in vegetation height in the presence and absence of cattle, but in a contrasting fashion. The difference in response between rabbits and voles may result from reduced perceived predation risk, which is lowest in high vegetation for voles, but in short vegetation for rabbits, which depend on their burrows for safety. The use of large herbivores in grassland conservation management can thus have a contrasting effect on different species of small herbivores.     

Species and structural diversity of church forests in a fragmented Ethiopian Highland landscape

Question: Thousands of small isolated forest fragments remain around churches (“church forests”) in the almost completely deforested Ethiopian Highlands. We questioned how the forest structure and composition varied with altitude, forest area and human influence. Location: South Gondar, Amhara National Regional State, Northern Ethiopia. Methods: The structure and species composition was assessed for 810 plots in 28 church forests. All woody plants were inventoried, identified and measured (stem diameter) in seven to 56 10 m x 10‐m plots per forest. Results: In total, 168 woody species were recorded, of which 160 were indigeneous. The basal area decreased with tree harvest intensity; understorey and middle‐storey density (<5 cm DBH trees) decreased with grazing; overstorey density (>5 cm DBH trees) increased with altitude. The dominance of a small set of species increased with altitude and grazing intensity. Species richness decreased with altitude, mainly due to variation in the richness of the overstorey community. Moreover, species richness in the understorey decreased with grazing intensity. Conclusions: We show how tree harvesting intensity, grazing intensity and altitude contribute to observed variations in forest structure, composition and species richness. Species richness was, however, not related to forest area. Our study emphasizes the significant role played by the remaining church forests for conservation of woody plant species in North Ethiopian Highlands, and the need to protect these forests for plant species conservation purposes.