How landscape modulators function: woody plant impact on seed dispersal and abiotic filtering

The Mediterranean landscape is characterized by a heterogeneous structure: a mosaic of woody plants (trees or shrubs) with scattered patches of herbaceous vegetation. Although the herbaceous and woody patches are adjacent to each other, plant species composition in them is substantially different. This could be attributed to either differences in environmental conditions between patch types (i.e., abiotic filters), or to dispersal limitations caused by the woody plants acting as dispersal filters. In this article, we focus on the relative impact of woody plants, applying these two filter types, in determining plant species composition in Mediterranean woodland. We experimentally manipulated shade and litter cover and examined the effect of each of these factors on plant species composition. We used seed-traps to evaluate seed arrival in the patches, and experimentally removed the shrub canopy to study the effect of the shrub as a physical barrier to seed entry. Results showed that plant species number and composition were not significantly affected by shade and litter manipulation. The number of trapped seeds were significantly higher in the open patches than in the woody patches, and removal of woody plants increased the number of trapped seeds in both open and woody patches, as a result of eliminating the physical obstacle to free seed movement. Our findings show that woody plants affect the herbaceous plant community by influencing seed dispersal, and highlight that they affect other organisms not only by modifying resource availability but also through the creation of a new landscape structure.     

Facilitation between woody and herbaceous plants that associate with arbuscular mycorrhizal fungi in temperate European forests

In late‐successional environments, low in available nutrient such as the forest understory, herbaceous plant individuals depend strongly on their mycorrhizal associates for survival. We tested whether in temperate European forests arbuscular mycorrhizal (AM) woody plants might facilitate the establishment of AM herbaceous plants in agreement with the mycorrhizal mediation hypothesis. We used a dataset spanning over 400 vegetation plots in the Weser‐Elbe region (northwest Germany). Mycorrhizal status information was obtained from published resources, and Ellenberg indicator values were used to infer environmental data. We carried out tests for both relative richness and relative abundance of herbaceous plants. We found that the subset of herbaceous individuals that associated with AM profited when there was a high cover of AM woody plants. These relationships were retained when we accounted for environmental filtering effects using path analysis. Our findings build on the existing literature highlighting the prominent role of mycorrhiza as a coexistence mechanism in plant communities. From a nature conservation point of view, it may be possible to promote functional diversity in the forest understory through introducing AM woody trees in stands when absent.     

Plant trait responses to grazing – a global synthesis

Herbivory by domestic and wild ungulates is a major driver of global vegetation dynamics. However, grazing is not considered in dynamic global vegetation models, or more generally in studies of the effects of environmental change on ecosystems at regional to global scale. An obstacle to this is a lack of empirical tests of several hypotheses linking plant traits with grazing. We, therefore, set out to test whether some widely recognized trait responses to grazing are consistent at the global level. We conducted a meta‐analysis of plant trait responses to grazing, based on 197 studies from all major regions of the world, and using six major conceptual models of trait response to grazing as a framework. Data were available for seven plant traits: life history, canopy height, habit, architecture, growth form (forb, graminoid, herbaceous legume, woody), palatability, and geographic origin. Covariates were precipitation and evolutionary history of herbivory. Overall, grazing favoured annual over perennial plants, short plants over tall plants, prostrate over erect plants, and stoloniferous and rosette architecture over tussock architecture. There was no consistent effect of grazing on growth form. Some response patterns were modified by particular combinations of precipitation and history of herbivory. Climatic and historical contexts are therefore essential for understanding plant trait responses to grazing. Our study identifies some key traits to be incorporated into plant functional classifications for the explicit consideration of grazing into global vegetation models used in global change research. Importantly, our results suggest that plant functional type classifications and response rules need to be specific to regions with different climate and herbivory history.     

Response of plant species and life form diversity to variable fire histories and biomass in the jarrah forest of south‐west Australia

Frequent fires reduce the abundance of woody plant species and favour herbaceous species. Plant species richness also tends to increase with decreasing vegetation biomass and cover due to reduced competition for light. We assessed the influence of variable fire histories and site biomass on the following diversity measures: woody and herbaceous species richness, overall species richness and evenness, and life form evenness (i.e. the relative abundance or dominance among six herbaceous and six woody plant life forms), across 16 mixed jarrah (Eucalyptus marginata) and marri (Corymbia calophylla) forest stands in south‐west Australia. Fire frequency was defined as the total number of fires over a 30‐year period. Overall species richness and species evenness did not vary with fire frequency or biomass. However, there were more herbaceous species (particularly rushes, geophytes and herbs) where there were fewer shrubs and low biomass, suggesting that more herbaceous species coexist where dominance by shrubs is low. Frequently burnt plots also had lower number and abundance of shrub species. Life form evenness was also higher at both high fire frequency and low biomass sites. These results suggest that the impact of fire frequency and biomass on vegetation composition is mediated by local interactions among different life forms rather than among individual species. Our results demonstrate that measuring the variation in the relative diversity of different woody and herbaceous life forms is crucial to understanding the compositional response of forests and other structurally complex vegetation communities to changes in disturbance regime such as increased fire frequency.     

Effect of artificial shade and grazing removal on degraded grasslands: Implications of woody restoration for herbaceous vegetation

Extensive degraded short tussock grasslands of New Zealand's eastern South Island were dominated by woody vegetation prior to burning and livestock grazing associated with human settlement starting 800 years ago. There is increasing interest in restoring some of these grasslands back to a woody state. However, because of the long time frames involved in establishing a woody cover, it is difficult to predict the impacts that woody restoration will have on the extant herbaceous flora. Using a factorial trial with artificial shade and grazing exclusion, we assessed the potential impact of woody restoration on the structure and composition of the herbaceous flora over a six‐year period. The imposition of artificial shade resulted in significant increases in total species richness and the total cover of herbaceous vegetation, increases in cover of several individual forb and grass species and decreases in the cover of bare ground, moss and lichen in shade treatments. There were also changes in the overall community composition of shaded treatments reflecting these changes in vegetation cover and species richness. We found no statistically significant effects of grazing exclusion. We suggest that increased soil moisture resulting from shade addition plays an important role in increasing the herbaceous component of the flora. While woody restoration will have a range of effects on the herbaceous understorey, for example through competition and changes in soil conditions, our findings are important for planning future woody restoration in these degraded tussock grasslands. In particular, our results suggest that the best approach to ensure the persistence of herbaceous vegetation in woody restorations might be to ensure that restoration plantings result in a spatially heterogeneous vegetation arrangement.     

用于全球变化研究的中国植物功能型划分

 植物功能型(Plant functional types, PFTs)作为沟通植物的结构和功能与生态系统属性的桥梁,随着全球变化与植被的关系研究的深入而受到广泛重视。植物功能型的划分依赖于研究的背景、尺度和要解决的问题。为了区域尺度全球变化研究的需要,该文提出了一个基于植物关键特征的植物功能型划分方法。该方法首先选择了6项植物特征,包括3项冠层特征：木本-草本、常绿-落叶和针叶-阔叶,以及3项生理特征：光合途径(C3 / C4)、植物的水分需求和热量需求,作为划分植物功能型的关键特征;然后,先根据植物冠层特征划分得到5个基本类型,再根据水分和热量条件进行详细划分,得到29种备选类型;需要时,再根据研究目的从这29种备选类型中选择所需类型。根据这个方法,在充分考虑了我国季风气候条件下特有的水热配置和高海拔环境对植物的形态和功能特征影响的基础上,从备选类型中选择了一套适合中国气候和植被特征的植物功能型体系。这套体系包括18类植物功能型,其中含7类‘树’功能型、6类‘灌木’功能型和5类‘草’功能型,另根据需要设置2类‘裸地’功能型。并且根据植物的生理生态特征和中国植被的地理分布确定了用于限制植物功能型分布的气候因子,这些气候因子包括绝对最低温度、最暖月平均温度、有效积温、年最热月平均温和最冷月平均温之差、湿润指数、年均降水量。应用表明,这套植物功能型可用于模拟我国植被在当前气候条件下的分布。该研究为发展适于我国的植被模型和区域气候模型、评估全球变化对我国植被的影响及植被变化对气候的反馈作用提供依据与参数。     

基于无人机和决策树算法的榆树疏林草原植被类型划分和覆盖度生长季动态估计

植被覆盖度是评估生态环境质量与植被生长的重要指标,也是全球众多陆面过程模型和生态系统模型中表达植被动态的重要参数。卫星遥感和地面测量是估算植被覆盖度的常见方法。然而,如何精确估计榆树疏林草原上木本、草本不同类型植被的覆盖度仍然具有挑战性。无人机飞行系统有效的补充了区域尺度低空间分辨率的卫星遥感影像与样地尺度实地调查之间的缺口,为精确的监测、评估疏林草原的植被动态提供了新途径。利用无人机监测平台和决策树算法构建了一套快速、准确、自动获取景观尺度植被类型和估算植被覆盖度的自动化工具,以浑善达克沙地榆树疏林草原为对象,应用无人机监测平台对榆树疏林草原长期定位监测大样地2017年生长季植被状况进行7次监测。结果表明:1)无人机植被监测平台数据飞行高度100 m,获取的样地数字正射影像空间分辨率为2.67 cm/像元,远高于高分卫星影像,利用决策树算法基于数字正射影像可以实现自动划分榆树疏林草原木本和草本植被类型和估算植被覆盖度; 2)生长季内榆树疏林草原木本植被覆盖度为(19±2)%,草本植被覆盖度为(50±8)%,植被总覆盖度为(69±9)%,相对于木本植被,草本植被生长季内盖度变幅较大; 3)在整个生长季中,木本植被和草本植被对植被总覆盖度的平均贡献率分别为27%和73%,草本植被对植被总盖度的贡献远大于木本植被,榆树疏林草原植被的盖度主要受草本植被的影响。本研究证明无人机监测平台是一种高效、准确的植被监测工具,结合机器学习算法,实现了景观尺度植被类型的自动划分和不同类型植被覆盖度快速获取;在浑善达克沙地榆树疏林草原地区首次获取了木本植被和草本植被覆盖度的生长季动态。该平台未来可应用于各种类型生态系统植被类型划分、监测和评估。     

Interactive effects of vegetation type and elevation on aboveground and belowground properties in a subarctic tundra

An improved knowledge of how contrasting types of plant communities and their associated soil biota differ in their responses to climatic variables is important for better understanding the future impacts of climate change on terrestrial ecosystems. Elevational gradients serve as powerful study systems for answering questions on how ecological processes can be affected by changes in temperature and associated climatic variables. In this study, we evaluated how plant and soil microbial communities, and abiotic soil properties, change with increasing elevation in subarctic tundra in northern Sweden, for each of two dominant but highly contrasting vegetation types, namely heath (dominated by woody dwarf shrubs) and meadow (dominated by herbaceous species). To achieve this, we measured plant community characteristics, microbial community properties and several soil abiotic properties for both vegetation types across an elevation gradient of 500 to 1000 m. We found that the two vegetation types differed not only in several above‐ and belowground properties, but also in how these properties responded to elevation, pointing to important interactive effects between vegetation type and elevation. Specifically, for the heath, available soil nitrogen and phosphorus decreased with elevation whereas fungal dominance increased, while for the meadow, idiosyncratic responses to elevation for these variables were found. These differences in belowground responses to elevation among vegetation types were linked to shifts in the species and functional group composition of the vegetation. Our results highlight that these two dominant vegetation types in subarctic tundra differ greatly not only in fundamental aboveground and belowground properties, but also in how these properties respond to elevation and are therefore likely to be influenced by temperature. As such they highlight that vegetation type, and the soil abiotic properties that determine this, may serve as powerful determinants of how both aboveground and belowground properties respond to strong environmental gradients.     

Plant diversity in three types of hedgerows adjacent to cropfields

The farming landscape of eastern Canada is dotted with three main types of hedgerows: (1) natural woody, (2) planted woody and (3) herbaceous. The objective of this study was to compare the value of these habitats as a repository of plant biodiversity in agricultural areas of southern Quebec. The overall plant diversity was higher in natural hedgerows and they contained more plant species of conservation values than other hedgerow types. Plant species richness per quadrat was, however, higher in planted woody hedgerows, and together with the species composition, lead to the conclusion that planted hedgerows in their entirety consisted of an ecotone type of vegetation such as is found in field edges which usually support high plant diversity and productivity but where transient plant species predominate. Consequently, this study indicated that natural hedgerows fare better than planted hedgerows in terms of diversity of plants of conservation interest. In spite of that, planted woody hedgerows contained plant (and bird) species of some interest and should be favoured over more desolate herbaceous hedgerows. In areas where hedgerows were removed and are not re-establishing naturally, a mixture of deciduous trees and conifers should be encouraged in further windbreak planting programs so as to conciliate both the conservation and agronomic objectives. Furthermore, management practices should optimise the growth of establishing plants of conservation values.     

A functional classification of herbaceous hedgerow vegetation for setting restoration objectives

Hedgerows are valuable habitats for biodiversity in farmed landscapes. The herbaceous vegetation at the hedge base is an important component of this habitat but its condition in Britain has deteriorated due to a combination of nutrient and pesticide contamination, and inappropriate management or neglect. The condition of herbaceous hedgerow vegetation is included in policy targets for biodiversity conservation, so a strategy is required for its restoration. This vegetation can be highly variable, so a classification of the main types is required to set realistic objectives. Vegetation classifications based on species’ functional characteristics can have more general application that those based on species identity. Using existing datasets from a countrywide survey, a functional classification of herbaceous vegetation from hedgerows in Britain was developed. Cluster analysis of vegetation plots, based on attributes of the species present, produced thirteen vegetation types in six broad groups. These were differentiated by the association of the component species with woodland, grassland or arable habitats and by gradients of soil nutrient status and pH, light availability, disturbance and grazing tolerance. By using species’ ecological characteristics as a basis for the classification, the condition of vegetation can be established and the prevailing environment predicted. From this information, a realistic strategy for restoration can then be determined.     

Groundwater drawdown drives ecophysiological adjustments of woody vegetation in a semi‐arid coastal ecosystem

Predicted droughts and anthropogenic water use will increase groundwater lowering rates and intensify groundwater limitation, particularly for Mediterranean semi‐arid ecosystems. These hydrological changes may be expected to elicit differential functional responses of vegetation either belowground or aboveground. Yet, our ability to predict the impacts of groundwater changes on these ecosystems is still poor. Thus, we sought to better understand the impact of falling water table on the physiology of woody vegetation. We specifically ask (a) how is woody vegetation ecophysiological performance affected by water table depth during the dry season? and (b) does the vegetation response to increasing depth to groundwater differ among water‐use functional types? We examined a suite of physiological parameters and water‐uptake depths of the dominant, functionally distinct woody vegetation along a water‐table depth gradient in a Mediterranean semi‐arid coastal ecosystem that is currently experiencing anthropogenic groundwater extraction pressure. We found that groundwater drawdown did negatively affect the ecophysiological performance of the woody vegetation. Across all studied environmental factors, depth to groundwater was the most important driver of ecophysiological adjustments. Plant functional types, independent of groundwater dependence, showed consistent declines in water content and generally reduced C and N acquisition with increasing depths to groundwater. Functional types showed distinct operating physiological ranges, but common physiological sensitivity to greater water table depth. Thus, although differences in water‐source use exist, a physiological convergence appeared to happen among different functional types. These results strongly suggest that hydrological drought has an important impact on fundamental physiological processes, constraining the performance of woody vegetation under semi‐arid conditions. By disentangling the functional responses and vulnerability of woody vegetation to groundwater limitation, our study establishes the basis for predicting the physiological responses of woody vegetation in semi‐arid coastal ecosystems to groundwater drawdown.     

Functional correlates of allelopathic potential in a successional plant community

Allelopathy, plant–plant interactions mediated through chemical production, is an active area of ecological research. Despite this widespread interest, we still lack community scale information on the prevalence of this interaction and the types of species that may be expected to be allelopathic. To address this research need, the allelopathic potential of 65 plant species from all stages of succession in the Piedmont region of New Jersey, USA, was determined with laboratory bioassays. The strength of each species’ allelopathic activity was then related to life form, origin, and fundamental plant traits. The vast majority of species tested exhibited significant allelopathic effects in the bioassays, with many of these having fairly strong effects. Overall, the allelopathic potential of species decreased with life span, roughly following the successional transitions from short-lived to long-lived herbs and to woody species. Herbaceous species on average were more allelopathic than woody species, but there was no difference between native and non-native species once life form was accounted for. In a principal components analysis, allelopathy was associated with other plant traits, but these relationships differed between woody and herbaceous species. Allelopathic potential was positively associated with plant height in herbaceous species, but negatively associated with height, leaf mass, and seed mass in woody species. These results indicate that allelopathy may be a quite common ecological strategy in plants and is equally common in both native and non-native species. The linkage of allelopathy with other plant functional traits suggests that allelopathy can and should be integrated into the broader suite of plant strategies that are studied.     

Diversity and occurrence of herbaceous communities in West African savannas in relation to climate,land use and habitat

In the face of the current changes in land use and climate as well as habitat destruction, it is important to study herbaceous vegetation as an indicator of changes occurring in savanna ecosystems. We investigated the effects of climate, land use and habitat, both alone and in combination, on the diversity and occurrence of West African savanna herbaceous plant communities. Floristic data and environmental variables were sampled in Burkina Faso and subjected to ordination and indicator species analysis to explore the variation in nine vegetation types. Regression analyses showed that climate, land use, humidity gradient, soil fraction and vegetation structure discriminate herbaceous plant communities. Climate, habitat and their interaction had the greatest effect on the occurrence of these communities. Changes in species richness of the studied communities were mainly due to climate, land use and their interaction, which were more important for increasing rather than decreasing diversity. In all cases, climate conditions remained the most important environmental factor driving vegetation variation in West African savannas. Beside this, the effects of habitat degradation in interaction with land use and climatic conditions indicate land use to be a threat for the diversity of the herbaceous vegetation.     

Cattle and Weedy Shrubs as Restoration Tools of Tropical Montane Rainforest

Over the last 150 years, a large proportion of forests in Latin America have been converted to pastures. When these pastures are abandoned, grasses may slow re‐establishment of woody species and limit forest regeneration. In this study, we explored the use of cattle in facilitating the establishment of woody vegetation in Colombian montane pastures, dominated by the African grasses Pennisetum clandestinum (Kikuyo) and Melinis minutiflora (Yaraguá). First, we described woody and herbaceous vegetation in grazed and non‐grazed pastures. Second, we tested the effect of grazing and seed addition on the establishment and growth of woody species. We also determined if the effect of grazing was different in P. clandestinum and M. minutiflora pastures. We found that low stocking density of cattle greatly increased density, number of branches per individual (a measure of “shrubiness”), and basal area of woody species, but also reduced woody plant species richness and diversity. In the grazed area, the shrubs Baccharis latifolia (Chilca) and Salvia sp. (Salvia) were the most abundant. The combined effect of grazing and shading from the shrubs reduced herbaceous vegetation by 52 to 92%. In the grazing/seed addition experiment, grazing increased establishment of woody seedlings, particularly of the shrub Verbesina arborea (camargo), but the largest effect was seed addition. Where grasses are an important barrier to regeneration, grazing can facilitate the establishment of shrubs that create a microhabitat more suitable for the establishment of montane forest tree species.     

Associations between vegetation patterns and soil texture in the shortgrass steppe

A recent conceptual model of controls on vegetation structure in semiarid regions includes the hypothesis that the balance between the dominance of woody and herbaceous species is partly controlled by soil texture. The model predicts that the dominance of woody plants is associated with coarse textured soils, and that ecotones between woody and herbaceous plant functional types are associated with soil textural changes. We analyzed vegetation and soil data (from US Soil Conservation Service maps) for an area of shortgrass steppe in Northern Weld County, Colorado, in a canonical correlation procedure to test the hypothesis at a regional scale. In support of the model, we found significant correlations between (a) a canonical vegetation variable correlated with C₃ grass biomass and shrub biomass, and a canonical soil variable correlated with sandy topsoils, and (b) a canonical vegetation variable correlated with succulent biomass, and a canonical soil variable correlated with clay soils. Relatively sharp transitions between shrub- and grass-dominated vegetation types occur in a number of areas in the shortgrass steppe of northeastern Colorado and southeastern Wyoming, and we selected four sites to test the above hypothesis at a local scale. We gathered data on vegetation cover and soil texture from transects (50 m long) positioned across the transition zones from grassland to shrubland. We conducted a further canonical correlation analysis of the vegetation and soil data to test for the relationships between vegetation structure and soil texture, and a performed regression analyses on individual site data to describe site-specific relationships between vegetation and soil texture variables. Vegetation structure along the transects, at the level of plant functional types, was similar at all four sites. The transition from grassland to shrubland encompassed a change from a C₄ grass/half-shrub complex to a shrub/C₃ grass/succulent complex. At two of the sites these transitions were associated with a change to coarser-textured soils in the shrubland zone. Within the context of the shortgrass steppe, our overall findings support the predictions of the conceptual at a regional scale, but indicate that soil texture is only one factor that can influence vegetation structure at the local scale.     

Differential effects of goat browsing on herbaceous plant community in a two-phase mosaic

The impact of herbivores on herbaceous plant communities is usually attributed to direct consumption of plants. We hypothesized that goats affect herbaceous plants both directly (consumption by foraging) and indirectly, by changing environmental conditions through modification of woody plant structure. We assessed the effects of goats browsing on environmental conditions, landscape structure, and herbaceous plants to link the direct and indirect effects of goats on herbaceous communities. Our model system was the Mediterranean woodland in Mt. Carmel, Israel. This is a two-phase mosaic landscape, composed of herbaceous (open) and woody patches. We delineated 10 plots of 1000 m², goats were introduced to five plots and five plots remained without goats. We monitored plant species richness and composition in two adjacent patch types (woody and open) in each plot. For each patch type, in all plots, we collected data on environmental conditions. We analyzed landscape structure using landscape metrics derived from a high-resolution vegetation map. We found that goats modified the structure of woody plants and hence the landscape mosaic. This alteration was associated with changes in environmental conditions, with more light penetration and higher temperatures. The impact of goats on the herbaceous plant community depended on patch type. In open patches, goats affected the herbaceous community mostly by direct consumption, whereas in woody patches they affected the herbaceous community mainly by modification of abiotic conditions. Our results stress the importance of considering landscape and patch structure in analyzing the effect of herbivory on plant communities.     

Microsite and herbaceous vegetation heterogeneity after burning Artemisia tridentata steppe

Woody vegetation can create distinct subcanopy and interspace microsites, which often result in resource islands in subcanopies compared to interspaces. This heterogeneity in soil resources contributes to herbaceous vegetation heterogeneity in plant communities. However, information detailing the impact of disturbance, such as fire, that removes the woody vegetation on microsites and herbaceous vegetation heterogeneity is limited. The purpose of this study was to determine the influence of burning on microsites and herbaceous vegetation in subcanopies and interspaces. Six study sites (blocks) were located at the Northern Great Basin Experimental Range in shrub (Artemisia tridentata ssp. wyomingensis (Beetle & A. Young) S.L. Welsh)-bunchgrass plant communities and one half of each block was burned to remove A. tridentata. Herbaceous vegetation and microsite characteristics were measured 2 years post-fire in intact and burned subcanopies and interspaces. Burning resulted in microsite and herbaceous vegetation differences between intact and burned subcanopies and intact and burned interspaces. However, burned subcanopies and burned interspaces appeared to be relatively similar. The similarity in microsite characteristics probably explains the lack of differences in herbaceous vegetation cover and biomass production between burned subcanopies and burned interspaces (P > 0.05). However, some microsite and herbaceous vegetation characteristics differed between burned subcanopies and burned interspaces. Our results suggest that disturbances that remove woody vegetation reduced microsite and herbaceous vegetation heterogeneity within plant communities, but do not completely remove the resource island effect. This suggests soil resource heterogeneity may influence post-fire community assembly and contribute to diversity maintenance. The Eastern Oregon Agricultural Research Center is jointly funded by the USDA-Agricultural Research Service and Oregon State Agricultural Experiment Station. Mention of a proprietary product does not constitute a guarantee or warranty of the product by USDA, Oregon State University, or the authors and does not imply its approval to the exclusion of other products.     

Vegetation management shapes arthropod and bird communities in an African savanna

Habitat heterogeneity is a key driver of the diversity and distribution of species. African savannas are experiencing changes in their vegetation structure causing shifts towards increased woody plant cover, which results in vegetation structure homogenization. Given the impact that increasing woody plant cover has on patterns of animal use, resource managers across Africa are implementing habitat management practices that are intended to reduce woody plant cover. To understand the ecological implications of various habitat management practices on arthropod and bird communities, we leveraged large‐scale tree clearing and subsequent mowing in an African savanna to understand how changes in both the herbaceous layer and woody plant cover (i.e., structural heterogeneity) may shape arthropod and bird communities at the local scale. We focused on four replicated treatments: (1) annual summer mow, (2) annual winter mow, (3) >5 years since last mow (rest), and (4) an adjacent unmanipulated savanna to act as a control. We found that the mowing treatments significantly influenced vegetation structure both with respect to tree density and herbaceous layer. Both arthropod and bird community composition varied across treatments. Grass biomass was the best predictor of arthropod richness and abundance, with arthropods selecting for areas with high biomass. Insectivorous bird richness and abundance was driven by tree density (i.e., perching locations) and not arthropod abundance. Our results suggest that vegetation management practices contribute to habitat heterogeneity at the landscape scale and increase bird species richness through species turnover. However, we caution that if a single vegetation management practice dominates the landscape, it is plausible that it could lead to the simplification of the avian community.     

Characterisation of alternative stable vegetation assemblages in a mesic savannah in Kenya

The phenomenon of sharp boundaries between distinctive vegetation types occurring under the same climatic conditions has often been interpreted by plant ecologists to characterise alternative stable states (ASS). The phenomenon may be relevant in explaining two strikingly different vegetation formations (broad-leaved nonspiny Combretum and fine-leaved spiny Acacia) co-occurring in mesic savannah of southeastern Kenya. We hypothesise that the two vegetation within southeastern Kenya ecosystems represent ASS whose transition may be a response to soil characteristics switch. To explore our hypothesis, we analysed empirical field data of woody species and soil characteristics from 57 plots that included 25 from Combretum and 32 from Acacia vegetation formations. We compared floristic composition and soil characteristics between the two systems and correlated edaphic statuses and vegetation states. We encountered 2,749 woody plant individuals, representing 115 species, 87 genera and 40 families. We found that the two vegetation had discrete woody species composition and soil characteristics, and also a significant species–edaphic association. The results are consistent with the ASS theory demonstrating that soil characteristics are among the important micro-environmental filters driving and maintaining woody vegetation mosaics in the tropics. Importantly, understanding ASS has ramifications for sustainable utilisation of woody plant resources in East African savannahs.     

The role of leaf lobation in elongation responses to shade in the rosette-forming forb Serratula tinctoria (Asteraceae)

BACKGROUND AND AIMS: Lobed leaves are considered selectively advantageous in conditions of high irradiance. However, most studies have involved woody species, with only a few considering the role of leaf lobation in herbaceous rosette species. In this study, it is hypothesized that, in addition to its adaptive value in high light, leaf lobation may add to the function of petioles as vertical spacers in herbaceous species in conditions of strong competition for light. METHODS: To test this hypothesis, leaf development was examined under seasonally changing natural light conditions and a field experiment was conducted in which light climate was manipulated in a wooded meadow population of Serratula tinctoria. KEY RESULTS: No changes in leaf lobation were observed in response to experimental shading or different natural light conditions. However, in tall herbaceous vegetation, plants with highly lobed leaves achieved significantly greater vertical elongation than plants with less-lobed leaves. In contrast to herbaceous shade, tree shade had no effect on leaf elongation, suggesting differential responsiveness to competition from neighbouring herbs versus overhead shade. In shading treatments, imposed shade could only be responded to by the elongation of leaves that were produced late in development. CONCLUSIONS: The results show that extensive leaf lobation can enable greater leaf elongation in response to shade from surrounding herbaceous vegetation. The different morphological responses displayed by Serratula tinctoria to different types of shade demonstrate the importance of critically assessing experimental designs when investigating phenotypic plasticity in response to shade.