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Aim of the study: The aim of this study is to provide information on species-specific basic wood density (g cm-3) and moisture content (%) in Mediterranean shrublands. Area of study: The study covers two sites of the sclerophyllous shrubland in central Chile, Cortaderal (34°35’S 71°29’W) and Miraflores (34°08’S 70°37’W), characterized by different climatic and topographic conditions. Material and methods: The sampling area covers 4,000 m2 over four plots at two sites. Shrub species were identified and size-related attributes such as height and crown size measured. A total of 322 shrubs were sampled at 0.3 m aboveground to determine basic wood density and moisture content. Species-specific differences and similarities were analyzed by multiple pairwise comparisons (post-hoc tests) and by ordination and hierarchical clustering. Main results: We found high variation across species in wood density (0.46-0.77 g cm-3) and moisture content (41.6-113.1%), with many significant differences among species in wood density and among sites in moisture content. Because intraspecific variability could not be explained by shrub size and pronounced differences in wood density (0.49-0.64 g cm-3) also occurred between species of the same genus (e.g., Baccharis linearis and Baccharis macraei), our results suggested that phylogenetic affinity may be less important than adaptation to local conditions. Research highlights: The values presented here were variable according to the type of species and environmental conditions, necessitating the determination of basic wood density (BWD) and moisture content at site – and species-specific level. The provided BWD estimates allow converting green volume to aboveground biomass in shrubland areas and are an essential source of information for estimating the carbon stocks.

The effect of shrub encroachment on soil carbon (C): nitrogen (N): phosphorus (P) stoichiometric ratios are largely still unknown. We investigated this effect and the effect of shrub size in a high altitude forest cutover among four common shrub species: Cerasus trichostoma, Ribes glaciale, Rosa omeiensis and Salix sphaeronymphe. The difference in topsoil C:N ratio between meadows and shrub islands was greatly influenced by shrub species and plant sizes. Topsoil N:P and C:P ratios were always higher in shrub islands than in meadows, irrespective of shrub species and plant size. The expansion of shrubs merely increased the topsoil C:N ratio beneath Cerasus and Rosa, and increased the topsoil N:P and C:P ratios beneath the four shrub species. The increase in stoichiometric ratio followed an identical pattern among the four shrub species as shrub size increased. There were always higher topsoil C:P and N:P ratios beneath Ribes than under the other shrub species with the same plant size. This study clearly suggests that the effect of shrub islands on soil C:N:P stoichiometric ratios was dependent on shrub species and size. Our results are conducive to clarifying the currently confusion in secondary successional trends of soil C:N:P stoichiometry.

Introduction: Many semiarid regions around the world are presently experiencing significant changes in both climatic conditions and vegetation. This includes a disturbed coexistence between grasses and bushes also known as bush encroachment, and altered precipitation patterns with larger rain events. Fewer, more intense precipitation events might promote groundwater recharge, but depending on the structure of the vegetation also encourage further woody encroachment.Materials and Methods: In this study, we investigated how patterns and sources of water uptake of Acacia mellifera (blackthorn), an important encroaching woody plant in southern African savannas, are associated with the intensity of rain events and the size of individual shrubs. The study was conducted at a commercial cattle farm in the semiarid Kalahari in Namibia (MAP 250 mm/a). We used soil moisture dynamics in different depths and natural stable isotopes as markers of water sources. Xylem water of fifteen differently sized individuals during eight rain events was extracted using a Scholander pressure bomb.Results and Discussion: Results suggest the main rooting activity zone of A. mellifera in 50 and 75 cm soil depth but a reasonable water uptake from 10 and 25 cm. Any apparent uptake pattern seems to be driven by water availability, not time in the season. Bushes prefer the deeper soil layers after heavier rain events, indicating some evidence for the classical Walter’s two-layer hypothesis. However, rain events up to a threshold of 6 mm/day cause shallower depths of use and suggest several phases of intense competition with perennial grasses. The temporal uptake pattern does not depend on shrub size, suggesting a fast upwards water flow inside. δ2H and δ18O values in xylem water indicate that larger shrubs rely less on upper and very deep soil water than smaller shrubs. It supports the hypothesis that in environments where soil moisture is highly variable in the upper soil layers, the early investment in a deep tap-root to exploit deeper, more reliable water sources could reduce the probability of mortality during the establishment phase. Nevertheless, independent of size and time in the season, bushes do not compete with potential groundwater recharge. In a savanna encroached by A. mellifera, groundwater will most likely be affected indirectly.

Introduction: Many semiarid regions around the world are presently experiencing significant changes in both climatic conditions and vegetation. This includes a disturbed coexistence between grasses and bushes also known as bush encroachment, and altered precipitation patterns with larger rain events. Fewer, more intense precipitation events might promote groundwater recharge, but depending on the structure of the vegetation also encourage further woody encroachment. Materials and Methods: In this study, we investigated how patterns and sources of water uptake of Acacia mellifera (blackthorn), an important encroaching woody plant in southern African savannas, are associated with the intensity of rain events and the size of individual shrubs. The study was conducted at a commercial cattle farm in the semiarid Kalahari in Namibia (MAP 250 mm/a). We used soil moisture dynamics in different depths and natural stable isotopes as markers of water sources. Xylem water of fifteen differently sized individuals during eight rain events was extracted using a Scholander pressure bomb. Results and Discussion: Results suggest the main rooting activity zone of A. mellifera in 50 and 75 cm soil depth but a reasonable water uptake from 10 and 25 cm. Any apparent uptake pattern seems to be driven by water availability, not time in the season. Bushes prefer the deeper soil layers after heavier rain events, indicating some evidence for the classical Walter's two-layer hypothesis. However, rain events up to a threshold of 6 mm/day cause shallower depths of use and suggest several phases of intense competition with perennial grasses. The temporal uptake pattern does not depend on shrub size, suggesting a fast upwards water flow inside. δ2H and δ18O values in xylem water indicate that larger shrubs rely less on upper and very deep soil water than smaller shrubs. It supports the hypothesis that in environments where soil moisture is highly variable in the upper soil layers, the early investment in a deep tap-root to exploit deeper, more reliable water sources could reduce the probability of mortality during the establishment phase. Nevertheless, independent of size and time in the season, bushes do not compete with potential groundwater recharge. In a savanna encroached by A. mellifera , groundwater will most likely be affected indirectly. [ABSTRACT FROM AUTHOR]

• A. ordosica had positive effects on understorey species in this dune system. • Shrub–herb interactions were driven by shrub size and dune stabilization. • Species-specific differences in facilitation within a community depend on herb life-history groups. • Communities are suggested to be sets of hidden interaction groups with contrasting functional strategies. Shrubs play a pivotal role in reversing desertification and in promoting ecological rehabilitation in severe environments. However, how the interactions between shrubs and their understorey species change during restoration remains unclear. Here, we report the results of an observational study conducted in the Mu Us Desert of northern China. This study explored how dune stabilization and the size of individual shrubs affect shrub–herb interactions. In particular, we aimed to determine how different life-history groups and performance indicators (e.g., biomass and richness) of subordinate species respond to shrub–herb interactions during dune stabilization. The shrub Artemisia ordosica had positive effects on understorey species in this dune system. The ability of the shrub to promote the growth of understorey species increased with dune stabilization, but decreased from small to large shrubs. This effect was due to an increase in the relative abundance and biomass of perennials and their higher sensitivity to the positive effects of the shrubs. In contrast, the ability of shrubs to improve the richness of understorey species decreased with dune stabilization, but increased from small to large shrubs. This effect occurred because perennials suffered high strain during recruitment in disturbed open patches of the semi-fixed dunes, particularly below small shrubs. Our results support the theory claiming that communities are sets of hidden interaction groups that have contrasting responses (neutral for annuals, but facilitative for perennials) to dominant neighbors in a single community, depending on their functional strategies. Furthermore, our study highlights the high efficiency of A. ordosica in facilitating ecological restoration of dry and disturbed sandy communities. [ABSTRACT FROM AUTHOR]

The effect of shrub encroachment on soil carbon (C): nitrogen (N): phosphorus (P) stoichiometric ratios are largely still unknown. We investigated this effect and the effect of shrub size in a high altitude forest cutover among four common shrub species: Cerasus trichostoma, Ribes glaciale, Rosa omeiensis and Salix sphaeronymphe. The difference in topsoil C:N ratio between meadows and shrub islands was greatly influenced by shrub species and plant sizes. Topsoil N:P and C:P ratios were always higher in shrub islands than in meadows, irrespective of shrub species and plant size. The expansion of shrubs merely increased the topsoil C:N ratio beneath Cerasus and Rosa, and increased the topsoil N:P and C:P ratios beneath the four shrub species. The increase in stoichiometric ratio followed an identical pattern among the four shrub species as shrub size increased. There were always higher topsoil C:P and N:P ratios beneath Ribes than under the other shrub species with the same plant size. This study clearly suggests that the effect of shrub islands on soil C:N:P stoichiometric ratios was dependent on shrub species and size. Our results are conducive to clarifying the currently confusion in secondary successional trends of soil C:N:P stoichiometry. [ABSTRACT FROM AUTHOR]

We experimentally determined how an apparently unpalatable and fire-sensitive shrub, Richea acerosa (Lindley) F.Muell., responded to the single and interactive effects of grazing and burning over 3-24 years at two subalpine sites in Tasmania. At the Middlesex Plains site, a low-intensity burn killed most individuals of the species 3 years after fire and fencing. At the Lake Botsford site, total grazing exclusion for 24 years resulted in a strong reduction of the number of small shrubs of the species, and in a lower proportion of dead material in plants of any given size. An open shrub layer results from the absence of R. acerosa seedlings in the open centres of senescing plants and their preferential location along the margins of the foliage of mature and senescing plants. Thus, the persistence of R. acerosa appears to require an absence of frequent fire and the presence of sufficient grazing pressure from vertebrate herbivores to produce lawn between shrubs. Richea acerosa is, thus, an unpalatable shrub that depends on grazing. [ABSTRACT FROM AUTHOR]