Impacts of shrub introduction on soil properties and implications for dryland revegetation.

The intensive introduction of shrubs to drylands can alter species composition and affect a series of biotic and abiotic processes. This topic has attracted increasing attention by researchers. To assess the response of soil properties to vegetation succession in arid regions of China, we measured the soil water content (SWC) to a depth of 5-m and determined soil properties of surface (0-5 cm) and subsurface (20-25 cm) layers in areas of natural grasses (NGs) and planted shrubs (PSs). The patch size of Caragana korshinskii shrubs resulted in different soil water storage losses (small shrub patch: 206.67 ± 35.58 mm; medium shrub patch: 416.88 ± 35.12 mm; large shrub patch: 588.63 ± 72.00 mm; degraded shrub patch: 740.54 ± 17.00 mm). Shrub cover showed an initial increase but then decreased as shrubs extracted soil water from the deep soil layers (>1 m). The species richness index in the PSs decreased with increasing shrub patch sizes. Surface soil organic carbon (SOC), extractable nitrogen (NH4+-N and NO3--N), and available phosphorous contents and saturated soil hydraulic conductivity (Ks) in the PSs were all significantly (p < 0.05) lower than those in NGs. Soil particles in the range of 0.002-0.2 mm explained 28.0% and 47.3% of the total variability of these surface indices under NGs and PSs, respectively. The differences in SOC, NH4+-N, NO3--N, Ks, and field capacity between the surface and subsurface layers declined significantly (p < 0.05). The introduction of shrubs affected the plant community by increasing the spatial heterogeneity of soil resources (e.g. water and nutrient contents). Therefore, the strong feedback between SWC and vegetation succession should be carefully considered when revegetating drylands. The evaluation of regional soil property responses to vegetation succession aids in a better understanding of soil water-vegetation feedback and provides important implications for future revegetation in arid regions.

Zhang C ，Wang Y ，Jia X ，Shao M ，An Z ... -  《-》

[Soil organic carbon dynamics and the prediction of their spatial changes in response to anthropogenically introduced shrub encroachment in desert steppe of the Eastern Ningxia, China.].

Zhao YN ，DU YY ，Ma YP ，Zhao YB ，Zhou YR ，Wang HM ... -  《-》

[Spatial heterogeneity of soil water content under introduced shrub (Caragana korshinskii) in desert grassland of the eastern Ningxia, China].

Zhao YN ，Zhou YR ，Wang HM 《-》

Soil organic carbon in drylands: shrub encroachment and vegetation management effects dwarf those of livestock grazing.

Dryland ecosystems occur worldwide and play a prominent, but potentially shifting, role in global biogeochemical cycling. Widespread woody plant proliferation, often associated with declines in palatable grasses, has jeopardized livestock production in drylands and prompted attempts to reduce woody cover by chemical or mechanical means. Woody encroachment also has the potential to significantly alter terrestrial carbon storage. However, little is known of the long-term biogeochemical consequences of woody encroachment in the broader context of its interaction with common dryland land uses, including "brush management" (woody plant clearing) and livestock grazing. Present assessments exhibit considerable variation in the consequences of these land use/land cover changes, with evidence that brush management may counteract sizeable impacts of shrub encroachment on soil biogeochemical pools. A challenge to assessing the net effects of brush management in shrub-encroached grasslands on soil organic carbon (SOC) and total nitrogen (N) pools is that land management practices are typically considered in isolation, when they are co-occurring phenomena. Furthermore, few studies have assessed spatial patterns in brush management and how these are affected in decades following treatment on sites with contrasting grazing histories. To address these uncertainties and interactions, we quantified the impacts of shrub encroachment and their subsequent mortality resulting from brush management (herbicide application) on SOC and N pools in a Sonoran Desert grassland where long-term grazing manipulations (>100 yr) co-occur with shrub encroachment and brush management. Pools of SOC and N associated with herbicided shrubs declined markedly over ~40 yr, offsetting 66% of the increases from shrub encroachment. However, spatial patterns in SOC induced by shrubs persisted over the decades following brush management. Century-long protection from grazing did little to change SOC and N pools. Accordingly, shrub encroachment and shrub mortality from brush management each far outweighed livestock grazing impacts. Consideration of the patterns of SOC and N through space (e.g., bole-to-dripline gradients), time (e.g., shrub age/size), land use (e.g., livestock grazing and brush management), and their interactions will position us to improve predictions of SOC and N responses to land use/land cover change, inform C-based management decisions, and objectively evaluate trade-offs with other ecosystem services.

Throop HL ，Archer SR ，McClaran MP 《ECOLOGICAL APPLICATIONS》

[Rainfall and soil moisture redistribution induced by xerophytic shrubs in an arid desert ecosystem].

Wang ZN ，Wang XP ，Liu B 《-》