Cutting improves the productivity of lucerne-rich stands used in the revegetation of degraded arable land in a semi-arid environment

Understanding the relationships between vegetative and environmental variables is important for revegetation and ecosystem management on the Loess Plateau, China. Lucerne (Medicago sativa L.) has been widely used in the region to improve revegetation, soil and water conservation, and to enhance livestock production. However, there is little information on how environmental factors influence long-term succession in lucerne-rich vegetation. Our objective was to identify the main environmental variables controlling the succession process in lucerne-rich vegetation such that native species are not suppressed after sowing on the Loess Plateau. Vegetation and soil surveys were performed in 31 lucerne fields (three lucerne fields without any management from 2003-2013 and 28 fields containing 11-year-old lucerne with one cutting each year). Time after planting was the most important factor affecting plant species succession. Cutting significantly affected revegetation characteristics, such as aboveground biomass, plant density and diversity. Soil moisture content, soil organic carbon, soil available phosphorus and slope aspect were key environmental factors affecting plant species composition and aboveground biomass, density and diversity. Long-term cutting can cause self-thinning in lucerne, maintain the stability of lucerne production and slow its degradation. For effective management of lucerne fields, phosphate fertilizer should be applied and cutting performed

A dominant dwarf shrub increases diversity of herbaceous plant communities in a Trans-Himalayan rangeland

Plant communities are structured by both competition and facilitation. The interplay between the two interactions can vary depending on environmental factors, nature of stress, and plant traits. But, whether positive or negative interactions dominate in regions of high biotic and abiotic stress remains unclear.We studied herbaceous plant communities associated with a dwarf shrub Caragana versicolor in semi-arid, high altitude Trans Himalayan rangelands of Spiti, India. We surveyed 120 pairs of plots (within and outside shrub canopies) across four watersheds differing in altitude, aspect and dominant herbivores. Herbaceous communities within shrub canopies had 25% higher species richness, but similar abundance when compared to communities outside the canopy, with the shrub edge having higher diversity than the center of the canopy. Grasses and erect forbs showed positive associations with the shrub, while prostrate plants occurred at much lower abundance within the canopy. Rare species showed stronger positive associations with Caragana than abundant species. Experimental removal of herbaceous vegetation from within shrub canopies led to 42% increase in flowering in Caragana, indicating a cost to the host shrubs. Our study indicates a robust pattern of a dwarf shrub facilitating local community diversity across this alpine landscape, increasing diversity at the plot level, facilitating rare species, and yet incurring a cost to hosts from the presence of herbaceous plants. Given these large influences of this shrub on vegetation of these high altitude rangelands, we suggest that the shrub microhabitat be explicitly considered in any analyses of ecosystem health in such rangelands

An ecohydrological approach to managing dryland forests: Integration of leaf area metrics into assessment and management

We review the use of leaf area metrics (LAM) for assessing and managing dryland forests. We propose a framework integrating individual tree to whole-ecosystem metrics representing a variety of forest features and review theory, empirical evidence and knowledge gaps. Four basic concepts underlie the LAM framework: (1) Max-LAI - an ecosystem can be characterized by an upper potential leaf area index (LAI) dictated mainly by water availability, (2) Leaf area distribution - the distribution of leaf area is proportional to the distribution of resources among vegetation components, (3) Safe-LAI - maintaining Ecosystem-LAI below Max-LAI is a way to reduce drought stress and (4) tree leaf area (TLA) - the leaf area of an individual tree as a proportion of its potential TLA, represents its vigour. Implementation of the LAM strategy requires the following: (1) better understanding how edaphic conditions and vegetation characteristics interact with climate in determining Max-LAI, (2) better understanding how leaf area is related to water use across species, vegetation strata and light regimes, (3) better understanding the interaction between LAI development and stand dynamics, (4) better capability of measuring or estimating individual tree leaf area and (5) development of species-specific references for tree vigour based on leaf area. The LAM strategy is promising for managing dryland forests under increasing drought stress

An ecohydrological approach to managing dryland forests: Integration of leaf area metrics into assessment and management

We review the use of leaf area metrics (LAM) for assessing and managing dryland forests. We propose a framework integrating individual tree to whole-ecosystem metrics representing a variety of forest features and review theory, empirical evidence and knowledge gaps. Four basic concepts underlie the LAM framework: (1) Max-LAI - an ecosystem can be characterized by an upper potential leaf area index (LAI) dictated mainly by water availability, (2) Leaf area distribution - the distribution of leaf area is proportional to the distribution of resources among vegetation components, (3) Safe-LAI - maintaining Ecosystem-LAI below Max-LAI is a way to reduce drought stress and (4) tree leaf area (TLA) - the leaf area of an individual tree as a proportion of its potential TLA, represents its vigour. Implementation of the LAM strategy requires the following: (1) better understanding how edaphic conditions and vegetation characteristics interact with climate in determining Max-LAI, (2) better understanding how leaf area is related to water use across species, vegetation strata and light regimes, (3) better understanding the interaction between LAI development and stand dynamics, (4) better capability of measuring or estimating individual tree leaf area and (5) development of species-specific references for tree vigour based on leaf area. The LAM strategy is promising for managing dryland forests under increasing drought stress