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

Session 17 Ecophysiology

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Linking patterns and processes in alpine plant communities: A global study

Predictable relationships among patterns, processes, and properties of plant communities are crucial for developing meaningful conceptual models in community ecology. We studied such relationships in 18 plant communities spread throughout nine Northern Hemisphere high-mountain subalpine and alpine meadow systems and found linear and curvilinear correlative links among temperature, precipitation, productivity, plant interactions, spatial pattern, and richness. We found that sites with comparatively mild climates have greater plant biomass, and at these sites strong competition corresponds with overdispersed distribution of plants, reducing intraspecific patchiness and in turn increasing local richness. Sites with cold climates have little biomass, and at these sites a high proportion of species benefit from strong facilitative effects of neighbors, leading to an aggregated distribution of plants. Sites with intermediate, or relatively moderate climates are intermediate in biomass, and at these sites interactions are weak (or competition may be counterbalanced by facilitation), corresponding with a nearly random distribution of plants. At these sites species richness is lower than average. We propose that the relationship between interspecific spatial pattern and community richness reflects niche differentiation and/or construction, which allows for the coexistence of more species than would be possible with random, unstructured spatial distributions. Discovering the mechanisms that drive the relationships described here would further link functional and structural components of plant communities and enhance the predictive capability of community ecology

Restoration of a limestone quarry: effect of soil amendments on the establishment of native Mediterranean sclerophyllous shrubs

Limestone quarries are spread over theMediterranean Basin and have a strong environmental impact on the landscape, causing vegetation losses and soil losses. A reclamation project was conducted in a limestone quarry, situated in Arra´bida Natural Park (southwest Portugal), that is dominated by mediterranean vegetation. Revegetation was conducted using three evergreen sclerophyllous shrub species (Ceratonia siliqua, Olea europaea, and Pistacia lentiscus), and new techniques were assayed to improve plant water status and nutrient status during the first phases after plantation. A water-holding polymer (gel), fertilizer, and mycorrhiza inoculum were applied in a factorial experiment in a randomized complete block design. The success of these techniques was evaluated during 1.5 years, through monitoring of growth and ecophysiology of plants. Plant survival was high, the lowest values (95%) being recorded in C. siliqua. There were species-specific responses to the treatments applied. Ceratonia siliqua showed the highest growth rates and was the only species with growth stimulated by fertilizer application. However, the application of fertilizer induced changes in leaf characteristics of the other two species, increasing chlorophyll and nitrogen contents. Mycorrhiza inoculumhad no effect on plant response. The addition of the water-holding polymer induced higher midday plant water potentials in C. siliqua, O. europaea, and P. lentiscus, but in the latter two species the simultaneous addition of gel and fertilizer induced the lowest water potentials. The addition of fertilizer and gel is recommended in future revegetation programs but not the combination of both when revegetating with O. europaea and P. lentiscus. The results of this experiment indicate that the use of these mediterranean species, adapted to nutrient and water stress, can circumvent harsh conditions of the quarry

Imaging the crustal structure of the Central Iberian Zone (Variscan Belt): The ALCUDIA deep seismic reflection transect

ALCUDIA is a 230 km long, vertical incidence deep seismic reflection transect acquired in spring 2007 across the southern Central Iberian Zone (part of the pre-Mesozoic Gondwana paleocontinent) of the Variscan Orogen of Spain. The carefully designed acquisition parameters resulted in a 20 s TWTT deep, 60–90 fold, high-resolution seismic reflection transect. The processed image shows a weakly reflective upper crust (the scarce reflectivity matching structures identified at surface), a thick, highly reflective and laminated lower crust, and a flat Moho located at 10 s TWTT (30 km depth). The transect can be divided into three segments with different structural styles in the lower crust. In the central segment, the lower crust is imaged by regular, horizontal and parallel reflectors, whereas in the northern and southern segments it displays oblique reflectors interpreted as an important thrust (north) and tectonic wedging involving the mantle (south). The ALCUDIA seismic image shows that in an intracontinental orogenic crust, far from the suture zones, the upper and lower crust may react differently to shortening in different sectors, which is taken as evidence for decoupling. The interpreted structures, as deduced from surface geology and the seismic image, show that deformation was distributed homogeneously in the upper crust, whereas it was concentrated in wedge/thrust structures at specific sectors in the lower crust. The seismic image also shows the location of late Variscan faults in spatial association with the lower crustal thickened areas