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We evaluated invasive exotic weeds and plant species diversity in relation to depth to groundwater (DTW) and microtopography in areas with DTW from 0·3–4 m in Owens Valley, California. Transects dominated by common plant species of the area were read at 1-cm intervals, and species cover was obtained at different scales: 1-m transect portions (microsites), whole transects (68 m average length), and the whole study area. Species richness and the Shannon–Wiener diversity index were obtained in microsites. DTW and microtopographical variation (soil-surface relative elevations) were jointly measured along the vegetation transects. Found in 34% of the sampled transects, the annual Bassia hyssopifolia was the most common exotic weed of the area. Its cover in the whole study area was only 0·9%, but it was the second most dominant species (19% cover) in microsites. B. hyssopifolia coexisted mainly with herbaceous species, typically in places with shallow groundwater (average

This study was designed to better define the nature of the relationship among vegetation, groundwater level and microtopography in an arid area where depth to groundwater (DTW) was 0–4 m. Plant cover, DTW and relative elevations were jointly measured along 67 vegetation transects throughout the Owens Valley, CA, USA. These transects were dominated by major species of the area: Artemisia tridentata, Atriplex torreyi, Ericameria nauseosa, Distichlis spicata, Juncus arcticus, Leymus triticoides, Sarcobatus vermiculatus and Sporobolus airoides. Plant species occurrence was associated with different DTW. J. arcticus and D. spicata occurred more frequently in areas with the shallowest groundwater ( 2·0 m). Species were also linked to different microtopographic positions: L. triticoides and J. arcticus were mainly restricted to depressions whereas A. torreyi and A. tridentata were widely distributed in higher positions on the microtopographical gradient. Only 6% of the variation in vegetation cover was accounted for by DTW throughout the study area (N = 820). Cover of individual species was usually unaffected by DTW variation. Results suggest that species distribution is linked to groundwater conditions, but cover of vegetation is only partially affected by DTW variation. This is possible because water tables in our study area are within the rooting depth of most species and plants appear to be well adapted to shallow DTW variations. Copyright © 2011 John Wiley & Sons, Ltd.

This study measured water-use efficiency of wildland vegetation at the whole-plant level during two contrasting years to better understand ecosystem responses to precipitation fluctuations in the Great Basin, USA. Biome-representative species included grasses (Distichlis spicata, Leymus triticoides, and Sporobolus airoides), desert shrubs (Artemisia tridentata, Atriplex confertifolia, and Ericameria nauseosa), wetland/riparian plants (Glycyrrhiza lepidota, Juncus arcticus, and Salix exigua), and an exotic annual (Salsola tragus). Plants were grown in 5·8 m2 plots in a common garden in eastern California. Four watering treatments were applied monthly during two summers: control (no water other than natural precipitation), low (1·3 cm), medium (2·6 cm), and high (3·9 cm). Water-use efficiency, here termed water to production (WTPa), was the ratio of water transpired to aboveground biomass produced. Biomass production was 50% lower and WTPa was five times higher during 2009 than 2010. WTPa decreased with watering during 2009 but increased with watering during 2010. Year differences determined vegetation productivity and response to summer watering and were related to the lower winter/spring precipitation during 2009 than 2010. Desert shrubs were more drought tolerant than grasses and wetland plants. Yet, an increase in summer precipitation would primarily benefit herbaceous species and not desert shrubs. Desert shrubs achieved greater standing crop but lower root-to-shoot ratio (RSR) than herbaceous species. Nonetheless, the grass S. airoides had the greatest standing crop overall, mainly because of its greater root production (RSR 5·5). Species differences in growth, WTPa, and biomass allocation should be considered in land management and conservation practices. Copyright © 2012 John Wiley & Sons, Ltd.