A survey of plant composition along a regional gradient of aridity in California

A full description of objectives, methods, and results can be found in Journal of Vegetation Science. (Citation to come)<br>An under-examined component of the shrub-annual relationship is how regional drivers, such as climate, may alter the sign or magnitude of positive interactions. Interspecific interactions between plants have been shown to be strongly linked to climate, particularly temperature and precipitation. The stress-gradient hypothesis (SGH) predicts that higher abiotic stress (i.e. for deserts, increasing temperature and reduced precipitation) will increase the frequency of positive interactions among shrubs and their annual understory. Regional climate gradients also have indirect effects on plant composition, such as determining consumer abundance and soil nutrient composition. Nutrient availability is particularly affected by precipitation because of altered decomposition rates of organic matter and mineralization. Therefore, the strength of facilitation and operating mechanism of a shrub on the annual plant community may change along a regional gradient.<br>A seven sites along a gradient of aridity, 30 shrub-open pairs were selected. In each of these paired sites, three phytometer plant species were planted at 0.3 g (Phacelia tanacetifolia, Plantago insularis, and Salvia columbariae). These seeds were sown in fall of 2015 and 2016. A nutrient addition was added to half the plots. Following winter rains, these plants were surveyed once January 2016/2017 and at peak biomass in March 2016/2017. Shrub morphology and landscape characteristics were also measured. Lastly, we measured the soil nutrients. <br><b>Six files are available in this dataset. </b><b>Metadata -</b> A file that emails the columns in each of the other datasets<b>ERG.shrub - </b>Measurements of shrub morphology and landscape characteristics<b>ERG.soilnutrients </b>- Measured soil nutrients along the gradient in each microsite (only conducted for 2017)<b>ERG.phytometer.census - </b>Measurements of the three phytometers in each census<b>ERG.communitydata - </b>Measurement of the natural/ambient plant community present in each microsite but outside the phytometer plots<b>ERG.specieslist -</b> A list of the full species names present in the community data