DOI: 10.5061/dryad.rn7c5
title: Data from: Shrubs as ecosystem engineers across an environmental gradient: effects on species richness and exotic plant invasion

description: Ecosystem-engineering plants modify the physical environment and can
 increase species diversity and exotic species invasion. At the individual
 level, the effects of ecosystem engineers on other plants often become
 more positive in stressful environments. In this study, we investigated
 whether the community-level effects of ecosystem engineers also become
 stronger in more stressful environments. Using comparative and
 experimental approaches, we assessed the ability of a native shrub
 (Ericameria ericoides) to act as an ecosystem engineer across a stress
 gradient in a coastal dune in northern California, USA. We found increased
 coarse organic matter and lower wind speeds within shrub patches. Growth
 of a dominant invasive grass (Bromus diandrus) was facilitated both by
 aboveground shrub biomass and by growing in soil taken from shrub patches.
 Experimental removal of shrubs negatively affected species most associated
 with shrubs and positively affected species most often found outside of
 shrubs. Counter to the stress-gradient hypothesis, the effects of shrubs
 on the physical environment and individual plant growth did not increase
 across the established stress gradient at this site. At the community
 level, shrub patches increased beta diversity, and contained greater
 rarified richness and exotic plant cover than shrub-free patches. Shrub
 effects on rarified richness increased with environmental stress, but
 effects on exotic cover and beta diversity did not. Our study provides
 evidence for the community-level effects of shrubs as ecosystem engineers
 in this system, but shows that these effects do not necessarily become
 stronger in more stressful environments.
description: Shrub
 heightPositions of
 non-experimental Ericameria ericoides shrubs used in community analysis.
 Shrub position on the stress gradient is given in m. Canopy height given
 in cm.AssociationShrubHeight.csvSand SizeSand particle size and coarse organic matter content in soil samples from 46 paired shrub and shrub-free patches.SandSize.csvSoil CarbonCarbon content in soil samples from a subset of the 46 shrub-free and shrub covered patches.SoilCarbon.csvWind SpeedSpring wind speeds recorded in 70 study shrubs where shrub aboveground canopy and stems was either left intact or physically removed with clippers. Wind speeds were recorded with a digital handheld anemometer 3 cm above the soil surface in the same location in each shrub on each visit.WindSpeed.csvBromus MassFinal aboveground dry biomass of Bromus diandrus (Poaceae) plants grown either in soil from shrub patches or from outside of shrub patches and either under shrubs or outside of shrubs.BromusMass.csvCommunity CoverAbsolute percent cover of vascular plants in 92 pairs of shrub covered and open habitat patches. Values are ocular estimates of cover measured in a 20 x 30 cm quadrat placed at a random location within each shrub and open habitat patch.CommunityCover.csvCommunity AbundanceNumber of individual vascular plants rooted in 92 pairs of shrub covered and open habitat patches. Values are total numbers of individuals of each species counted in a 20 x 30 cm quadrat placed at a random location within each shrub and open habitat patch. Quadrat locations were the same as those used for the estimated plant cover values in "CommunityCover.csv".CommunityAbundance.csvRemoval ExperimentThe total aboveground biomass of vascular plant species collected in 70 experimental shrub patches in 2010 and 2011. Values are total dry mass of aboveground plant material for each species harvested from a 20 x 30 cm quadrat placed at a random location within each experimental shrub patch. Different quadrat locations were sampled in 2010 and 2011.RemovalExperiment.csvDune SpeciesLife-history, nativity and family information for the plant species found in the study plots.DuneSpecies.csv