DOI: 10.7291/d10x19
title: Native annual forb and vegetation data for ten paired grazed and ungrazed prairies in coastal California grasslands at two time periods 15 years apart

description: Livestock grazing is often used as a land management tool to maximize
 vegetation diversity in grassland ecosystems worldwide. Prior research has
 shown that cattle grazing benefits native annual forb species in
 California’s coastal prairies, but drought and increasing aridity may
 alter this relationship. In 2016 and 2017, we resurveyed the vegetation
 structure, native annual forb cover, and native annual forb richness in
 ten grazed and ungrazed prairies that were originally measured in 2000 and
 2001 along a 200-km gradient from Monterey to Sonoma counties in
 California. We found that grazed prairies continued to have significantly
 lower vegetation height and thatch depth than ungrazed prairies, and that
 shrub encroachment over the 15-year period was significantly greater in
 ungrazed prairies. Furthermore, grazed prairies continued to have greater
 native annual forb richness (4.9 species per site) than ungrazed sites
 (3.0 species per site), but that native annual forb richness declined by
 2.8 species per site in grazed prairies and 0.1 species per site in
 ungrazed prairies between survey periods. We suggest that severe drought
 and increasing aridity may be driving declines in native annual forb
 richness in grazed prairies. The species we recorded only in earlier
 surveys were disproportionately wetland-associated and had higher average
 specific leaf area than species that remained through the second survey
 period. Finally, cover of native annual species increased regardless of
 whether prairies were grazed, suggesting that the high precipitation in
 2017 may have benefitted the native annual forb species that persisted at
 sites between surveys. Our study shows that weather conditions affect the
 outcomes of land management strategies.
description: In 2000–2001, we surveyed 26 paired grazed
 and ungrazed coastal prairie sites across 400 km of coastline between San
 Luis Obispo and Mendocino counties in California, USA. In 2016–2017, we
 resampled ten sites along 200 km in the central area of the prior survey
 extent (Monterey to Sonoma Counties) where we could obtain permission from
 landowners for access and grazing patterns had been maintained since
 2000-2001. At all sites, paired
 plots were less than 2 km apart, on similar slopes and aspects, and
 transects were placed at least 5 m from fence lines to avoid edge effects.
 Cattle were the only domestic grazing animals present at the sites, there
 was no evidence of prior mechanical soil disturbance, and soils were
 deeper than 40 cm and not ultramafic (serpentine). We sampled from April
 through May, traveling from southern sites to northern sites to follow the
 peak flowering phenology of most species. At each site, we relocated T1
 50-m line transects using a Garmin eTrex 20 GPS. There were five transects
 each in the grazed and ungrazed portions at each site.  We quantified community composition by recording
 the identity of each species that intersected a 1.8-mm-diameter pin at 1-m
 intervals along the transects. We recorded each species that intercepted
 the pin once. Our nomenclature and species origin information follow the
 Jepson Manual and online Jepson eFlora database. At 5-m intervals, we
 measured vegetation height using a piece of paper dropped onto foliage and
 recording the lowest point, and thatch depth (i.e., build-up of dead plant
 biomass) by pushing a 1.8-mm pin to the soil surface and measuring the
 tallest standing dead biomass. We calculated shrub cover as the number of
 woody shrubs intercepts along each transect as a percent of the 50
 intercepts total along the transect. Finally, we carefully searched for
 and quantified the cover of all native annual forbs (to the nearest
 cm<sup>2</sup>) present within a 1-m belt transect centered
 over the 50-m transect. We compiled specific leaf area (SLA, leaf area/leaf dry mass) for 40 of the 55 native annual forbs species from the TRY Plant Trait Database and data collected by others. We also collected data from species present in and near our sites during spring and summer 2018. Most of these data came from grazed plots, since this is where the species were more prevalent, though we selected individuals that showed no evidence of recent grazing. When data for a single species was available from multiple sources, we averaged the values, which are available here. We also gathered the US Army Corps of Engineer wetland indicator status of the native annual forbs.
description: All data are shared as .csv files.