Grazing affects vegetation diversity and heterogeneity in California vernal pools

Abstract

Disturbance often increases local-scale (α) diversity by suppressing dominant competitors. However, widespread disturbances may also reduce biotic heterogeneity (β diversity) by making the identities and abundances of species more similar among patches. Landscape-scale (γ) diversity may also decline if disturbance-sensitive species are lost. California's vernal pool plant communities are species rich, in part because of two scales of β diversity: (1) within pools, as species composition changes with depth (referred to here as vertical β diversity), and (2) between pools, in response to dispersal limitation and variation in pool attributes (referred to here as horizontal β diversity). We asked how grazing by livestock, a common management practice, affects vernal pool plant diversity at multiple hierarchical spatial scales. In terms of abundance-weighted diversity, grazing increased α both within local pool habitat zones and at the whole-pool scale, as well as γ at the pasture scale without influencing horizontal or vertical β diversity. In terms of species richness, increases in α diversity within habitat zones and within whole pools led to small decreases in horizontal β diversity as species occupancy increased. This had a dampened effect on species richness at the γ (pasture) scale without any loss of disturbance-sensitive species. We conclude that grazing increases species richness and evenness (α) by reducing competitive dominance, without large disruptions to the critical spatial heterogeneity (β) that generates high landscape-level diversity (γ).

Vernal pool wetlands respond to livestock grazing, exclusion and reintroduction

“…Rancho Seco (38.34°N, −121.11°W) is a 458.10-ha site in Northern California that consists of Mediterranean grassland with vernal pools. Rancho Seco hosts Northern Hardpan vernal pools which span a range of characteristics, including soil type (Redding Gravelly Loam and Corning Complex) and pool size (9.16-336.94 m 2 ), which influence plant composition at this site (Michaels et al, 2021), and across vernal pools, in general (Kneitel, 2015). The climate is Mediterranean with an average annual precipitation of 526.2 mm per water year (CIMIS Weather Station, 21-year avg.…”

“…We focused our sampling efforts in the transition zone ecotones within the pools where the pool bottom meets the non-inundated uplands surrounding the pool (Marty, 2015;Michaels et al, 2021;Robins & Vollmar, 2002). The transition zones are small in area compared to the area of the uplands and pool bottoms, but are areas of conservation concern because of their high diversity and sensitivity to grazing (Marty, 2015;Michaels et al, 2021).…”

“…We focused our sampling efforts in the transition zone ecotones within the pools where the pool bottom meets the non-inundated uplands surrounding the pool (Marty, 2015;Michaels et al, 2021;Robins & Vollmar, 2002). The transition zones are small in area compared to the area of the uplands and pool bottoms, but are areas of conservation concern because of their high diversity and sensitivity to grazing (Marty, 2015;Michaels et al, 2021). We delineated these transition zones in early spring 2016, after the pools dried down and before plant taxa were identifiable, by recording water marks across the slope that indicated differences in flooding duration.…”

An Improved Method for Monitoring Multiscale Plant Species Diversity of Alpine Grassland Using UAV: A Case Study in the Source Region of the Yellow River, China

“…Plant species diversity (PSD) describes vegetation community structures and plays a critical role in ecosystem multifunction and conservation of grassland (Lu and He, 2017 ; Moorsel et al, 2018 ; Pires et al, 2018 ; Yamamura et al, 2021 ). Investigating the spatial and temporal variations of species diversity in natural real-world communities provides essential information for understanding ecosystem multifunction and evolutionary processes, and developing reasonable conservation and management strategies of grassland (Hodkinson, 2005 ; Genung et al, 2020 ; Michaels et al, 2021 ).…”

Effects of Plateau Pika Disturbance on the Spatial Heterogeneity of Vegetation in Alpine Meadows

“…Herbivores are considered as important biotic factors that influence the spatial heterogeneity of vegetation in grasslands ( Jones et al, 1997 ; Adler and Lauenroth, 2000 ; Davidson et al, 2012 ; Wei et al, 2019 ). Large herbivore grazing has been verified to increase the spatial heterogeneity of vegetation in grasslands ( Adler and Lauenroth, 2000 ; Adler et al, 2001 ; Song et al, 2020 ; Michaels et al, 2021 ). In addition to large herbivores, many kinds of small semi-fossorial herbivores inhabit grasslands ( Bagchi et al, 2006 ; Questad and Foster, 2007 ; Lindtner et al, 2020 ; Wei et al, 2020 ) and these small semi-fossorial herbivores often cause extensive disturbance to grassland vegetation and soil ( Hobbs and Huenneke, 1992 ; Liu et al, 2017 ; Smith et al, 2019 ).…”