DOI: 10.5061/dryad.hhmgqnkvr
title: Dry-season grazing with small ruminants enhances native diversity in invaded oak woodlands

description: Oak woodlands are biodiversity hotspots that provide critical ecosystem
 services and hold significant cultural value. However, these ecosystems
 are increasingly threatened by invasive grasses, which suppress native
 plant diversity, elevate fire risk, and disrupt ecosystem processes. While
 targeted grazing is gaining popularity as a management technique for
 controlling invasives, the ecological impacts of dry-season grazing are
 understudied, as are outcomes for native species. We evaluated the
 effectiveness of targeted summer grazing with small ruminants for reducing
 invasive grass fuel loads and enhancing plant diversity in oak woodlands
 of California by comparing plant species richness and abundance in paired
 grazed and ungrazed plots over multiple years. Grazing substantially
 increased richness and cover of native forbs. Nonnative cover was
 unaffected, though minor increases in nonnative forb numbers were
 observed. Ordination analysis revealed that grazing shifted plant
 community composition, largely driven by increases in native forb species
 and to a lesser extent nonnative forbs. Indicator species analysis
 revealed similar patterns, with increases in multiple forb species
 detected with grazing, highlighting the potential for grazing to support a
 diversity of plant species. These benefits likely stem from reduced thatch
 accumulation, improved light availability, and the creation of favorable
 microsites for seedling establishment. Practical application: Dry-season
 grazing with goats and sheep presents a multi-benefit strategy for land
 stewardship, helping to reduce invasive grass thatch, enhance native plant
 diversity, and lower fire risk in invaded woodlands. While grazing alone
 is unlikely to effectively suppress invasive grasses and may encourage
 certain nonnative forbs, it can dramatically improve the ability of native
 species to coexist with nonnatives. To maximize benefits, practitioners
 should integrate grazing with complementary management strategies when
 controlling nonnative plants is a priority. Careful management of grazing
 intensity, timing, and duration, coupled with long-term monitoring, will
 aid in balancing these ecological trade-offs. Incorporating targeted
 dry-season grazing into a broader restoration framework could aid in the
 conservation of biodiversity in grass-invaded dryland ecosystems
 worldwide.
description: # Dry-season grazing with small ruminants enhances native diversity in
 invaded oak woodlands Dataset DOI:
 [10.5061/dryad.hhmgqnkvr](https://doi.org/10.5061/dryad.hhmgqnkvr) ##
 Description of the data and file structure Vegetation monitoring was
 conducted at the Wantrup Preserve in Napa County, California—a 730-acre
 mosaic of blue oak (*Quercus douglasii*) woodlands and interspersed annual
 grasslands managed by the Land Trust of Napa County. The experiment was
 designed to assess the long-term effects of targeted grazing on native and
 nonnative plant communities within this invaded oak woodland ecosystem.
 Paired 1 m² plots (one grazed, one ungrazed) were established across the
 preserve, initially on an interior grid and later along accessible
 perimeter transects. Ungrazed plots were enclosed with fencing, while
 grazed plots remained open to livestock. Goats were used for grazing from
 2016 to 2019 and sheep from 2020 to 2022, with treatments applied each
 summer to remove accumulated dry biomass. Vegetation surveys were
 conducted annually each spring from 2019 to 2022 to quantify plant species
 richness and cover following the previous year’s grazing treatment.
 Percent cover and species identity were recorded for all vascular plants,
 with supplemental sampling later in the season to capture late-flowering
 forbs and geophytes. In total, data were collected from 176
 grazed–ungrazed plot pairs (352 total plots). The resulting dataset
 provides a robust, multi-year record of plant community composition and
 structure under different grazing regimes within a Mediterranean-type oak
 woodland system. ### Files and variables #### File: veg_data.csv
 **Description:** .csv file containing raw data on species abundance (i.e.,
 percent cover), as well as abundance and richness by functional group
 (e.g., native or nonnative, forb or grass) **Plot definitions**:
 definitions of plot properties (Columns A-G), including plot identifiers,
 plot type, year of sampling, type of ruminant used for grazing, and the
 grazing interval/history of the plot. | **Column name** | **Explanation**
 | | :-------------- |
 :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | index\_g | Unique identifier for each plot and sampling time | | plot\_type | Plot type (P = plots installed at the permimeter of fencing between grazed and ungrazed areas; W = original plots installed within the interior of the Wantrup Preserve's grazed area) | | plot\_name | Unique plot identifier | | year | Year of vegetation sampling | | treatment | Plot treatment (grazed or ungrazed) | | grazer | Ruminat type used for grazing (sheep or goats) | | interval | Grazing interval (i.e, newly added plots, plots grazed one year prior, or plots grazing two years prior) | **Vegetation definitions**: definitions of vegetation metrics analyzed (Columns H-S), including the abbreviation used, the type of metric (plant functional group abundance or richness), nativity of the native functional group (native or nonnative), and type of plant functional group (all species, forbs, or grasses) | **abbreviation** | **metric** | **nativity** | **functional group** | | :--------------- | :--------- | :----------- | :------------------- | | a\_nat\_all | abundance | native | all | | a\_nat\_frb | abundance | native | forb | | a\_nat\_grs | abundance | native | grass | | a\_non\_all | abundance | non-native | all | | a\_non\_frb | abundance | non-native | forb | | a\_non\_grs | abundance | non-native | grass | | r\_nat\_all | richness | native | all | | r\_nat\_frb | richness | native | forb | | r\_nat\_grs | richness | native | grass | | r\_non\_all | richness | non-native | all | | r\_non\_frb | richness | non-native | forb | | r\_non\_grs | richness | non-native | grass | 
 
 ### File: species_data.csv **Description:** .csv file containing raw data
 on species codes used in veg_data.csv file, scientific names, and
 information on origin (native or nonnative) and functional group (grass or
 forb). **species_data**: definitions of all plant species' codes
 (gen_spec), the full genus and species (genus*species), and whether the
 species is native or not (is_native; TRUE or FALSE), a forb (is_forb; TRUE
 or FALSE), or a grass (is_grass: TRUE or FALSE) ## Code/software All
 analyses were conducted using **R version 4.4.1** (R Core Team 2024), an
 open-source statistical computing environment freely available at
 [https://www.r-project.org](https://www.r-project.org). The analyses can
 be fully reproduced using R and the following packages: * **lme4** and
 **glmmTMB** — for fitting generalized linear mixed models (GLMMs) with
 normal and negative binomial error structures. * **MuMIn** — for
 information-theoretic model selection using Akaike’s Information Criterion
 (AICc). * **DHARMa** and **performance** — for diagnostic checks of
 residuals, overdispersion, and model singularity. * **car**, **vcd**,
 **pscl**, and **fitdistrplus** — for exploratory data analysis,
 distribution testing, and model assumption validation. * **vegan** — for
 community ecology analyses, including non-metric multidimensional scaling
 (NMDS), environmental vector fitting, and permutational multivariate
 analysis of variance (PERMANOVA). * **indicspecies** — for indicator
 species analysis using abundance-based association tests. Data
 visualization, summary statistics, and model diagnostics were performed
 within RStudio (Posit, version 2024.04) using base plotting functions and
 **ggplot2**. ## Access information This is original data collected by the
 authors.