DOI: 10.5061/dryad.rxwdbrvbq
title: Long-term livestock exclusion increases plant richness and reproductive capacity in arid woodlands

description: Aim Herbivore exclusion is implemented globally to recover ecosystems from
 grazing by introduced and native herbivores, but evidence for large-scale
 biodiversity benefits is inconsistent in arid ecosystems. We examined the
 effects of livestock exclusion on dryland plant richness and reproductive
 capacity. Location Central Australia. Methods We collected data on plant
 species richness and seeding (reproductive capacity), rainfall, vegetation
 productivity and cover, soil health, and herbivore grazing intensity from
 68 sites across 6500 km2 of arid Georgina gidgee (Acacia georginae)
 woodlands between 2017 and 2020. Sites were on an actively grazed cattle
 station and two destocked conservation reserves. We used structural
 equation modelling to examine indirect (via soil or vegetation
 modification) versus direct (herbivory) effects of grazing intensity by
 two introduced herbivores (cattle, camels) and a native herbivore (red
 kangaroo), on seasonal plant species richness and seeding. Results Soil
 health and rainfall were the strongest drivers of variation in richness
 and seeding. Cattle and camel grazing indirectly led to lower seasonal
 richness and seeding by reducing soil health. Kangaroos had a small but
 negative direct impact on richness, but no impact on soil health. Both
 introduced and native herbivores reduced annual chenopod shrub richness
 and seeding, whereas only cattle directly reduced perennial shrub richness
 and seeding. Camels indirectly reduced perennial shrub richness by
 impacting shrub abundance. Introduced herbivores reduced native grass
 richness and seeding indirectly via impacts on soil health, whereas forbs
 responded positively to cattle and camel activity. Main conclusion
 Considering indirect impacts improves evaluations of the effects of
 disturbances on biodiversity, as focusing only on direct effects can mask
 critical mechanisms of change. Our results indicate substantial
 biodiversity benefits from excluding livestock and controlling camels in
 drylands. Reducing introduced herbivore impacts will improve soil and
 vegetation condition, ensure reproduction and seasonal persistence of
 species, and protect native plant diversity.
description: Site background and selection Our study
 occurred across 6600 km<sup>2</sup> of the north-eastern
 Simpson Desert, central Australia, on three properties, Ethabuka Reserve
 (23°51’S, 138°28’E, 2330 km<sup>2</sup>, cattle removed 2004),
 Pilungah Reserve (23°8’S, 138°26’E, 2130 km<sup>2</sup>,
 cattle removed 2006, previously known as Cravens Peak) and Carlo Station
 (23°29’S, 138°32’E, 2110 km<sup>2</sup>, still grazed by
 cattle). The average annual precipitation of nearby long-term weather
 stations is 198 mm (Bedourie; 1933–2020) to 211 mm (Boulia; 1887-2020)
 (Bureau of Meteorology, 2021), but rainfall is highly variable and years
 with below-average rainfall are more frequent than years with above
 average rainfall (Dickman, Mahon, Masters, & Gibson, 1999). The
 area is on the eastern edge of the Simpson Desert, and is dominated by
 linear sand dunes 5–20 m high vegetated with spinifex
 (<em>Triodia</em> <em>basedowii</em> E.Pritz.)
 grassland and scattered shrubs. Georgina gidgee
 (<em>Acacia</em> <em>georginae</em> F.M.Bailey)
 woodlands occur patchily on clay swales between dunes as well as on
 calcareous and alluvial soils fringing the dunefields, with typical patch
 sizes ranging from 0.5 ha to 10 ha. We selected 17 gidgee woodland patches
 across the three properties. Patches were selected to represent a range of
 grazing intensities but located specifically to avoid areas immediately
 adjacent to watering points, which are often extremely heavily grazed.
 Each patch had four sites set up at 300-m intervals along a 1 km line,
 resulting in 16 sites on Carlo Station (in 4 patches; site selection was
 limited due to the density of artificial watering points in relation to
 accessible gidgee patches), 24 sites on Pilungah (in 6 patches) and 28
 sites on Ethabuka (in 7 patches). Each site comprised a 100-m-long
 transect. Sites were monitored during 4 trips: September 2018, May and
 September 2019, and September 2020. Appropriate permissions and licences
 to conduct the fieldwork were obtained from the Queensland Government
 (Permits WITK15192514 and WISP15192514). Grazing
 intensity To assess the recent relative abundance of
 large herbivorous mammals we conducted dung surveys every monitoring
 session. All dung was removed from transects after counting, ensuring that
 transects would be clear for the next visit.  Soil
 health At each site, we measured soil surface
 attributes and ground cover characteristics along a 100-m line transect,
 with the direction of each transect determined randomly. We took a
 measurement every 5 m along the transect, resulting in 20 measurements per
 transect. Plant foliage projected ground cover (vegetation &lt;0.5 m
 tall) and litter cover (including dropped seeds and dead vegetation) were
 estimated within 0.5 m x 0.5 m quadrats and recorded as a percentage of
 the quadrat area. At each quadrat, a pocket penetrometer (Handheld
 Penetrometers, QA Supplies, Norfolk, VA) was used to measure the strength
 of the soil surface. For each variable, we averaged all 20 measurements to
 derive an overall value per 100-m transect per trip per variable. An index
 of soil health was calculated as the arithmetic mean of the standardized
 (z-transformed) values of the three surface attributes (soil strength,
 plant foliage projected ground cover and litter cover) per site per
 trip. Woody cover At each site, we
 measured gidgee stand structure along a 100-m belt transect. For 68 of the
 transects, the belt width was 10 m (1000 m<sup>2</sup>). For
 the remaining 16 transects the belt was increased to 20 m (2000 m2) to
 enable at least ten trees to be measured (these transects were more
 sparsely vegetated and distributed across all three properties). For every
 tree on the transect, we measured tree canopy diameter at 1.5 m from the
 ground and canopy density (% cover, visual estimation). We converted
 canopy diameter to area, representing total canopy cover per tree, and
 multiplied this by its canopy density to create a derived relative cover
 value. Relative cover was summed for all trees in the transect to derive a
 final cumulative canopy cover variable per site. We also quantified the
 relative abundance of perennial shrubs per 1000 m<sup>2</sup>
 at each site, by counting all perennial shrubs along the same 10 m by 100
 m belt as the tree structure monitoring. Plant
 richness and reproductive capacity To quantify plant
 richness, we identified every plant species along the 100-m x 10-m belt
 transect each trip. To quantify changes in plant condition over time, we
 estimated fruiting activity each trip for all plants along the 100-m belt
 transect using a scoring system. An index of reproductive output for each
 plant species per plot was recorded at each transect. All plant species
 that were fruiting or seeding were scored on a rank scale for the presence
 of fruits/seeds, from 0 (fruit/seed absent) to 5 (fruit/seed profuse, all
 individuals seeding). Each plant species received a relative abundance
 score (1–5, where 1 is very low abundance/a few individuals present and 5
 is relatively high abundance). Diaspores that would be dispersed were
 recorded as ‘seeds’ and included fruits (e.g. pods on peas rather than the
 seeds within each fruit) and single seeds. We calculated a reproductive
 capacity score for each species by multiplying its fruiting or seeding
 score by its relative abundance score and summed individual species scores
 to derive a single fruiting score per transect. For example, if on
 Transect A, species X was given a seeding index of 4 with a presence of 3,
 then its relative seeding activity would be 12. If on the same transect,
 two other species were recorded, Y and Z, with relative abundance scores
 of 10 and 8 respectively, then the seeding activity for transect A would
 be 30 (12+10+8). The cumulative summed seeding activity scores for each
 site per trip were then used in statistical analyses.
 Rainfall and Productivity Rainfall was the
 cumulative rainfall for the previous 12 months before the survey at the
 closest weather station (there are 12 weather stations across the three
 properties). Productivity was estimated using the mean greenness for the
 site over the previous 180 days, derived from the green fraction of a
 timeseries of single date fractional cover data (Joint Remote Sensing
 Research Program, 2021). We also calculated a long-term rainfall variable
 (average of the annual cumulative rainfall over the past 20
 years). 
description: # Long-term livestock exclusion increases plant richness and reproductive
 capacity in arid woodlands 
 The attached Excel spreadsheet contains all data used in the study
 "Long-term livestock exclusion increases plant richness and
 reproductive capacity in arid woodlands". Please contact
 ayesha.tulloch@qut.edu.au for queries. Tab 1: Descriptions of each
 variable measured and used in Structural Equation Models in this study.
 Tab 2: Data inputs for models.