DOI: 10.5061/dryad.7wm37pvtp
title: Field survey quadrat data - Exotic perennial grass invasion profiles differ between temperate threatened grassy communities

description: Aim: Exotic perennial grasses are significant invaders of native grassy
 communities and frequently multiple species invade communities, some from
 nearby agricultural areas.  There is little understanding of the
 landscape distribution of many species, making prioritisation for control
 a difficult decision. Location: New South Wales, Eastern Australia
 Methods: We undertook field surveys of exotic perennial grasses at 139
 sites from nine grassy threatened ecological communities across four
 regions and assessed whether the profiles of exotic species varied amongst
 regions and communities.  We used a ranking of invasion risk
 based on plant characteristics to identify exotic perennial grasses that
 were likely to be the most invasive and then tested whether this ranking
 predicted the level of invasion measured in the survey. Results: Using
 multivariate analysis we found that the threatened grassy communities
 surveyed were significantly invaded by exotic perennial grasses and that
 these assemblages were regionally distinct and distinct for most plant
 communities. Five widespread invaders were particularly established in all
 regions and communities, but regions also had distinct sets of invaders
 contributing significantly to degradation. Invasion by trade-off species
 was the most significant threat to grassy communities in all
 regions.  We showed that species with higher risk rankings based
 on plant characteristics were recorded in more sites but there were a few
 grasses that were more invasive than their ranking predicted. Main
 conclusions: Our findings indicate that management of grassy plant
 communities for exotic perennial grasses should be undertaken at the
 community level although there are a suite of species that are important
 invaders in the whole landscape where improved understanding of pathways
 of invasion are needed for management across regions.  We
 identified a set of species which are important invaders but are not a
 focus in management currently, largely because many of these are species
 used in pastures.  Our study illustrates that higher levels of
 invasion were associated with species that were ranked more invasive on
 plant characteristics and this ranking could be used to initially allocate
 priorities for management of threatened plant communities. Trade-off
 species remain the major cause of degradation and must be included in
 discussions of regional conservation.
description: Nine ecological communities with prominent grassy understories
 were surveyed across the four climatic regions (Table 1, Fig. 1). Two
 threatened ecological communities, Themeda Grasslands on Seacliffs, and
 White Box Yellow Box Grassy Woodlands occurred across two regions, and we
 split the surveys for each of these communities into each region (Table 1,
 Fig. 1). All other communities occurred in a single region. These
 communities are of conservation significance as they are listed as
 threatened under state or federal legislation (<em>Environment
 Protection and Biodiversity Conservation Act</em>, 1999;
 <em>Biodiversity Conservation Act No 63</em>, 2016). As each
 ecological community varies in size and geographic range the number of
 surveys per community differed to ensure each was adequately represented
 (Table 1). The sites chosen were a mix of reserve land, travelling stock
 reserves, cemeteries, significant roadside vegetation, other uncleared
 crown land (owned and managed by state government) and agricultural land.
 We used government data, government officials who look after these
 communities, and other organisations (<em>Friends of
 Grasslands</em>, 2021; <em>Grassy Ecosystems Conservation
 Management Networks</em>, 2010) to find sites. Survey data from
 external projects in the north coast (J Hunter, personal communication, 9
 sites) and south coast (J Miles, personal communication, 3 sites) within
 <em>Themeda grassland</em> sites were included in our
 analysis. In total, data was collected for 139 sites across the nine
 communities. The number of sites for each community varied due to
 availability and access to these communities and their rarity.
 Surveys were completed over 2018-2020 during drought which may
 have decreased grass cover in habitats, particularly away from the coast.
 Thus, measurements of percentage cover of grasses were deemed inaccurate
 and were replaced by measurements of occupancy. To ensure coverage of the
 site we measured the occupancy of EPGs in plots placed along multiple
 transects through the site. The number of transects at a site increased as
 site size increased until a threshold size was reached (20 ha) with number
 of plots varying from 3 – 90 (average 22) according to site size (See
 Appendix S2 in Supporting Information). Linear transects varied between
 50-800 m long depending on site size and shape. In each plot the presence
 of every grass species, native or non-native, was recorded in a10m x 2m
 area. The number of plots where a species was present divided by the total
 number of plots surveyed at a site was calculated as the proportion of
 occurrence. Shared survey data at both locations gathered species cover
 (%) in plots within a site, allowing equivalent proportion of occurrence
 to be calculated (Miles J, personal communication, Hunter J, personal
 communication). Survey data was taken from the most recent year i.e.,
 2017/18 for north coast sites, and 2016 in the south coast
 sites.