Trajectories of floristic change in grassland: landscape, land use legacy and seasonal conditions overshadow restoration actions

Abstract

Questions How does ground‐layer plant composition respond to the imposition of woodland habitat restoration treatments following the removal of long‐term pastoral management? Do different vegetation types have different trajectories of change? Location A long‐term ecological research site comprising temperate eucalypt grassy woodland and forest in south‐eastern Australia, converted from pastoral use to conservation management. This has involved the implementation of habitat restoration treatments in addition to the cessation of livestock grazing and fertilizer inputs. Methods We surveyed ground‐layer floristic composition over a 4‐yr interval, in 96 1‐ha sites that had been subjected to combinations of restoration treatments aimed at improving the condition of the woodland habitat for fauna: (1) Reduced kangaroo grazing intensity; (2) Addition of coarse woody debris; and (3) Burning. We used nonmetric multidimensional scaling (NMDS) to plot the sites, and to analyse the average trajectories of floristic change for each of six initially identified vegetation types, and the restoration treatments. We partitioned Bray–Curtis dissimilarity measures to rank individual species’ contributions to floristic change in each vegetation type between 2007 and 2011. Results The identities of the six vegetation types identified at time zero was strongly retained over the 4‐yr observation period. There was generally a uniform change across the vegetation types, which was the result of increases in biomass of the characteristic dominant perennial grasses, and increases in some native forbs. The two vegetation types with evidence of past fertilization showed some convergence with native vegetation types due to the decrease in some exotic species. The restoration treatments had no significant influence on species composition. Conclusions The native herbaceous vegetation in the woodland was largely resistant to compositional change, although seasonal conditions increased the biomass of the perennial grasses defining the different vegetation types. However, sites with an evident history of past fertilization and notable amounts of exotic pasture species changed slightly but significantly, with some pasture species declining and floristic convergence with native vegetation over 4 yr. These rates of change need to be considered in the application of vegetation offsetting policy.

Transient shifts in composition of degraded temperate native grassland following grazing exclusion

“…The finding that exclusion of grazing did not produce changes in lowland grassland composition finds much support in the literature on grazing exclusion in southeastern Australian temperate grasslands; Zimmer et al (2010), Lewis et al (2008), Foreman (1996), Schultz et al (2014), McIntyre et al (2017) and Souter and Milne (2009) all found that species richness did not change significantly with grazing exclusion. By contrast, studies in more productive grasslands have shown that grazing exclusion will quickly (2–5 years) disadvantage inter‐tussock flora (e.g.…”

Herbivore management for biodiversity conservation: A case study of kangaroos in the Australian Capital Territory (ACT)

“…Efforts in Canberra Nature Park to reverse the effects of historic heavy livestock grazing, and ongoing kangaroo grazing, show only modest recovery of grazing‐sensitive species, and document a perennial flora that is resistant to change, even after four years of favourable rainfall and reduced grazing pressure (McIntyre et al. 2010, 2017). It should be noted that localised species losses would likely be permanent within the fragmented grassy ecosystems of Canberra Nature Park; therefore, a consistent landscape scale approach to the management of kangaroo populations is essential for the conservation of endangered ecological communities in this context.…”

Long‐term and year‐to‐year stability and its drivers in a Mediterranean grassland

“…Such long‐term directional trends can be due to land‐use changes, climate change or to succession after disturbance, among other processes, and are particularly frequent in grasslands (Lepš, Götzenberger, et al, 2019; Stevens et al, 2011; Valencia, de Bello, Lepš, et al, 2020). Land‐use changes such as fertilization can lead to the presence of relatively long‐term trends due to the legacy effects over time of past fertilization treatments and can modulate the impact of climate change (McIntyre et al, 2017). Long‐term trends present a methodological and conceptual issue when studying synchrony and community stability (Lepš, Götzenberger, et al, 2019; Valencia, de Bello, Lepš, et al, 2020).…”