Long‐term changes in the vegetation after the cessation of livestock grazing in Eucalyptus marginata (jarrah) woodland remnants

Abstract

This paper documents changes in the floristic composition of Eucalyptus marginata Donn (jarrah) woodlands over 7 years of recovery from continual, intensive livestock grazing. In remnants of native woodland left after agricultural clearing, which have been subjected to livestock grazing, comparisons were made between the floristics of fenced exclosure plots and open plots that continued to be grazed. The vegetation in nearby remnants, which had not been subjected to livestock grazing, was also surveyed. An initial increase in annual exotic pasture species after grazing relief was only temporary and highly influenced by fluctuations in annual climatic patterns, particularly rainfall distribution and abundance. Subsequent years saw a decrease in exotic annuals in exclosure plots and an increase in native perennials, in a trend towards becoming more floristically similar to the ungrazed sites. Germination of overstorey species was observed in the exclosure plots, however, development of seedlings and saplings was sparse. Results indicate that for jarrah woodland in southwestern Australia, natural regeneration is possible after the removal of livestock, with the return (within 6 years) of native species richness to levels similar to those found in ungrazed vegetation. Re-establishment of cover, however, appears to take longer. The floristic dynamics are described in terms of a nonequilibrium model. Two vegetation states exist, degraded remnants with an understorey dominated by annual species, and ungrazed vegetation with an understorey dominated by perennial shrubs and herbs. The former state is maintained by continual heavy grazing by livestock. Upon relief from grazing, the vegetation undergoes a transition towards floristic similarity to ungrazed vegetation. After 6 years, vegetation change in the exclosure plots appears to be continuing and therefore it is still in transition.

Rainfall variability may modify the effects of long-term exclosure on vegetation in Mandalgobi, Mongolia

“…1; Table 2) differ from the results of previous studies (e.g., Pettit and Froend, 2001;Valone et al, 2002;Guo, 2004;Firincioglu et al, 2007). The latter studies reported that grazing exclusion increased the cover of perennial grasses or forbs that are generally palatable and decreased the cover of unpalatable forbs and annual weeds.…”

“…Previous studies have reported that grazing exclusion increased the cover of perennial grasses and forbs, which are generally palatable (Pettit and Froend, 2001;Valone et al, 2002;Guo, 2004;Firincioglu et al, 2007;Sasaki et al, 2007), increased species richness (Guo, 2004;Firincioglu et al, 2007), and increased the soil organic matter content (Eldridge and Robson, 1997;Shirato et al, 2005;Su et al, 2005). These results generally agree with the concepts of ecological succession, in which vegetation communities replace one another in a predictable and directional manner following disturbance, culminating in a stable climax state (Dyksterhuis, 1949).…”

Using historical ecology to understand patterns of biodiversity in fragmented agricultural landscapes

“…Moore, 1973; Adamson & Fox, 1982; Wilson, 1990; Sivertsen, 1993; Pettit et al. , 1995; Pettit & Froend, 2001). Grazing trials have demonstrated that recovery after grazing exclusion is not assured: some sites remain in a degraded steady state, some have improved in composition and structure, whilst some have become further degraded.…”

“…In many remnant ecosystems, certain ecological thresholds have been passed which may be irreversible without further human intervention (Yates et al. , 2000; Pettit & Froend, 2001; Allcock, 2002; Spooner et al. , 2002).…”

Resource heterogeneity and persistence of exotic annuals in long-ungrazed Mediterranean-climate woodlands

“…Some studies have demonstrated a decline in exotic annuals after initial disturbances have ceased (McLendon and Redente 1991;Pettit and Froend 2001;Spooner and Briggs 2008;Prober et al 2011). In other cases exotic annuals persist (Prober et al 2005;Standish et al 2006Standish et al , 2007aSmallbone et al 2007;Briggs et al 2008), suggesting they are superior competitors compared with native species (especially in the absence of their natural enemies Keane and Crawley 2002), or that underlying ecological processes have changed (Keane and Crawley 2002;Seabloom et al 2003;Blank and Sforza 2007).…”