Legacy effects of livestock grazing on vegetation of an arid landscape exist more than 30 years after livestock were excluded

Introduction: Globally, livestock grazing is key driver of vegetation
degradation in arid rangelands. This degradation tends to be most severe
near artificial water points which are focal points for livestock
activity. Conservation reserves have been established on former
rangelands, however, the timeframes for vegetation recovery following the
cessation of livestock grazing are poorly understood. 
Objectives: To assess changes in rangeland vegetation structure and
composition following long term herbivore exclusion to inform
understanding of the timeframes required for rangeland vegetation
recovery.  Methods: We quantified recovery of vegetation
following the removal of livestock in an Australian arid rangeland by
comparing vegetation structure and composition inside and outside of
herbivore exclosures that had been established for 36 years and were
situated along gradients of distance from water.  Results: Inside
of long-term exclosures, vegetation cover was higher and taller and forb
density was higher than in unfenced control plots. Inside exclosures,
annual species richness was higher but did not respond to distance from
water. Perennial species richness did not respond to herbivore exclusion
but increased with distance from water both inside and outside of
exclosures.   Conclusions: After 36 years of livestock
exclusion, vegetation recovery occurred structurally but floristically,
recovery was mainly represented by short-lived annual species. That the
richness of perennial species inside of herbivore exclusion increased with
increasing distance from water suggests that the composition of perennial
plant species was a legacy of the effects that water-focused livestock
grazing had on vegetation when the plots were established 36 years
previously. Implications for practice: Following livestock removal,
timeframes for vegetation recovery may vary depending on the indicator
used. Changes in ground layer structure, community composition and
abundance of annuals may be observed within a decade, however, recovery of
slow growing perennials may occur over multiple decades. A key implication
of this study is that the progress of full passive recovery in arid plant
communities following livestock removal should, at the minimum, be
expressed in the order of decades. Active recovery approaches such as
direct seeding or out-planting may be required to enhance the rate of
recovery of perennial plants following the livestock removal.