Ian D. Lunt

A framework to predict the effects of livestock grazing and grazing exclusion on conservation values in natural ecosystems in Australia

Grazing by domestic livestock has greatly degraded many Australian ecosystems and its legacy will be long-lasting in many areas. Although livestock are usually removed from conservation reserves because they are perceived to be incompatible with the conservation of natural ecosystems, they have been retained in several reserves in south-eastern Australia as a management tool to achieve conservation outcomes. These cases highlight the fact that no framework currently exists to address the question, under what circumstances (and in what ecosystems) is livestock grazing—or the removal of grazing—likely to have positive, negative, neutral or uncertain impacts on the diversity and composition of native plants? This paper provides a conceptual framework to predict the effects of livestock grazing and grazing exclusion on the conservation values of native vegetation across natural ecosystems in Australia. It should prove equally relevant to other ecosystems around the world which have evolved without heavy grazing by large herbivores. The framework is based on disturbance- and grazing-ecology literature from Australia and elsewhere, and incorporates the following six main factors: (1) impacts of livestock grazing on soil and ecosystem processes, (2) historical exposure to grazing, (3) site productivity, (4) relative palatability of dominant species, (5) species-specific factors influencing plant recruitment and (6) spatial scale and landscape context. These factors are integrated into a decision tree to describe the potential impacts of livestock on native vegetation in a particular area. Livestock grazing is likely to have detrimental impacts on conservation values in many ecological contexts, especially in relatively intact, uninvaded ecosystems on unproductive soils. By contrast, it may be a useful management tool to achieve conservation objectives where it either (1) controls the biomass of existing potentially dominant, grazing-sensitive plants (native or exotic), (2) prevents encroachment by undesirable, grazing-sensitive, potential dominants, (3) provides disturbance niches required by rare or significant plant species, (4) maintains fauna habitat structure or (5) enhances the diversity of species and vegetation structures across the landscape, especially when most of the landscape is ungrazed. In many cases, other disturbance regimes (especially burning) may achieve similar outcomes; however, other disturbances will not necessarily be more effective than grazing per se, especially in degraded or invaded areas. The framework provides a coarse-level filter to inform management decisions and to allow the findings from individual studies to be placed in a larger ecological context. Although the framework is intended to improve decisions about conservation management, it is clear that much more research is needed to assess the role of grazing exclusion in previously grazed ecosystems, and that modifications to current grazing regimes require testing, perhaps by using adaptive management principles, to ensure optimal outcomes for biodiversity conservation.

Identifying ecological barriers to restoration in temperate grassy woodlands: soil changes associated with different degradation states

Temperate grassy woodlands were once the dominant vegetation across many agricultural regions of south-eastern Australia, but most of these are now highly degraded and fragmented. Adequate conservation of these woodlands is dependent on successful ecological restoration; however, ecological barriers often limit ecosystem recovery once degrading processes are removed. To help identify these barriers, we used a state and transition framework to compare topsoils of little-disturbed (reference) and variously degraded remnants of grassy Eucalyptus albens Benth. and E. melliodora Cunn. ex Schauer woodlands. Topsoils of degraded remnants showed a repeated pattern, with the most compacted, most acidic and most depleted topsoils occurring in remnants dominated by Aristida ramosa R.Br. or Austrodanthonia H.P.Linder and Austrostipa scabra (Lindl.) S.W.L.Jacobs & J.Everett; the least compacted and most nutrient rich topsoils in remnants dominated by annual exotics; and generally intermediate topsoils in remnants dominated by Bothriochloa macra (Steud.) S.T.Blake or Austrostipa bigeniculata (Hughes) S.W.L.Jacobs & J.Everett. Surprisingly, topsoils beneath trees in reference sites (supporting Poa sieberiana Spreng.) were similar to topsoils supporting annual exotics for most soil properties. Chemical properties of topsoils from open areas of reference sites [supporting Themeda australis (R.Br.) Stapf] were usually intermediate and similar to Bothriochloa macra and Austrostipa bigeniculata topsoils. The most striking exception to these trends was for soil nitrate, which was extremely low in all reference topsoils and showed a high correlation with annual exotic abundance. We discuss the potential for positive feedbacks between soil nitrogen cycling and understorey composition and the need for intervention to assist possible nitrate-dependent transitions between annual and perennial understorey states. Dominant grasses, trees and annual weed abundance may be useful indicators of soil conditions and could inform selection of target sites, species and techniques for restoration projects.

Effects of time-since-fire on the tussock dynamics of a dominant grass (Themeda triandra) in a temperate Australian grassland

Changes in tussock attributes and sward structure with time-since-fire were documented for the dominant tussock grass, Themeda triandra, at the Derrimut Grassland Reserve in southern Victoria, Australia. When the inter-fire interval exceeded 6 yr, the number of tillers per tussock and the total number of tussocks declined, and by 11 yr, few live tillers or tussocks remained in the sward. Below-ground biomass was also substantially lower at this time. With increasing time-since-fire, the canopy of live leaves was elevated high above the soil surface and dead leaves accumulated around and over the tussock bases. Productivity declined in long unburnt areas and by 11 yr without disturbance, the canopy “collapsed” upon itself, forming a thick layer of dead thatch over the soil surface. A single fire in an area previously unburnt for 12 yr did not immediately return the tussocks to a state more characteristic of a site with a 4 yr inter-fire interval burnt at the same time. Inter-fire intervals of ⩽5 yr would appear necessary to maintain the health and competitiveness of Themeda triandra. These findings have important implications for the maintenance of faunal habitat and the potential for weed invasion into remnant grasslands.

Determining reference conditions for management and restoration of temperate grassy woodlands: relationships among trees, topsoils and understorey flora in little-grazed remnants

Temperate grassy woodlands were once widespread and dominant in many agricultural regions of south-eastern Australia. Most are now highly degraded and fragmented and exist within a context of broadscale landscape degradation. Greater understanding of natural processes in these woodlands is needed to benchmark management and restoration efforts that are now critical for their ongoing survival. We studied physical and chemical properties of topsoils from rare, little-grazed remnants of grassy Eucalyptus albens Benth. and E. melliodora Cunn. ex Schauer woodlands in central New South Wales and examined natural patterns in topsoil properties and understorey flora in relation to trees and canopy gaps. Topsoils were generally low in available macronutrients (nitrogen, phosphorus and sulfur), but were favourable for plant growth in most other measured characteristics. Topsoils beneath trees were notably more fertile than in open areas, particularly in total carbon, total nitrogen, available phosphorus, available potassium and salinity. Higher nutrient concentrations, particularly of available phosphorus, may have contributed to patterns in understorey dominants, with Themeda australis (R.Br.) Stapf predominating in open areas and Poa sieberiana Spreng. beneath trees. Trees were also associated with a higher native-plant richness, possibly resulting from their influence on the competitive dynamics of the dominant grasses. We discuss the implications of these interactions for the use of burning, grazing and slashing in woodland management and re-establishment of native grasses and trees in restoration efforts.

Effects of invasion by the indigenous shrub Acacia sophorae on plant composition of coastal grasslands in south-eastern Australia

Invasion of natural ecosystems by weeds is often associated with increasing levels of disturbance. However, there is substantial evidence that cessation of disturbance can also lead to plant invasions, especially of woody species. In some coastal grasslands in south-eastern Australia, removal of grazing and burning appears to have triggered invasion by the indigenous shrub, Acacia sophorae. To quantify the impacts of such invasions on plant diversity, this study focussed on the coastal grasslands in Eurobodalla National Park, NSW. Analysis of aerial photographs indicated that 96 ha of the 479 ha study area (20%) was invaded by Acacia between 1944 and 1994, with the most rapid expansion from the late 1970s when grazing was removed. Vegetation sampling demonstrated a strong negative correlation between Acacia cover and plant species richness. A linear regression between the species richness of each quadrat and the number of growth rings on the largest Acacia branch showed an average loss of 7.5 species (38% of species) after 10 years of Acacia invasion and 15 species (76%) after 20 years. Long-term invasion favoured just a small group of shade tolerant, rhizomic grasses and sedges. Without active ecosystem management, grassland plant diversity should continue to decline and the nationally threatened herb, Thesium australe, is likely to disappear. An adaptive management program should be implemented promptly to assess the effects of different management regimes on Acacia abundance and plant diversity at ENP.

Integrating plant- and animal- based perspectives for more effective restoration of biodiversity

Ecological restoration of modified and degraded landscapes is an important challenge for the 21st century, with potential for major gains in the recovery of biodiversity. However, there is a general lack of agreement between plant- and animal-based approaches to restoration, both in theory and practice. Here, we review these approaches, identify limitations from failing to effectively integrate their different perspectives, and suggest ways to improve outcomes for biodiversity recovery in agricultural landscapes. We highlight the need to strengthen collaboration between plant and animal ecologists, to overcome disciplinary and cultural differences, and to achieve a more unified approach to restoration ecology. Explicit consideration of key ecosystem functions, the need to plan at multiple spatial and temporal scales, and the importance of plant–animal interactions can provide a bridge between plant- and animal-based methods. A systematic approach to restoration planning is critical to achieving effective biodiversity outcomes while meeting long-term social and economic needs.

Restoration treatments enhance early establishment of native forbs in a degraded temperate grassy woodland.

We investigated effects of three understorey restoration treatments, carbon (sugar) addition, spring burning and re-establishment of the perennial native grass Themeda australis (R.Br.) Stapf, on early establishment of eight species of native forbs in a degraded white box (Eucalyptus albens Benth.) woodland dominated by exotic annuals, in central New South Wales, Australia. Forb seeds and seedlings were introduced to treatments in a randomised, irrigated field trial and monitored for 4–8 months. Treatments significantly altered vegetation structure and composition, resulting in higher native grass and lower exotic grass cover on sugar and burnt plots (especially if seeded with Themeda), a proliferation of broadleaf exotic annuals on burnt plots, and continued high cover of exotic annual grasses and broadleaf annuals on control plots. Forb germination was largely confined to three large-seeded forbs, Bulbine bulbosa (R.Br.) Haw., Dichopogon fimbriatus (R.Br.) J.F.Macbr. and Microseris lanceolata (Walp.) Schultz-Bip., and few germinants of three small-seeded forbs were observed. Overall, germination (% emergence, and seedling numbers after 4 months) was significantly greater on sugar than burnt and control plots, while transplant survival was significantly enhanced by both sugar and burning treatments for up to 8 months after planting. Re-introduced Themeda swards significantly promoted seedling germination and transplant survival in burnt plots. While long-term seedling survival was extremely low owing to severe drought, we concluded that (i) the applied restoration treatments (especially carbon addition) have considerable potential for promoting forb establishment in degraded woodlands, (ii) reduced competition with exotic annuals associated with carbon addition outweighed potential disadvantages of reduced nutrient levels, (iii) competition with broadleaf annuals and/or exposure to more extreme environments associated with burning may be problematic for forb germination and (iv) Themeda swards may be more conducive to establishment of native forbs than swards of exotic annuals, owing to their contrasting growth strategies.

The influence of land-use history on roadside conservation values in an Australian agricultural landscape

We investigated the influence of land-use history on roadside conservation values in a typical agricultural landscape of southern New South Wales (NSW), Australia. Historical information on the development of rural road reserves was collated from recently digitised 19th and 20th century pastoral and parish maps, such as road-reserve age and original survey width, as well as data relating to locations of old fence lines, county or parish boundaries, previous reserves, stock routes and road re-alignments. Ordinal regression statistics showed that road-reserve age and road width were significant predictors of roadside conservation values. Importantly, analyses showed that the first roads surveyed during the pastoral era (1840–1860s) were often of lower conservation value than roads surveyed in the 1870s, when major clearing of these landscapes commenced. Most roads were surveyed at one-chain width (20.12 m); however, pre-1870s historic roads, traveling stock routes (TSRs) and county or parish boundaries were significantly wider, decisions that have indirectly led to higher present-day conservation values. In separate analyses, historical data also formed a useful model to predict the absence of short-lived shrub species. These results highlight the influence and prevailing imprint of historical land-use on current roadside conservation values.

Effects of fire frequency and mowing on a temperate, derived grassland soil in south-eastern Australia

Frequent disturbances such as fire are widely considered important drivers of plant composition and diversity in productive grassy ecosystems. Effects of fire frequency on grassland soils, however, are less well understood. We established replicated disturbance regimes in a high-quality, representative Themeda australis-Poa sieberiana-derived grassland in south-eastern Australia that had historically been burnt every 4-8 years. Effects on soil chemical, physical and biological properties were measured after 10 years of application of 2-, 4-, and 8-yearly burning, 2-yearly mowing and an undisturbed treatment. Contrary to other grassy ecosystems, there were no detectable effects of disturbance regime on total soil nitrogen and carbon, or a range of other soil chemical properties in the top 10 cm. However, a cumulative effect of burning on the grassland soil was evident from a suite of changes to soil surface properties, available nutrients and biological activity. In particular, on biennially burnt plots, reduced litter and plant protective cover were associated with increased soil surface compaction, decreased infiltration and decreased soil biological activity, which in turn were related to poor sward recovery after fire and drought. These relationships indicate potential for positive feedbacks whereby repeated removal of soil protective cover and changes to soil surface chemistry through very frequent burning ultimately lead to further reduction in soil protective cover through reduced productivity. However, this is only likely in extreme cases: data from unburnt plots indicated that soils that had historically been burnt every 4-8 years had not passed a threshold beyond which such soil changes were irreversible or damaging. Contrary to other predictions, cessation of burning for 13 years did not lead to detectable soil nutrient release through senescence of dominant grasses. Biennial mowing with slash retention was an effective alternative disturbance for maintaining sward vigour while avoiding soil surface damage.

The Distribution and Environmental Relationships of Native Grasslands on the Lowland Gippsland Plain, Victoria: an Historical Study

Historical survey plans were studied to document the distribution and ecological relationships of treeless native grasslands on the lowland Gippsland plain, eastern Victoria. Grasslands occupied about 600 square kilometres, mostly in the Sale—Maffra—Heyfield area, which receives about 600 mm mean annual rainfall. All grassland regions have been developed for irrigation farming and not a single remnant is known to survive. Topography and soils appear to be the major factors promoting grasslands. They occurred on flat plains on clay loam and loam topsoils, above a clay subsoil. Burning by Aboriginals probably affected plant composition but appears unlikely to have been the principal factor leading to treelessness.