Managing and Conserving Grassy Woodlands

S McIntyre, JG McIvor, KM Heard, S McIntyre, JG McIvor, KM Heard

• Publisher: CSIRO PUBLISHING
• Year: 2004
• ISBN:
  9780643099227
• Topic: Tecnologia e ingegneria
• Subtopic: Agricoltura sostenibile

In eastern Australia, grassy eucalypt woodlands have been under severe pressure from agricultural development, with problems of land degradation and species decline being most severe in the cropping lands of south-eastern Australia.

Managing and Conserving Grassy Woodlands describes a set of principles that will enable landholders to maintain or increase productivity without compromising ecological sustainability, and at the same time maintaining a substantial proportion of the native flora and fauna. The book provides the technical foundations underpinning the principles and explains the importance of planning at a landscape scale.

Each major principle is addressed in a separate chapter which explains the scientific understanding behind the principle and which discusses some of the issues relating to its practical application. Additional chapters outline the basic ecological concepts underpinning the principles and the responses of landholders who have had the opportunity to discuss and reflect on the principles. For those interested in translating the principles into a property plan, a final chapter explores the steps that can be taken.

Managing and Conserving Grassy Woodlands is intended for those at the interface of disciplinary research and on-ground application, whether they are working in research, regional planning, extension, landcare or land management.

1

Understanding grassy
woodland ecosystems

J. G. McIvor and S. McIntyre

What are grassy woodlands and why are they important?

All Australians know grassy eucalypt woodlands, although they may not realise it. Picture the classic Australian pastoral scene depicted by early landscape artists — a wide open grassed landscape, some sheep, and large gum trees (Figure 1.1). Drive through a typical rural landscape — trees along the roadside verge, scattered clumps or single trees in the more open paddocks (Figure 1.2). This most familiar landscape is the focus of our book. Grassy woodlands with an overstorey of eucalypts and a grass-dominated understorey occur in the intermediate rainfall zone between the forests of the high rainfall areas and the shrublands and deserts of the arid interior. They form an almost continuous band in eastern Australia from Tasmania to the Cape York Peninsula. They also include the tropical savannas arching over northern Australia and important areas in the southern parts of South Australia and Western Australia.

Grassy eucalypt woodlands typically have a tree layer of eucalypt (Eucalyptus) and bloodwood (Corymbia) species. In woodlands, the tree canopies are clearly separated, but tree density varies with environment and management, so that canopies may be well separated (forming open woodlands) or touching (forming grassy forests). The ground layer is herbaceous (that is not woody). Tall perennial tussock grasses dominate, but there are numerous smaller grasses and an array of forbs (dicots, lilies, orchids, sedges). These smaller plants contribute much of the plant diversity but contribute little to the bulk of the grassy sward (Trémont and McIntyre 1994). The larger perennial tussock grasses provide structure to the ground layer vegetation, with the smaller grasses and forbs growing in the inter-tussock spaces. A variable amount of bare ground and litter also occurs between the tussocks. Shrubs may occur in small amounts and grassy understoreys may intergrade with those dominated by shrubs. In this book we are primarily concerned with grassy woodlands. Eucalypt woodlands with a shrubby understorey are widespread in parts of western New South Wales and southern Western Australia.

Figure 1.1. Summer, 1909, by Hans Heysen depicts a grassy eucalypt woodland. Scenes like this helped to shape the image of the bush for Australians. Note the size of the mature eucalypt. (© Christopher Heysen, reproduced with permission. Collection: Art Gallery of NSW.)

Figure 1.2. A common grassy woodland scene for the motorist in rural areas — a treed roadside reserve, open paddocks with scattered and clumped eucalypts with a grassy understorey and some cropping on the creek flats (Photo K. M. Heard).

Grassy woodlands tend to occur on relatively fertile soil types and the richly grassed, open landscapes that the pastoral settlers encountered were very attractive for settlement and agricultural development (Yates and Hobbs 2000). With the introduction of domestic livestock and intensive agriculture, the grassy woodlands have changed greatly over two hundred years. This is most apparent in southeastern Australia, where cropping has largely replaced the grassy woodland in many landscapes (Figure 1.3), with the remaining areas being altered by tree clearing, changed fire patterns, exotic species and fertiliser application. In the tropical north, the grassy woodlands (known as savannas) are grazed, but are not generally cleared (Figure 1.3). In the subtropics, there is an intermediate level of use.

Grassy woodlands represent some of the most significant agricultural land in Australia, forming the heart of the mixed grazing and cereal growing belt. They have been important for nearly two centuries and will continue to be so into the future.

Figure 1.3. Map of Australia showing areas where eucalypt woodland (both grassy and shrubby) naturally occurred (shaded pink) and areas of eucalypt woodland that have been extensively cleared of native vegetation (diagonal lines). (Sources — vegetation: Groves 1981; Tasmanian vegetation: Kirkpatrick et al. 1988, clearing: AUSLIG 1990).

Human alteration of grassy woodlands

To understand the changes that agriculture and pastoral use have made on grassy woodlands, it is helpful to consider the tree layer and the grass layer separately. Sometimes the tree layer is killed, but the native grassland is retained as pasture. This commonly occurs in south-east Queensland (Figure 1.4). Alternatively, the tree layer might be kept, but the native ground layer is removed or radically changed through the combined effects of grazing, soil disturbance, and added plants and nutrients (McIntyre and Martin 2001). Both these situations represent degrees of modification of the grassy woodlands. When both layers are removed (for example with cropping), the grassy woodland and the habitats that it provides for fauna, can be considered to be replaced, or destroyed.

The words ‘modification’ and ‘destruction’ are important ways of describing how agriculture has altered vegetation. Many agricultural landscapes are described as ‘fragmented’, where the original vegetation is reduced to small areas existing in a matrix of crops and sown pastures. The habitat has been destroyed for many species that are dependent on native vegetation. However, the term fragmentation is too limited for grassy woodlands, and four alteration states (intact, variegated, fragmented, relictual) are needed to describe the full spectrum of human impacts that are seen (McIntyre and Hobbs 1999) (Figure 1.5).

Figure 1.4. Human modification of eucalypt grassy woodland in south-east Queensland. The trees in the foreground have been killed by stem injection with herbicide, leaving the native grass understorey. In the subtropics this is a common method of increasing pasture production. Subsequent tree regeneration may range from dense to non-existent, depending on management, the tree species involved, and the seasonal conditions (Photo S. McIntyre).

Figure 1.5. Differently altered landscapes that are associated with rural lands. These are defined by the extent of habitat destruction and the amount of habitat remaining. The figure also indicates the degree of modification that is likely to be associated with the four alteration states. Arrows indicate the range of alteration states (intact, variegated and so on) that are generally associated with grassy woodlands in different regions. The degree of alteration is generally linked to the economic rewards of pasture development and cropping (modified from McIntyre and Hobbs 1999).

Figure 1.5 depicts a trend, at least on the mainland, for southern regions to have more highly altered habitats. For example, in the wheat–sheep belt in parts of southern New South Wales, there may be only small remnants of grassy woodlands remaining (a relictual landscape) and these are highly modified. The suitability of this region for agriculture has led to cropping and sown pastures dominating these landscapes. Also prevalent is the variegated landscape, which results from grazing of the natural grasslands without significant inputs, and from limited amounts of cropping. In this modified landscape the tree layer may be less extensive than the grassy layer, as clearing trees in grassy woodlands can increase grass production The particular focus of this book — variegated landscapes — can be found in all the eastern states. If there is natural or native pasture, and/or remnant woodland covering 60–90% of the landscape, it is classed as variegated.

The contrasting characteristics of variegated and fragmented landscapes are important for conservation management. Because variegated landscapes still have significant amounts of native vegetation, it makes sense for management to focus on retention and augmentation of existing vegetation rather than on restoring large areas. Using the natural capacity of ecosystems to recover through regeneration is preferred over expensive and demanding restoration methods such as tree planting.

Ecological sustainability

The widespread changes to woodlands, the poor condition of the resources and declines in productivity have led to concerns about the sustainability of current land use. ‘Sustainability’ has become a widely used term in the last decade. It has many meanings and definitions. However, most people agree that sustainability has economic, ecological and social components and that all three components are essential. Most definitions also include the idea that sustainability involves maintaining natural resources for future generations.

Maintaining ecological health in landscapes goes hand-in-hand with sustainability (see glossary). We know from experiences in the most intensively developed regions that there are limits to agricultural development of grassy woodlands. Indications that our landscapes are no longer healthy have started to appear and symptoms include dryland salinity, accelerated rates of soil acidification (Williams 1980), local extinctions of plants (Lunt 1992) and animals (Robinson and Traill 1996), and accelerated death of trees (Reid and Landsberg 2000). Particular woodland communities are at risk of extinction due to development being targeted towards more fertile land types. Even in south-east Queensland where less clearing has taken place, clearing for agriculture is a major contributor to 44 of the 145 regional ecosystems being classed as ‘of concern’ and 11 as ‘endangered’ (Sattler and Williams 1999). These changes are evidence of unsustainable use of land and can lead to large losses of agricultural productivity and losses of species and communities.

In variegated landscapes, these symptoms of poor ecological health may not be as acute as in heavily fragmented landscapes. This is because there is more even representation of extensive and intensive land uses. However, variegated landscapes are on a knife edge — further development may push the ecosystem into poor health. Even when intensive land uses are limited, they also need to be located in appropriate parts of the landscape (see Chapter 2). This book is about achieving the right mix of land uses on properties and locating them so that a sustainable grazing enterprise is maintained. Our goal is to sustain the productive capacity of the land, and maintain the bulk of native plant and animal species. Grassy woodlands are suitable for this integration of conservation and production, because a diverse native grassland is compatible with commercial livestock grazing if managed appropriately. Appropriate management is management that respects the ecological constraints of the ecosystem.

Why we need to know how ecosystems work

Science has played a major role in the development of agriculture and land management in Australia and can continue to contribute, as we seek new approaches to the way we utilise our land. What knowledge is needed to manage our grassy woodlands sustainably?

For us to have responsible management o...

Table of contents

• Cover
• Title
• Copyright
• Contents
• Dedication
• Preface
• Acknowledgements
• Glossary
• Chapter 1: Understanding grassy woodland ecosystems
• Chapter 2: Principles for property planning
• Chapter 3: Soils
• Chapter 4: Pastures
• Chapter 5: Trees
• Chapter 6: Wildlife and core conservation areas
• Chapter 7: Watercourses and riparian areas
• Chapter 8: Barriers and opportunities for adoption
• Chapter 9: The way forward — from principles to practice
• References
• Index