Plantation forests and biodiversity conservation.Introduction
Plantations of trees (defined here as planted forests of commercially important tree species) cover extensive parts of the earth's surface: 187 million ha in 2000 (FAO FAO,
n See Food and Agriculture Organization. 2001). In Australia the plantation estate was estimated to be almost 1.5 million ha in 2000 (Wood et al. 2001). The primary aim of almost all plantations is the production of large quantities of wood and fibre (e.g. for timber and paper production). However, there are often important opportunities for biodiversity conservation within plantations (Hartley 2002). In this paper, we explore approaches that promote nature conservation within Australian plantations. We take a hierarchical approach by exploring issues first at the landscape scale and then at the stand level. Our focus is primarily on medium to large plantings (over several hundred to several thousand and tens of thousands of hectares). We have not examined smaller plantings, such as those typically undertaken in agricultural areas by farmers in rural Australia (widely termed 'farm forestry'; sensu Race et al. 1998). Our literature review indicated that very limited research has been undertaken on small-scale plantings. This is a major area that requires additional research, given that the biodiversity benefits of farm forestry have been widely promoted but remain to be quantified.
A model for biodiversity conservation in plantations
Plantation forestry can be thought of as a continuum extending from simple plantation forestry, as defined by Kanowski (1997), to complex plantation forestry (see Fig. 1). 'Simple plantation forestry' refers to a narrow and intensive management focus on producing a forest crop for a limited array of purposes. Complex plantation forestry, while still having a relatively intensive management regime, attempts to include other land uses and values within plantation boundaries, and aims to produce goods and services In economics, economic output is divided into physical goods and intangible services. Consumption of goods and services is assumed to produce utility (unless the "good" is a "bad"). It is often used when referring to a Goods and Services Tax. in addition to wood products. Kanowski (1997) argued that complex plantation forestry is an important way forward in many situations because society will demand outputs in addition to wood and pulp from plantations, and simple plantation forestry is not congruent with the principles of ecological sustainability. In the medium to long term, simple plantation forestry risks creating environmental problems similar to those that currently afflict af·flict
tr.v. af·flict·ed, af·flict·ing, af·flicts
To inflict grievous physical or mental suffering on.
[Middle English afflighten, from afflight, agricultural enterprises in many parts of Australia (Hobbs et al. 2002). Indeed, Holling and Meffe (1996) have shown that land use practices that are narrowly focused invariably in·var·i·a·ble
Not changing or subject to change; constant.
in·vari·a·bil perform poorly in maintaining key ecological functions.
The biota biota /bi·o·ta/ (bi-o´tah) all the living organisms of a particular area; the combined flora and fauna of a region.
The flora and fauna of a region. of conifer conifer (kŏn`ĭfûr) [Lat.,=cone-bearing], tree or shrub of the order Coniferales, e.g., the pine, monkey-puzzle tree, cypress, and sequoia. Most conifers bear cones and most are evergreens, though a few, such as the larch, are deciduous. plantations
Most studies have found that animal assemblages in conifer plantations are less diverse than those of native forests. Vertebrates such as hollow-using birds and arboreal arboreal
pertaining to trees, treelike, tree-dwelling. marsupials as well as nectarivorous, frugivorous frugivorous
fruit-eating. , foliage-gleaning and canopy-feeding birds are absent or greatly reduced in abundance in radiata pine radiata pine
see pinusradiata. plantations. This is most probably because these exotic conifer-dominated stands lack key nesting and foraging resources for these species. While the biota of conifer plantations is depauperate, these areas are not 'biological deserts' because they provide foraging habitat or nesting habitat or both for a range of birds, small mammals and invertebrates. The occurrence of much of the biodiversity found in conifer plantations is strongly related to the mosaic of patches of native forest among them, and the treatment history of planted areas (e.g. thinning regimes and stand ages). These key topics are explored in greater detail in subsequent sections of this paper.
The biota of eucalypt and other types of plantations
Work on biodiversity conservation within eucalypt and other types of plantations has a far shorter history and is much less extensive than the research in radiata pine plantations. Much of the limited work has been recent (e.g. Borsboom et al. 2002; Hobbs et al. 2002; Klomp and Grabham 2002). Vertebrate and invertebrate invertebrate (ĭn'vûr`təbrət, –brāt'), any animal lacking a backbone. The invertebrates include the tunicates and lancelets of phylum Chordata, as well as all animal phyla other than Chordata. assemblages are less diverse than those in native vegetation, largely because of the relative structural simplicity of the plantations (Hobbs et al. 2002). Nevertheless, as for pine plantations, bluegum plantations are not 'biological deserts' but provide habitat or resources for a range of species, including a selection of bird species considered to be at conservation risk.
Plantations versus cleared land
Borsboom et al. (2002) and Klomp and Grabham (2002) showed that the diversity of birds was higher in planted eucalypt forests than in pastures, although species assemblages were still depauperate in comparison with native woodlands. However, greater species diversity is not always the best outcome for nature conservation. It is often better to use the composition of particular faunal assemblages as a measure. Lindenmayer et al. (2001) have found that the species assemblages of newly established plantations are different from (but not necessarily 'better' than) those of semi-cleared grazing lands.
Conserving biodiversity in plantations
We believe there are several key issues associated with the conservation of biodiversity within plantations at the landscape level. These are: (i) the location of plantations; (ii) the role of landscape mosaics created by the retention of eucalypt patches and riparian riparian adj. referring to the banks of a river or stream. (See: riparian rights) vegetation within plantations; (iii) the adjacency effects of remnant vegetation next to plantations; (iv) the contribution of harvest scheduling to biodiversity conservation; and (v) the value of landscape restoration.
[FIGURE 1 OMITTED]
The location of plantations
The pre-existing conservation values of areas where new plantations might be established warrant careful consideration. We believe that clearing native vegetation to establish plantations (e.g. as in Tasmania) is an inappropriate land use practice given the well-documented negative impacts of land clearing. In parts of southern NSW NSW New South Wales
Noun 1. NSW - the agency that provides units to conduct unconventional and counter-guerilla warfare
Naval Special Warfare and Victoria, plantation expansion will take place on semi-cleared grazing lands which support patches of remnant native forest and woodland. Even though many remnant patches are small (often less than 3 ha; see Gibbons and Boak 2003), they can have considerable conservation value (Fischer and Lindenmayer 2002).
The role of landscape mosaics created by the retention of eucalypt patches and riparian vegetation within plantations
Many studies have highlighted the value for conservation of maintaining patches of remnant native forest or woodland within plantations (e.g. Friend 1982; Recher et al. 1987a). In general, the larger the patches of retained native vegetation within plantations the more the species of vertebrates they support (Lindenmayer et al. 1999). However, retained patches do not always have to be large to be useful--areas as small as 0.5-1 ha have been found to be valuable for forest birds, reptiles, frogs and mammals and invertebrates. Riparian vegetation is known to be particularly valuable for native biota within plantations. Other features which can add to landscape heterogeneity and enhance biodiversity conservation include dams and open areas such as clearings and firebreaks.
The adjacency effects of remnant vegetation next to plantations
The greatest diversity and abundance of native animals in plantations occur in stands adjacent to native vegetation (for example see Friend 1982; Lindenmayer et al. 2002). The adjacency of native forest also may assist in the biocontrol bi·o·con·trol
See biological control.
See biological control. of pest invertebrate populations in eucalypt plantations (Strauss 2001). However, there can be some negative impacts of the adjacency of plantations to native forests such as increased browsing damage by native and introduced animals--a phenomenon observed in both eucalypt and conifer plantations (e.g. Barnett et al. 1977; Montague 1996; Bulinski 1999).
The contribution of harvest scheduling to biodiversity conservation
There can be positive benefits for biodiversity conservation arising from changes in the spatial and temporal pattern of harvesting in plantation forests. For example, given differences in the biotas of plantations of different ages (see below), maintaining landscapes with a mosaic of stand age classes may increase the biodiversity conservation value of plantations (Gepp 1976). Smith (2000) predicted that the rare Tasmanian carnivorous car·niv·o·rous
1. Of or relating to carnivores.
2. Flesh-eating or predatory: a carnivorous bird.
3. snail Tasmaphena lamproides Tasmaphena lamproides is a species of gastropod in the Rhytididae family. It is endemic to Australia. Its natural habitat is temperate forests. It is threatened by habitat loss. Source
The value of landscape restoration
There is scope within some plantations to promote biodiversity conservation through the restoration of targeted areas. Riparian zones, in particular, may be valuable places for such work. Harvesting is often restricted in riparian areas because of water quality and aquatic habitat considerations. Therefore, it is useful to exempt riparian areas from tree planting in new plantations and to allow the regeneration of native vegetation there, or to actively restore native vegetation cover following the final clearfelling operation within already established plantations.
A number of matters can be considered in enhancing biodiversity conservation within a plantation program.
The contribution of species mixtures
A diversity of plant species can be positively related to the diversity and abundance of a range of animal taxa. Recher et al. (1987b) found that several native species of birds persisted within stands of radiata pine because the presence of scattered regrowth Re`growth´
n. 1. The act of regrowing; a second or new growth.
The regrowth of limbs which had been cut off.
- A. B. Buckley. eucalypts created the effect of a mixture of tree species.
Stand age effects on biodiversity
Plantations can have a significant impact on many elements of biodiversity. Borsboom et al. (2002) recorded increasing vertebrate species richness This article or section is in need of attention from an expert on the subject.
Please help recruit one or [ improve this article] yourself. See the talk page for details. with increased stand age in eucalypt (Eucalyptus cloeziana Eucalyptus cloeziana, 'Gympie Messmate, is a small to tall tree with rough bark on most or the whole of the trunk and larger branches. The bark is soft, flaky, tessellated, light brown or yellow-brown, where smooth, greyish white or yellowish above. ) plantations in south-eastern Queensland. Bird species diversity may increase with stand age within conifer plantations. For example, Gepp (1976) attributed such findings to older stands supporting more structurally diverse conditions.
The contribution of biological legacies to species conservation
Biodiversity conservation in plantation forests can be promoted through the retention of elements of the original stand (termed 'biological legacies'; sensu Franklin et al. 2000) at the time of harvesting. For example, trees retained at the time of regeneration harvesting have been found to be used by many species of birds (Kavanagh and Turner 1994). Bonham et al. (2002) emphasised the importance of leaving thinnings and prunings or logging 'waste' to rot on the forest floor to provide habitat for invertebrates in Tasmanian plantation forests. Several of these species of invertebrates would otherwise be sensitive to timber harvesting operations. Windrows of cleared eucalypts left within softwood plantations are useful for many native taxa (e.g. Friend 1982).
Pest animals in plantations
Some elements of biodiversity in plantations may have undesirable effects. For example, both Australian conifer and eucalypt plantations are vulnerable to damage caused by native and introduced animals (Bulinski 1999). Radiata pine plantations in Australia support more than 40 species of pest invertebrates and most of these are introduced (Neumann 1979). Strauss (2001) noted that more than 85 invertebrate species are pests of eucalypt plantations in Australia. Most of these are native and have been found on the same tree species or closely-related tree species within stands of native vegetation. She argued that the extent of the pest invertebrate problem in eucalypt plantations was likely to increase in the future as the size of the plantation estate increases and exchanges of animals between regions takes place--highlighting a need for strict quarantine protocols within Australia. Large numbers of introduced animals can occur in plantations, including rodents, the rabbit, the red fox and the feral feral
untamed; often used in the sense of having escaped from domesticity and run wild. cat (Hobbs et al. 2002).
'Genetic pollution' is a potential problem associated with plantations of eucalypts in Australia. That is, there may be genetic invasion from pollen dispersal and subsequent hybridisation between eucalypt tree species used to establish plantations and eucalypts endemic to an area (Potts et al. 2001). This may, in turn, alter natural patterns of genetic variability Introduction
Tensions between biodiversity conservation and other plantation objectives
Significant tensions exist between management practices to maintain or increase wood and pulp production in plantations, and practices designed to promote biodiversity conservation within plantations (Keenan et al. 1997). Some of these tensions are outlined below.
(1) It is generally recognised that more elements of the biota will occur where there are more plant taxa, and this is supported by evidence gathered in Australian studies of plantations.
However, in most commercial plantations emphasis has been placed on the growth of a single tree species--including those that have been subject to considerable genetic modification.
(2) It is well established that there are strong relationships between the structural complexity of forests and the diversity of species (see Lindenmayer and Franklin 2002). However, most silvicultural practices in plantations result in stand simplification. For example, structural complexity (and its associated biodiversity) can be reduced through the removal of windrows to control pest herbivores (le Mar 2000), the application of herbicides to eliminate unwanted or competing plants, and even the application of fertiliser to promote tree growth (Pampolina et al. 2002).
(3) Virtually all studies to date have highlighted the conservation value of remnant native vegetation within plantations, even patches that are relatively small (including single large old trees). In addition, many species can use plantations if native vegetation is nearby. However, retaining native vegetation means forgoing plantations on some land--although sometimes these areas are unsuitable for planting (e.g. steep and rocky terrain). In addition, retained vegetation can retard the growth of neighbouring plantation trees (Bi et al. 2002).
(4) Retained areas of native vegetation also can create problems for plantation managers through harbouring browsing vertebrates which can inflict serious damage on plantations, particularly at their periphery. Plantations can be a major source of weeds that can erode the habitat quality of neighbouring areas of native vegetation. In eucalypt plantations, planted trees also can be a source of pollen to create new hybrids within adjacent vegetation and, in turn, alter patterns of genetic variability.
Tensions of the four types just described can make it difficult to reconcile many aspects of plantation management and biodiversity conservation. The extent to which forestry practices can be modified to accommodate biodiversity conservation will depend on the flexibility possible within the objectives of plantation management, as well as the degree to which agreements such as the certification of sustainable practices are seriously embraced by state government agencies and private plantation owners. Perhaps the greatest opportunities lie in the establishment of new plantations on semi-cleared grazing lands. In these cases, there will be advantages in articulating plans and visions of what future plantation landscapes might look like, so that values other than wood and pulp production can be embraced. As outlined above, existing remnant vegetation in these areas is extremely important. In addition, there will be a significant conservation role of existing (and restored) riparian native vegetation in these landscapes--a role that need not necessarily have a major negative impact on wood and pulp production, given water quality considerations.
The authors thank the Rural Industries Research and Development Corporation The Rural Industries Research and Development Corporation (RIRDC) is a statutory Corporation formed in July 1990 under the Primary Industries and Energy Research and Development (PIERD) Act 1989. and the Joint Venture Agroforestry ag·ro·for·est·ry
A system of land use in which harvestable trees or shrubs are grown among or around crops or on pastureland, as a means of preserving or enhancing the productivity of the land. Program (and particularly Roslyn Prinsley) for funding our work on plantations and biodiversity conservation.
Revised manuscript received 6 January 2003
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D.B. Lindenmayer (1), R.J. Hobbs (2) and D. Salt (1)
(1) Centre for Resource and Environmental Studies, The Australian National University, Canberra, ACT 0200, Australia Email: firstname.lastname@example.org
(2) School of Environmental Studies, Murdoch University, Murdoch, WA 6150, Australia