|| Home || Search || Contact || Publications Eshop || Privacy Statement ||
Complete report can be purchased from our online shop
By
B.R. Maslin
Dept. Conservation and Land
Management, Locked Bag 104, Bentley Delivery Centre, WA
and
M.W.
McDonald2
CSIRO Forestry and Forest
Products, PO Box E4008, Kingston, ACT 2604
Report to the Joint Venture Agrofestry Program
Publication No 03/017
Executive
summary
This report identifies,
evaluates and provides detailed information for Acacia species considered
prospective as new woody crop plants in the agricultural region of southern
Australia (within the 250–650 mm rainfall zone). The impetus for the study
is the need to undertake large-scale commercial plantings with perennial
plants as a treatment for salinity control in these regions.
Emphasis is given to fast growing species with potential for producing large amounts of wood biomass that may find uses as solid and reconstituted wood products and for bioenergy, and which may possess commercially attractive by-products such as extractives (especially tannin and gum) and fodder. There is currently no large-scale commercial use of Acacia within the southern Australian agricultural zone despite the fact that this genus, in terms of species numbers, is the largest plant group in the area.
Acacia is a diverse and enormous genus with almost 1 000 species currently recognized for Australia.
Species of this genus represent a vast resource for economic, environmental and social utilisation, but to date their major usage has been abroad. Many Australian acacias produce good quantities of wood biomass and display a range of variation in growth form, growth rate, longevity and coppicing/suckering ability. They are adapted to a wide range of soil types and climates, including drought- and frost-prone areas. Acacia species have hard-coated and relatively large seeds (which are amenable to direct-sowing techniques), have the ability to improve soil fertility through nitrogen fixation, are usually easy to germinate and grow, and generally show good survival and rapid growth rates under cultivation. These favourable attributes provide the encouragement for considering Acacia species for development as new woody crop plants for southern Australia.
The target area for this study encompasses the States of Western Australia, South Australia, Victoria and New South Wales and includes the predominantly winter rainfall region (south of the Lachlan River, N.S.W.) from about 650 mm annual precipitation down to the limits of agriculture (which coincides with the 250 mm isohyet in eastern Australia and the 300 mm isohyet in Western Australia).
Species were considered for this project if their natural distribution occurred wholly or partially within the target area, although a few species with known agroforestry potential that occurred just outside the region were also assessed. The areas of greatest species richness for Acacia within Australia are located within, or are peripheral to, this target area.
Species were evaluated against a set of plant characteristics that indicate their potential suitability as feedstocks for selected products.
These selection criteria were developed in consultation with appropriate specialists, especially those associated with the Search and FloraSearch projects, and are summarised in Table 3.
Emphasis was given to products that have large markets, require large amounts of biomass for their manufacture, and for which short cycle Acacia crops could provide suitable feedstock. Therefore, the most important plant characteristic was the ability for rapid production of commercial volumes of harvestable wood biomass, particularly low density wood .
Existing knowledge was adequate to enable all species within the target area to be assessed on the basis of their expected growth rate, and their ability to produce acceptable quantities of wood biomass. These two important attributes took pre-eminence in the selection process and in the ranking of species, but they were supplemented by other plant characteristics relating to morphology, biology, ecology, silviculture and wood quality where these data were available (from both published and unpublished sources, and from our field assessment of the taxa). A knowledge of the taxonomic relationships among species was also helpful in screening the large numbers involved. Unfortunately not all information necessary for a thorough evaluation of Acacia as a woody crop is currently available. There are critical data relating to wood and plant characteristics, and silviculture which need to be obtained from field trials and from further detailed study of plants in their native habitats. Also, there is a need for technical testing to determine how well the species meet the feedstock requirements of various end products.
There are 462 Acacia species (comprising 538 taxa) that occur naturally within the target area (these taxa are listed in Appendix 1). Thirty five taxa (referred to herein as ‘species’) have been identified as having some crop potential for the southern Australian agricultural zone; however, because these species vary considerably they have been subjectively ranked to indicate how well each might be expected to perform as crop plants capable of delivering anticipated end products. The rankings used are 1 (most prospective) through 4 (least prospective) and are shown in Table 6 which also lists some of the more important growth characteristics that render the species prospective. It is important to remember that these rankings are provisional and should be treated with caution because they may change in the light of future studies. Furthermore, it is not expected that all 35 species will become new crop plants. Some will undoubtedly be eliminated after testing their growth rates, wood attributes, performance under cultivation, or by their inability to meet end-product requirements. In some cases their potential weed risk may constrain use to their native range.
Species ranked 1 and 2 are considered the most prospective.
They can be expected to display fast or moderately fast growth rates and produce high or moderately high volumes of wood biomass. They have potential to be cultivated over a reasonably wide geographic area, although in a number of cases this area is restricted to the temperate outer peripheral regions of the target zone.
Species ranked 3 and 4 are regarded as less prospective. While these species possess acceptable growth characteristics, they display certain attributes that tend to reduce their potential for crop development (most commonly these attributes are poor growth form, reduced wood biomass production, or relatively slow growth rates).
Nevertheless, they should not be discounted at this early stage of the testing process.
Species ranking and Australian States of occurrence (given in parentheses) for the 35 prospective species are as follows:
Category 1:
A. saligna (W.A.)
Category 1-2:
A. leucoclada subsp.
leucoclada (N.S.W.)
A. linearifolia (N.S.W.)
A. retinodes ‘typical’
variant (S.A.)
A. salicina (N.S.W.,
N.T., Qld, S.A., Vic., ?W.A.)
Category 2:
A. decurrens (A.C.T.,
N.S.W.)
A. lasiocalyx (W.A.)
A. mearnsii (A.C.T.,
N.S.W., S.A., Tas., Vic.)
A. microbotrya (W.A.)
A. pycnantha (A.C.T.,
N.S.W., S.A., Vic.)
A. retinodes ‘swamp’
variant (S.A., Vic.)
Category 2-3
A. bartleana (W.A.)
A. dealbata subsp. dealbata
(N.S.W., Tas., Vic.)
A. murrayana (N.S.W.,
N.T., Qld, S.A., W.A.)
A. neriifolia (N.S.W.,
Qld)
A. rivalis (S.A.,
?N.S.W.)
Category 3
A. acuminata (W.A.)
A. baileyana (N.S.W.)
A. doratoxylon (A.C.T.,
N.S.W., Vic.)
A. filicifolia (N.S.W.,
Qld.)
A. hakeoides (N.S.W.,
Qld., S.A., Vic., W.A.)
A. implexa (N.S.W.,
Qld, Tas., Vic.)
A. melanoxylon (A.C.T.,
N.S.W., Qld, S.A., Tas., Vic.)
A. parramattensis (A.C.T.,
N.S.W.)
A. retinodes ‘Normanville’
variant ........(S.A.)
A. retinodes var.
uncifolia (S.A., Tas.)
A.. rostellifera (W.A.)
A. stenophylla
(N.S.W., N.T., Qld., S.A., Vic., W.A.)
A. victoriae (N.S.W.,
N.T., Qld., S.A., Vic., W.A.)
A. wattsiana (S.A.)
Category 3-4
A. argyrophylla (S.A.,?Vic.)
Category 4
A. cyclops (W.A.,
S.A.)
A. dodonaeifolia (S.A.)
A. euthycarpa (S.A.,
Vic.)
A. affin. redolens
(W.A.)
A comprehensive cluster of information is presented for each of these 35 prospective species. This includes a summary of available information, assembled from both published and unpublished sources, covering plant growth and morphological characteristics, taxonomy, phenology, biology, ecology, distribution, silviculture and utilisation. The crop potential of each species is also discussed. Maps showing species natural distributions and bioclimatic maps showing their predicted growing areas are provided. The bioclimatic maps represent a first approximation of areas where the species may possibly grow and should be treated with some caution because there are many factors (especially soils) that may preclude species from being successfully cultivated in the areas indicated by these maps. The climatic and soil conditions under which the species grow naturally are summarised in Table 5. The plate of photographs provided for each species shows variation in growth form, wood characteristics and attributes useful in identification.
Of the 35 prospective species, 10 occur in Western Australia, 19 in South Australia, 12 in Victoria and 18 in New South Wales (these numbers do not include naturalized occurrences). The significant number of prospective species in each state provides the opportunity to focus early commercial development on species within their natural geographic range (or within the IBRA region in which each occurs), thereby avoiding the need to translocate species to more distant botanical regions and thus invoking the complex issue of environmental weed risk.
Twenty of the 35 prospective species occur in the botanical section Phyllodineae and a majority of these species are not too far removed taxonomically from the seven species of section Botrycephalae. It is these two sections that contain a majority of the most highly ranked species. The other two sections, Plurinerves and Juliflorae, contain only eight species and, except for A. lasiocalyx, are not highly ranked. Species from these last two sections are commonly slow growing and produce dense wood; in fact, many of the arborescent species occurring in or near the target area that were not considered prospective for this project are contained in these two sections (see Table 4).
While all the 35 prospective species produce at least reasonable quantities of wood biomass the largest volumes of wood are generally found in the arborescent species which grow in (or just outside) the temperate peripheral parts of the target area in eastern Australia (e.g. A. dealbata, A. decurrens, A. implexa, A. leucoclada, A. linearifolia, A. mearnsii, A. melanoxylon, A. neriifolia, A. retinodes ‘swamp’ and ‘Normanville’ variants). In the drier inland regions of N.S.W., S.A. and W.A. many species are smaller in stature and often develop a form resembling the ‘mallee’ growth habit with wood contained in many rather slender stems (e.g. A. argyrophylla, A. euthycarpa, A. hakeoides, A. murrayana, A. rivalis, A. wattsiana). However, A. salicina and A. stenophylla are notable exceptions in that they develop into substantial trees, despite growing (along water courses) in the driest inland parts of the eastern target area. Some arborescent species do, however, occur in the drier semi-arid parts of the target zone (e.g. A. bartleana, A. lasiocalyx, A. microbotrya, A. pycnantha, A. retinodes ‘typical’ variant, A. saligna).
Although woody crops could take many forms there are three commercial crop types likely to be suitable for salinity control in southern Australian agricultural systems. These three types can be briefly defined as follows (more detail is provided in Table 2):
Current indications are that a majority of the prospective Acacias from the southern Australian agricultural zone have potential as phase crops. Indeed, 31 of the 35 prospective species are assessed here as having some potential for development as phase crop plants; 13 species may possibly have prospects as long cycle crops while only 8 species appear to have any prospects as coppice crops (see Table 6). Plant establishment by direct seeding is essential for the commercial viability of phase crops, and also confers a cost advantage in the establishment of coppice crops and long cycle crops. Therefore, one of the attractive attributes of Acacias as potential crop plants (apart from their rapid growth rate, nitrogen fixation capability, etc.) is their large seeds that are amenable to direct-seeding technology (possibly using conventional large-scale cereal seeding equipment). The ability to reliably and vigorously re-sprout after harvest is an essential character for coppice crops. Although very little is known about this characteristic in Acacia it is seemingly uncommon among the 35 prospective species. Acacia saligna would appear to have the best potential as a coppice crop although A. implexa, A. linearifolia, A. microbotrya, A. murrayana, A. retinodes ‘Normanville’ variant, A. salicina and A. stenophylla may possibly have some prospects.
Some potential difficulties for the management of Acacia as a tree crop include the early prolific seed production and/or the capacity to root sucker that occurs in a number of the species. Precocious seed production in cultivated stands may create a soil seed bank that may cause weed problems in adjacent or subsequent annual crops. However, in an agricultural context such regeneration might be regarded as fodder or green manure, or be easily controlled by modifying existing weed control methods.
Vigorous or moderately vigorous root suckering appears to be common in a number of the highly ranked species, namely, A. bartleana, A. leucoclada, A. microbotrya, A. retinodes ‘typical’ variant and A. salicina. However, very little is known about this character, including how it varies within species or what factors (apart from root disturbance) are responsible for promoting it. The ability to root sucker may or may not be advantageous in cultivation, it depends upon whether or not this attribute is desirable in the farming system in which the species is placed. Suckering may be advantageous in situations where soil stabilization is required, or where regeneration by this method has a commercial advantage, but it also has the potential to complicate the management of Acacia as a tree crop. If ways were devised to manage suckering to advantage in crop systems it would substantially increase the value of about one third of the species detailed here.
Many Acacia species have the potential to display various aspects of weediness. A primary strategy adopted in this study to minimize the environmental weed risk was to assess only those species that occurred naturally within, or very close to, the target zone. It was considered inappropriate at this early stage of the selection process to preclude or unduly negatively weight species on the basis of weed potential. To do so would preempt the development of effective control measures through management, breeding and other strategies, should these be deemed necessary. As crop development progresses the knowledge of the biology and ecology of the species will expand, thus allowing a more rigorous prediction of weed risk that might occur should species be considered for translocation outside their natural area of occurrence. This strategy provides a safe development pathway for Acacia crops. Based on existing knowledge the following eight species perhaps have the greatest weed potential: A. baileyana, A. cyclops, A. dealbata, A. decurrens, A. mearnsii, A. melanoxylon, A. pycnantha and A. saligna. However, half of these species express weediness in relatively high rainfall areas, so it is not known to what extent (if at all) they will develop similar tendencies in the drier, semi-arid environments of the target area. It is important therefore to assess weed risk within the environment where species are intended to be cultivated. The three species that might pose greatest weed risk in the target area are A. cyclops, A. pycnantha and A. saligna. Notwithstanding the above it is noted that a number of prospective species grow naturally in disturbed agricultural landscapes with no recorded weed problems, e.g. A. argyrophylla, A. acuminata, A. doratoxylon, A. microbotrya, and more.
Weed issues are discussed in the introduction to this report (where some weed reduction strategies are suggested) and also under each of the 35 species profiles. A subjective assessment of the weed potential of the 35 species is summarised in Table 6.
Identification of the 35 prospective species that are detailed in this report provides the crucial first step in the development of Acacias as potential new crops for the southern Australian agricultural zone.
However, to further progress the domestication of these species much essential data is still needed.
The most critical areas of need (excluding obvious ones like wood sampling and conducting field trials) include the following.
|
