Rural Industries Research & Development Corporation |
|| Home || Search || Contact || Free Publications || Eshop || Privacy Statement |
|
Rural Industries Research & Development Corporation |
|| Home || Search || Contact || Free Publications || Eshop || Privacy Statement |
 |
The
 Report |
No 99: Designing Blue Gum Alley Farms
This is a summary of a full report Blue gum timberbelt design for alley farming published by RIRDC (Pub. No. 00/154, DAw-70A) by Tony Albertsen, Peter Eckersley, Simone Blennerhasset, Agriculture Western Australia, Richard Moore, Bob Hingston, Department of Conservation and Land Management.
This report is available in hardcopy for $10 from RIRDC (phone 02 6272 4819) or can be downloaded for free from RIRDC’s website: www.rirdc.gov.au/reports/ Index.htm
Tasmanian blue gum Eucalyptus globulus is being extensively planted across parts of southern Australia for the production of pulpwood. Unless another more profitable land use such as horticulture is an option, blue gum plantations are the most profitable land use on sites where rainfall is greater than 700 mm/yr, stumpage exceeds $25/m3 and MAI greater than 25 m3/ha/yr.
Previous estimates have shown the equivalent annual return at this yield and price to be $266/ha. Earlier research has indicated that grazing gross margin rarely exceeds this level in the beef industry, and on half the farms surveyed in this earlier study, gross margin was less than $172/ha/ year (the returns for blue gum alleys with a MAI of 20m3/ha/year).
The gross margin/ha is generally lower in the sheep and cropping industry. An earlier survey of Kojonup (Western Australia) farms, where the dominant land use is sheep grazing with some cropping provides evidence of this.
Statistics provided by Bank West show that farms in the top quartile (profit based) of surveyed farms in Kojonup Shire produced an operating return of $145.70/ha in 1997.
Gross margin is marginally higher than operating return because cash overheads have been deducted as well as variable costs.
In contrast to traditional plantation arrangements, alley farming of blue gums presents a profitable means of cultivating blue gums in areas of lower (<700mm/yr) rainfall.
Alley farms comprise trees planted in belts, separated by alleys used for agricultural production. This approach to blue gum cultivation offers the potential to enhance the sustainability of an agricultural enterprise, whilst diversifying the economic base of the operation. Earlier research has indicated that dispersed arrangement of blue gum alleys across an agricultural system will contribute to the sustainability of the agricultural system by:
In addition, the harvesting
of the blue gums at approximately 10 years of age provides a direct economic
return to the landowner. The researchers anticipate that Eucalyptus globulus
is able to coppice for subsequent harvests at approximately 10 year intervals,
and that E. globulus can profitably yield 3 crops (in 30 years) before
the stand needs to be replaced.
Belt Width
Choice of belt width is an important design variable within a blue gum alley farming enterprise. Blue gums planted in narrow belts offer the advantage of increased wood volumes on edge trees, relative to the volume of wood on inside row trees. The researchers determined that the mean volume of wood produced in the edge row is approximately 50% more than that of the second row after 5 years.
Therefore row 1 is significantly different from row 2, although rows 2 and 3 are not significantly different. Towards harvestable age (8.7yrs), this edge effect represents approximately 75% greater wood volume in row 1 relative to row 2.
This edge tree advantage diminishes rapidly as belt width increases and showed significant variation between the study sites.
Net Present Value of a 40
ha blue gum alley farming project with 40 m alleys under alternative assumptions
about extra wood production of edge trees.
Although the data was extrapolated to apply to narrow tree belts, the research indicates that two-row belts have a particular advantage in areas with lower rainfall, where both tree growth rate and stumpage are likely to be lower. The report suggests that two-row belts also have the advantage that the risk of drought deaths in blue gums is likely to be reduced.
The increased wood volume produced by the edge trees necessitates pruning. However, it has been shown that the pruning costs do not negate the advantages of the edge effect. Low-pruning of edge trees enables harvesting equipment to operate satisfactorily, so that edge trees are then able to be harvested using conventional equipment. The advantages of pruning include:
Alley Width
In determining an optimal blue gum alley design, the choice of alley width is mainly affected by the relative profitability of grazing and blue gums as separate enterprises.
The report shows that blue gum alleys are only profitable for alley widths between 40 m and 80 m if Gross Margin (GM) is $150/ha/yr.
When GM is $50/ha/yr, blue gum alleys are profitable for all alley widths. The researchers found that a comparatively higher stumpage and yield of blue gums enhanced the value of narrow alleys relative to wide alleys.
This should be considered within the context that trees within two tree heights of each other compete for resources, thus mutually suppressing growth and substantially reducing profitability.
At harvestable age (10 years), blue gums in plantations yielding 20 m3 of blue gum pulplogs/ha/ yr reach a maximum height of approximately 20 m.
This corresponds with a minimum alley width within a blue gum alley farming enterprise of 40 m.
In fact the research indicates that alleys 40 m wide represent the most profitable spacing of belts.
Additionally, independent hydrological research has shown that trees will not affect desired water use beyond 10-30 m, and that for alleys wider than 50 m, trees may have little effect on watertables within the alleys. This has implications for those alley farms where the primary function is to contribute to catchment sustainability.
Orientation of Alleys
Total wood volume produced from a blue gum alley farm has not been found to correlate strongly with a specific orientation of the alleys.
However, optimal pasture production is likely to be achieved where blue gum belts are oriented running in a north/south direction, rather than in an east/west direction. This orientation has been shown to minimise the tree/pasture interface competition, the subsequent pasture loss and, ultimately, grazing (or fodder conservation) losses. The research indicates that as the tree age increases, the tree/pasture interface competition increases, resulting in an increasing width of pasture loss.
Predicting Effects on Pasture
For predictions of total seasonal pasture loss for an existing tree belt at any given tree age, a linear regression has been developed: Total seasonal loss width (m) = 0.64 (tree age in years) + 2.73 r² = 0.76 Where predictions are required for future expected autumn pasture loss, the linear regression relationship between the tree age and the width of pasture loss is: Autumn loss width (m) = 0.95 (tree age in years) + 2.5 r² = 0.87 In this study, autumn pasture yield losses were found to be greater than those recorded for the total season pasture loss. This wider autumn pasture loss distance may exacerbate the autumn/winter feed gap, with the potential to reduce whole farm profitability where blue gum alley farming is an integral part of that operation.
The researchers anticipate that the tree/pasture interface competition effect on pasture yield loss during the entire second and third tree harvest cycles will approximate (if not exceed) that predicted for the first harvest cycle.
The report finds that, for the two rainfall categories of < 750 mm and > 750mm, tree belt orientation and tree age were the two significant variables that affected the interface competition between trees and adjacent pasture. Within the rainfall ranges studied, the available moisture did not limit tree growth.
Consequently, exacerbated
tree/pasture interface competition was avoided.
|
|
Summary
This research has generated useful information regarding the optimal design of treebelts within blue gum alley farming enterprises.
However, due to differences between sites in terms of tree growth, soil depth and fertility, grazing returns and distance to the chip mill, a single best design for all situations cannot be determined.
The ultimate choice of design for planting blue gums in an alley farming layout must rest with the landowner, contingent with whole farm planning principles.
Future research may focus
on the variation of the edge tree effect, by fully integrating all variables
within the economic model.
|
