The economics of managing tree - crop competition in windbreak and alley systems

Abstract

Re-introducing trees and shrubs into agricultural landscapes as agroforestry systems establishes a tension between long-term objectives, such as increasing shelter, water use, nature conservation and harvesting tree products, and the short-term objective of maximising crop and pasture profitability. This paper describes the growth of crops, pastures and trees at the tree–crop interface in agroforestry systems and the economic returns from alley farming and windbreak systems using various tree–crop competition management strategies in the Esperance region of Western Australia. Severing lateral tree roots (root-pruning), harvesting mallees and allowing them to coppice, or thinning trees for sawlog regimes increased the yield of crops and pastures in the competition zone. In some instances, these increases were significant: root-pruning increased the annual return from crops grown in the competition zone of Pinus radiata by up to $548/km of the tree line at 1 site. Conversely, root-pruning reduced tree growth by 14–43% across all sites. Therefore, where trees provide benefits, such as shelter from damaging winds, the benefits of reduced tree–crop competition may not offset the consequent reduction in rate of tree growth. For mallee–crop alley systems on agriculturally productive soils, mallee growth rates must be high enough to compensate for crop losses in the competition zone. On less agriculturally productive soils, block-planting mallees may be more profitable than alley systems or crops without competition (sole-crops). This research has shown that competition management strategies can be used to manipulate the relative productivity of trees, crops and pasture at the tree–agriculture interface. The use of these strategies will depend on the relative economic value of tree and crop products and the value placed on other tree benefits, such as shelter and reduced groundwater recharge.

The extent and cost of mallee - crop competition in unharvested carbon sequestration and harvested mallee biomass agroforestry systems

“…Harvesting mallees on a 1-2-year interval and root-pruning of unharvested mallees have been shown to improve agricultural production in the competition zone at a limited number of sites (Sudmeyer 2001;Sudmeyer and Flugge 2005). However, more recent analysis has suggested that harvest intervals significantly longer than 2 years are necessary to achieve commercially attractive mallee biomass yields (Bartle and Abadi 2010).…”

“…Sheep income was derived from average productivity of wool and sheep enterprises for the various regions as given in Bankwest (2006Bankwest ( , 2008 and updated according to the indexes of prices paid and received (ABARES 2011). The cost of root-pruning was assumed to be $15 km -1 for each side of the belt (Sudmeyer and Flugge 2005) and was indexed according to ABARE's index of prices paid (ABARES 2011). Input costs for pasture were applied for all distances !2 m from the belt, but only where crop had actually been sown for a particular site-year.…”

“…Australian research has shown that competition for water is the primary cause of reduced agricultural yields in the competition zone and that the economic impacts of competition are generally not offset by the productivity benefits of wind-speed reductions and associated micrometeorological changes (George-Jaeggli et al 1998;Jones and Sudmeyer 2002;Sudmeyer et al 2002aSudmeyer et al , 2002bUnkovich et al 2003;Oliver et al 2005;Sudmeyer and Flugge 2005;Bennell and Verbyla 2008;Huth et al 2010).…”

“…Growing the mallees in this way maximises the mallee-agriculture interface and the ability of the mallees to capture resources from the competition zone alongside the belts. However, this increased mallee growth comes at the cost of competition with adjacent crop and pasture (Sudmeyer 2001;Sudmeyer and Flugge 2005).…”

A sustainable agricultural landscape for Australia: A review of interlacing carbon sequestration, biodiversity and salinity management in agroforestry systems

“…Shelterbelts are planted usually in a linear configuration of perennial woody vegetation and are maintained primarily to conserve soil moisture, reduce wind erosion (Sudmeyer and Flugge, 2005), and provide protection for crops, pastures and livestock (Carberry, 1997 andBrouwer, 1998). Economic analyses for the National Windbreaks Program across southern Australian agricultural regions found that windbreaks either lead to only a small financial gain or were cost neutral (Cleugh, 2003); carbon-offsetting benefits were not considered in this analysis.…”