Alley coppice: an evaluation of integrating short rotation coppice and timber trees

This paper summarises the main results from a recent research project focused on an innovative Alley Coppice (AC) land use system. We report on an AC system comprising standard trees for the production of valuable wood and the alley intercropping of short rotation coppice trees (SRC) for the production of bioenergy. Much of this work was carried out within the European project AgroCop (2012-2014) that combined field experimentation with bio-economic modelling. Two experimental plantations are located in Italy and France. The first plantation (9 years old) was used to study the intercropping of Pyrus spp. and Sorbus spp., as standard trees, with poplar SRC. Current measurements do not show any difference in stem height between intercropped standard trees and trees in pure plantation forestry. This was probably due to shading by the SRC canopy on standard trees. Nevertheless, this light competition has improved the stem form of standard trees, with a main bole almost straight and free of defects. In France, the poplar SRC crop was established into the alleys of a hybrid walnut tree plantation (18 years old) in a system we term: delayed alley coppice. Poplar growth was strongly limited by the shade of the walnut trees, although some microclimatic mitigation of water stress was observed on poplar shoots during the peak of summer heat. Biophysical modelling was conducted with the calculation tool YDEAL, comparing AC (hybrid walnut intercropped with poplar SRC) vs SRC monoculture vs walnut forestry monoculture. Simulations were performed on a 60 years rotation cycle of AC (harvesting cycle for the standard trees), and three cycles of 20 years for the poplar SRC, with triennial coppicing. Three growth condition scenarios were studied, namely poor, medium and optimum site conditions, mostly according to average yield data of poplar SRC (6, 10 and 15 t dry matter ha-1 year-1, respectively). The financial analysis was performed using a calculation tool named FinAC. The AC system could be as profitable as the forestry monoculture, in the best financial and environmental scenarios, with the wood price determining absolute system profitability. AC can provide a landowner with a periodical annual income during the growth of standard trees. The feasibility of AC is partly limited by wood market uncertainty, the use of farmland for a medium-long period with the same culture, and the current difficulty in estimating AC profitability. AC could be used as a temporary system (10-15 years) to improve the stem form and wood quality of standard trees