Effects of spacing, species and coppicing on leaf area, light interception and photosynthesis in short rotation forestry
Introduction
Short rotation forestry (SRF) is one option by which the European Union may achieve its stated objective of increasing the proportion of its energy obtained from renewable sources from 5% to 12% by 2010 [1]. SRF offers several advantages over the use of fossil fuels. It is carbon neutral and produces 80% less sulphur emissions during combustion than fossil fuels although NOx emissions are 10% greater [2]. In addition, SRF provides environmental benefits due to increased biodiversity when compared to arable systems. Insect and bird populations are enhanced due to the complex structure and physical diversity associated with SRF [3].
Rapid establishment of SRF is important both environmentally and economically. Early growth of at least some species has been shown to be highly sensitive to weed competition [4], [5]. To minimise the use of herbicides, with consequent environmental and economic benefits, canopy cover by the trees is needed to suppress the competing ground vegetation. Full site occupancy is achieved more rapidly at close spacing but the additional cost of planting material represents a major proportion of the investment during establishment [6], [7]. Maximum yields may not occur for 6–8 years, by which time intense inter-plant competition may increase the risk of damage from pests and disease due to plants being subjected to greater stress at closer spacing [8]. In addition to planting density, the decision to produce coppice or single stems may also affect the time taken to reach canopy closure. Few comparisons have been made regarding the early canopy development in coppice and single stems and those that do exist have often confounded site differences with cultural treatments [9].
The aim of the present study was to quantify the factors that influence early canopy development and growth in SRF on a converted agricultural site in Central Scotland. Particular focus was on species differences and how these are affected by planting density and by coppicing.
Section snippets
Site description
The experiment was established on agricultural land previously cropped for spring barley and located in central Scotland (55°40′N,3°52′W) at an elevation of above sea level. Soils in the area are poorly drained eutric gleysols making them difficult to manage for agriculture due to poor trafficability during much of the year. The climate is cool-temperate with annual precipitation of and mean monthly temperatures ranging from 0°C to 15°C.
Three species have been used in the present
Survival
Survival was high (>95%) in all treatments except for alder coppice which suffered 50% mortality following coppicing in winter 1989. This led to uneven stocking of around in alder coppice with an average spacing of , similar to that in the single stem treatments [10].
Biomass
Total above-ground biomass in July 1995 ranged from 51 to dry matter with an average dry matter production of approximately (Table 1). Values for alder and poplar single stems planted at
Discussion
Annual yields in the present study lie in the range reported by Mitchell et al. [7] for similar species growing in the UK and agree with expected yields of 10– for SRF in temperate climates [12], [13]. Red alder is known to be prone to damage when coppiced [14], [15] with factors such as season, shoot diameter and age all affecting survival and resprouting following coppicing [14], [16]. In the present study, the mild winter prior to coppicing and the cut-back taking place in late
Acknowledgements
The authors acknowledge the co-operation of staff from the Central Scotland Countryside Trust and from Hartwood Home Farm in the establishment and maintenance of the experimental site. This work was funded by the Scottish Executive Environment and Rural Affairs Department.
References (30)
- et al.
Establishment needs for short rotation forestry in the EU to meet the goals of the commission's white paper on renewable energy (November 1997)
Biomass and Bioenergy
(1998) Environmental justification for short-rotation forestry in Sweden
Biomass and Bioenergy
(1998)Short rotation coppice for energy: towards ecological guidelines
Biomass and Bioenergy
(1998)- et al.
Short-rotation forestry—operations, productivity and costs based on experience gained in the UK
Forest Ecology Management
(1999) New cultural treatments and yield optimisation
Biomass and Bioenergy
(1995)- et al.
Short-rotation coppiced vs non-coppiced poplara comparative study at two different field sites
Biomass and Bioenergy
(1996) - et al.
Comparison of biomass production in coppice and single stem woodland management systems on an imperfectly drained gley soil in Central Scotland
Biomass and Bioenergy
(1999) - et al.
Radiation interception measurement in poplarsample size and comparison between tube solarimeters and quantum sensors
Agriculture Forest Meteorology
(1997) - et al.
Short-rotation plantations of balsam poplars, aspen and willows on former arable land in the Federal Republic of Germany. I. Site-growth relationships
Forest Ecology Management
(1999) Effects of cutting season, stump height and harvest damage on coppicing and biomass production of willow and birch
Biomass and Bioenergy
(1994)