Assessment of regional willow coppice yield in Sweden on basis of water availability

doi:10.1016/S0378-1127(98)00556-8

Forest Ecology and Management

Volume 121, Issues 1–2, August 1999, Pages 57-65

https://doi.org/10.1016/S0378-1127(98)00556-8 Get rights and content

Abstract

The aim of this paper is to assess the limitations by water on yield in southern Sweden on the basis of long-term records of precipitation and known water relations of willow. Data concerning relationship with water comes from a field experiment in central Sweden and data on yield, obtained in commercial cultivations, comes from a number of locations in southern Sweden. A simple water-limited yield model based on the concept of water-use efficiency was used to estimate regional production. The model showed good agreement with the actual yield at a large number of locations in southern Sweden. The model was then used to produce a map of average maximum stemwood production and it showed that the annual production would be 8–9 t ha in the northeastern part of southern Sweden, 9–10 t in eastern Sweden, 11–12 t in the very south and reach a maximum of 16–17 t in a narrow belt along the west coast. Relating these yield values to data, reported in literature regarding economics of short-rotation forestry, shows that water will be a critical factor in order to obtain good profitability in short-rotation forestry in Sweden.

Introduction

At present, the main reason for growing short-rotation forests (SRF) in Sweden is to produce fuel for energy. There are several benefits from this; one important advantage being the reduction of CO₂ emissions when wood fuels are used to replace fossil fuels. The profitability of such cultivation, from the farmers point of view, is highly dependent on the annual yield of wood. The economics of SRF depends on many factors, but in a situation typical for Swedish conditions, the yield must be above 8 t of wood dry matter per hectare per year to reach a positive result before land rental costs (Rosenqvist, 1997). With land rental costs included, an annual production of 12–16 t of wood dry matter per hectare is necessary to reach a break-even level in willow plantations. Considering also root and leaf growth, such production of wood biomass requires a total annual dry matter production of ca. 25 t. To obtain such production levels in the long term, it is necessary to add fertilisers on all soil types and when nutrients are not limiting the production, then other factors such as water might become limiting.

The studies on water balance of willow SRFs in Sweden have previously shown that the evaporation during the growing season is high compared to the Penman open water evaporation (Grip et al., 1989; Lindroth and Iritz, 1993; Persson and Lindroth, 1994). Lindroth and Halldin (1988)analysed evaporation from hypothetical willow stands, growing at potential (no water and nutrient limitation) rates, at different locations in southern Sweden for a 15-year period using a simulation model (Halldin, 1989) and they estimated mean seasonal evaporation to be ca. 700 mm for such stands. In the southern part of Sweden, the precipitation during the growing season varies between 350 and 550 mm on average (Eriksson, 1992), except for a shallow belt along the west coast where it reaches 750 mm. This, in connection with a relatively large annual variation, means that water availability will be a crucial growth factor at many sites. In fact, the results so far from the commercial cultivation indicate that the yield will be far below the potential levels and that water is one of the main limiting factors.

In this paper, we try to assess the limitations by water on yield in southern Sweden on the basis of long-term records of precipitation and known water relationship of willow. Data on water relationship come from a field experiment in central Sweden and data on yield comes from a number of locations in southern Sweden. A simple water-limited yield model is proposed and then used to estimate regional production.

Section snippets

Water use and water relationship of willow

The water use of willow was determined in a field experiment at Ultuna (59°49′ N, 17°40′ E, 5 m asl) near Uppsala in central Sweden. A former agricultural field of 2.7 ha was planted with two cuttings of Salix viminalis L. per m² in 1984 on heavy clay soil. The stand was irrigated and fertilised and it was cut for the first time in winter 1986/1987. The evaporation from the field was measured in 1986 and 1988 during the main part of the growing seasons using the energy balance Bowen ratio method.

Results and discussion

The evaporation measurements during 1986 and 1988 clearly show that willow plantations use a large amount of water (Fig. 3). The maximum values are around 7 mm day⁻¹ in 1986 and slightly lower in 1988. The evaporation of willow is about twice that of the traditional type of forests, a mixed pine and spruce forest, growing in the same region (Grelle et al., 1997). The values are also consistently larger than the Penman evaporation, except at a few occasions. In general, Penman evaporation reaches

Acknowledgements

This study was financed by the Swedish Board for Industrial and Technical Development (NUTEK).

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Assessment of regional willow coppice yield in Sweden on basis of water availability

Abstract

Introduction

Section snippets

Water use and water relationship of willow

Results and discussion

Acknowledgements

J. Hydrology

J. Hydrol.

J. Hydrol.

Water use by intensively cultivated willow using estimated stomatal parameter values

Hydrol. Proc.