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The hypothesis that fast-growing breeds of willow (Salix spp.) are more sensitive to nutrient and water stress and less efficient in nutrient- and water-use than slower-growing natural willow clones was tested. Cuttings of a natural clone of S. viminalis L. collected in Sweden (L78183) and a hybrid clone of S. schwerinii E. Wolf. x S. viminalis L. ("Tora") were grown outdoors in pots under various experimental conditions in a full-factorial design. The experimental conditions included three fertilization, two irrigation and two temperature regimes. Classical growth analysis techniques, based on an initial and a final harvest, were used as a screening method, together with calculation of intrinsic water-use efficiency (foliar carbon isotope ratio; delta13C). In addition, nitrogen-use efficiency was calculated as the product of nitrogen productivity and mean residence time of nitrogen on an annual basis. There were significant differences in plant structural parameters (leaf area ratio, specific leaf area) and water-use efficiency between the clones. Furthermore, several clone x treatment interaction effects on various growth parameters indicated that the clones adapted to specific environments in different ways. "Tora" plants produced up to 25% more shoot biomass than plants of the natural clone in response to high rates of fertilization and irrigation, whereas clone ranking was reversed in most other treatments. The results support the hypothesis that fast-growing hybrids are more sensitive to nutrient and water stress than slower-growing natural clones. The hypothesis that natural clones have higher resource-use efficiency than fast-growing hybrids was supported with respect to water, but not nitrogen.

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This chapter provides a practical worldwide overview of the environmental applications of poplars and willows. The chapter aims to synthesize the latest knowledge on these applications with respect to sustainable livelihoods, land use and restoration. The applications covered include land protection, watershed stabilization, waste management and other ecosystem services.

Summary1. The effects of previous-year environment on current growth response were tested in seedlings of Mountain Birch ( Betula pubescens Ehrh. ssp. czerepanovii [Orlova] Hämet-Ahti), a subarctic tree species with indeterminate shoot growth. 2. Mountain Birch seedlings were pot-grown outdoors in subarctic Sweden for 2 years and showed a clear delay in growth response when fertilization and temperature were reduced after the first year. The seedlings were grown under four experimental treatments (two temperatures and two nutrient availabilities) in 1994, and under low-temperature / low-nutrient conditions in 1995. 3. When nutrient supply and /or temperature was reduced in 1995 compared to 1994, the seedlings maintained the high relative growth rates (RGR) of the previous growing season, although the internal plant N accumulation rate was lower than in 1994. This resulted in decreasing plant N concentration (PNC), and a poor relationship between RGR and PNC during 1995. The high RGR in 1995 was achieved in response to phenotypic adjustments (e.g. number of foliar buds) to a more favourable environment in the past, and by dilution of the internal nutrient storage. 4. The effects of delayed responses found in this study indicate problems for the interpretation of results from growth studies performed under any climate with great yearto-year variability, such as the subarctic, because a delay in growth response could distort the relationships between plant growth, resource availability and climate. Predictions of current growth are therefore meaningless if the previous history of the plants is not taken into account.