Effects of nurse trees, spacing, and tree species on biomass production in mixed forest plantations

ABSTRACT

Growing concern about increasing concentrations of greenhouse gases in the atmosphere, and resulting global climate change, has spurred a growing demand for renewable energy. In this study, we hypothesized that a nurse tree crop may provide additional early yields of biomass for fuel, while in the longterm leading to deciduous stands that are believed to better meet the demands for other ecosystem services. Ten different species combinations were planted, with two different stocking densities, at three different sites in Denmark. Significant differences, with regard to biomass production, were observed among the different sites (P < .001) and species combinations (P < .001) after 12–13 growing seasons. Compared to pure beech stands, mixtures with beech and Japanese larch on average produced 4.4 t ha⁻¹ yr⁻¹ more biomass. The additional biomass production was similar to what was obtained in stands with conifers only (Sitka spruce, Douglas-fir and Japanese larch), which produced 4.9–6.1 t ha⁻¹yr⁻¹ more biomass than the pure beech stands. No effects of initial planting density (P = .19), or of initial weeding (P = .81), on biomass production were observed. Biomass production of the broadleaved crop was in most cases reduced due to competition. However, provided timely thinning of nurse trees, the qualitative development of the trees will allow for long-term timber production.

KEYWORDS:

• Biomass production
• energy
• conifer
• broadleaves
• growth

Acknowledgments

We would like to thank Anders Tærø Nielsen and Palle Madsen for their effort, commenting on previous versions of this manuscript. Finally, we wish to thank Tania Fredborg Nielsen for careful language editing.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The project was supported by a special grant from the Danish Nature Agency, Ministry of Environment, and was conducted within the Nordic Energy Research supported ENERWOODS project.