Effects of Short Rotation Forestry on earthworm community development in the UK

Abstract

Short Rotation Forestry (SRF) has been introduced to the UK as a method to increase woody biomass production. However, some SRF species have raised concerns about potential impacts on the environment. A largely unknown aspect of SRF is the quality and quantity of leaf litter, and its impact on soil fauna, of which the earthworm community is a major component. Earthworms have direct impacts on soil biogeochemistry of SRF systems, and the tree species can impact on the associated earthworm community. The aim of this study was to determine the effects of SRF species on earthworm diversity and population growth. Earthworm surveys and a litter mass loss study were conducted at a range of SRF trial sites. Associated laboratory experiments were also carried out to examine the direct effect of SRF litter on earthworm growth and reproduction. Overall survey results suggested that SRF affects earthworm community development depending on tree species, soil type and land-use history. Six years of Eucalyptus nitens development on a former arable loamy soil significantly (p<0.05) increased earthworm density (152m−2) compared with similarly derived Eucalyptus gunnii (47m−2) and an arable control (51m−2). However, 5years of similar Eucalyptus development on a reclaimed site supported earthworm community development similar to the adjacent pasture control. A leaf litter mass loss (litterbag) study at an ex-arable site with high earthworm density (298m−2) and species richness (n=6) suggested that leaf litter removal was 100% for Fraxinus excelsior after 9months whilst Acer pseudoplatanus, Betula pendula, Castanea sativa and E. nitens lost more than 85% mass over 12months. Laboratory feeding experiments with hatchling and mature Lumbricus terrestris, a deep burrowing earthworm species, showed that the litter of non-native E. nitens supported earthworm production rates similar to those of some native SRF species such as B. pendula, and F. excelsior. Alnus glutinosa yielded the highest earthworm production whilst C. sativa had the lowest compared with other selected SRF species. In terms of development and maintenance of earthworm populations, this work suggests use of rapid-growing native tree species such as A. glutinosa, B. pendula, F. excelsior and non-native E. nitens for SRF production.