Jouni K. Nieminen

Abstract Wood ash effects on soil animals in a boreal forest ecosystem are reviewed focusing on recent results on interactive effects of wood ash and organic amendments, and laboratory microcosms as a tool to understand soil food webs are discussed. Loose wood ash can reduce the populations of enchytraeids, collembo — lans and mites, but increase nematode populations particularly in experimental laboratory ecosystems with little or no primary production. Recent studies indicate that the repressive effect on enchytraeids depends on carbon availability. Carbohy­drate supply seemed to alleviate the negative wood ash effect on enchytraeid body size and abundance. The fact that carbon alleviated wood ash effects on enchy — traeids without any change in pH supports the view that wood ash effects on soil animals are partly indirect consequences of altered food resources. Experimental evidence suggests that the negative wood ash effect on enchytraeids is partly linked to increased bacteria-to-fungi ratio after wood ash application, and that this may be counteracted by carbohydrate addition.

4.1 Introduction

Only a fraction of the wood ash generated in power plants is recycled back to the forest ecosystem. For example, in Finland some 50% of the wood ash generated in energy production is utilized, and most of this is used for purposes other than forest fertilization (Finnish Forest Industries Federation 2008). Although the forest eco­system would, in principle, benefit from recycling the nutrients back to the har­vested sites, there are also problems such as short-term effects of elevated pH and levels of heavy metals on soil biota (Pitman 2006; see Chap. 1, Knapp and Insam 2011). In their review, Aronsson and Ekelund (2004) concluded that wood ash effects on soil fauna need to be investigated further.

J. K. Nieminen

Department of Biological and Environmental Science, University of Jyvaskyla, 40014 Jyvaskyla, Finland

e-mail: jouni. k.nieminen@jyu. fi

H. Insam and B. A. Knapp (eds.), Recycling of Biomass Ashes,

DOI 10.1007/978-3-642-19354-5_4, © Springer-Verlag Berlin Heidelberg 2011

Wood ash effects on soil animals have been investigated both in small-scale laboratory microcosms and in large-scale field experiments. Most laboratory experiments did not include any plants or included only one small tree seedling. Microcosms containing only heterotrophs are subsequently called heterotrophic microcosms, and microcosms including plants are called autotrophic microcosms. Further, loose wood ash was used in most studies, but today granulated ash is increasingly used as a forest fertilizer. Ash granules dissolve slowly in forest soil and increase the pH and the concentration of exchangeable cations slower than loose ash (Eriksson 1998). The properties of pure wood ash used in some studies are well known. The ash content of young and deciduous trees is higher than that of old and coniferous trees and the ash content of bark is manyfold that of stem wood (Hakkila and Kalaja 1983). Wood ash contains 1-6% phosphorus (P), 6-22% potassium (K), 19-33% calcium (Ca) and 2-5% magnesium (Mg), depending on the tree species and the component (Hakkila and Kalaja 1983). The Ca content of bark and branch ash is higher in relation to P, K and Mg than that of stem wood ash, and compared with other tree species, birch and alder ashes are P-rich (Hakkila and Kalaja 1983). The quality of ash obtained from power plants is more variable, depending on the fuel used (Korpijarvi et al. 2009). For example, in Finland the ash used in forest fertilization is typically a mixture of wood (logging residue, bark, sawdust) and peat ash, which contains less P, K, Ca and Mg but more aluminium and iron than wood ash (Hakkila and Kalaja 1983), and some nutrients are lost during the process. Consequently, the nutrient concentrations of ash from power plants are somewhat lower than those of pure wood ash. It is difficult to see whether differing wood ash effects were due to experimental conditions or ash properties. Specifically, tests of wood ash effects on soil animals at different levels of organic carbon availability were lacking until recently.

In this minireview I first briefly summarize the literature on wood ash effects on soil animals in general. Then I focus on recent laboratory microcosm experi­ments (plants excluded) and greenhouse experiments (grasses and conifer seedlings included) testing the effects of loose wood ash at different levels of carbon availability on enchytraeids and nematodes. Finally, the results are discussed focusing particularly on the use of laboratory microcosms as a research method.