Wood Ash Application Reduces Bryophyte Cover and Changes Species Composition in a Norway Spruce (Picea abies) Plantation

Ditte Ethelberg-Findsen,Flemming Ekelund,Regin Rønn

doi:10.3390/f12020178

Abstract

Return of wood ash from power plants to plantations makes it possible to recycle nutrients, counteract acidification, and to reduce economically costly waste deposition of the wood ash. However, current legislation restricts the amount of wood ash that can be applied and it is desirable to increase the allowed application dose, if possible, without negative effects on the plantation ecosystems. Here, we applied wood ash in levels corresponding to 0, 3, 9, 15, 30, and 90 t ash ha−1 and monitored the effect of the different ash doses on bryophytes in a Norway spruce (Picea abies) plantation with a dense bryophyte cover dominated by Hypnum jutlandicum, Dicranum scoparium, and Pleurozium schreberi. We used two complementary methods, image analysis, and pinpoint registration during a three-year period. To our knowledge, we are the first to apply this combined effort, which provides a much more exhaustive description of the effects than the use of each method separately. Moreover, the inclusion of a wide range of different wood ash levels enabled us to establish detailed dose-response relationships, which previous authors have not presented. The bryophyte cover decreased with increasing ash level with concomitant changes in species composition. At ash doses above the currently allowed 3 t ha−1, the ash significantly reduced the bryophyte cover, which only re-established very slowly. With increasing wood ash dose, the dominating species changed to Brachythecium rutabulum, Ceratodon purpureus, and Funaria hygrometrica. We conclude that application of more wood ash in spruce plantations than currently allowed will reduce total cover of bryophytes and cause a pronounced change in bryophyte species composition. These changes will in particular harm bryophyte species with specific environmental requirements and generally impair the bryophyte cover as habitat for invertebrates and its economic value for moss harvesting.

Highlights

Burning of fossil fuels is a serious threat to the global environment due to its climate changing effects
The soil pH increased with increasing wood ash doses in an asymptotic fashion up to a value of about 8 (Figure 2A)
We divided the values into two groups, those corresponding to the low ash doses (0–9 t ha−1) and those corresponding to the high ash doses (15–90 t ha−1)

Summary

Introduction

Burning of fossil fuels is a serious threat to the global environment due to its climate changing effects. Wood from energy plantations is increasingly used in power plants as a renewable alternative to fossil fuels. The removal of wood from the plantations results in net export of nutrients and causes acidification of the forest floor [1]. Recycling the wood ash to the plantations may solve both problems, as wood ash has a high pH and retains most of the plant nutrients, except N [2]. Wood ash contains potentially harmful heavy metals [2] and most countries have implemented legislation that restricts the amount of ash to be recycled. In Denmark, the maximum amount of wood ash that may be legally applied to a forest is 3 t ha−1 per 10 years, with an upper limit of three applications of 3 t ha−1 per 75 years [3]. The recommendations in Sweden, Finland, and Lithuania are very similar with respect to wood ash dose and frequency of ash application [4]

Methods

Results

Discussion

Conclusion