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Doctoral thesis, 2000

Steam treatment of forest ground vegetation to improve tree seedling establishment and growth

Norberg, Gisela


Mechanical soil scarification is the commonly used site preparation technique in Sweden today and there is a need for alternative site preparation methods to fulfil some environmental goals in Swedish forestry. Thermal vegetation control could be an alternative method that reduces the competing forest ground vegetation with minimal disturbance to the mineral soil and ground floor. The aim with this work has been to investigate if it is possible to control forest ground vegetation by steam treatment as an alternative site preparation method before planting or seeding. Studies were conducted on four sites, each representing main Swedish forest vegetation types, i.e. the ground vegetation was dominated by crowberry (Empetrum hermaphroditum Hagerup), bilberry (Vactinium myrtillus L.), heather (Calluna vulgaris (L.) Hull) and wavy hair grass (Deschampsia flexuosa (L.) Trin.). Steam generally controlled recolonisation of vegetation on all investigated sites for a longer time than soil scarification. Especially in controlling grass vegetation steam treatment was much more effective than soil scarification. The establishment and growth of seeded Scots pine seedlings also improved after vegetation control by steam treatment compared to that in intact vegetation. For all sites, both steam treatment and soil scarification improved seedling height growth compared to seedlings planted in intact vegetation. In the bilberry and heather dominated sites seedling growth in steam treated plots was even better than for seedlings planted in mechanical soil scarified plots. Further, key biological soil processes such as microbial activity and mycorrhizal colonisation were not negatively affected by steam treatment. The conclusion made from these studies is that steam treatment has the potential to be used as an alternative site preparation method especially on sites dominated by ericaceous vegetation. However, the method requires some further technical development before it may be used on an operational scale.


Calluna vulgaris; Deschampsia flexuosa; Empetrum hermaphroditum; Norway spruce; Scots pine; soil scarification; thermal vegetation control; Vaccinium myrtillus

Published in

Acta Universitatis Agriculturae Sueciae. Silvestria
2000, number: 170
ISBN: 91-576-6054-9
Publisher: Department of Forest Vegetation Ecology, Swedish University of Agricultural Sciences

Authors' information

Norberg, Gisela
Swedish University of Agricultural Sciences, Department of Forest Vegetation Ecology

UKÄ Subject classification

Forest Science

URI (permanent link to this page)