Ann Dolling

Interference of bracken (Pteridium aquilinum L. Kuhn) with Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst.) seedling establishment

Abstract The nature of interference of bracken with Scots pine and Norway spruce seedling establishment was considered in three field experiments. In a seeding experiment, it was found that Scots pine germination was highest on exposed mineral soil and lowest when intact bracken litter and humus were present, suggesting adverse effects of litter and humus on pine regeneration probably due to phytotoxicity. In a second experiment, smothering by bracken caused high mortality of Scots pine seedlings while Norway spruce seedlings were relatively unaffected. Mortality for both Scots pine and Norway spruce seedlings was low when planted in a adjacent Scots pine-bilberry stand with no bracken. Annual shoot growth of Norway spruce was higher in bracken than in Scots pine-bilberry vegetation while no differences in shoot growth between these two vegetation types occurred for Scots pine. In a third experiment, activated carbon was added to the ground under Norway spruce seedlings planted in bracken to adsorb possible phytotoxic compounds released by bracken. The addition of carbon had no effect on seedling mortality or growth rate, indicating that the seedlings were not susceptible to allelochemicals released by bracken. Since large Norway spruce seedlings were relatively unaffected by bracken interference in this study, artificial regeneration with containerized Norway spruce seedlings is suggested to achieve an acceptable conifer tree establishment on clear-cuts invaded by bracken.

SEASONAL VARIATION IN PHYTOTOXICITY OF BRACKEN (Pteridium aquilinum L. KUHN)

Laboratory bioassays were used to test for the phytotoxicity of volatile compounds, fresh plant material as a seed bed, and water extracts from bracken [Pteridium aquilinum (L.) Kuhn] pinnules to germination and seedling growth of aspen (Populus tremula L.) and Scots pine (Pinus sylvestris L.). Fronds were sampled from two bracken populations, one in the south and one in the north of Sweden. All three bioassays showed inhibitory effects, and these varied seasonally with the most inhibitory effects occurring in May, June, and September. The peak of inhibition in May and June coincides with the start of the growing season when bracken still is immature and vulnerable to interference from other species. The increase in inhibitory effects in September appears to be due to transformation of natural products or an accumulation of inhibitory compounds that are released during decomposition following frond death. Addition of activated carbon did not remove the inhibitory effects.

The vegetative spread of Pteridium aquilinum in a hemiboreal forest : invasion or revegetation?

Abstract The purpose of this study was to determine whether Pteridium aquilinum (L. Kuhn) invades new ground or remain static under a closed forest canopy. It was also to study whether the species invades into new areas or revegetate previous occupied ground after clear-cutting in the hemiboreal zone. Two separate experiments were conducted over a six-year period: (1) The change in P. aquilinum frond density and cover under a closed tree canopy was studied on permanent plots; (2) P. aquilinum spread after clear-cutting was studied in terms of expanding fronts into new ground. The density of fronds did not change beneath the closed tree canopy during the study period. Expansion of the front of adjacent established P. aquilinum into one of two clear-cut sites was extremely rapid indicating an already present rhizome system, while expansion into the other site without rhizomes present was very slow. The results indicate that P. aquilinum does not increase its frond density or colonize new ground in the closed forest or invade new ground on clear-cut areas in the studied forest stands, but instead revegetates clear-cut areas in which it has previously been more abundant. However, forestry practices such as clear-cutting in areas in which P. aquilinum is sparsely distributed in the field layer in the closed forest prior to clear-cutting results in an increasing density of P. aquilinum which is sufficient to restrain forest regeneration.

Can rehabilitation in boreal forests help recovery from exhaustion disorder? The randomised clinical trial ForRest

Modern society is faced with increasing incidence of mental and behavioural disorders. The objective of this study was to evaluate whether visits to boreal forests can be utilised for rehabilitation from exhaustion disorder (ED). This randomised controlled trial comprised of a forest rehabilitation group (n = 35) and a waiting list group (control group) (n = 43) with subsequent cognitive behavioural rehabilitation (CBR) for all participants in both groups. The recovery from ED was compared between the forest rehabilitation and the control group at baseline, after the forest rehabilitation (3 months), and at the end of the CBR (1 year). Both groups had enhanced recovery from ED after the 3-month intervention period and at the end of the CBR (1 year), and there were no significant differences between the groups in terms of psychological health measures. Mental state, attention capacity and preferences for different forest environments were studied during the forest visits. Mental state was improved, but it showed some seasonal differences. A significant effect on attention capacity was found for single forest visits, but there was no effect found for the rehabilitation period as a whole. The most popular forest environments contained easily accessible, open and bright settings with visible water and/or shelter. Forest rehabilitation did not enhance the recovery from ED compared to the control group, but the participants’ well-being was improved after single forest visits.

Steam treatment as a vegetation management method on a grass-dominated clearcut

A field experiment was established to investigate whether a new site preparation technique by steam treatment could be used to control Deschampsia flexuosa vegetation. The experiment was conducted at a south Swedish clearcut dominated by Deschampsia. Growth and survival of planted Norway spruce seedlings in steam-treated plots were compared to seedlings planted in traditional soil scarified plots and in intact vegetation. A second experiment was conducted to study the duration of the heat in the soil during and after a steam treatment and its impact on vegetation reduction. Steam treatment efficiently killed the vegetation and duration for 60 s or more reduced the vegetation to less than 25% of that in untreated plots for 2 years. Steam treatment also reduced the vegetation to a greater extent than soil scarification. After the third growing season the total seedling height was greatest for spruce seedlings grown in steam-treated plots and soil scarified plots. The number of spruce seedlings attacked by pine weevil was about the same in steam-treated plots as in intact plots, however, seedling survival was significantly lowest in intact plots. Pine weevil damage on seedlings grown in steam-treated plots may have affected seedling growth negatively.