Minna Malmivaara-Lämsä

Effects of wear and above ground forest site type characteristics on the soil microbial community structure in an urban setting

We studied the effects of wear on the understorey vegetation and the soil microbial community structure (phospholipid fatty acid pattern) in urban forests of medium fertility and of varying size in the capital area of Finland, Helsinki. These forests are important sites of recreation for a large number of residents. Consequently, the cover of understorey vegetation is affected by trampling. In the study, the cover of ground layer plant species (mosses) was found to be lower than in rural reference areas. We found that microbial activity, measured as soil respiration, was lower in the most worn forest patches as compared to less worn sites. Further, the microbial community structure of the humus layer changed due to the effects of wear. By comparing the PLFA pattern in trampled and un-trampled forest patches, we found out that the most important factors affecting the structure of microbial community were the dominant tree species (the proportion of broad-leaved tree species in relation to conifers), and the composition of the understorey vegetation. Thus, we could conclude that wear affects the microbial community structure through changes in vegetation, in the quality of litter shed, and through resultant changes in the humus pH, rather than only through soil compaction.

Quantifying the effects of trampling and habitat edges on forest understory vegetation – A field experiment

We investigated the effects of human trampling on boreal forest understory vegetation on, and off paths from suburban forest edges towards the interiors and on the likelihood of trampling-aided dispersal into the forests for three years by carrying out a trampling experiment. We showed that the vegetation was highly sensitive to trampling. Even low levels of trampling considerably decreased covers of the most abundant species on the paths. Cover decreased between 10 and 30% on paths which had been trampled 35 times, and at least by 50% on those trampled 70-270 times. On-path vegetation cover decreased similarly at forest edges and in the interiors. However, some open habitat plant species that occurred outside the forest patches and at forest edges dispersed into the forests, possibly through the action of trampling. A higher cover percentage of an open habitat species at the forest edge line increased its probability to disperse into the forest interior. The vegetation community on, next to, and away from lightly trampled paths remained the same throughout the trampling experiment. For heavily trampled paths, the community changed drastically on the paths, but stayed relatively similar next to and away from the paths. As boreal vegetation is highly sensitive to the effects of trampling, overall ease of access throughout the forest floor should be restricted to avoid the excessive creation of spontaneous paths. To minimize the effects of trampling, recreational use could be guided to the maintained path network in heavily used areas.

The effects of soil fertility on the abundance of rowan (Sorbus aucuparia L.) in urban forests

The amount of rowan saplings has increased considerably in urban forests in Finland. In this study, we investigated the effects of soil fertility on rowan abundance. Urban forests studied were more fertile than rural forests, and consequently included more rowans than reference areas. The abundance of rowan increased with increasing soil fertility in urban areas, being the highest at forest edges. Furthermore, rowan did not suffer from trampling, and the presence of other trees and saplings did not restrict its growth in relatively open urban forests. We conclude that the effects of urbanization, e.g., edge effects, and factors related to trampling (e.g., dog excrement), may increase forest soil fertility creating favorable conditions for rowan. To control the spread of rowan in urban forests, we recommend that open forest edges with a large number of broad-leaved trees should be avoided, and recreational use of forests should be guided to the maintained path network.

Short-term effects of mechanical and biological treatments on Sorbus aucuparia L. sprouting in mesic forests in Finland

Abstract In reforestation areas in Finland, rowan (Sorbus aucuparia L.) can form dense thickets restricting the growth of commercially more valuable conifers. In this study we compared three different management methods to control excessive growth of rowan. These methods were traditional (mechanical cutting 10–15 cm above ground level), 1 m cut height treatment (saplings were cut 1 m above ground level), and biological control (as traditional method, but freshly cut stumps were squirted with mycelium of a fungus, Chondrostereum purpureum [Pers. ex Fr.] Pouzar). The short-term results one year after the treatments revealed that biological control was the best way to restrict rowan sprouting as the proportion of dead stumps was highest. Furthermore, the number and height of stump sprouts were even two times lower in the biological control than in the mechanical treatments. Although the biological control had the highest number of root suckers, the total number of stump sprouts and root suckers together was indicatively lower than in the other methods (p < 0.10). Based on our results C. purpureum treatment seems promising. Yet, more efficient fungus strains and better methods to spread the fungus on stumps are needed before this method is applicable at commercial scale.