Trampling tolerance of understorey vegetation in different hemiboreal urban forest site types in Finland

Abstract

The effects of trampling on the understorey vegetation were studied in boreal urban forests of different fertility in the greater Helsinki area, Finland. The three studied forest types in decreasing order of fertility were: 1) herb-rich heath forest, 2) mesic heath forest, and 3) sub-xeric heath forest. We inventoried the cover percentages of understorey vegetation in 40 herb-rich, 75 mesic and 40 sub-xeric biotopes located in 51 urban forests varying in size (0.6–502 ha). Cover percentages were compared to those of untrampled reference areas. In our study, trampling tolerance increased with increasing fertility of the forest type. Wear of understorey vegetation correlated positively with the number of residents (i.e. recreational pressure) around the forest patch. In general, understorey vegetation cover in all three forest types was lower than in the same forest types in untrampled reference areas. Ground layer cover in urban forests was less than half of that in reference areas. Mosses, lichens, and dwarf shrubs, especially Vaccinium vitis-idaea, proved to be sensitive to trampling and consequently decreased in cover. The cover of tree saplings, mainly Sorbus aucuparia, and some resilient herbs increased.