Changes in the abundance of keystone forest floor species in response to changes of forest structure

Question Does the abundance of keystone forest floor species change in response to changes in the forest structure? Location Sweden Methods We used data from the S wedish N ational F orest Inventory to investigate changes in the abundance of three common species, as well as the total abundance of all understorey vascular plants (the field layer) in forests in the boreal and temperate parts of S weden. GLM s and GAM s were used to relate species abundance and temporal changes in abundances to forest structure and forest structural change. Results Productivity, measured as the site index, was the most important determinant of individual species' abundance. The volume of P icea abies , the density of tree stems and forest age were among the most important forest structural variables. We found that the dwarf shrub V accinium myrtillus , the narrow‐leaved grasses (mainly A venella flexuosa ) and the total field layer cover decreased in boreal S weden from 1994 through 2010 and that these changes coincided with an increase in forest density and with a reduction in forest age. Conclusions Changes in S wedish forests to higher tree layer density and younger age appear to contribute significantly to current changes in forest floor vegetation. The use of more intensive thinning practices to reduce the total density of the forest and to increase the proportion of broad‐leaved tree species and P inus sylvestris would favour the forest floor species in this study. Moreover, increasing forest age (i.e. the length of rotation periods) might favour V . myrtillus in particular, for which the time since disturbance is important for the recovery of pre‐disturbance abundance. However, increased thinning intensity and forest age will reduce the potential for wood production, implying a trade‐off between production of wood and maintenance of well‐developed forest floor vegetation.