Interactive effects of past land use and recent forest management on the understorey community in temperate oak forests in South Sweden

Questions: Past agricultural land use and forest management have shaped and influenced the understorey composition in European forests for centuries. We investigated whether understorey vegetation assemblages are affected by (a) legacies from a historical infield/outland agricultural system (i.e., a system with nutrient-enriched vs nutrient-depleted areas), (b) recent management intensity (i.e., thinning/felling activities), and (c) the interaction of recent management and potential legacies. Location: Oak forests in Skane, south Sweden. Methods: We use three vegetation surveys (1983, 1993/94 and 2014) and notes on management and land-use history, available for 62 permanent 500 m(2) plots. We conducted linear mixed effect modelling to detect both main and interactive effects of past land use and recent management on understorey diversity measures and vegetation indicator values for light and fertility. We combined nonmetric multidimensional scaling with permutational multivariate analysis of variance and indicator species analysis to detect compositional differences caused by past land use and/or recent management. Results: Understorey diversity was mainly affected by management activities, but the former infield/outland agricultural system was an important determinant of understorey composition. Understorey composition of former infields reflected higher nutrient availability and lower light availability compared to former outland. Past land use and recent management had interactive effects on light-related understorey variables: for the less intensively managed plots, the outland plots contained more light-demanding species than the infield plots, while for the more intensively managed plots, the light-demanding signature of the understorey was similar for infield and outland plots. Conclusions: Different intensities of past land use as well as recent forest management influenced the composition of the forest understorey, and interactions were present. Therefore, careful consideration of both the long-term land-use history and the more recent disturbances due to forest management are necessary when making future predictions of understorey composition and diversity

Generation, Ranking and Unranking of Ordered Trees with Degree Bounds

We study the problem of generating, ranking and unranking of unlabeled ordered trees whose nodes have maximum degree of $\Delta$. This class of trees represents a generalization of chemical trees. A chemical tree is an unlabeled tree in which no node has degree greater than 4. By allowing up to $\Delta$ children for each node of chemical tree instead of 4, we will have a generalization of chemical trees. Here, we introduce a new encoding over an alphabet of size 4 for representing unlabeled ordered trees with maximum degree of $\Delta$. We use this encoding for generating these trees in A-order with constant average time and O(n) worst case time. Due to the given encoding, with a precomputation of size and time O(n^2) (assuming $\Delta$ is constant), both ranking and unranking algorithms are also designed taking O(n) and O(nlogn) time complexities.Comment: In Proceedings DCM 2015, arXiv:1603.0053