Natural revegetation on forest topsoil and subsoil along roadsides in boreal forest

Questions: Does natural revegetation from indigenous soil improve the restoration success of roadside areas? What are the effects of topsoil, subsoil and fertilization on natural revegetation? Location: Akershus county, SE Norway (10°25′ E, 59° 44′ N). Methods: We used a recently constructed road through a boreal coniferous forest for a three year (2000–2002), fully replicated revegetation experiment (six replications). Treatments were soil type (two levels; one topsoil and one subsoil type) and fertilization (two levels; NPK and unfertilized control). Ordination methods, constrained ordination methods as well as univariate statistical methods, such as Wilcoxon's signed‐rank test and correlation analysis, were used to assess the relative importance and significance of treatments on the plant species composition. Results: There was no fertilization effect on species composition. The species composition on both soil types was stabilised by the second year. The species dominating the topsoil were more in accordance with the indigenous vegetation than was the case on the subsoil. The significant difference in species composition among blocks, persisting for the entire study period, indicated that local factors are important determinants of the outcome of revegetation. Conclusions: Unfertilized topsoil provides a revegetation result in better accordance with the indigenous vegetation than does subsoil.     

Partitioning the variation in a plot‐by‐species data matrix that is related to n sets of explanatory variables

Abstract. Variation partitioning by (partial) constrained ordination is a popular method for exploratory data analysis, but applications are mostly restricted to simple ecological questions only involving two or three sets of explanatory variables, such as climate and soil, this because of the rapid increase in complexity of calculations and results with an increasing number of explanatory variable sets. The existence is demonstrated of a unique algorithm for partitioning the variation in a set of response variables on n sets of explanatory variables; it is shown how the 2n– 1 non‐overlapping components of variation can be calculated. Methods for evaluation and presentation of variation partitioning results are reviewed, and a recursive algorithm is proposed for distributing the many small components of variation over simpler components. Several issues related to the use and usefulness of variation partitioning with n sets of explanatory variables are discussed with reference to a worked example.     

Disentangling complex fine‐scale ecological patterns by path modelling using GLMM and GIS

Question: How can statistical modelling tools (GLMM) and GIS be used as an aid in understanding complex ecological patterns? This general question was approached by using bryophyte demography data as an example. More specifically, we asked what is the contribution of terrain shape to explaining the performance and fate of plant individuals, controlling for all other known relationships? Location: Norway. Methods: Information on demography was obtained for 140 populations of the perennial clonal bryophyte Hylocomium splendens in Norway spruce forests during an 11‐year period (1992‐2002). Performance (size and branching pattern) was recorded for mature segments and fate was recorded for growing points. Positions of each of the more than 30 000 recorded bryophyte ramets were coupled with (micro‐) topographic characteristics (slope and convexity) derived from fine‐scale digital elevation models in a GIS framework. Carefully planned sequences of generalised linear mixed models (GLMM) were performed to test predictions from a conceptual path model. Results: We demonstrate strong dependence of size on branching, fate and on vertical position in the bryophyte carpet, and an effect of vertical position on branching pattern. Micro‐topography contributed to explaining plant performance by four different mechanisms: (1) a direct effect of slope on the segment's vertical position in the carpet; (2‐3) direct effects of both slope and convexity on fates of individuals via controls on risk of burial; and (4) an indirect effect of convexity on branching pattern via a direct effect on size. No indication of a direct effect of terrain on branching was found. Conclusions: Our study exemplifies the usefulness of GLMM for disentangling complex ecological relationships. Specifically, we recognise micro‐topography as a potentially important factor for plant demography in general and for performance and fate of individuals in particular.