No abstract

We compared four types of 30-year-old forest stands growing on spoil of opencast oil shale mines in Estonia. The stand types were: (1) natural stands formed by spontaneous succession, and plantations of (2) Pinus sylvestris (Scots pine), (3) Betula pendula (silver birch), and (4) Alnus glutinosa (European black alder). In all stands we measured properties of the tree layer (species richness, stand density, and volume of growing stock), understory (density and species richness of shrubs and tree saplings), and ground vegetation (aboveground biomass, species richness, and species diversity). The tree layer was most diverse though sparse in the natural stands. Understory species richness per 100-m 2 plot was highest in the natural stand, but total stand richness was equal in the natural and alder stands, which were higher than the birch and pine stands. The understory sapling density was lower than 50 saplings/100 m 2 in the plantations, while it varied between 50 and 180 saplings/100 m 2 in the natural stands. Growing stock volume was the least in natural stands and greatest in birch stands. The aboveground biomass of ground vegetation was highest in alder stands and lowest in the pine stands. We can conclude that spontaneous succession promotes establishment of diverse vegetation. In plantations the establishment of diverse ground vegetation depends on planted tree species.

A phylogenetic trend previously observed is further supported: mixotrophy is rarely supported by 13C enrichment in the Chimaphila + Moneses clade, whereas it is frequent in the Pyrola + Orthilia clade. Moreover, pyroloid mixotrophy does not respond plastically to ageing or to light level. This contrasts with the usual view of a convergent evolution with orchids, and casts doubt on the way pyroloids use the carbon gained from their mycorrhizal fungi, especially to replace photosynthetic carbon.

The establishment of plantations is the most common method of opencast reclamation, but few studies have addressed the influence of planted trees on the recovery of biodiversity in new forest sites. The goal of this study was to determine whether the formation of herbaceous vegetation was dependent on the tree species planted on the spoil of a reclaimed oil shale opencast in northeastern Estonia. From 2002 to 2005, the vegetation in eight different site types (distinguished according to the age and composition of tree layer) was surveyed. The results confirmed that the development of herbaceous vegetation was controlled by the dominant species of tree layer. The highest number of herbaceous species was recorded in naturally developed mixed stands. As compared with other site types, the herb layers of the pioneer stage (the vegetation in recently reclaimed sites) and alder stands were the most different. In the terms of the competitive, stress-tolerant, and ruderal strategy types, alder (Alnus spp.) stands tended to enhance the growth of competitors, whereas stress-tolerant species were more abundant in pine stands. Herbaceous vegetation remained sparse in coniferous stands, whereas broad-leaved trees tended to improve the performance of herbaceous species. Our results concur with the suggestions that planting with different tree species is one prerequisite for the development of diverse herb layer.

Evergreen boreal plant species express high variability in their leaf traits. It remains controversial whether this within-species variability is constrained to the same leaf trait relationships as has been observed across species. We sampled leaves of three boreal evergreen woody species along a latitudinal gradient (from 57856 0 N to 69855 0 N). Leaf longevity (LL) of Pinus sylvestris L. and Vaccinium vitis-idaea L. correlated negatively with mean annual air temperature (MAT), whereas the LL of Ledum palustre L. was not affected by MAT. V. vitisidaea and L. palustre had a negative relationship between leaf mass per area (LMA) and MAT. In P. sylvestris, the LMA-MAT relationship was positive. A negative correlation between LL and LMA was significant only for P. sylvestris. Leaf nitrogen concentration was positively related to leaf phosphorus concentration in all three species. Leaf potassium concentration was related to nitrogen concentration only in L. palustre, and to phosphorus concentration in P. sylvestris and L. palustre. Our results demonstrate that although within the studied species the variation in some of the leaf traits may have the same degree as interspecific variation, there is no such intercorrelation of leaf traits within the studied species as has been observed across species.