Environmental predictability of taxonomic and functional community composition in high‐latitude streams

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Responses of ground vegetation species to clear-cutting in a boreal forest: aboveground biomass and nutrient contents during the first 7 years

Rapid growth of ground vegetation following clear-cutting is important to site productivity because vegetation retains nutrients in the ecosystem and can decrease nutrient leaching prior to stand re-establishment. Aboveground biomass, nutrient contents (N, P, K and Ca) and species composition of ground vegetation were determined 1 year before and for 7 years after clear-cutting of a mixed forest dominated by Norway spruce [Picea abies (L.) H. Karst.] in eastern Finland. The biomass of the feather mosses [Pleurozium schreberi Brid. and Hylocomium splendens (Hedw.) B. S.& G.] and the dwarf shrubs (Vaccinium myrtillus L. and V. vitis-idaea L.), which had dominated the ground vegetation in the mature forest, significantly decreased after clear-cutting. However, with the exception of H. splendens, these species had recovered within 3–5 years. The biomass of Deschampsia flexuosa (L.) Trin. considerably increased soon after clear-cutting, and Epilobium angustifolium L. appeared 3–5 years after cutting. These species contributed to the retention of nutrients not simply because of their biomass but also because of higher nutrient concentrations in their tissues. Total biomass and nutrient contents of the ground vegetation exceeded those of the pre-cutting levels. The proportion of ground vegetation biomass and nutrient contents represented by mosses decreased after cutting, while V. myrtillus, although reduced after cutting, remained a marked nutrient sink. The results suggest that H. splendens is the most sensitive species to cutting, but the biomass of P. schreberi, V. myrtillus and V. vitis-idaea return to initial levels soon after clear-cutting as do the nutrient contents of ground vegetation.     

Changes in the Above- and Below-ground Biomass and Nutrient Pools of Ground Vegetation After Clear-cutting of a Mixed Boreal Forest

Ground vegetation may act as a sink for nutrients after clear-cutting and thus decrease leaching losses. Biomass and nutrient (N, P, K, Ca) pools of ground vegetation (mosses, roots and above-ground parts of field layer) were determined one year before and five years after clear-cutting of a Norway spruce (Picea abies (L.) H. Karst.) dominated boreal mixed forest stand in eastern Finland (63°51′ N, 28°58′ E). Before clear-cutting the average biomass of ground vegetation was 5307 kg ha⁻¹, with nutrient contents of 46.9 kg N ha⁻¹1, 4.1 kg P ha⁻¹1, 16.2 kg K ha⁻¹1 and 13.9 kg Ca ha⁻¹1. The biomass and nutrient pools decreased after clear-cutting being lowest in the second year, the biomass decreasing by 46–65% in the cut plots. The nutrient pools decreased as follows: N 54–72%, P 36–68%, K 51–71% and Ca 57–74%. The decrease in ground vegetation nutrient uptake, and the observed reduced depth of rooting may decrease nutrient retention after clear-cutting and decomposing dead ground vegetation is a potential source of leached nutrients. These negative effects of clear-cutting on the nutrient binding capacity of ground vegetation was short-lived since the total biomass and nutrient pools returned to pre-cutting levels or were even greater by the end of the 5-year study period.     

The effects of habitat edges and trampling on understorey vegetation in urban forests in Helsinki,Finland

Question: How do habitat edges and trampling affect mesic (Myrtillus type) understorey vegetation in fragmented urban forests, and what are the relative strengths and spatial extent of these effects? Location: The city of Helsinki, southern Finland. Methods: Vegetation sample plots were placed at different distances from the forest edge. At each distance we selected plots on, next to and away from paths of different levels of wear, and the covers and frequencies of plant species were sampled. We used generalized linear mixed models and ordination techniques to test our hypotheses. Results: The effect of the edge penetrated up to 50 m into the forest interior. Only light effects of trampling were found in seemingly untrampled areas, in addition to the direct effects of trampling on the paths. Both trampling and edge effects changed the forest understorey species composition. Trampling changed plant species composition locally on paths, and provided opportunities for new species to establish in previously unbroken forest vegetation. Urban forest edges were characterised by species better adapted to sunny, warm and dry conditions. These species, such as grasses, replaced more sensitive forest species, such as dwarf shrubs and mosses. We observed a large number of light demanding deciduous trees at the edges, which may be one of the factors increasing soil fertility and consequently promoting the high abundance of fast growing species, such as grasses and herbs related to more fertile site types. Conclusions: We recommend that urban forest fragments left within urban development should be at least 2–3 ha in size and that the shape of the patch and the number of potential recreational users should be taken into account when preserving true forest understorey vegetation from the effects of edges and trampling.     

Responses of aerobic microbial communities and soil respiration to water-level drawdown in a northern boreal fen

On a global basis, peatlands are a major reserve of carbon (C). Hydrological changes can affect the decomposition processes in peatlands and in turn can alter their C balance. Since 1959, a groundwater extraction plant has generated a water-level gradient at our study site that has gradually changed part of the wet fen into a dry peatland forest. The average water-level drawdown of the gradient (from a pristine 9 cm to 26 cm in the dry end) is close to an estimate predicted by an increase in mean global temperature of 3°C. We studied the total microbial community of the aerobic surface peat in four locations along the gradient through phospholipid fatty acid and PCR-DGGE methods. Additionally, field measurements of soil respiration showed a threefold increase in the C-emission rate at the driest location compared with the wettest one, indicating enhanced decomposition. Also, both fungal and bacterial biomass increased in the drier locations. At the species level, the fungal community changed due to water-level drawdown whereas actinobacteria were less sensitive to drying. The majority of fungal sequences were similar to ectomycorrhizal (ECM) fungi, which dominated throughout the gradient. Our results indicate that ECM fungi might act as important facultative decomposers in organic-rich environments such as peatlands.     

Kindlins: essential regulators of integrin signalling and cell-matrix adhesion

Integrin-mediated cell-ECM (extracellular matrix) adhesion is a fundamental process that controls cell behaviour. For correct cell-ECM adhesion, both the ligand-binding affinity and the spatial organization of integrins must be precisely controlled; how integrins are regulated, however, is not completely understood. Kindlins constitute a family of evolutionarily conserved cytoplasmic components of cell-ECM adhesions that bind to beta-integrin cytoplasmic tails directly and cooperate with talin in integrin activation. In addition, kindlins interact with many components of cell-ECM adhesions--such as migfilin and integrin-linked kinase--to promote cytoskeletal reorganization. Loss of kindlins causes severe defects in integrin signalling, cell-ECM adhesion and cytoskeletal organization, resulting in early embryonic lethality (kindlin-2), postnatal lethality (kindlin-3) and Kindler syndrome (kindlin-1). It is therefore clear that kindlins, together with several other integrin-proximal proteins, are essential for integrin signalling and cell-ECM adhesion regulation.     

Tawny owl reproduction and offspring sex ratios under variable food conditions

Tawny owl reproduction and offspring sex ratios have been considered to depend on the abundance of small voles. We studied reproductive performance (laying date, clutch and brood size) during 1995–2003 and offspring sex ratios from 1999 to 2003 in relation to the abundance of small voles and food delivered to the nest in a tawny owl population in southern Finland. Abundance of small voles (field and bank voles) was based on trappings in the field, and estimates of food delivery was based on diet analysis of food remains in the nest boxes. In this population, reproductive output was not related to the abundance of small voles. Analysis of food delivered to the nest showed that the prey weight per offspring varied more than twofold between years and revealed that this difference was mainly related to the proportion of water voles in the diet. Only the number of water voles correlated with laying dates. Offspring sex ratios were weakly male biased (55%) but did not differ from parity. Sex ratios were not related to the abundance of small voles, and we found no evidence that parents delivered more food to nests with proportionally more offspring of the larger (female) sex. Our results underline the notion that populations may differ in their sex allocation pattern, and suggest such differences may be due to diet.     

Reliability of egg morphology to detect conspecific brood parasitism in goldeneyes Bucephala clangula examined using protein fingerprinting

Eadie (1989) developed a method based on variation between females in egg length, width and weight to detect conspecific brood parasitism in the field: using these three egg measures, Euclidean distance between all pairs of eggs within a clutch is calculated, and if maximum Euclidean distance (MED) between any two eggs exceeds a threshold value the nest is considered parasitized. The MED method has been tested in Finnish and Scottish common goldeneye Bucephala clangula populations but the results have been contradicting. Here we use protein fingerprinting to assess the validity of the MED method. Data comprised 35 clutches of which we knew, based on protein fingerprinting, how many different females laid the clutch (range 1–5 females). The mean MED of non-parasitized clutches (laid by 1 female only) was 1.470 (95% CI: lower 1.169, upper 1.771; n=21) and that of parasitized clutches (laid by 2 or more females) was 3.654 (95% CL: lower 3.083, upper 4.225; n=14). Using a MED>3.0 as a criterion to identify parasitized clutches 89% of all clutches were classified correctly either parasitized or non-parasitized when compared to the identification based on protein fingerprinting. Clutch size and the number of females (beyond 2 females) did not affect the clutch MED, whereas the status of parasitism did. Repeatability of egg length, width and weight were: 0.63, 0.76 and 0.80, respectively, implying that, variation in these egg measures occurs among rather than within females. Our new results confirm that the MED method is reliable enough to detect parasitism in common goldeneye.     

Carbon balance and allocation of assimilated CO2 in Scots pine, Norway spruce, and Silver birch seedlings determined with gas exchange measurements and 14C pulse labelling

Carbon dioxide is released from the soil to the atmosphere in heterotrophic respiration when the dead organic matter is used for substrates for soil micro-organisms and soil animals. Respiration of roots and mycorrhiza is another major source of carbon dioxide in soil CO₂ efflux. The partitioning of these two fluxes is essential for understanding the carbon balance of forest ecosystems and for modelling the carbon cycle within these ecosystems. In this study, we determined the carbon balance of three common tree species in boreal forest zone, Scots pine, Norway spruce, and Silver birch with gas exchange measurements conducted in laboratory in controlled temperature and light conditions. We also studied the allocation pattern of assimilated carbon with ¹⁴C pulse labelling experiment. The photosynthetic light responses of the tree species were substantially different. The maximum photosynthetic capacity (P _max) was 2.21 μg CO₂ s⁻¹ g⁻¹ in Scots pine, 1.22 μg CO₂ s⁻¹ g⁻¹ in Norway spruce and 3.01 μg CO₂ s⁻¹ g⁻¹ in Silver birch seedlings. According to the pulse labelling experiments, 43–75% of the assimilated carbon remained in the aboveground parts of the seedlings. The amount of carbon allocated to root and rhizosphere respiration was about 9–26%, and the amount of carbon allocated to root and ectomycorrhizal biomass about 13–21% of the total assimilated CO₂. The ¹⁴CO₂ pulse reached the root system within few hours after the labelling and most of the pulse had passed the root system after 48 h. The transport rate of carbon from shoot to roots was fastest in Silver birch seedlings.