Forest drainage: a threat to benthic biodiversity of boreal headwater streams?

1. Forest drainage, including mainly ditching of waterlogged peatlands in order to increase wood growth, has caused substantial changes in the hydrology and water quality of Finnish streams. However, knowledge on the ecological impact of these changes is poor. This paper studies the potential impact of forest drainage, catchment characteristics and habitat factors on the water quality and benthic macroinvertebrates in headwater streams of the River Isojoki, western Finland. An intensive programme of water sampling was carried out at nine study sites, while zoobenthic samples covered a total of 18 streams. 2. According to multivariate regression models concentrations of aluminium and suspended solids in stream water at nine study sites increased significantly with increasing forest drainage of the catchment area. Further, drainage intensity contributed significantly to the decrease in minimum values of alkalinity. 3. In a Canonical Correspondence Analysis, the variation in macroinvertebrate species distribution and abundance was largely explained by drainage intensity, moss coverage and the concentrations of aluminium and iron in stream water. A significant positive correlation was established between the species richness of benthic macroinvertebrates and the proportional cover of vegetation on the stream bed, whereas a significant negative correlation was found between species richness and sand cover. 4. The results suggest that drainage has significantly contributed to the deterioration of water quality and habitat structure, and impoverishment of benthic communities in the headwater streams of the River Isojoki. In order to protect the ecological integrity of such boreal headwater streams, more effective protection schemes in forestry practices and rehabilitation of the adversely affected streams and their catchment areas are needed. © 1998 John Wiley & Sons, Ltd.     

Use of modeled photosynthesis and decomposition to describe tree growth at the northern tree line

Growth of subarctic Scots pine (Pinus sylvestris L.) trees was investigated by a combination of process-based models and dendroecological approaches. Tree ring width indices were strongly autocorrelated and correlated with simulated photosynthetic production of the previous year and with organic matter N mineralization of the current year. An autoregressive model, with photosynthesis and N mineralization as external inputs, explained growth of the trees well. However, relationships for the period 1950-1992 differed significantly from relationships for the period 1876-1949; the slope of the regression of tree ring width index and photosynthesis was lower for the 1950-1992 period. Also, the autocorrelation structure of the data changed. First-order autocorrelation decreased and second-order autocorrelation increased from the earlier to the later period. This means that growth is becoming less sensitive to variations in photosynthetic production, whereas the relationships between growth and N mineralization are remaining fairly constant. We postulate that, although photosynthesis has increased in response to increasing CO2 concentrations, tree growth rate cannot parallel the increase in photosynthesis because potential growth rate is limited directly by temperature.     

The role of collinear interaction in dislocation-induced hardening

We connected dislocation-based atomic-scale and continuum models of plasticity in crystalline solids through numerical simulations of dislocation intersections in face-centered cubic crystals. The results contradict the traditional assumption that strain hardening is governed by the formation of sessile junctions between dislocations. The interaction between two dislocations with collinear Burgers vectors gliding in intersecting slip planes was found to be by far the strongest of all reactions. Its properties were investigated and discussed using a multiscale approach.     

Fear erasure in mice requires synergy between antidepressant drugs and extinction training

Antidepressant drugs and psychotherapy combined are more effective in treating mood disorders than either treatment alone, but the neurobiological basis of this interaction is unknown. To investigate how antidepressants influence the response of mood-related systems to behavioral experience, we used a fear-conditioning and extinction paradigm in mice. Combining extinction training with chronic fluoxetine, but neither treatment alone, induced an enduring loss of conditioned fear memory in adult animals. Fluoxetine treatment increased synaptic plasticity, converted the fear memory circuitry to a more immature state, and acted through local brain-derived neurotrophic factor. Fluoxetine-induced plasticity may allow fear erasure by extinction-guided remodeling of the memory circuitry. Thus, the pharmacological effects of antidepressants need to be combined with psychological rehabilitation to reorganize networks rendered more plastic by the drug treatment.     

The use of moss,lichen and pine bark in the nationwide monitoring of atmospheric heavy metal deposition in Finland

Mosses, lichens and pine bark were compared as indicators of atmospheric heavy metal deposition in Finland. The samples were collected from the nationwide sampling network systematically covering the country as a whole. All three bioindicators showed a fairly similar result concerning heavy metal deposition. The major emission sources and the areas affected were reflected in the metal concentrations in the samples. However, there were differences between the accumulation of metals. The correlation between concentrations in mosses and lichens was generally higher than that between mosses and bark or lichens and bark. Concentrations in lichens were the highest and lichens reflected the regional differences in background areas as well as the local emission sources. The concentrations in the mosses were slightly lower than those in lichens and also the mosses pinpointed the emission sources and the extend of the areas polluted. Bark had the lowest concentrations and bark did not generally reveal regional differences as well as mosses and lichens. In spite of the differences, all three bioindicators proved to be suitable for monitoring atmospheric heavy metal deposition.