Ari Nikula

LANDSCAPE FRAGMENTATION AND FOREST COMPOSITION EFFECTS ON GROUSE BREEDING SUCCESS IN BOREAL FORESTS

We examined the breeding success of forest grouse in relation to anthropogenic forest fragmentation in Finland. Employing Geographic Information Systems (GIS) and grouse data derived from Finnish wildlife triangle censuses conducted during 1989–1994, we combined the locations of 2267 Black Grouse (Tetrao tetrix) and 1060 Capercaillie (T. urogallus) females after the breeding season in mid-August with landscape data. The indicators of breeding success were the proportion of grouse hens with a brood and brood size. Two study areas (each 45 000 km2) in the boreal zone were selected for investigation. The breeding success of grouse was negatively correlated with both fragmentation of forest area per se by farmland and the decreasing proportion of older forest as a result of clear-cutting. The extent of landscape accounting best for variation in nesting success was an order of magnitude larger (∼100 km2) than the area most probably used by a grouse female and her brood during the summer, which suggests that la...

Abundances of red fox and pine marten in relation to the composition of boreal forest landscapes.

The effects of human-caused fragmentation of boreal forest on the abundance of red fox Vulpes vulpes L. and pine marten Martes martes L. were studied by combining the Finnish wildlife-triangle snow-track data (1990-94) with land-use and forest resources data employing the GIS. Two study areas (each 45 000 km(2) ) located in northern and southern Finland were selected for the investigation. The extent of landscape that best explained predator abundance (tracks per 10 km 24 h(-1) ) was the same (about 100 km(2) ) in both species and study areas. The decreasing proportion of older forest and the increasing proportions of young forest and agricultural land in the landscape positively affected track density of red fox. The relationship between agricultural land and fox abundance, however, was characterized by a convex curve peaking at 20-30% of agricultural land. With the habitat classification used, landscape composition explained 26% and 11% of the spatial variation in fox abundance in the northern and southern study area, respectively. The relationship between landscape composition and pine marten abundance was not as clear as in that of red fox. Landscape composition explained 10% and 6% of spatial variation in pine marten abundance in the northern and southern study area, respectively. In both areas a positive impact occurred with the increasing proposition of young forest in the landscape, but in the northern area the negative effect of increasing proportion of agricultural land was dominant. The abundances of red fox and pine marten were not negatively correlated, indicating that competition or intraguild predation by red fox do not determine abundance of pine marten on a landscape scale. A general increase in predation pressure by generalist predators in fragmented forest landscapes has been an intensively discussed conservation problem during recent years. We conclude that the red fox is a species potentially able to cause elevated predation pressure in boreal landscapes fragmented by human activities, but that the evidence against the pine marten is weaker.

Forest management is associated with physiological stress in an old-growth forest passerine.

We investigated how physiological stress in an area–sensitive old–growth forest passerine, the Eurasian treecreeper (Certhia familiaris), is associated with forest fragmentation and forest structure. We found evidence that the concentrations of plasma corticosterone in chicks were higher under poor food supply in dense, young forests than in sparse, old forests. In addition, nestlings in large forest patches had lower corticosterone levels and a better body condition than in small forest patches. In general, corticosterone levels were negatively related to body condition and survival. We also found a decrease in corticosterone levels within the breeding season, which may have been a result of an increase in food supply from the first to the second broods. Our results suggest that forest fragmentation may decrease the fitness of free–living individual treecreepers.

Habitat selection of adult moose Alces alces at two spatial scales in central Finland

The habitat selection criteria of moose Alces alces at several scales are the basic sets of information needed in moose management planning. We studied moose habitat use in central Finland during 1993–1996 using data from radio collared moose, satellite image based forest and land cover data, and applied the principles of compositional analysis. The habitat compositions of 54 home ranges (10 males during summer, six males during winter, 23 females during summer and 15 females during winter) were first compared with the overall landscape. The habitat compositions around moose locations within their home ranges were then compared with the habitat composition of the home range. Seasons and sexes were compared at both scales. In summer, there was only a slight difference between moose home ranges and the overall landscape. Based on tree species composition, home ranges are located in slightly more fertile areas than the overall landscape. Within their home ranges, moose favoured non-pine dominated habitats and mature forests, and avoided human settlements. In winter, the moose home ranges included significantly more pine-dominated plantations and other young successional stages than the overall landscape. The role of pine-dominated peatland forests/ shrub land was especially pronounced in winter. Winter home ranges included less agricultural land and human settlements than the overall landscape, probably due to the more distant location of important winter habitats from man-made landscapes. Within the home ranges, both sexes used non-pine dominated habitats more, and mature forests and human settlements less than expected. At the home range scale, there were no statistical differences between the sexes with respect to habitat use in either season. Within their home ranges, males and females used slightly different habitats during both seasons, suggesting spatially segregated habitat use by the individual sexes. The difference is more clear in winter when males tend to use more pine-dominated, young successional habitats than females. Compared to the situation in the summer, winter ranges are located in slightly more pine-dominated habitats with fewer settlements and agricultural fields. The shift in habitat use between the two seasons is more pronounced with respect to habitat use within the home range. Our results indicate that moose habitat selection criteria vary among different hierarchical levels of selection. We stress the importance of multi-scale assessment of the habitat and other resource selection of animals.

Effects of landscape structure and forest reserve location on old-growth forest bird species in Northern Finland

Old-growth forest birds in Fennoscandia have sharply declined in numbers during the last decades apparently due to commercial forest harvesting and fragmentation of old-growth forests. Conservation measures have led to the establishment of a forest reserve network to assure the persistence of forest birds at a regional scale. However, little is known about the effects of landscape structure within and around the reserves on the distribution of old-growth forest birds. We used a hierarchical approach to address the questions of how landscape structure and composition within forest reserves, landscape composition of surrounding areas and reserve location affect the abundance of resident, old-growth forest birds in the Northern Finnish forest reserve network. The positive role of particular landscape features on bird distribution indicates that both the proportion of old-growth forests and the structure of boreal landscape mosaic has an important role in determining the distribution of these birds. The landscape composition surrounding the reserves proved to be only a weak predictor in species distribution models, which argues against the primary role of the surrounding matrix in determining species distribution within forest reserves. Reserves located near the Russian border showed a higher abundance of old-growth birds than more western ones. Once east-west gradients in overall landscape composition had been accounted for, however, reserves did not differ significantly in the number of species present. These results suggest that landscape gradients, rather than ecological processes such as the presence of source areas located along the border with Russia, are the main determinant of the distribution of old-growth forest birds in the Finnish reserve network. We propose that to enhance regional persistence of old-growth forest birds, conservation efforts should be primarily directed towards the protection and enhancement of forest habitat quality and natural heterogeneity of landscapes within targeted areas.

Forest fragmentation is associated with primary brood sex ratio in the treecreeper (Certhia familiaris)

We studied the primary brood sex ratio of an old–growth forest passerine, the Eurasian treecreeper (Certhia familiaris), along a gradient of forest fragmentation. We found evidence that male nestlings were more costly to produce, since they suffered twofold higher nestling mortality and were larger in body size than females. Furthermore, the proportion of males in the brood was positively associated with the provisioning rate and the amount of food delivered to the nestlings. During the first broods, a high edge density and a high proportion of pine forests around the nests were related to a decreased production of males. The densities of spiders, the main food of the treecreeper, were 38% higher on spruce trunks than on pine trunks. This suggests that pine–dominated territories with female–biased broods may have contained less food during the first broods. The observation was further supported by the fact that the feeding frequencies were lower in territories with high proportions of pines. In the second broods, territories with a high forest patch density produced female–biased broods, whereas high–quality territories with a large amount of deciduous trees and mixed forests produced male–biased broods. Our results suggest that habitat quality as measured by habitat characteristics is associated with sex allocation in free–living birds.

Concentrations of Foliar Quercetin in Natural Populations of White Birch (Betula pubescens) Increase with Latitude

We investigated latitudinal and regional variations in the composition and concentrations of foliar flavonoids and condensed tannins in wild populations of white birch (Betula pubescens EHRH) in a large climatic transect in Finland. Concentrations of quercetin derivatives were correlated positively with latitude. By contrast, the concentrations of apigenin and naringenin derivatives were correlated negatively with latitude. These compound-specific latitudinal gradients compensated each other, resulting in no changes in the concentration of total flavonoids. Our results thus demonstrate a qualitative, but not quantitative, latitude-associated gradient in the foliar flavonoids in white birch. Due to higher antioxidant capacity of the quercetin derivatives in relation to other flavonoids, the qualitative change can reflect higher adaptation to light in the north than south. An investigation on a regional scale in the northern boreal zone showed that the temperature sum was correlated positively and soil P concentration was correlated negatively with the concentrations of foliar flavonoid, while the concentration of condensed tannins was correlated with slope. The variation in concentrations of flavonoids at large-scale geographical patterns is in line with the conjecture that foliar flavonoids are synthesized for protection against photooxidative stress.

Survival of male Tengmalm’s owls increases with cover of old forest in their territory

The loss and fragmentation of forest habitats have been considered to pose a worldwide threat to the viability of forest-dwelling animals, especially to species that occupy old forests. We investigated whether the annual survival of sedentary male Tengmalm’s owls Aegolius funereus was associated with the cover of old coniferous forests in Finland. Survival and recapture probabilities varied annually with density changes in populations of the main prey (Microtus voles). When this variation was controlled for, and relationships between survival and proportions of the three different forest age classes (old-growth, middle-aged, and young) were modeled separately, the old-growth model was the most parsimonious. Survival increased with the cover of old forest, although the extent of old forest within owl territories was relatively small (mean ∼12%, range 2–37%). This association, however, varied among years and appeared especially in years of increasing vole abundance. At such times, old forests may sustain high populations of bank voles Clethrionomys glareolus, shrews and small passerines. In addition, old forests may serve as refuges against large avian predator species, such as Ural owls Strix uralensis and goshawks Accipiter gentilis. Our results suggest that changes in habitat quality created by agriculture and forestry may have the potential to reduce adult survival, an essential component of fitness and population viability.

Modeling the Location of the Forest Line in Northeast European Russia with Remotely Sensed Vegetation and GIS-Based Climate and Terrain Data

Abstract GIS-based data sets were used to analyze the structure of the forest line at the landscape level in the lowlands of the Usa River Basin, in northeast European Russia. Vegetation zones in the area range from taiga in the south to forest-tundra and tundra in the north. We constructed logistic regression models to predict forest location at spatial scales varying from 1 × 1 km to 25 × 25 km grid cells. Forest location was explained by July mean temperature, ground temperature (permafrost), yearly minimum temperature, and a Topographic Wetness Index (soil moisture conditions). According to the models, the forest line follows the +13.9°C mean July temperature isoline, whereas in other parts of the Arctic it usually is located between +10 to +12°C. It is hypothesized that the anomalously high temperature isoline for the forest line in Northeast European Russia is due to the inability of local ecotypes of spruce to grow on permafrost terrain. Observed patterns depend on spatial scale, as the relative significance of the explanatory variables varies between models implemented at different scales. Developed models indicate that with climate warming of 3°C by the end of the 21st century temperature would not limit forest advance anywhere in our study area.

Lek area characteristics of capercaillie (Tetrao urogallus) in eastern Finland as analysed from satellite-based forest inventory data

Abstract Lek area characteristics of capercaillie were studied in eastern Finland. Lekking site data of 42 leks were collected in spring 2000. Satellite images and the Geographical Information System were used to divide the landscape into eight classes and described by means of circles of 11 different sizes (radius 250–4000 m) around the leks. The leks were compared with the average landscape, represented by 50 random points, and studied according to male lek attendance. Mature forests and thinning forests were more abundant and advanced seedling stands less abundant around the leks than in an average landscape. Most of these differences extended up to 750 m distance from the lek. The number of males per lek was best explained by the proportion and patch size of the thinning forests. The effects of landscape structure on the number of cocks were detectable over a wide range, but were strongest within a radius of 1–2 km. The results are discussed in relation to landscape ecology and management applications.