J Jokimaeki, E Huhta, M Moenkkoenen, A Nikula Ecoscience 7:33, 256-266, 2000 ... coelebs L.), and... more J Jokimaeki, E Huhta, M Moenkkoenen, A Nikula Ecoscience 7:33, 256-266, 2000 ... coelebs L.), and redpoll (Carduelis flammea L.) showed higher temporal variability, whereas sedentary and virgin forest species such as cuckoo (Cuculus canorus L.), raven (Corvus corax L.), and ...
mys volans boreal forest landscape in northern Finland. We used three different methods for asses... more mys volans boreal forest landscape in northern Finland. We used three different methods for assess- ing critical landscape thresholds with reference to spatial scale. First, we carried out a broad-scale landscape analysis to estimate the relationship between mature forest cover and the occurrence of the Siberian flying squirrel regionally. Second, we collected data on the presence/absence status of the species
Nikula, A., Hallikainen, V., Jalkanen, R., Hyppönen, M. & Mäkitalo, K. 2008. Modelling the factor... more Nikula, A., Hallikainen, V., Jalkanen, R., Hyppönen, M. & Mäkitalo, K. 2008. Modelling the factors predisposing Scots pine to moose damage in artificially regenerated sapling stands in Finnish Lapland. Silva Fennica 42(4): 587-603.
Old-growth forest birds in Fennoscandia have sharply declined in numbers during the last decades ... more 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.
The breeding success of grouse was negatively correlated with both fragmentation of forest area p... more 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 ...
In this study, we surveyed habitat characteristics of the Siberian flying squirrel in northern Fi... more In this study, we surveyed habitat characteristics of the Siberian flying squirrel in northern Finland. Forest structure in currently occupied sites was compared with random forest sites within the same old-growth forest area. We also studied whether the same habitat selection patterns can be detected directly from satellite images at the home-range scale. For this purpose we analysed forest characteristics
Mykrä, S., Kurki, S. & Nikula, A. 2000: The spacing of mature forest habitat in relation to speci... more Mykrä, S., Kurki, S. & Nikula, A. 2000: The spacing of mature forest habitat in relation to species-specific scales in managed boreal forests in NE Finland. -Ann. Zool. Fennici 37: 79-91.
Lek area characteristics of capercaillie were studied in eastern Finland. Lekking site data of 42... more 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 ...
Proceedings of the Royal Society B: Biological Sciences, 2004
We manipulated the primary brood size of Eurasian treecreepers (Certhia familiaris) breeding in d... more We manipulated the primary brood size of Eurasian treecreepers (Certhia familiaris) breeding in different sized forest patches (0.5-12.8 ha) in moderately fragmented landscapes. We examined the effects of brood size manipulation (reduced, control, enlarged) and forest patch size on physiological stress (heterophillymphocyte ratios; H/L), body condition and cell-mediated immunocompetence (phytohaemagglutinin test). Nestlings' H/L ratios were negatively related to forest patch area in control and enlarged broods, whereas no effects were found in reduced broods. The effects of forest patch area were strongest in enlarged broods, which had, in general, twofold higher H/L ratios than control and reduced broods. The elevated H/L ratios were positively related to nestling mortality and negatively correlated with bodycondition indices suggesting that the origin of stress in nestlings was mainly nutritional. Cell-mediated immunity of nestlings was not related to brood manipulation or to forest patch size. Also, the H/L ratios of adults were not related to brood manipulation or forest patch size. In addition, parental H/L ratios and body condition were not related to nestling H/L ratios. Our results suggest that during the breeding period the deleterious effects of habitat loss are seen explicitly in growing young.
Proceedings of the Royal Society B: Biological Sciences, 2003
We studied the primary brood sex ratio of an old-growth forest passerine, the Eurasian treecreepe... more 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.
Proceedings of the Royal Society B: Biological Sciences, 2003
We investigated how physiological stress in an area-sensitive old-growth forest passerine, the Eu... more 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 freeliving individual treecreepers.
Koivunen, V. 2003. Habitat composition as a determinant of reproductive success of Tengmalm's owl... more Koivunen, V. 2003. Habitat composition as a determinant of reproductive success of Tengmalm's owls under fluctuating food conditions. -Oikos 100: 162-171.
The loss and fragmentation of forest habitats have been considered to pose a worldwide threat to ... more 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 diVerent forest age classes (old-growth, middleaged, 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 Wtness and population viability.
We investigated latitudinal and regional variations in the composition and concentrations of foli... more 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 compoundspecific 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.
J Jokimaeki, E Huhta, M Moenkkoenen, A Nikula Ecoscience 7:33, 256-266, 2000 ... coelebs L.), and... more J Jokimaeki, E Huhta, M Moenkkoenen, A Nikula Ecoscience 7:33, 256-266, 2000 ... coelebs L.), and redpoll (Carduelis flammea L.) showed higher temporal variability, whereas sedentary and virgin forest species such as cuckoo (Cuculus canorus L.), raven (Corvus corax L.), and ...
mys volans boreal forest landscape in northern Finland. We used three different methods for asses... more mys volans boreal forest landscape in northern Finland. We used three different methods for assess- ing critical landscape thresholds with reference to spatial scale. First, we carried out a broad-scale landscape analysis to estimate the relationship between mature forest cover and the occurrence of the Siberian flying squirrel regionally. Second, we collected data on the presence/absence status of the species
Nikula, A., Hallikainen, V., Jalkanen, R., Hyppönen, M. & Mäkitalo, K. 2008. Modelling the factor... more Nikula, A., Hallikainen, V., Jalkanen, R., Hyppönen, M. & Mäkitalo, K. 2008. Modelling the factors predisposing Scots pine to moose damage in artificially regenerated sapling stands in Finnish Lapland. Silva Fennica 42(4): 587-603.
Old-growth forest birds in Fennoscandia have sharply declined in numbers during the last decades ... more 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.
The breeding success of grouse was negatively correlated with both fragmentation of forest area p... more 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 ...
In this study, we surveyed habitat characteristics of the Siberian flying squirrel in northern Fi... more In this study, we surveyed habitat characteristics of the Siberian flying squirrel in northern Finland. Forest structure in currently occupied sites was compared with random forest sites within the same old-growth forest area. We also studied whether the same habitat selection patterns can be detected directly from satellite images at the home-range scale. For this purpose we analysed forest characteristics
Mykrä, S., Kurki, S. & Nikula, A. 2000: The spacing of mature forest habitat in relation to speci... more Mykrä, S., Kurki, S. & Nikula, A. 2000: The spacing of mature forest habitat in relation to species-specific scales in managed boreal forests in NE Finland. -Ann. Zool. Fennici 37: 79-91.
Lek area characteristics of capercaillie were studied in eastern Finland. Lekking site data of 42... more 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 ...
Proceedings of the Royal Society B: Biological Sciences, 2004
We manipulated the primary brood size of Eurasian treecreepers (Certhia familiaris) breeding in d... more We manipulated the primary brood size of Eurasian treecreepers (Certhia familiaris) breeding in different sized forest patches (0.5-12.8 ha) in moderately fragmented landscapes. We examined the effects of brood size manipulation (reduced, control, enlarged) and forest patch size on physiological stress (heterophillymphocyte ratios; H/L), body condition and cell-mediated immunocompetence (phytohaemagglutinin test). Nestlings' H/L ratios were negatively related to forest patch area in control and enlarged broods, whereas no effects were found in reduced broods. The effects of forest patch area were strongest in enlarged broods, which had, in general, twofold higher H/L ratios than control and reduced broods. The elevated H/L ratios were positively related to nestling mortality and negatively correlated with bodycondition indices suggesting that the origin of stress in nestlings was mainly nutritional. Cell-mediated immunity of nestlings was not related to brood manipulation or to forest patch size. Also, the H/L ratios of adults were not related to brood manipulation or forest patch size. In addition, parental H/L ratios and body condition were not related to nestling H/L ratios. Our results suggest that during the breeding period the deleterious effects of habitat loss are seen explicitly in growing young.
Proceedings of the Royal Society B: Biological Sciences, 2003
We studied the primary brood sex ratio of an old-growth forest passerine, the Eurasian treecreepe... more 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.
Proceedings of the Royal Society B: Biological Sciences, 2003
We investigated how physiological stress in an area-sensitive old-growth forest passerine, the Eu... more 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 freeliving individual treecreepers.
Koivunen, V. 2003. Habitat composition as a determinant of reproductive success of Tengmalm's owl... more Koivunen, V. 2003. Habitat composition as a determinant of reproductive success of Tengmalm's owls under fluctuating food conditions. -Oikos 100: 162-171.
The loss and fragmentation of forest habitats have been considered to pose a worldwide threat to ... more 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 diVerent forest age classes (old-growth, middleaged, 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 Wtness and population viability.
We investigated latitudinal and regional variations in the composition and concentrations of foli... more 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 compoundspecific 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.
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Papers by Ari Nikula