Risto A. Väisänen

How are extensive, human-caused habitat alterations expressed on the scale of local bird populations in boreal forests?

We studied long-term population changes in 43 abundant species of forest birds using line transect censuses conducted in northern Finland from 1941 to 77. Previous studies have suggested that human-caused habitat changes are a major reason for regional, long-term changes of bird populations. Birds of old taiga forests have decreased in number because of clear-cutting and forest fragmentation. Many southern species have increased during the period studied, probably partly because of an overflow of individuals from increasing populations in southern Finland, partly as a consequence of habitat changes (increase of bushy young forests and forest edges) in northern Finland. While the median northern species decreased by about one-third, the median southern species increased 5-fold in northern Finland during the study period. How do the regional patterns translate to the local scale? An area characterized by mature forest and peatlands in Simo was censused in 1959 and 1977-81. Between these censuses the area changed drastically due to clear-cutting and draining. Species trends were similar to those observed regionally but more species declined, probably because, on average, the local habitat changes were more extreme than those on the regional scale. In contrast, another local study area, a luxuriant spruce forest (Tormivaara), remained intact from a first census in 1915 until censused again in 1981-83. In this area the local stability expected was overshadowed by the regional changes: in the 1980s the reserve-like Tirmiivaara was no longer characterized by the typical bird species of northern old forests, but the bird populations had changed largely as in managed forests in northern Finland. This result suggests that the bird populations in small forest reserves in northern Finland are not closed but affected by the dynamics of the regional populations.

Ecological gradients of boreal forests in South Finland: an ordination test of Cajander's forest site type theory

Ecological gradients in the field layer of southern boreal forests in South Finland were studied in relation to the dominant tree species and the age of forest stands. The data are from a systematic sample of 529 plots from an area of 150 × 200 km, collected in the Third National Forest Inventory in 1951–53. Detrended correspondence analysis (DCA) was applied to log-transformed species cover values. It revealed three main gradients: fertility, moisture, and the effect of cattle grazing in forests (still extensive in the early 1950s). The fertility gradient dominated the first axis and the two latter sources of variation confounded with it in a complex manner in the first two axes of DCA. The second DCA axis was associated with canopy effects on understory pattern, with Pinus and Picea having opposite and Betula intermediate effects. These results were compared with an ordination model of Cajanders forest site types, based on DCA of independent, ideal data of 107 indicator species. The fertility gradient recovered by the model was almost identical to that obtained from the field data. The gradient was also stable from intermediate-age (40–69 yrold) to older forests. The forest site types showed rather large overlaps with main neighbouring types in composition of ground vegetation or nutrient status of the humus. Competitively efficient feather-mosses, which are dependent on nutrients released from the tree crowns, are considered important regulators of the understory vegetation. Accordingly, alternative approaches to the forest site type classification to be used in boreal forests treated by modern intensive forestry should give more weight to the effect of the canopy trees.

Ecological zoogeography of North European waders, or Why do so many waders breed in the North?

tative censuses (4900 observations on 26 wader species). Most variables used to describe latitudinal gradients have their maxima in the north: number of species, proportion of wader species in the land bird fauna, density of waders and proportion of wader density, biomass of waders and proportion of wader biomass, and energy demand of waders and proportion of total energy demand. No trends were observed in species diversity (Shannon function), while the evenness of the species-abundance distribution decreases northwards. The patterns can apparently be explained by effects of habitat heterogeneity: presence of seashore and mountain habitats increase numbers of wader species by 5-6 and 2-3, respectively, while species richness on peatlands is known to increase northwards at least partly due to habitat complexity. The high productivity (e.g. dipterans) of temporary shallow waters during the hatching period of the birds may also contribute to the northward increase in density and number of species of waders. North European waders could be grouped ecogeographically in five distribution types, which correlated well with the faunal types of the species.

The importance of hunting pressure, habitat preference and life history for population trends of breeding waterbirds in Finland

Populations of migratory species have undergone dramatic changes in recent decades, but little is known about the factors actually driving those changes. Of particular concern are quarry species such as migratory ducks (Anatidae), many of which have an unfavourable conservation status in Europe. By including both quarry and non-quarry species, as well as habitat preference and life history characteristics of the species, we investigated the relative importance of hunting pressure, both in Finland and at the European level, in explaining population changes of 16 species of migratory waterbirds in Finland during 1986–2011. Ban of lead shot in 1996 resulted in considerably lower annual hunting bags in Finland thereafter. Species which had the highest hunting pressure had the most negative slopes in population trends from 1986 up to 1997, suggesting that hunting probably limited those populations. However, in general population trends of the species were not strongly associated with hunting pressure in Finland or in Europe. Nor were basic life history characteristics (body mass and clutch size) associated with population trends of the species. In contrast, recent population declines were associated with habitat preferences of the species: those breeding mainly in eutrophic lakes had more negative population trends than those breeding in oligotrophic lakes or generalist species. Reasons for the relatively poor status of species preferring eutrophic lakes probably include over-eutrophication of nutrient-rich lakes, resulting in less abundant food resources, and increased nest depredation.

Climatic Changes, Habitat Changes, and Competition: Dynamics of Geographical Overlap in Two Pairs of Congeneric Bird Species in Finland

The relative densities and overlap zones of Parus cinctus (northern) and P. cristatus (southern), and of Fringilla montifringilla (northern) and F. coelebs (southern) were studied in censuses made in Finland in 1910-29, 1936-49, 1952-63 and 1973-77. The population changes of the species are described. P. cinctus greatly decreased, first in the southern and later in the middle parts of its range. P. cristatus first expanded both northwards and to the Aland Islands, but then decreased, particularly in the north. In their overlap zone, both species decreased drastically (by 90-95%). F. montifringilla was stable, except for a temporary decrease in the 1940s. F. coelebs increased, but the 1:1 zone of the Fringilla species has fluctuated mainly owing to fluctuations in the numbers and range of F. montifringilla. Two major theories purport to account for the dynamics of North European biota: either the climatic amelioration of the past 100 yr is of major importance, or recent habitat changes (often due to man or his livestock) are more effective. Recent changes in climate and habitats are compared with bird population changes in order to test the two biogeographic theories. Climatic amelioration may account for some, but certainly not all population changes. Habitat changes (including the abandonment of forest grazing, the increase of spruce, increased edge effect, and extensive clear-cuttings particularly in N Finland) may explain all long-term trends. A few short-term population changes were probably due to exceptional winter or spring weather. The presumed interspecific competition between the congeners studied is examined critically. Standard competition equations do not adequately model the dynamics of the species pairs, but at least three additional points must be taken into account: environmental changes, population changes in relation to ecological saturation, and the evolutionary time scale.

Long-term population changes of the most abundant south Finnish forest birds during the past 50 years

1. Population indices based on bird censuses (especially line transects) are given for south Finnish forest birds (40 species). The indices refer to 1926–27, 1936, 1936–49, 1952–63 and 1973–77. 2. Population increases were observed to be much more frequent than decreases. The main reason for the changes is presumably that the structure of the Finnish forests has changed considerably in recent decades. Many bird populations are thus probably well adapted to habitat changes caused by forestry. However, certain species need habitats destroyed by modern forestry (e. g. old forests); in consequence, it is necessary to maintain sufficient old forests areas for conservational purposes. 1. Für die 40 häufigsten Waldvögel Südfinnlands werden, meist auf der Grundlage von Linientaxierungen, Populationsindices ermittelt. Diese Indices beziehen sich auf die Jahre 1926/27, 1936, 1936–49, 1952–63 und 1973. 2. 22 Arten (Gruppe A der Tabelle) haben eindeutig zugenommen. Die Gründe hierfür sind wohl in Veränderungen der Struktur finnischer Wälder zu suchen, nämlich Zunahme der Fläche von Jungbeständen, der Ausdehnung der Strauchschicht in Altbeständen, der Bedeutung der Fichte als Waldbestandteil und schließlich der Waldränder. 3. 7 Arten (Gruppe B) nahmen einheitlich zu mit Ausnahme im SW-Teil des Landes, wo die Zunahme sehr gering war. Diese Arten scheinen in gleicher Weise von den Strukturänderungen finnischer Wälder beeinflußt worden zu sein wie die in Gruppe A. Doch wiesen diese 7 Arten schon 1926/27 im SW Finnlands relativ hohe Dichten auf. Da alle Arten dieser Gruppe hauptsächlich im Süden verbreitet sind, bedeutet die Zunahme in Finnland, daß offenbar die meisten Arten dieser Gruppe ihr Areal nach Norden ausdehnten, was schließlich zu einem deutlichen Populationsanstieg im Untersuchungsgebiet führte. 4. 7 Arten (Gruppe C) zeigten keine deutlich erkennbaren Trends. Die Erklärung hierfür scheint in hohen jährlichen Fluktuationen der Populationsgröße als auch in möglichen interspezifischen Konkurrenzverhältnissen zu suchen zu sein. 5. 4 Arten (Gruppe D) nahmen deutlich ab, wahrscheinlich in erster Linie infolge der Abnahme des Flächenanteils alter Waldbestände oder der zunehmenden Schwierigkeiten, alte Bäume zu finden. 6. So wurden also Zunahmetendenzen weit häufiger als Abnahmetendenzen festgestellt. Diese Ergebnisse stimmen mit anderen Untersuchungen von langfristigen Bestandstrends nordeuropäischer Vogelarten überein. Sie weisen ferner daraufhin, daß offenbar viele Vogelpopulationen an die Habiate, die durch moderne Forstwirtschaft entstehen, gut angepaßt sind. Jedoch sollten diese Ergebnisse vom Standpunkt des Naturschutzes aus nicht falsch interpretiert werden. Sinn des Naturschutzes ist nicht, die Populationsgröße sehr häufiger Arten positiv zu beeinflussen, sondern die Abnahme der Populationsgrößen bedrohter Arten zu verhindern. In diesem Zusammenhang sei auf die Notwendigkeit des Schutzes genügend großer Flächen alter Waldbestände hingewiesen, da eine Reihe von Arten davon im höchsten Maße davon abhängig sind.

Ganglion cells in the frog retina: Discriminant analysis of histological classes

Neurons in the ganglion cell layer were studied in Golgi-stained flat-mounted frog (Rana temporaria) retinas. Complementary data were obtained from methylene blue- and HRP-stained retinas. On the basis of qualitative criteria, 55 neurons were ordered into six groups, one class of amacrine cell (A1) and five classes of ganglion cells (G1-G5). A discriminant function analysis based on seven morphological variables resulted in a separation of the cell classes in the space of three axes. The A1 cells are small axonless neurons with knotty and dense dendritic trees. The G1 cells are also small, and apparently very numerous, while the G2 cells are medium-sized neurons with two loose dendritic layers, one vitreal and another (less conspicuous) scleral. The rest of the cells are medium-sized to large neurons with sturdy primary dendrites and more distinct dendritic layers, which in some cells (G3) spread both sclerally and vitreally, in other cells in a single either scleral (G4) or vitreal (G5) layer. The relation between our data and the classification of frog ganglion cells recently presented by Frank and Hollyfield is discussed at length, and in that context problems related to statistical classifications are dealt with. A hypothetical identification of the morphological types with the functional cell classes studied in the Helsinki laboratory is discussed.

Growth and sexual dimorphism in the skull of the Capercaillie Tetrao urogallus: a multivariate study of geographical variation

In autumn 1981, Capercaillie skulls (N = 813) were collected from Finnish hunters. On the basis of ossification of the skull, five growth groups (from 0 to 4 yr) were formed in males and three (from 0 to 2 yr) in females. Growth groups corresponded moderately well with multivariate-estimated age groups. Of the 26 variables measured, accelerated sexual dimorphism was most obvious in the length and height growth of the beak as well as in the growth of the bony structures to which the beak is attached. Selection for the robust beak of males might be based on their need (1) to compete for females on spring leks, and (2) to effectively handle winter food of pine needles during the short days of winter. Discriminant function analysis of skull measurements revealed geographical trends over the boreal zone, which were based on variation in the cranial dimensions of the skull, especially those of the braincase. The large subspecies T. u. urogallus breeds in the north and the small T. u. uralensis in the south. The transition zone between these shows similarities with other mid-boreal zoogeographical boundaries. In addition, the effect of the large Central European T. u. major is seen in the population of southernmost Finland.