Tissue water relations of Thuja occidentalis representing natural populations from two different moisture habitats were analyzed from pressure-volume curves. Xylem water potential, osmotic potential, ...and the water potential at incipient plasmolysis of mature trees in the field were more negative in dry upland populations than in wet lowland populations. Analyses of seedlings grown from seed collected at each site, and grown in both wet and dry conditions, indicated that the site of seed origin did not affect the water relations of these seedlings. Seedlings grown under xeric conditions, however, developed a more negative water potential, osmotic potential, and water potential at incipient plasmolysis than did seedlings grown under wet conditions. The ability of T. occidentalis seedlings to acclimate as a response to variations in moisture availability, rather than ecotypic differences, probably plays an important role in allowing growth in both wet and dry sites.
Understanding links between habitat characteristics and foraging efficiency helps predict how environmental changes influence populations of top predators. This study examines whether measurements of ...prey (clupeids) availability varied over stratification gradients, and determined if any of those measurements coincided with aggregations of foraging seabirds (common guillemot Uria aalge and Manx shearwater Puffinus puffinus) in the Celtic Sea, UK. The probability of encountering foraging seabirds was highest around fronts between mixed and stratified water. Prey were denser and shallower in mixed water, whilst encounters with prey were most frequent in stratified water. Therefore, no single measurement of increased prey availability coincided with the location of fronts. However, when considered in combination, overall prey availability was highest in these areas. These results show that top predators may select foraging habitats by trading-off several measurements of prey availability. By showing that top predators select areas where prey switch between behaviours, these results also identify a mechanism that could explain the wider importance of edge habitats for these taxa. As offshore developments (e.g. marine renewable energy installations) change patterns of stratification, their construction may have consequences on the foraging efficiency of seabirds.
Edge habitats resulting from the construction and maintenance of forest roads favour pioneer, shade-intolerant and disturbance-adapted plant species. The effect of roads on the spread of non-native ...species has been frequently studied, but few studies have focused upon their effects on native tree species. We studied the effect of forest roads on the expansion dynamics of trembling aspen (
Populus tremuloides
Michx.) in a boreal forest landscape of eastern Canada. We determined whether roads act as a habitat and dispersal corridor for trembling aspen, and whether populations that established along roads act as a starting point for aspen expansion into adjacent stands. We evaluated the effect of forest roads on the distribution of trembling aspen by surveying the vegetation along 694 km of roads. In 19 stands, we compared the density and age of individuals in 100 m transects established parallel and perpendicular to roads, to determine the role of roads. Trembling aspen is abundant along the forest road network. Forest roads act sometimes as habitat corridors for trembling aspen, but their effects on its density extend only over a short distance (10 m) on each side of the roads. The forest roads did not act as a starting point for the expansion of trembling aspen into adjacent stands. Forest roads are particularly favourable habitats for trembling aspen. Although roads did not act as a starting point for aspen dispersal away from roads, these habitats would be vulnerable to invasion following a disturbance that would reduce the thickness of the organic layer.
Leaf-cutting ants are dominant herbivores in Neotropical rain forests, and their colony densities increase in disturbed habitats such as forest edges. However, while it is well-established that ...leaf-cutting ants profit from changes to the food-plant community, the phylogenetic dimension of this ant–plant interaction remains poorly understood in fragmented forests. We studied diet composition of Atta cephalotes in the edge and interior of Atlantic forest in north-east Brazil (8°30′S, 35°50′W). We applied phylogenetic signal analysis to investigate the diet across plant lineages and performed phylogenetic generalized linear models to analyse the diet in both habitats. We found a phylogenetic signal in diet and in leaf mechanical resistance, which means that A. cephalotes selects closely related food plants with less resistant leaves. Most preferred species belong to Malpighiales, Rubiaceae and Melastomataceae. We also found that irrespective of phylogeny, ants select food plants with less resistant leaves, both in edge and interior. However, ants choose more abundant plants only in edges. High abundance of optimal diet facilitates foraging in forest edges and explains why colony densities increase in disturbed habitats. Finally, by favouring or disfavouring specific clades, leaf-cutting ants contribute to changes in the phylogenetic structure of tropical rain forests, e.g. phylogenetic impoverishment.
Efficient conservation planning in managed forest landscapes requires knowledge about the location of functional habitat for specialised species. We explored the importance of different variables to ...predict habitat suitability for the white-backed woodpecker (Dendrocopos leucotos Bechstein), a proposed umbrella species in deciduous forest. Specifically, we tested whether biophysical proxy variables indicating management intensity and the occurrence of natural processes constituted a useful complement to traditional remotely sensed data on tree species composition and forest stand age for modelling the woodpecker's habitat. Presence–absence of the woodpecker during the study period (1986–2006) in southwestern Sweden was explained by the area of edge habitats (forest bordering water or farmland) and wetland forest, and location relative to the historical marine limit. The number of years with occurrence of the woodpecker in a territory was explained by the area of forest bordering water and wetland forest. Among traditional forest variables, the area of deciduous forest had a strong positive effect on both woodpecker presence–absence and the number of years with occurrence. The results support the hypothesis that edge habitats and forest types subject to natural processes favouring deciduous trees and dead wood creation are valuable to the woodpecker and should be prioritised in conservation planning.
The western Kenya highland has been experiencing dramatic landuse changes in the past three decades. Landuse change has been hypothesized to be one of the mechanisms for malaria epidemics in African ...highlands because it can alter the physical and chemical characteristics of mosquito breeding habitats. One important landuse change in western Kenya highland is deforestation. The current study examined the effects of forestation or deforestation on the survivorship of Anopheles gambiae larvae and colonization of other aquatic insects in larval habitats in Kakamega forest (elevation 1,500–1,700 m above sea level), western Kenya. We found that the survivorship of An. gambiae larvae was reduced from 55 to 57% in habitats fully exposed to sunlight (open habitats) to 1–2% in habitats with full forest canopy coverage (forest habitats) and partial canopy coverage (forest edge habitats) in two out of three trials. The average daily water temperature of the open habitats was ≈3–3.4°C higher than the forest habitats. Insect species in the orders of Diptera, Coleoptera, and Odonata colonized the larval habitats, but the three habitat types differed greatly in the animal assemblage. Canonical correspondence analysis found that water temperature and amount of leaf litter were the significant variables associated with animal assemblages. Redundancy analysis revealed that openness and the presence of predatory animals were significantly related to An. gambiae survivorship. This result suggests that deforestation facilitates the survival of the immature stage of An. gambiae in the highland.
Although considered by some as a less “ecologically suitable” forestry model than “near-natural” stand management, even-aged plantation forest management, with regeneration procedure involving ...clearcutting, creates temporary habitat for many early-successional birds. The present study addresses the question of the conservation value for birds of clearcutting-related open areas in European temperate forest, in the context of a mixed woodland–farmland landscape. The point count technique was used to census the breeding birds on 300 sampling plots, distributed in the eight main habitat types of the Ardenne region (southern Belgium), including agricultural land, edge habitats, closed forest habitats and open areas in forest. Most of these open areas in forest derive from clearcutting practices, rapidly planted with young Norway Spruce (
Picea abies). We quantified the conservation value of a given habitat type by using a “conservation value index”, integrating the frequency of occurrence of each species in the considered habitat and their conservation status in Europe or in southern Belgium. Both conservation value index and species richness were higher for edge habitats and open areas in forest, compared to forest interior and agricultural land. Detrended Correspondence Analysis of the plot species lists showed that bird assemblages from open area in forest are not intermediate between forest and agricultural open land, as opposed to external edge habitats. Hence, open areas in forest do not contain bird assemblages composed of forest species mixed with colonizing agricultural species but rather shelter specific bird assemblages. An Indicator Species analysis further emphasized this specificity and identified seven species, which, in the Ardenne context, form a group of species specific to open areas in forest. Due to major changes of land use in the Ardenne during the 20th century, which leads to a tremendous decrease of moor, heath and fallow land areas, clearcut openings in the plantation forest progressively gained high conservation value at the regional scale. Further studies about habitat requirement of the conservation interest species inhabiting these open areas is needed, including a better understanding of how early-successional species react to forest planning. If plantation forestry evolves to an uneven-aged and more permanently closed forest, then other options, including semi-natural habitat restoration, are urgently required to save early-successional bird communities.
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