Spatial Distribution Of Tree Species Research Articles

The spread of gray birch (Betula populifolia) in eastern Quebec: landscape and historical considerations

The understanding of recent changes of the spatial distribution of tree species occurring in agricultural landscapes is essential to realistically predict future positions of the range limit of tree species. In Quebec (Canada), it has recently been suggested that gray birch (Betula populifolia Marsh.) is spreading rapidly eastward. We tested the hypothesis that this tree migration is strongly facilitated by human activities. Herbarium specimens, historical landscape reconstructions, botanical surveys in mined peatlands and old fields, and dendrochronological data were used to reconstruct past and recent distribution limits of gray birch in the study area (Bas-Saint-Laurent region). Gray birch has been present in the Bas-Saint-Laurent region since at least 1945. However, herbarium specimens and botanical surveys indicate that gray birch individuals were scarce before 1970. The introduction of gray birch in the Bas-Saint-Laurent region seems to be associated with peat mining activities. All mined peatlands located between Rivière-Ouelle and Isle-Verte were colonized by gray birch, but only 11% of old fields surveyed contained at least one gray birch individual. This suggests that the spread of an early successional tree species in an agricultural landscape is facilitated more by the presence of a few large patches favorable to the growth of the species (mined peatlands) than by numerous small patches (old fields). The recent expansion of gray birch populations in the Bas-Saint-Laurent region could be a major concern for peat mining companies because massive invasions of gray birch in abandoned mined bogs may impede successful restoration of these ecosystems.Key words: Betula populifolia, gray birch, Quebec, peatland, old field, landscape ecology.

Substrate conditions, foliar nutrients and the distributions of two canopy tree species in a Costa Rican secondary rain forest

A 28 yr old secondary lowland rain forest in Costa Rica was dominated by two tree species of contrasting ecologies, Vochysia ferruginea - a species typical of well-drained but infertile soils of high Al saturation, and Cordia alliodora, a species requiring soils of at least moderate fertility. The two species exhibited markedly different spatial distributions in the forest and we sought to determine whether or not these different distributions were related to variation in substrate conditions and the nutrient requirements of the two species. Two soil types were present: Ultisols (Typic Haplohumults) and Inceptisols (Typic Dystropepts) and topography was of low hills. The study formed part of an analysis of site quality for timber production in the two species and therefore used standard forestry methods for such analyses. 36 plots of 20 m×20 m were established using predetermined criteria of site uniformity, presence of at least four dominant trees of at least one of the study species, and absence of disturbance. The abundance (number of individuals ≥ 10 cm dbh) of each species was determined in each plot. Soil samples were taken in 27 of the 36 plots, 9 plots being considered to replicate conditions already sampled, and 14 soil chemical and physical variables were measured using standard methods. Foliar nutrient analyses were carried out for trees of both species with crowns fully exposed to sunlight, distributed across the gradient of soil conditions. Variations in species abundances were not related to soil type, but plots in which Vochysia ferruginea was more abundant tended to be on steeper slopes with soils of higher exchangeable acidity and lower concentrations of Mn; Cordia alliodora was more abundant on gentler topography where soils had much lower exchangeable acidity but higher Mn. Differences between the two species in foliar nutrient concentrations were marked and supported previous interpretations of their nutrient requirements; foliar nutrients of Vochysia ferruginea were typical of tree species of moist tropical forest on infertile soils, and those of Cordia alliodora typical of a species requiring more fertile soils. Factors such as the distributions of seed trees at site abandonment may affect the spatial distributions of tree species in secondary forests such as that studied. The relationships of the distributions of the two species to substrate variation, however, and their evidently different nutrient requirements, support the hypothesis that variation in the composition and structure of the forest studied is at least partially related to exchangeable acidity and its dominant cation, Al.

A Comparison of Spatial Patterns of Trees in Some Tropical and Temperate Forests

A Comparison of Spatial Patterns of Trees in Some Tropical and Temperate Forests