birch (betula sp.) is considered as extinction species and its natural regeneration in iranian forests ‎is very slow. difficulties in regeneration as well as natural seed germination of birch tree besides ‎high levels of seed contaminations have justified the application in‏ ‏vitro culture with respect to its ‎conservation and genetic improvement. hence, the in vitro culture initiation using se...

To examine Late Quaternary vegetation change across the modern vegetation gradient from continuous boreal forest (central Alaska) to Betula shrub tundra (Bristol Bay region), pollen records from Idavain and Snipe Lakes are described and compared to those of four other sites in southwest Alaska. Major features of the vegetation history at Idavain Lake include herb-dominated tundra (ca. 14}12 ka ...

BACKGROUND AND AIMS Betula L. (birch) is a genus of approx. 60 species, subspecies or varieties with a wide distribution in the northern hemisphere, of ecological and economic importance. A new classification of Betula has recently been proposed based on morphological characters. This classification differs somewhat from previously published molecular phylogenies, which may be due to factors su...

The immature stages of Kuwanina betula Wu & Liu are described and illustrated. Based on morphological and molecular data (18S and 28S rDNA), it is argued that K. betula is closer to Pseudochermes Nitsche than to Kuwanina Cockerell in Fernald and so this species is transferred to Pseudochermes as P. betula (Wu & Liu) comb. nov..

The capture of patchily distributed nutrients by tree roots has received extensive research, but the fate of those nutrients has not. We performed experiments to determine if nutrient transport within tree species is preferentially transported from specific roots to specific branches. Saplings of five species with contrasting growth requirements were examined: two Betula species (B. papyrifera ...

The phylogenetic relationships within the genus Betula (Betulaceae) were investigated using a part of the nuclear ADH gene and DNA sequences of the chloroplast matK gene with parts of its flanking regions. Two well-supported phylogenetic groups could be identified in the chloroplast DNA sequence: one containing the three American species B. lenta, B. alleghaniensis, and B. papyrifera and the ot...

Thermal conditions at the beginning of the year determine the timing of pollen seasons of early flowering trees. The aims of this study were to quantify the relationship between the tree pollen season start dates and the thermal conditions just before the beginning of the season and to construct models predicting the start of the pollen season in a given year. The study was performed in Krakow ...

i (1) We investigated interactions between snowshoe hares (Lepus americanus) and their food plants in winter during a cyclic fluctuation in numbers at Kluane, Yukon, between 1977 and 1985. • (2) The winter diet of hares at Kluane was dominated by four species of shrubs and trees. Betula glandulosa, the most preferred species, was common on only four of nine study plots. Salix glauca was eaten m...

In cold-temperate ecosystems of the upper Great Lakes Region, evergreen conifer-dominated forests were once common. As a result of past management practices, early-successional deciduous forests now dominate the landscape. Embedded in this matrix are stands of shade-tolerant conifers, including Thuja occidentalis . For the past several decades, large-scale T. occidentalis regeneration in remnan...

In high-latitude ecosystems climate change induced plant community shifts towards dominance of shrubs and trees will potentially have large consequences for soil carbon dynamics. Changes in the litter layer due to an altered quantity and quality of litter input, or by its indirect effect on microclimatic conditions, might affect the decomposer community. To be able to predict the effects of inc...