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Birch Forest (birch + forest)
Selected AbstractsWeathering rates of buried machine-polished rock disks, Kärkevagge, Swedish LaplandEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2002Colin E. Thorn Abstract Some 48 dolomite, 37 granite, and 19 limestone machine-polished disks were buried at soil horizon boundaries in 16 soil pits to maximum depths of 0·5,0·6 m within Kärkevagge, a presently periglacial, glaciated trough in Arctic Sweden. The objective of the ongoing study is to determine near-surface ,potential' weathering rates beneath birch forest, Dryas heath, heath, meadow, solifluction meadow, and willow vegetation cover types. Selected disks were excavated after 1 year, and all disks were excavated after 4 or 5 years. The limestone disks weathered fastest, followed closely by the dolomite disks, but the granite disks weathered at much slower rates. Mean annual percentage mass loss over 4 or 5 years was 0·473 ± 0·145% (two standard errors) for dolomite disks, 0·032 ± 0·005% (two standard errors) for granite disks, and 1·104 ± 0·446% (two standard errors) for limestone disks. For dolomite disks the Dryas heath and heath environments weathered the most slowly, a trend that was generally followed by the granite disks. Poor drainage (i.e. increasing wetness) and decreasing pH were found to promote dolomite weathering rates in a statistically significant manner. Surficial and subsurface weathering rates at individual sites were generally found to be correlated for dolomite, but not granite. Copyright © 2002 John Wiley & Sons, Ltd. [source] Shifting altitudinal distribution of outbreak zones of winter moth Operophtera brumata in sub-arctic birch forest: a response to recent climate warming?ECOGRAPHY, Issue 2 2007Snorre B. Hagen Climatic change is expected to affect the extent and severity of geometrid moth outbreaks, a major disturbance factor in sub-arctic birch forests. Previous studies have reported that the two geometrid species involved, autumnal moth and winter moth, differ in their temperature requirements and, consequently, in their altitudinal and latitudinal distribution patterns. In this study, we document the altitudinal distribution of winter moth outbreaks in a large coastal area in northern Norway. We show that, in the present winter moth outbreak, defoliated birch stands were seen as distinct zones with a rather constant width in the uppermost part of the forest and where the upper limit coincided with the forest line. The outbreak zone closely followed the spatially variable forest line as an undulating belt, although some of the variation in outbreak zone width was also related to variation in topographical variables, such as distance from the coast, forest line altitude, and slope of the terrain. A distinct outbreak zone at the altitudinal forest line is the typical picture that has been depicted in more qualitative historical records on previous outbreaks of autumnal moth rather than winter moth. We suggest that the recent documented climate warming in this region may have induced a shift in distribution of the winter moth both relative to topography and geography. Further investigation is, however, required to substantiate these suspicions. [source] Using classification tree analysis to reveal causes of mortality in an insect populationAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 2 2010Chris J. K. MacQuarrie 1Invasive species pose significant threats to native and managed ecosystems. However, it may not always be possible to perform rigorous, long-term studies on invaders to determine the factors that influence their population dynamics, particularly when time and resources are limited. We applied a novel approach to determine factors associated with mortality in larvae of the sawfly Profenusa thomsoni Konow, a leafminer of birch, and a relatively recent invader of urban and rural birch forests in Alaska. Classification tree analysis was applied to reveal relationships between qualitative and quantitative predictor variables and categorical response variables in a large data set of larval mortality observations. 2We determined the state (living or dead) of sawfly larvae in samples of individual leaves. Each leaf was scored for variables reflecting the intensity of intra-specific competition and leaf quality for leafminers, year of collection and degree-days accumulated were recorded for each sample. We explored the association of these variables with larval state using classification tree analysis. 3Leafminer mortality was best explained by a combination of competition and resource exhaustion and our analysis revealed a possible advantage to group feeding in young larvae that may explain previously observed patterns of resource overexploitation in this species. Dead larvae were disproportionately found in smaller leaves, which highlights the potential effect of competition on mortality and suggests that smaller-leaved species of birch will better able to resist leafminer damage. 4We show that classification tree analysis may be useful in situations where urgency and/or limited resources prohibit traditional life-table studies. [source] | ||||||||||