No description available.

The main objectives of this investigation were to determine the impact of climate on mountain birch (Betula pubecens ssp. czerepanovii (Orlova)) growth and to develop a regional chronology of autumnal moth outbreaks. To accomplish the objective, cores of mountain birch were taken from 21 sites in Norrbotten, Sweden. Tree-ring chronologies were developed for each site. Climatic influences were determined by correlating ring widths to climatic variables (average monthly temperature, average monthly precipitation and NAO). Outbreaks were recovered from the ring width indices using the non-host method with Scots pine (Pinus sylvestris (L.)) as the non-host. This method removes the climatic influence on growth to enhance other factors. Patterns of synchrony and regional outbreaks were detected using regression and cluster analysis techniques. The primary climatic influences on the tree ring growth of mountain birch are June and July temperatures; precipitation during October is of secondary importance. Climate explained 46% of yearly tree ring width variation. Outbreaks of the autumnal moth occur at varying time intervals depending on the scale of study. Intervals between outbreaks on the tree level are twice as long as at the plot level. On the regional scale plots within the same valley had more similar outbreak intervals and magnitudes of outbreaks. Elevation is a driver in determining the length of outbreaks and length between outbreaks. The percent monocormicity of a plot is also a determining factor of the length between outbreaks. This study is the first regional scale study on climate and outbreaks of the autumnal moth on mountain birch. The results complement research being conducted on autumnal moth larval densities and will help in modeling and assessing the effects of outbreaks with increasing climatic change.

Climate change has coincided with expansion of deciduous shrub species in the Arctic. Increased deciduous vegetation in the tundra could have profound implications on regional climate, carbon balance, and biogeochemical cycling of nutrients. Winter biological processes may be a mechanism explaining shrub expansion in the Arctic. Tall shrubs accumulate relatively deep snowcover, raising winter soil temperature minima, enhancing microbial activity and promoting nitrogen mobilization that may then be taken up by shrubs. However, it has yet to be determined if shrubs can acquire winter-mobilized nitrogen, and if so, whether they acquire it early in the spring, or over the growing season. The purpose of this study was to test if increased snow alone or the combination of vegetation-type and snow depth affect nitrogen cycling and plant uptake. To test this, inorganic 15nitrogen tracer was added to control and experimentally deepened snow plots (using snowfences) in low birch hummock tundra, and to tall birch-dominated plots near Daring Lake, N.W.T. in the Canadian low Arctic. The first study (Chapter 2) characterizes soil 15nitrogen cycling over a single winter to investigate if experimentally deepened snow in low birch hummock ecosystems enhances nutrient availability to plants in the early spring. In addition, 15nitrogen cycling in low birch hummock and tall birch ecosystems were compared to characterize the combined impacts of vegetation-type and snow depth on nutrient availability to plants by early spring. The second study (Chapter 3) investigated the longer term fate of added 15nitrogen to determine if 15nitrogen acquisition and allocation differs among plant species over a two year period. Together, the results indicate that nitrogen cycling in the low birch hummock tundra was not significantly affected by deeper snow over short (after one winter) or longer terms (two years). By contrast, nitrogen availability in early spring, and birch shrub 15nitrogen uptake after two years were enhanced in the tall birch as compared to the low birch hummock ecosystem. These results suggest that the combination of vegetation-type and snow depth effects in the tall birch ecosystem could be a mechanism contributing to tundra to shrubland transitions across the Arctic. / Thesis (Master, Biology) -- Queen's University, 2009-09-18 13:36:29.401

Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.

Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniversitet, 2005. / Härtill 4 uppsatser.

Diss. (sammanfattning). Umeå : Sveriges lantbruksUniversity. / Härtill 4 uppsatser.

Diss. (sammanfattning). Umeå : Sveriges lantbruksuniv. / Härtill 4 uppsatser.

Licentiatavhandling (sammanfattning) Luleå : Luleå tekniska univ., 2005. / Härtill 5 uppsatser.

Lic.-avh (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2006. / Härtill 3 uppsatser.

This thesis compare various uses of silver birch (Betula pendula Roth.) as a preparatory species during afforestation by silver fir (Abies alba Mill.). In this experiment, silver fir was planted at fall of 2015 and measurements were conducted in the vegetation season 2016. There were four variants of experiment with respect to the silver birch: clearcut, birch stand with 50 % stocking density, narrow embankment cut and birch stand with a full stocking density. Air temperature, precipitation, vapor pressure deficit, soil moisture and transmittance of photosynthetically active radiation were measured from the environmental variables. On plants, the growth increment, chlorophyll fluorescence, shoot water potential and needle mas per area were studied. Preparatory forest stand eliminated extreme temperatures, both positive and negative. Maximum temperatures were by 7 °C lower under the forest canopy than on clearcut. Spring frost was eliminated by 2.2 °C which was enough to protect fresh shoots from freezing. On the other hand soil moisture under the birch was by 23 till 47 % lower than at the clearcut. Tallest growth increment of 12 cm was at the clearcut, shortest of 7 cm under the birch without thinning. Needle mass per area corresponded to light availability and it was highest at clearcut and lowest under the birch. Chlorophyll fluorescence in dark did not suggest any differences between treatments (Fv/Fm was higher than 0.80) and therefore differences in growth can be accounted to the light availability. Data suggest that for the silver fir saplings is best to grow under severely thinned silver birch canopy with low stocking density which allows for enough light and soil moisture but still protects saplings against inclement weatherFormula clause:I declare that I am working, "Birch as a preparatory tree species in reforestation calamity clearings silver fir: the impact of environmental conditions and selected ecophysiological parameters fir" worked independently and all used sources and information mention in the list of references. I agree that my work has been published in accordance with § 47 b of the Act no. 111/1998 Coll., On universities, as amended and in accordance with directives on the publication of university theses. I am aware that my work covered by Act no. 121/2000 Coll., The Copyright Act, and the Mendel University in Brno has the right to conclude a license agreement and use this work as school work pursuant to Section 60 paragraph. 1 of the Copyright Act. I also agree that, before drawing up licensing agreements on the use of a work by another person (the subject), I request a written opinion by the university that the subject license agreement is not contrary to the legitimate interests of the university and undertake to pay any contribution to the costs associated with the creation of the work, and up to the full amount