Vinsamlegast notið þetta auðkenni þegar þið vitnið til verksins eða tengið í það: http://hdl.handle.net/1946/19791
Extensive literature exists on birch silviculture in North America and Europe (Perala & Alm 1990, Hynynen et al. 2010). Birches are managed by both coppicing and seedling-based regeneration with good success. High light levels are considered essential for vigorous growth and therefore clear-felling or seed-tree silvicultural systems are recommended rather than selection systems (Perala & Alm 1990). Similar to most other birches, native downy birch in Iceland (Betula pubescens Ehrh. ssp. czerepanovii [N. I. Orlova] Hämet-Ahti) is light-demanding and regenerates readily from stump sprouts. Regeneration from seed is most successful on partially vegetated land but less so within woodlands (Aradóttir & Eysteinsson 2005). Traditional tree harvesting in Iceland, where all trees in a given area were removed (Blöndal & Gunnarsson 1999), is accurately described as clear-felling. Regeneration often failed due to livestock grazing and fodder harvesting, eventually resulting in the nearly complete deforestation of Iceland (Bjarnason 1942). During the early 20th century, the Iceland Forest Service promoted single-tree selection instead of clear-felling, the goal being to prevent forest clearing. Harvesting of birch generally ceased during the 1940s, but a few natural birch forests have been managed for wood production by single-tree selection for over a century (Blöndal & Gunnarsson 1999). Recently, mechanised harvesting has resulted in slightly heavier felling, more accurately described as group selection. Selection-based silviculture works in the management of Icelandic birch woods, the managed forests having improved in height and straightness with no regeneration failure (Blöndal & Gunnarsson 1999). However, saplings surrounded by taller trees tend to be slender. Slow diameter growth lengthens the rotation period and possibly also increases the likelihood of various types of damage. These perceived negative outcomes awakened questions as to the possibility of improving early diameter growth by regeneration after clear-felling. Despite the long experience with birch regeneration after selection-felling in Iceland, it has never been properly documented and never compared to other silvicultural systems such as clear-felling. This paper compares regeneration and growth of Betula pubescens ten years after selection-felling and clear- felling in a forest in north Iceland.
|Throstur Eysteinsson 2012.pdf||179.43 kB||Opinn||Heildartexti||Skoða/Opna|