Epsilon Archive for Student Projects

Abstract

Idag lämnas så kallade evighetsträd efter slutavverkning för att minska den negativa påverkan på den biologiska mångfalden i produktionsskogen. Dessa träd kan vara naturvärdesträd, som redan uppvisar någon form av naturvärde, eller utvecklingsträd, som lämnas för att få utveckla naturvärden i framtiden. Idag saknas kunskap om hur stor del av evighetsträden som överlever efter slutavverkning och hur stor del av dessa som kan klassas som naturvärdesträd. I den här studien undersöks också hur sälgens överlevnad skiljer sig från andra träd. I detta arbete har 23 slutavverkningsytor undersökts för att få fram bättre underlag för naturvårdsplaneringen i slutavverkning. Detta gjordes genom att en-hektars provytor slumpades ut och i dessa mättes samtliga träd för diameter, höjd, naturvärde, vitalitet, position på hygget, vindfällning samt markberedning inom krongräns.

Resultatet visade att fyra år efter avverkning var 13,9 procent av de kvarlämnade träden vindfällda och de träd som lämnades i hyggeskant hade en signifikant lägre risk att vindfällas än de som lämnades i grupp eller solitärt ute på avverkningsytan. Andelen av evighetsträden som klassades som naturvärdesträd var 19,3 procent och de vanligaste naturvärdesstrukturerna var grov bark och avvikande grenar. Över hälften av naturvärdesträden uppvisade endast en naturvärdesstruktur eller tillhörde ett avvikande trädslag utan naturvärdesstruktur, vilket visar på en brist av mycket biologiskt rika träd i produktionsskogen. Andelen sälgar som fyra år efter avverkningstillfället fortfarande levde var 63,2 procent, vilket var lägre än övriga evighetsträd och jämfört med andra studier. Detta tyder på att sälgen behöver extra hänsyn i skogsbruket om dess värde för den biologiska mångfalden ska bevaras.

In Swedish forestry it is common practice to leave retention trees after final felling to reduce the negative impact on biodiversity. These trees can either already possess important biological structures, such as rough bark formation or woodpecker cavities, or they do not yet have a high biological value but are left on the site to be allowed to gain these in the future. The Swedish forestry agency categorize which trees that can be said to have an important biological function and call these “naturvärdesträd” (trees with high conservation value). The retention trees that do not qualify for trees with high conservation value are called “utvecklingsträd” (development trees). In this paper the proportion of retention trees that survive after final felling and how many of them that already possess some kind of important biological function are examined. In addition to this the survival of goat willow (Salix caprea L.) is examined in further detail, due to its importance to biodiversity as it blossoms in early spring and provides food to many different insects and birds. The aim is to increase the knowledge of retention tree survival and biodiversity for future planning in final felling.

23 clear-cuts were examined four years after final felling and one-hectare plots were randomized positioned on each clear-cut. On these plots, each tree was measure in diameter, height, biological structure, position on the clear-cut surface, whether or not the tree was wind thrown and scarification (soil preparation) within 5 meters of the stem. The results showed that 13.9 percent of the retention trees had been wind thrown, but the trees that were left in clear-cut edges had a significantly lower mortality than those left as solitary trees or in groups more that 15 meters away from clear-cut edges. The proportion of retention trees that had an important biological function were 19.3 percent and the most common biological structures were rough bark formation and abnormal branches. More than half of all the nature trees were considered so either because they were a rare tree species without an important biological structure or because they only possessed one important biological structure. This shows a lack of trees with several biological structures and large importance to biodiversity in the managed forest landscape. The goat willow had a survival of 63.2 percent, which was lower than the total survival of the measured retention trees. The goat willows survival was also lower compared to other scientific studies, although these showed a slightly higher mortality than the retention trees in this study. This shows that additional conservational measures are needed to preserve the important biological structures of the goat willow in the forest landscape.