Damaged and dead trees in Swedish forests : assessment and prediction based on data from the National Forest Inventory

• Main Author: Fridman, Jonas
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2000
• Subjects: Forest Science; Norway; Northern Sweden
• Online Access: https://pub.epsilon.slu.se/17682/; https://pub.epsilon.slu.se/17682/1/fridman_j_201005.pdf

Trees in the forest die, and this fact has implications for both forest production and biological diversity. This thesis deals with different aspects of damaged and dead trees in Swedish forests using data provided by the Swedish National Forest Inventory (NFI). A model system for risk assessment of snow and wind damage to trees on a site, i.e., windthrow and stem breakage, was developed with logistic regression. The models use characteristics of the largest sample tree, together with site and stand characteristics on a plot, to predict the risk. Estimated probabilities o f the risk can be used to adapt silvicutural treatments to limit damage caused by snow and wind. The method used by the NFI for acquisition of data on dead wood (DW) is described together with estimates based on data collected in 1994-1996. Estimates show that the volume of DW decreases from almost 10 m3 ha-1 in northern Sweden to about 4 m3 ha-1 in the south, giving an average on productive forestland of 6 m3 ha-1 for the whole country. Results showing the lack of large dimensions of DW, and the decrease in the volume of DW after logging are also presented. In 1994 and 1996 the NFI included plots within reserves, i.e., national parks, nature reserves, and Forest Service reserves, in the inventory. That data, together with data from 1983 to 1987 for plots on land that were later established as reserves, were used for analyses of the Swedish reserve network in terms o f proportion of forest, stand age, site quality, tree species composition, and tree volumes. The results show that the proportion of productive forest within reserves is 20% compared to 60% of the land area of non-reserves, and that the volume of dead trees is higher within reserves. In general the distribution of forests within Swedish reserves is skewed towards old low-productivity Norway spruce (Picea abies L. Karst) forests in Northwest Sweden. This allocation might not meet the demands for protection of the habitats of endangered species. Tree mortality functions were developed using logistic and linear regression. The 3-step approach consisted of: (I) estimating the probability of mortality on a sample plot, (II) quantifying the mortality in terms o f the proportion of basal area on a sample plot, and (III) distributing the mortality among individual trees on the plot. Independent variables used for steps I and II were specific to site, stand, and plot size. Step III models were specific to tree species, and in addition to site and stand variables tree variables such as diameter and competition indices were included. In summary, this thesis provides tools for inclusion in long-term management planning that would improve the possibilities for analyses of silvicultural treatments and their impact on risk of snow and wind damage, and also for their impact on the conditions for species depending on dead trees. The thesis also presents background data on the state of the forest within reserves, and the volume, structure and dynamics of dead wood on productive forestland in Sweden.