Mortality Dynamics Across Time and Site Class Gradient

Abstract

Forest poses an important role by providing multiple ecological services such as regulating climate, recycling nutrients and carbon- storing etc. These services are highly dependent on the existing forest dynamics which is largely determined by tree mortality. Tree mortality is caused by many factors such as warming climate, drought, fire, competition, wind, pest attack etc. The study tries to aim of the study is to quantify and compare the rate of mortality across time on forest types of Norway. For this, secondary data from Norwegian National Forest Inventory data (2004 –2018); both plot and tree data were used for the study. The analysis was performed using R computing statistical tool. To be more specific, the mortality value was relative to the volume without bark was quantified on the base of DBH class, site index, volume, and basal area. Based on the analysis, three dominant trees i.e. (spruce, pine, and common birch) are estimated to have the highest volume loss (mortality) of 4.12 m3 /ha with an annual mortality rate of 0.2753 m3 /ha /yr. This shows that the mortality rate is low compared to other European countries. While going through the stand types, spruce has the highest mortality rate 0.51 m3 /ha/yr, whereas pine and common birch have the mortality of 0.32 m3 /ha/yr and 0.24 m3 /ha/yr respectively. Considering the different factors, the annual tree mortality estimates that the decline of tree numbers is relatively in low rate in comparison to the European tree mortality rates). The mean DBH (17.4 cm), basal area (0.031 m2 ) and volume for Pine dominated stands (237 m3 ) is greater than spruce and birch dominated stands. The tree mortality at high site quality is over 0.6 m3/ha greater on average than medium and high site quality mortality volume. The high-quality site has an average of 2.68 ± 5.81 m3 /ha tree mortality, whereas, the medium and low site quality observed tree mortality of 2.09 ± 5.19 m3 /ha 1.88 ± 4.93 m3 /ha, respectively. The error bar on site quality over mortality shows that majority of stand volume over other site quality is significantly not different. Thus, further statistical analysis is required to identify the significance of the data on site quality in different stand types over mortality.