Diana Laarmann

Estimating tree survival: a study based on the Estonian Forest Research Plots Network

Tree survival, as affected by tree and stand variables, was studied using the Estonian database of permanent forest research plots. The tree survival was examined on the basis of remeasurements during the period 1995–2004, covering the most common forest types and all age groups. In this study, the influence of 35 tree and stand variables on tree survival probability was analyzed using the data of 31 097 trees from 236 research plots. For estimating individual tree survival probability, a logistic model using the logit-transformation was applied. Tree relative height had the greatest effect on tree survival. However, different factors were included into the logistic model for different development stages: tree relative height, tree relative diameter, relative basal area of larger trees and relative sparsity of a stand for young stands; tree relative height, relative basal area of larger trees and stand density for middle-aged and maturing stands; and tree relative height and stand density for mature and overmature stands. The models can be used as preliminary sub-components for elaboration of a new individual tree based growth simulator.

Assessment of tree mortality after windthrow using photo-derived data.

We used sequential surface photography and photo-derived data to evaluate tree mortality in a windthrow area in eastern Estonia, where a storm occurred in 2001. The study is based on photographs taken from the edge of three completely destroyed areas with total canopy destruction in which wind-felled spruce trees (Picea abies) were left after disturbance. In total, 137 spruce trees were observed over a five-year period. We used a transition matrix to examine tree mortality dynamics and patterns. At the end of the five-year period, only 25% of the spruce trees survived in areas surrounding the windthrow. The mortality was highest in the second year after disturbance and the probability of a tree falling was surprisingly high over the entire study period. According to local observations, Ips typographus caused most of the tree deaths, but the co-influences of other factors were also important as there was a large proportion of falling trees in the area.

Monitoring and modeling of forest ecosystems: the Estonian Network of Forest Research Plots / Metsaökosüsteemide seire ja modelleerimine metsa kasvukäigu püsiproovitükkide võrgustiku abil

Abstract Forest research has long traditions in Estonia that can be traced back to the 19th century. Data from long-term forest experiments are available since 1921. The first studies mainly focused on silvicultural treatments and application of such data for understanding and modeling ecological processes was limited. The Department of Forest Management of the Estonian University of Life Sciences started to develop the Estonian Network of Forest Research Plots (ENFRP) in 1995. Since then, plots have been continuously re-measured with 5-year interval. Approximately 100-150 permanent sample plots were measured annually. In 2014, the long-term research network consisted of 729 permanent sample plots, of which 699 have been re-measured at least once, 667 plots - twice and 367 plots - three times. The total number of trees recorded in the network database amounts to 130,479. The plots are systematically distributed throughout the country. Detailed dendrometric measurements including tree spatial distribution are part of the survey protocol. Initially the network was set up to produce suitable data for development of individual tree growth models for Estonia. The significance of the network for the Estonian forest research is continuously increasing and nowadays ENFRP is recognized as an important national research infrastructure.

Estimation of change in forest height growth

Abstract Forest height increment rate is related to the forest growth conditions. Data bases of previous forest inventories contain information about forest heightage relationship on large number of forest stands while repeated measurements of permanent sample plots provide an excellent reference for comparison. Repeated airborne laser scanning of forest stands is an additional source for the estimation of change in forest structure. In this study, height growth of middle-aged and older forest stands for about 10 year period was compared to an algebraic difference model on permanent sample plots (66) and for a sample of forest stands with repeated airborne laser scanning data (61). The model was based on a large dataset of forest inventory records from the period of 1984–1993. Statistically significant increased forest height growth was found in permanent sample plots based on tree height measurements (9 cm yr−1) as well in stands with repeated laser scanning data (4.5 cm yr−1) in South-East Estonia compared to the algebraic difference model. The difference between the two data sets was explained by their mean age and site class, but the increased forest height growth compared to the old forest inventory data indicates improved growth conditions of forests in the test area. The results hint also that empirical data-based forest growth models need to be updated to avoid biased growth estimates.

Online streaming public participation in forest management planning

Abstract A new paradigm in forest management using a streaming input of public participation needs effective online solutions. The process should be real-time, secure, effective and efficient. People are expected to share their data and thoughts on forest management with forest owners for improving forest management and planning. The participatory approach supports communication within society and can be designed as an interactive web-based solution. Many pre-requisites have already been met and society is ready for a successful start of an interactive participatory forest planning system in Estonia. People use digital identification for various purposes and the state already maintains an online public forest register. Motivating people to participate in the planning process is always challenging yet important for the successful implementation of the system. The system should allow simulating the development and management of forest stands following the participatory input and using ecosystem models and economic calculations. The outputs from the system include management alternatives, risk assessments and financial reports. The system requires a reliable financial compensation scheme to ensure overall long-term stability of the system and agreements between interested persons or groups and forest owners.

Assessment of tree mortality on the Estonian Network of Forest Research Plots/ Puude väljalangevuse hindamine metsa kasvukäigu püsiproovitükkidel

Abstract Assessment of tree mortality provides deeper understanding of forest structure and functioning. This enables evaluation of stand sustainability and provides information on stand productivity, diversity and health condition. Tree mortality can be assessed by spatiotemporal patterns as well as by studying the processes and causes of mortality. Tree mortality is caused by specific disturbance agents or by the complex effect of various disturbances. The purpose of this study is to examine tree mortality in Estonian forests, determine the causes of tree death, and estimate how different management regimes affect tree mortality and its causes. This study is based on 360 sample plots measured in 2003-2005 and re-measured in 2008-2010. The sample plots were divided into recently managed (RM, 146 plots) and low intensity/unmanaged (LU, 214 plots) plots based on forest management regime. In total, 53,990 trees were measured, of which 20,020 were located on RM and 33,970 on LU plots. The tree mortality for 5-year period was 3.4% on RM plots and 8.0% on LU plots. The main cause of tree mortality in RM stands was insect damage, which attributes to 29.8% of tree mortality, whereas in LU stands the main cause was tree competition, which attributes to 45.4% of tree mortality. The analysis of tree mortality indicated that an increase in relative tree diameter in both stand types contributes to an increase in mortality due to insect, wind or fungal damage and diseases. Opposite results were received with respect to competition - the smaller the tree relative diameter, the more probable it is that a tree will die because of competition with neighbouring trees. The analysis of game damage and other causes of tree mortality showed that these were not dependent on the relative diameter of trees. The analysis of the overall probability of tree mortality revealed that relatively smaller trees have a higher probability of mortality than larger trees.