Timo Saksa

The Structure of Advanced Virgin Forests in Finland

The study deals with the structure of advanced virgin forests in Finland based on the national forest inventory carried out in the 1920s. At that time, virgin forests covered 2/3 of the forested area of Finland. Stand structure was described in terms of the d.b.h. distribution. The study material consisting of 10 x 50 m sample plots was grouped according to geographical region, site type and the age class of the overstorey. A stand was classified to be advanced if the age of the overstorey was at least half of the currently applied rotation age and if the stem volume exceeded 40 m3/nectare. About 60% of all virgin forests (i.e. 932 sample plots) were classified to be advanced. In the 1920s. the majority of advanced virgin forests were mixed stands with an all‐sized structure. Trees of small diameter prevailed and the stem number diminished rather steadily with increasing d.b.h. Even‐sized stands with a d.b.h. range of 15 or 20 cm and a normally distributed diameter frequency accounted for only 10 sample...

Predicting regeneration establishment in Norway spruce plantations using a multivariate multilevel model

This study predicts the regeneration establishment on 3-year-old Norway spruce (Picea abies (L.) Karst.) plantations in southern Finland using regeneration survey data. Regeneration establishment was described by seven response variables: number of planted spruces, natural Scots pines (Pinus sylvestris L.), natural spruces, natural seed-origin birches (Betula pubescens Ehrh. and B. pendula Roth.) and other broadleaves (i.e. sprout-origin birches and other broadleaves than birch), as well as height of crop-tree spruce and dominant height of broadleaves. Due to the multivariate (several responses for each plot) and multilevel (plot, stand, municipality, forest centre) structure, regeneration establishment was modelled by fitting a multivariate multilevel model with explanatory variables such as temperature sum, site fertility, soil quality and method of site preparation. In the model, the numbers of tree seedlings were modelled using over-dispersed Poisson distributed equations, and the tree heights were modelled using normally distributed linear equations. The estimated fixed and random parameters of the equations were logical, and there was no serious bias in predicting the regeneration establishment in the independent test data set. This modelling approach can be used to predict the regeneration establishment stochastically by taking into account the large unexplained variation in regeneration models.

Clear-cut Detection in Boreal Forest Aided by Remote Sensing

The study compares the applicability of different remote sensing data and digital change detection methods in detecting clear-cut areas in boreal forest. The methods selected for comparisons are simple and straightforward and thus applicable in practical forestry. The data tested were from Landsat satellite imagery and high-altitude panchromatic aerial orthophotographs. The change detection was based on image differencing. Three different approaches were tested: (1) pixel-by-pixel differencing and segmentation; (2) pixel block-level differencing and thresholding; and (3) presegmentation and unsupervised classification. The study shows that the methods and data sources used are accurate enough for operational detection of clear-cut areas. The study suggests that predelineated segments or pixel blocks should be used for image differencing to decrease the number of misinterpreted small areas. For the same reason the use of a digital forest mask is crucial in operational applications.

The effect of stand density on moose damage in young Pinus sylvestris stands

The relationship between moose damage and the stocking density of young Scots pine stands was investigated in the study. A regeneration area with an initial density of 14 700 seedlings ha‐1 was thi...

Ingrowth, survival and height growth of small trees in uneven-aged Picea abies stands in southern Finland

The purpose of the study was to analyse height growth, mortality, and ingrowth of individual small-sized trees in uneven-aged spruce-dominated stands. It was based on experimental data from 16 stands for a 15-year observation period including four measurements with a 5-year interval. In the data of this study, the heights of small-sized trees varied from 0.1 to about 9 m. Results showed that the growth of small trees was rather slow, particularly in the smallest size classes. With average growth rates it would take about 60 years for a freshly emerged spruce germinant to achieve 1.3 m in height. The stand density, site quality and selection cuttings affected the growth of small-sized spruces. Average five-year mortality rates for spruce, birch and pine were 17.0%, 40.9% and 33.9%, respectively. Annual ingrowth rates with the threshold height of 1.3 m for the three species were on average 30.4, 2.8 and less than 0.1 trees per hectare, respectively. Even if, a selection cutting of modest intensity (25% of basal area removed on average) seemed to have accelerated the growth of small spruces, it is recommended that more intensive harvestings be applied to enhance the survival and growth of small spruces. It is also concluded that shade intolerant species like birch and pine do not seem to be capable of developing into viable undergrowth in spruce selection stands with their current levels of stand density.

Effect of cleaning methods in mixed pine–deciduous stands on moose damage to Scots pines in southern Finland

Abstract The effect of different cleaning treatments on moose (Alces alces L.) damage to Scots pines (Pinus sylvestris L.) was examined using a generalized linear mixed model (GLMM) with a binomial response (logit-link function). The treatments were the following: no cleaning, point-cleaning of broadleaves (mainly birch, Betula pendula Roth and B. pubescens Ehrh.) within a radius of 1 m from the pine, point-cleaning delayed 2 years, topping of competing broadleaves (main stem cut at a height of 1.3 m) and total cleaning of broadleaves. A randomized complete block design with three replicates was established in three planted pine stands (mean height of pines 1.5 m). Measurements taken four growing seasons later (mean height of pines 3.5 m) showed that all cleaning treatments reduced moose damage, although the difference was not significant (p=0.078) in the case of topping. The proportion of damaged pines was predicted as a function of the characteristics of pines and broadleaves in two untreated, planted pine stands with a height of 3 m. Within these untreated stands the number of damaged pines increased in plots with a higher number of broadleaves and taller broadleaves. In conclusion, the results show that on relatively fertile growing sites of pine cleaning treatments reduced moose damage on pine. It is recommended that cleaning is performed before broadleaved trees occur as overgrowth above pines.

Predicting establishment of tree seedlings for evaluating methods of regeneration for Pinus sylvestris

Abstract This study predicts the establishment of regeneration in 3-, 4- and 5-year-old regeneration areas planted, direct seeded and naturally regenerated, respectively, for Scots pine (Pinus sylvestris L.) in southern Finland. Establishment of regeneration was described by the number of planted, seeded and natural tree seedlings, as well as by the height of pines and the dominant height of broadleaves. In planted stands, the number of natural crop-tree conifers was also predicted. For each regeneration method, establishment of regeneration was modelled by fitting a multilevel multivariate model to regeneration survey data. Temperature sum, altitude, site fertility, soil quality and method of site preparation were used as explanatory variables in the models. Stochastic simulations that accounted for the random between-stand variation in the regeneration result were conducted to evaluate the uncertainty and risk involved in different methods of regeneration for Scots pine. Counting both planted pines and supplementary natural crop-tree conifers, on relatively fertile growing site of Scots pine (Myrtillus type), planting was more effective than direct seeding and natural regeneration. On poorer sites (Vaccinium and Calluna types), in terms of the number of pine seedlings, direct seeding proved to be the most effective method for establishing pine stands.

Effects of early cleaning on young Picea abies stands

Young Norway spruce stands (Picea abies [L.] Karst) are typically cleaned of non-crop species on one or several occasions during young stand stage. In order to objectively evaluate the perceived benefits of early cleaning (EC), we studied the effects of EC on three study sites 2–2.5 years after receiving the treatment. Experiments were established as a randomised complete block design with a total of 40 blocks. Although height growth and mortality were not significantly affected, we found that EC substantially reduced canopy competition and, consequently, the mean diameter of released spruce grew 21–32% faster depending on the site. Furthermore, non-crop trees that were cleared during EC had fewer sprouts in two of the three sites and the sprouts were substantially smaller than the corresponding non-crop trees on control in all sites. EC can reduce the cost of pre-commercial thinning because EC reduced the estimated time needed for subsequent management by 18–49%. Thus, EC offers forest owners and managers an economically viable young stand management option.

Reliability of self-control method in the management of non-industrial private forests

This study seeks to determine the extent to which self-control data can be relied upon in the management of private forests. Self-control (SC) requires the forest workers to evaluate their own work quality to ensure the clients’ needs are met in terms of soil preparation, planting and young stand management. Self-control data were compared to an independent evaluation of the same worksites. Each dataset had a hierarchical structure (e.g., sample plot, regeneration area and contractor), and key quality indicators (i.e., number of mounds, planted seedlings or crop trees) were measured for each plot. Self-control and independent-assessments (IA) were analyzed by fitting a multivariate multilevel model containing explanatory variables. In the silvicultural operations studied, no practical differences for the quality control purposes were found. This was the case especially in soil preparation (number of mounds) and young stand management (number of crop trees). Self-control seemed to give about 10–20% overor underestimation depending on key quality indicator as compared to independent assessment. Discrepancies were discussed in terms of sampling and other explanatory factors. According to overall results, self-control methods are reliable at the main stages of the forest regeneration process. As such, the diverse utilizing of self-control data is possible in support of service providers operations.

Varhaisperkauksen vaikutus männyn taimien elossa oloon, kasvuun ja lehtipuuston aiheuttamiin latvavaurioihin

Seloste artikkelista: Saksa, T. & Miina, J. 2007. Cleaning methods in planted Scots pine stands in southern Finland: 4-year results on survival, growth and whipping damage of pines. Silva Fennica 41 (4) : 661-670