In the near future, the wood from silver birch (Betula pendula Roth) plantations will broadly increase as a source of raw material of saw and veneer logs. Due to the differences in growth rate and silviculture, the raw material from plantations is likely to have characteristics different from those of the wood harvested from naturally regenerated forests. In the further processing of sawn birch timber, the drying of wood is one of the most difficult phases: discolouration, deformation, moisture content gradient, being typical defects for dried birch timber.
The objective of this thesis was to study the drying behaviour and related wood and timber properties of plantation-grown silver birch. The wood procurement season and storage of logs were studied as a source of variation of wood properties and drying behaviour. To study the variation in wood properties and drying behaviour caused by the drying method, the conventional kiln drying (heat and vent drying) and vacuum drying were used. On the subject of drying method, wood colour, shrinkage, weight density, final moisture content, Brinell hardness and equilibrium moisture content were studied. The role of proanthocyanidins and their polymerisation as a chemical background for the discolouration was studied.
The drying behaviour, the initial moisture content of the wood, basic density and proanthocyanidin content were found to change with the wood procurement season. These changes were consequences of the physiological alterations in birch trees with the seasons and they were found to have an influence on colour, density, equilibrium moisture content and Brinell hardness of wood. Regarding the conventionally dried wood, the discolouration was the most intensive for summer-felled wood while the vacuum-dried wood discoloured the most intensively when it was felled in winter. In summer-felled and winter-felled wood the storage of timber as logs increased the discolouration of the wood during drying.
In this thesis are studied the role of decomposing logging residues and developing ground vegetation in nutrient dynamics of a clear-cut area. The main aims were to study how much nutrients are released from logging residues during the first three years after clear-cutting and what is the role of ground vegetation in the retention of nutrients on site after clear-cutting. The study was conducted in eastern Finland in a Norway spruce dominated mixed forest, part of which was clear-cut and part left uncut. The decomposition of Norway spruce (Picea abies Karsten), Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth.) logging residues i.e. foliage, fine roots (diameter ≤ 2 mm) and branches (diameter ≤ 1 cm), were studied using the litterbag method. Above- and below-ground biomass of the ground vegetation was sampled on one uncut plot and two clear-cut plots one year before and five years after clear-cutting.
In total, 33 % of the dry mass and C, 49 % of P, 90 % of K and 8 % of Ca were released from logging residues in three years, but there was no net release of N because more N accumulated in the roots and branches than was released from the foliage. The loss of mass, C, P and K was greatest during the first year, whereas there was no net release of Ca until the third year. Most of the released nutrients originated from the foliage. Total ground vegetation biomass and nutrient pools decreased after clear-cutting to one half or even lower, but returned to pre-cutting levels within 4-5 years, and the pools of P and K became even larger. In the first year after clear-cutting more N and Ca accumulated in the logging residues than were stored in the ground vegetation.
The results indicate that logging residues are a potential source of the elevated dissolved C and P, K and Ca observed in surface waters soon after clear-cutting, but are not a net source of N during the first three years. The ground vegetation is capable of taking up only a small fraction of the nutrients that are released from logging residues during the first two years after clear-cutting and the decomposing dead ground vegetation is a potential source of leached nutrients. The results suggest that nutrients released from logging residues are initially retained on site primarily through soil processes and microbial immobilization. Solely microbial immobilization in logging residues can initially play a more important role in the retention of N and Ca than the ground vegetation. Ground vegetation, however, recovers rapidly from clear-cutting and it becomes thereafter a significant nutrient sink.
Fast-growing, high-yield tree plantations are an increasingly significant source of wood in the tropics. In these areas, improved wood productivity is an important economic goal. In Costa Rica and other countries in Central America, most of the tree plantations, especially those of advanced age, have not had the productivity expected of them. In the general context of a closer relationship between management practices and quality wood production, the general objective of this research was to develop a set of intensive management scenarios that could lead to alternative timber production practices with attainable and promising economic returns.
Data for the different studies were collected in different regions of Costa Rica, covering almost all climatic conditions where T. grandis plantations have been established and where the species has adapted well. The study consisted fundamentally of the measurement of growth and yield parameters at the stand level and of the analysis of wood properties at the individual tree level and the interrelationship between silvicultural management and site conditions.
High intensity, timely thinnings yielded both individual tree and stand volume, i.e. the objective of high individual tree growth was met without a severe reduction in stand yield. Pruning up to a reasonable height and on time caused no reduction in tree growth and stand yield. Moreover, pruning may improve stem form (higher form factor, lower stem taper) and heartwood content.
Important characteristics, such as heartwood content and wood density, were found to be related more to tree age than to silvicultural management practices, especially at early plantation stages.
Growth scenarios for 20 and 30 year rotations with the objectives of high individual tree growth and high stand growth were developed for high, medium, and low quality sites. Different site classes, production objectives, rotation periods, and discount rates resulted in marked differences in the financial profitability projections of the developed scenarios.