Annual Report 2004 - Doctoral theses

High thinnings to improve economics of stand-level silviculture

The economics of stand-level silviculture could be improved by thinning not only the low-level growth but also the highest trees in the stand. Also the rotation length can be shortened especially in well-managed stands of Scots pine and Norway spruce. Kari Hyytiäinen presented these conclusions in a doctoral thesis that he defended at the University of Helsinki.

According to the calculations made as part of the research, economically the most optimal thinning does not meet the current silvicultural recommendations. Optimal thinning, in many cases, consists of high thinnings, in which not only trees of poor quality and small size are harvested but also the highest, log-diameter trees are cut. The stand left after thinning consists of well-growing and good-quality new-generation dominant trees. The optimal rotation time is shorter especially for well-managed and even-structured conifer stands. However, it is advisable to postpone final cuttings until the majority of trees have reached saw log dimensions.

Research results relating to forest ecology, economics and harvesting technology were combined in the thesis and useful new information was provided on economically optimal management. Mathematical optimisation models were applied and analysed to gain results about economically sensible cuttings (timing of thinnings and final thinnings, thinning intensity, principles of tree species selection in thinnings, etc.), juvenile density, value of forest stands and land, cost structure of forestry, and the long-run timber supply.

The profitability of silviculture can be improved by taking the economic factors and those relating to forest structure into account in detail when planning and implementing silvicultural measures. The best economic result is achieved when economic factors (prices, interests, costs), factors relating to tree stand (growth, stand size deviation, timber quality) and stand-specific factors (location and size of the plot) are simultaneously taken into account.

Predicting stand characteristics using limited inventory data

In forest planning, different types of forest stands necessitate different categories of information. For example, for seedling stands it is enough to have an estimate of silvicultural need and timing, whereas for final cutting stands an assessment of timber product distribution is needed. The forest planning systems used in Finland today require the same inventories of all stands, and the only way to affect the accuracy of the assessment result is through the inventory accuracy. This does not provide sufficient clearance for data collection, especially if the effects of inventory accuracy are not taken into consideration in calculations. Therefore, the current data collection system is not as cost-effective as it could be. In his doctoral dissertation submitted to the University of Joensuu Lauri Mehtätalo developed a prototype of a new computational method, in which the forest planner can affect the quality of the forest inventory data already when he selects which, and how many field inventory measurements are to be made. The planner can then use more time on the stands where exact data is needed and leave less time for stands of low-accuracy requirement.

The prototype was used in a simulation study to examine how the selected inventory combination affects the accuracy of the forest inventory data of Scots pine. The study indicated that the accuracy depends not only on the inventory combination but also the characteristics of the stand. This means that if the goal is to make the forest inventory as cost-effective as possible, a different inventory combination must be used for different stand characteristics.

The last part of the thesis described how the most cost-effective inventory combination can be sought by using non-linear optimisation. The algorithm can be programmed to a data collection device, and the programme then provides instructions, on the basis of the performed forest inventories, regarding which additional measurements should be executed.

Elevated carbon dioxide and ozone levels will affect the growth conditions of silver birch

Forest trees have an important role in controlling the elevation of carbon dioxide (CO2) in the atmosphere. The current CO2 content available for plant assimilation is limiting, and hence it is predicted that the rising level of CO2 will increase tree growth and assimilation especially in conditions where nutrients are sufficiently available.

On the other hand, the ozone in the lower atmospheric layer is a detrimental pollutant for plants; even low concentrations of ozone can slow down the growth and assimilation of silver birch and cause damage to the structure of leaves. Though the responses of silver birch for both gases have been studied separately, very little information is available of their combined effects.

In a field experiment implemented at the Suonenjoki Research Station of Metla two clones of silver birch were exposed to elevated concentrations of CO2 and O3 in open-roof greenhouse conditions during 1999 - 2001. Exposure to the gases were at levels corresponding to climate models predicted for the end of this century.

The results in Johanna Riikonen's doctoral thesis submitted to the University of Kuopio show that if the CO2 content is doubled from the current climate level, the growth of silver birch, depending on the genotype, increases as much as 40%. The increased growth is due to increased assimilation, the increased area of leaves and delayed aging of the leaves. The effects of the increase of CO2 could be observed as premature and increased seeding.

The research also indicated that the resistance of 10-year-old birches to elevated levels of ozone was better than expected. When the ozone concentration was doubled, it caused premature aging of leaves, and as a consequence, depending on the origin, the growth of roots and branches was weakened. Thus, the effects of elevated levels of ozone in the lower atmospheric layers can be assumed to be cumulative and the effects will be visible in growth with a delay. When the concentrations of CO2 and O3 were simultaneously increased, no loss of growth was observed. This indicates that the increase of CO2 content prevents O3 from being transferred into leaves and hence, it can prevent or compensate the growth losses caused by O3.

The results suggest that when changes take place in climate conditions, significant changes take place in the growth and physiology of silver birch and that genetic differences will play a key role when assessing the future success of silver birch. All members of the Finnish silver birch population will not be able to adapt to the changes that will occur in the carbon dioxide and ozone content.

Clear reduction in air-borne heavy metal deposition in Finland

When air pollutants are being examined, various bioindicators can be used. They are species that tend to collect contaminants. Bioindicators can be studied to attain information about the level of air pollutants in the environment. The most commonly used biomonitors are mosses and epiphytic lichens that mainly use rain water for their nutrient intake. Mosses have been used especially for monitoring deposition of heavy metals. In large concentrations heavy metals can be toxic to living organisms.

In his doctoral thesis submitted to the University of Oulu, Jarmo Poikolainen studied mosses and the heavy metal deposition in Finland and the changes observed during 1985-2000. The concentrations of heavy metals (cadmium, chromium, copper, iron, mercury, nickel, lead, vanadium, zinc) in mosses were usually higher in Southern Finland and lowest in Northern Finland. A few substantial sources of emission had a large effect on the copper, nickel and chromium concentrations in the vicinity of the sources. The concentrations of heavy metals, especially lead, cadmium and vanadium, have clearly reduced during the past 20 years. This is primarily due to the reduced amount of industry and traffic emissions in Finland and its neighbouring areas. The results indicate that heavy metal deposition in Finland is low, not counting the most southern part of Finland and a few areas close to large emission sources. The results also showed that mosses are better suited as bioindicators in regional studies than epiphytic lichens and bark.

Scots pine bark was separately used to study the spreading of emissions from industrial plants in the Kola Peninsula to Northern Finland. The effect of emissions could be seen in bark as relatively high sulphur and heavy metal concentrations even in the north-western parts of Finnish Lapland. The research also included a study on occurrence of green algae on coniferous trees in Finland. The clear increase of green algae is likely to be caused by the increase of nitrogen, decrease of sulphur and the gradual warming of the climate.

In the future, international collaboration on mapping air pollutants in the environment will be more important than ever. Researchers should be able to utilise the results gained in regional studies and combine them with effects at the ecosystem level. Collaboration will be needed also to harmonise the research methods. For data collection and exchange, for example, environmental specimen banks could have a more essential role than today.

The importance of forested mire margin plant communities for the diversity of managed boreal forests in Finland

Forested mires in the boreal coniferous zone play a key role in the diversity of plant and animal life associated with forests and mires. This is stated in the doctoral thesis that Leila Korpela defended at the University of Helsinki. Since forested mires are often along the gradients between forests and wetlands, subject to margin effects, their vegetation and ecology has features of both mires and forests.

In Finland forested mires are classified as wetlands, because they grow at least partially on peatland. Actually, the peat layer is usually so thin (approx. 30-100 cm) that trees and plants take their nutrients directly from mineral ground. Therefore, since mire and forest vegetation are mixed, it is difficult for a layman on foot to perceive a forested mire as wetland or in general, to realise that it is wetland at all.

Relatively few studies are available on forested mires, although they are appreciated for the sake of their diversity. In Finland forested mires have largely been drained for silvicultural reasons, due to the good growth potential of the tree stands. As a result the natural mire vegetation species have declined, and sometimes even become threatened. Today natural-state mires are not drained any longer. When compared with the situation in the early 1950s, only approx. 20 percent of the forested mires in Southern and Central Finland have remained undrained.

In the study, the focus was set on the species diversity and structural diversity of plants in mire-like forests, with all vegetation layers taken into consideration, including trees and bushes. The research also included studies on the drainage effects on the species and structural diversity of forested mires. The work is based on the vegetation and tree samples from the permanent sampleplot data of the 8th National Forest Inventory (NFI 8) collected between 1985-1986 by Metla.

The research area covered all of Finland except the regions of Finnish Lapland and north-eastern Finland, where the network of permanent sample plots is too sparse. The main results of the research indicated that both species diversity and structural diversity is most abundant in pristine forested mires. The ground vegetation consists mainly of hummocks (forest and mire herbs and grasses and bryophytes) and gradients (mostly Sphagnum, sedges, and herbs, typical wetland species), in the most exuberant sites sometimes even aquatic (e.g. sedges, herbs and dwarf shrubs) mosaic. Typical of the drained forested mire margin communities is the diversity of the different canopy layers in the tree and undergrowth vegetation. Though these forests are dominant with spruce and deciduous trees, they also have the most versatile selection of different tree species in Finland.

			Doctoral theses
ANNUAL REPORT 2004 Metla Director General's review Research Director's review Databanks, computations and models Forest ecosystems and forest use Doctoral theses International Metla Conferences and meetings New projects Research projects 2004 Publications Organisation Resources New appointments			High thinnings to improve economics of stand-level silviculture The economics of stand-level silviculture could be improved by thinning not only the low-level growth but also the highest trees in the stand. Also the rotation length can be shortened especially in well-managed stands of Scots pine and Norway spruce. Kari Hyytiäinen presented these conclusions in a doctoral thesis that he defended at the University of Helsinki. According to the calculations made as part of the research, economically the most optimal thinning does not meet the current silvicultural recommendations. Optimal thinning, in many cases, consists of high thinnings, in which not only trees of poor quality and small size are harvested but also the highest, log-diameter trees are cut. The stand left after thinning consists of well-growing and good-quality new-generation dominant trees. The optimal rotation time is shorter especially for well-managed and even-structured conifer stands. However, it is advisable to postpone final cuttings until the majority of trees have reached saw log dimensions. Research results relating to forest ecology, economics and harvesting technology were combined in the thesis and useful new information was provided on economically optimal management. Mathematical optimisation models were applied and analysed to gain results about economically sensible cuttings (timing of thinnings and final thinnings, thinning intensity, principles of tree species selection in thinnings, etc.), juvenile density, value of forest stands and land, cost structure of forestry, and the long-run timber supply. The profitability of silviculture can be improved by taking the economic factors and those relating to forest structure into account in detail when planning and implementing silvicultural measures. The best economic result is achieved when economic factors (prices, interests, costs), factors relating to tree stand (growth, stand size deviation, timber quality) and stand-specific factors (location and size of the plot) are simultaneously taken into account. Predicting stand characteristics using limited inventory data In forest planning, different types of forest stands necessitate different categories of information. For example, for seedling stands it is enough to have an estimate of silvicultural need and timing, whereas for final cutting stands an assessment of timber product distribution is needed. The forest planning systems used in Finland today require the same inventories of all stands, and the only way to affect the accuracy of the assessment result is through the inventory accuracy. This does not provide sufficient clearance for data collection, especially if the effects of inventory accuracy are not taken into consideration in calculations. Therefore, the current data collection system is not as cost-effective as it could be. In his doctoral dissertation submitted to the University of Joensuu Lauri Mehtätalo developed a prototype of a new computational method, in which the forest planner can affect the quality of the forest inventory data already when he selects which, and how many field inventory measurements are to be made. The planner can then use more time on the stands where exact data is needed and leave less time for stands of low-accuracy requirement. The prototype was used in a simulation study to examine how the selected inventory combination affects the accuracy of the forest inventory data of Scots pine. The study indicated that the accuracy depends not only on the inventory combination but also the characteristics of the stand. This means that if the goal is to make the forest inventory as cost-effective as possible, a different inventory combination must be used for different stand characteristics. The last part of the thesis described how the most cost-effective inventory combination can be sought by using non-linear optimisation. The algorithm can be programmed to a data collection device, and the programme then provides instructions, on the basis of the performed forest inventories, regarding which additional measurements should be executed. Elevated carbon dioxide and ozone levels will affect the growth conditions of silver birch Forest trees have an important role in controlling the elevation of carbon dioxide (CO2) in the atmosphere. The current CO2 content available for plant assimilation is limiting, and hence it is predicted that the rising level of CO2 will increase tree growth and assimilation especially in conditions where nutrients are sufficiently available. On the other hand, the ozone in the lower atmospheric layer is a detrimental pollutant for plants; even low concentrations of ozone can slow down the growth and assimilation of silver birch and cause damage to the structure of leaves. Though the responses of silver birch for both gases have been studied separately, very little information is available of their combined effects. In a field experiment implemented at the Suonenjoki Research Station of Metla two clones of silver birch were exposed to elevated concentrations of CO2 and O3 in open-roof greenhouse conditions during 1999 - 2001. Exposure to the gases were at levels corresponding to climate models predicted for the end of this century. The results in Johanna Riikonen's doctoral thesis submitted to the University of Kuopio show that if the CO2 content is doubled from the current climate level, the growth of silver birch, depending on the genotype, increases as much as 40%. The increased growth is due to increased assimilation, the increased area of leaves and delayed aging of the leaves. The effects of the increase of CO2 could be observed as premature and increased seeding. The research also indicated that the resistance of 10-year-old birches to elevated levels of ozone was better than expected. When the ozone concentration was doubled, it caused premature aging of leaves, and as a consequence, depending on the origin, the growth of roots and branches was weakened. Thus, the effects of elevated levels of ozone in the lower atmospheric layers can be assumed to be cumulative and the effects will be visible in growth with a delay. When the concentrations of CO2 and O3 were simultaneously increased, no loss of growth was observed. This indicates that the increase of CO2 content prevents O3 from being transferred into leaves and hence, it can prevent or compensate the growth losses caused by O3. The results suggest that when changes take place in climate conditions, significant changes take place in the growth and physiology of silver birch and that genetic differences will play a key role when assessing the future success of silver birch. All members of the Finnish silver birch population will not be able to adapt to the changes that will occur in the carbon dioxide and ozone content. Clear reduction in air-borne heavy metal deposition in Finland When air pollutants are being examined, various bioindicators can be used. They are species that tend to collect contaminants. Bioindicators can be studied to attain information about the level of air pollutants in the environment. The most commonly used biomonitors are mosses and epiphytic lichens that mainly use rain water for their nutrient intake. Mosses have been used especially for monitoring deposition of heavy metals. In large concentrations heavy metals can be toxic to living organisms. In his doctoral thesis submitted to the University of Oulu, Jarmo Poikolainen studied mosses and the heavy metal deposition in Finland and the changes observed during 1985-2000. The concentrations of heavy metals (cadmium, chromium, copper, iron, mercury, nickel, lead, vanadium, zinc) in mosses were usually higher in Southern Finland and lowest in Northern Finland. A few substantial sources of emission had a large effect on the copper, nickel and chromium concentrations in the vicinity of the sources. The concentrations of heavy metals, especially lead, cadmium and vanadium, have clearly reduced during the past 20 years. This is primarily due to the reduced amount of industry and traffic emissions in Finland and its neighbouring areas. The results indicate that heavy metal deposition in Finland is low, not counting the most southern part of Finland and a few areas close to large emission sources. The results also showed that mosses are better suited as bioindicators in regional studies than epiphytic lichens and bark. Scots pine bark was separately used to study the spreading of emissions from industrial plants in the Kola Peninsula to Northern Finland. The effect of emissions could be seen in bark as relatively high sulphur and heavy metal concentrations even in the north-western parts of Finnish Lapland. The research also included a study on occurrence of green algae on coniferous trees in Finland. The clear increase of green algae is likely to be caused by the increase of nitrogen, decrease of sulphur and the gradual warming of the climate. In the future, international collaboration on mapping air pollutants in the environment will be more important than ever. Researchers should be able to utilise the results gained in regional studies and combine them with effects at the ecosystem level. Collaboration will be needed also to harmonise the research methods. For data collection and exchange, for example, environmental specimen banks could have a more essential role than today. The importance of forested mire margin plant communities for the diversity of managed boreal forests in Finland Forested mires in the boreal coniferous zone play a key role in the diversity of plant and animal life associated with forests and mires. This is stated in the doctoral thesis that Leila Korpela defended at the University of Helsinki. Since forested mires are often along the gradients between forests and wetlands, subject to margin effects, their vegetation and ecology has features of both mires and forests. In Finland forested mires are classified as wetlands, because they grow at least partially on peatland. Actually, the peat layer is usually so thin (approx. 30-100 cm) that trees and plants take their nutrients directly from mineral ground. Therefore, since mire and forest vegetation are mixed, it is difficult for a layman on foot to perceive a forested mire as wetland or in general, to realise that it is wetland at all. Relatively few studies are available on forested mires, although they are appreciated for the sake of their diversity. In Finland forested mires have largely been drained for silvicultural reasons, due to the good growth potential of the tree stands. As a result the natural mire vegetation species have declined, and sometimes even become threatened. Today natural-state mires are not drained any longer. When compared with the situation in the early 1950s, only approx. 20 percent of the forested mires in Southern and Central Finland have remained undrained. In the study, the focus was set on the species diversity and structural diversity of plants in mire-like forests, with all vegetation layers taken into consideration, including trees and bushes. The research also included studies on the drainage effects on the species and structural diversity of forested mires. The work is based on the vegetation and tree samples from the permanent sampleplot data of the 8th National Forest Inventory (NFI 8) collected between 1985-1986 by Metla. The research area covered all of Finland except the regions of Finnish Lapland and north-eastern Finland, where the network of permanent sample plots is too sparse. The main results of the research indicated that both species diversity and structural diversity is most abundant in pristine forested mires. The ground vegetation consists mainly of hummocks (forest and mire herbs and grasses and bryophytes) and gradients (mostly Sphagnum, sedges, and herbs, typical wetland species), in the most exuberant sites sometimes even aquatic (e.g. sedges, herbs and dwarf shrubs) mosaic. Typical of the drained forested mire margin communities is the diversity of the different canopy layers in the tree and undergrowth vegetation. Though these forests are dominant with spruce and deciduous trees, they also have the most versatile selection of different tree species in Finland.

Updated:	02.08.2005 / REsk	Metla : Annual Report : Annual Report 2004