Articles by Yrjö Ilvessalo

The article gives an account of the organization of research work, which was started in the 18^th century at the Academy of Turku. It was later developed in the times of the Forest Institute at Evo, founded in 1862, but it was not until the highest forestry education was transferred to the University of Helsinki in 1908 that it got a more compact form. In 1909 the Finnish Society of Forestry was founded and in 1918, the Finnish Forest Research Institute. In addition, a number of special institutes and organizations have been established.

At first the number of different branches was small, but the number of fields has multiplied until the present day. The article describes development that has taken place within the fields of forest biology, silviculture, forest protection, soil science, peatland forestry, forest mensuration, forest management, forest technology, forest economics, and multiple-use forestry.

Development was promoted by the organization of research work and its division into branches. Improvement of vehicles used in collection of study material as well as of the equipment used for this purpose and for handling the material have been important for the development. Funds for research have increased. Contacts with other fields of science and participation in international research work, especially through IUFRO, team work and schooling new scientists, have been influential. In 1960 a State committee appointed for further development of forestry research presented a plan to this end.
The PDF includes a summary in English.

• Ilvessalo, E-mail: yi@mm.unknown

In the 1930s studies showed that state of the standing crop and forests of small private forest holdings in Finland was weak. In 1960s it was regarded necessary to study the possible change in the silvicultural state of these forests. Therefore, sample stands of the small holdings surveyed in 1930 by Osara were surveyed anew in the areas of Karelia and Savo, and in Central Finland in 1963–1964. A line plot survey was combined with ocular estimation as in 1930, but in 1963–1964 the lines and sample plots were placed denser than in 1930 to reach similar number of sample plots.

In 1930 the state of the forests of the small holdings was in average very weak, but according to Osara, the age classes younger than 50 years had similar stand volume than in the all the forests of the southern half of the country. The results of this survey show that the volume, structure, growth and development class structure of the forests in average have improved since 1930. In many respects the forests have reached the average state of forests in the southern half of Finland. The most serious problem is the large proportion of broadleaved trees. Thus, the silvicultural state of the forests should be further improved.

The PDF includes a summary in German.

• Ilvessalo, E-mail: mi@mm.unknown
• Ilvessalo, E-mail: yi@mm.unknown

Silva Fennica issue 52 includes presentations held in professional development courses, arranged for foresters working in public administration in 1938. The presentations focus on practical issues in forest management and administration, especially in regional level. The education was arranged by Forest Service.

This presentation describes different methods of assessing tree growth.

• Ilvessalo, E-mail: yi@mm.unknown

Silva Fennica issue 42 includes presentations held in professional development courses, arranged for foresters working in public administration in 1936. The presentations focus on practical issues in forest management and administration, especially in regional level. The education was arranged by Forest Service

This presentation describes the principles of forest taxation in Finland in 1930s.

• Ilvessalo, E-mail: yi@mm.unknown

Silva Fennica Issue 39 includes presentations held in professional development courses in 1935 that were arranged for foresters working in public administration. The presentations focus on practical issues in forest management and administration, especially in regional level. The education was arranged by Forest Service.

This presentation describes different forest inventory methods.

• Ilvessalo, E-mail: yi@mm.unknown

The article is a review on methods used in Central Europe and in Finland to construct growth and yield tables, and on their defects and advantages. One of the main defects of growth and yield tables prepared previously in Central Europe is that the site quality classes for different tree species have been formed independently and using different principles. Thus, the yields of different tree species on a similar site can’t be compared. In addition, the quality classes of this kind of growth and yield tables and growth series are artificial.

The Society of Forestry in Finland (now Finnish Society of Forest Sciences) started to prepare new yield tables for the most important tree species in Finland in 1916. The new yield tables aimed to improve the yield tables made in Central Europe in two aspects. Firstly, the quality of the site of each sample plot was assessed on the spot and independently from the standing crop. Thus the sample plots of each site class in setting up the growth series can be treated as independent groups. Consequently, the quality classes are be the same for all tree species. Secondly, mathematical-statistical methods were used to determine which of the stands that belong to the same quality class belong also to the same growth series.

The PDF includes a summary in Finnish.

• Ilvessalo, E-mail: yi@mm.unknown

One of the difficulties in constructing growth and yield tables has been to determine which of the sample plots growing the same tree species and belonging to the same forest site type, with reference to the quality of stands, have to be included in the same growth series.

New growth and yield tables for the most important tree species were constructed in Finland in 1916–1919, using new principles that aim at avoiding some of the common weaknesses. There were two main differences to the earlier work. First, the site quality class (forest site type) was determined for each sample plot when the sample plot was measured, independently of the stand occupying the site. In this way it was possible to treat the sample plots of each site as an independent group from the beginning, and so that the quality classes were the same for all the tree species. Second, mathematic-statistical methods were used to deduct the so-called stem frequency distribution series, when studying which of the sample plots of the same quality class belong to the same growth series. They represent the average number of stems of the different diameter classes. A more detailed description of the method used to create the growth and yield tables is published in Acta Forestalia Fennica no. 15.

In the PDF is included a summary in Finnish.

• Ilvessalo, E-mail: yi@mm.unknown

Line plot survey has proven the best method to assess forest resources in the Northern countries on a country level; it is cost effective and gives reliable results. The accuracy of the survey depends on, however, how close the lines are set. To get homogenous statistics of an entire country, the survey should not span over too long a period. Thus, the distance between the lines should be chosen wide enough to give accurate results quickly for the whole country, while accepting slightly less exact results for its smaller districts.

If line survey is performed on large areas, it is not possible to count and measure trees, measure the tree growth. etc. along the whole length of the line because of its costs. Therefore, more precise measurements are limited to sample plots, which are spaced evenly along the lines. Between the sample plots, the volume and growth of each stand touching the line are estimated visually. These visual estimates have often systematic faultiness, which can be eliminated with correlation calculations. Visual observations gather information, for instance, about land owner, soil type, land-use class, forest site type, tree species and age class of the stand, density, wood volume ja annual growth per hectare, and the current silvicultural state of the stand. With help of this kind of information it is possible to get sufficient statistics about the forest resources of a country.

A summary in Finnish is included in the PDF.

• Ilvessalo, E-mail: yi@mm.unknown

Examination of stands developed under natural conditions can be used to provide basis for comparison for study of the development and yield of stands treated with intermediate fellings. In Finland, the first investigation and the yield and the structure of natural normal stands were published in 1920. This investigation on development and yield of the natural forests of Kainuu in southeastern Northern Finland is based on 92 sample plots on three forest types; Empetrum-Vaccinium type (EVT), Empetrum-Calluna type (ECT) and Vaccinium-Myrtillus type (VMT).

The Scots pine (Pinus sylvestris L.) sample plots represented variation of age classes for construction of mean development series. The Norway spruce (Picea abies (L.) H. Karst.) of the region are so old that development series could be obtained only for dominant trees based on stem analysis.

The average development of Scots pine stand on EMT type within the region is on average more rapid and the yield in cubic volume quantitatively larger and structurally better than that on ECT type. Self-thinning during the early decades of EVT is slower. The pine stands are denser in the age of 70 in Kainuu compared to Central Northern Finland, but the development and yield are similar.

The development, yield and structure of natural Norway spruce stand on VMT proved considerably inferior to the average level of pine stands on EVT, and to a major part on ECT. The mixed pines on spruce sample plots have developed better than spruces of equal age. Spruce stands on VMT in the area developed markedly better than Geranium-Dryopteris-Myrtillus (GDMT) in Central Northern Finland.

It seems that a spruce stand seems to require more fertile site type in north than in the southern part of Finland. These fertile types are relative rare in the north. In the region, the best results are received with pine. As a rule, also the yield of birch (Betula sp.) is poor in the region.

The PDF includes a summary in English.

• Ilvessalo, E-mail: yi@mm.unknown

The first estimates on the forest resources of Finland were presented in the middle of the 1900^th century. The first line survey was conducted in 1912 in Central Finland. In 1921-1923 a survey of the forests of the whole country was commenced. The method consisted in measurement of sample plots in conjunction with ocular estimation of all the stands within the range of the lines. The methods were further developed in the second National Forest Survey in 1936-1938, which payed special attention to the silvicultural condition of the forests, and the growth in the light of climatic variation. When 3.3 million ha of forests were ceded to the Soviet Union in the peace treaty of 1944, the results of the survey had to be recalculated. The next survey was conducted 1951-1953. In this survey, the recovery of stands on drained peatlands was studied. The results of the inventories show that forest resources of Finland had icreased since the 1936-1938 survey.

The first investigation of wood utilization in Finland was carried out in 1927, after the first National Forest Survey had provided information on the forest resources, and knowledge of the other side of the forest balance was desired. The most difficult part was to determine the domestic wood consumption of the rural population. This was accomplished by studying 1,337 sample farms. The second investigation was commenced in 1938, and third in 1954.

These two investigations have made it possible to determine the annual removal and annual growth, and by comparing these results, growth balance. A forest balance is an essential condition for judicious forestry.

The Acta Forestalia Fennica issue 61 was published in honour of professor Eino Saari’s 60th birthday.

• Ilvessalo, E-mail: yi@mm.unknown

This special volume of Acta Forestalia Fennica is published in memory of professor A.K. Cajander (1879-1943), who was one of the founders of the Finnish Society of Forest Science. It contains a short biography, a complete list of his literary works and one of the papers on forest types he has written.

This PDF includes the short biography of professor Cajander in English. The Finnish biography can be found in a separate PDF (article id 7392).

• Ilvessalo, E-mail: yi@mm.unknown

This special volume of Acta Forestalia Fennica is published in memory of professor A.K. Cajander (1879-1943), who was one of the founders of the Finnish Society of Forest Science. It contains a short biography, a complete list of his literary works and one of the papers on forest types he has written.

This PDF includes the short biography of professor Cajander in Finnish. The English biography can be found in a separate PDF (article id 7393).

• Ilvessalo, E-mail: yi@mm.unknown

The relation between the occurrence of forest site types and swamp types was studied using data collected in the national line survey of Finnish forests carried out in 1921‒1924. The majority of peatlands in Finland has been formed by forest land becoming paludificated. When the peat layer is thin, the fertility of the peatland depends on the underlying mineral soil, consequently, good swamp types occur on fertile subsoil and poor types on poor subsoil. When the peat layer becomes thicker, the relationship weakens. The surrounding mineral soils influence the quality of the peatland by the runoff from the catchment area. The direct comparison of forest site and swamp types is not possible, because for one forest site type there are several swamp types that have different levels of humidity. According to the study, a very distinct mutual relation can be seen between occurrence of forest site types and swamp types.

The PDF includes a summary in English.

• Ilvessalo, E-mail: yi@mm.unknown

The article includes observations on forest site types in Canada and the United States, with special emphasis on forests of lodgepole pine (Pinus murrayana, now Pinus contorta Douglas ex Loudon) which the author considers a species that can become a favourite exotic tree species in Finland. Some notes are made also about Jack pine (Pinus banksiana Lamb.) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests. The author was not able to make a systematic forest type investigation, because the journey was made on another purpose. The article describes the vegetation and climate of the visited areas, and divides the forest site types in three groups: Dry forest site types, moist forest site types and grass-herb site types. The vegetation and plant species on several subtypes are described in detail.

The volume 34 of Acta Forestalia Fennica is a jubileum publication of professor Aimo Kaarlo Cajander.

• Ilvessalo, E-mail: yi@mm.unknown

A strip survey was performed in the counties of Sahalahti and Kuhmalahti in Häme, situated in Central Finland, to study the condition of the private forests. The forests cover 78% of the total land area of 37,420 hectares. The forest site types were relatively fertile. Scots pine (Pinus sylvestris L.) dominated forest covered 43%, Norway spruce (Picea abies (L.) H. Karst.) 30% and Betula sp. 23% of the forest land. The productivity of the forests could be improved by changing the species so that they suit the site. The volume of the standing crop is 67.2 m³ per hectare. The volume of the growing stock in the area could be 1 million m³ larger if the forests were nearer to the natural state. The annual growth of the forests is low, and could be much improved by correct forest management.

One of the aims of the survey was to study how the distance between survey lines should be adjusted to give acceptably accurate results, in a way that the strip-survey method can be adapted to large areas. The largest distance between the lines that gave results that differed less than 10% from the correct results, varied between 10 and 1.5 kilometres depending on the variables. For instance, to get accurate results for the rarest forest site types required line distance of 1.5 kilometres, but accurate results for the most common forest site types could be achieves with line distance of 10 kilometres.

The PDF includes a summary in German.

• Ilvessalo, E-mail: yi@mm.unknown

The study is based on the results of the soil studies by Valmari (1921) and the growth inventories of respective areas. The aim is to show the connection of soil fertility (nutrient content) and forest growth with means of correlation calculations. The examined nutrients were nitrogen, calcium and phosphorus, also the electrolyte content was studied.

• Ilvessalo, E-mail: yi@mm.unknown

The article statistically studies the vegetation patterns in different forest types.  

467 sample plots with area varying from one fourth of a hectare to one eighth, even one tenth of a hectare were collected. There are different amount of sample plots representing every forest type. The sample plots are located in 58 communes in southern parts of Finland, reaching from the Gulf of Finland up to Oulujärvi –see in northern Ostrobothnia. The vegetation was examined from rectangle shaped study plots in even structured and even-aged stands with one primary tree species.

The results are shown in tables for every forest type. The amount of species is at highest in the most nutritious forest types, and decreases with the shift to more infertile types. However, some species occur in all forest types, and some only or mostly on more barren types. The occurrence and abundance of most plant species does not seem to depend on the tree species of the stand, but there are some exceptions to this.

The possible shortcomings of the research method are discussed. The importance of systematic studying of the sample plots with a method of survey lines is emphasized.  

• Ilvessalo, E-mail: yi@mm.unknown

The article contains tree lectures given in the meeting of the Geographical Society in Finland on February 25^th 1921.  The titles of the lectures are I Forest types in general, II Forest types as a basis for new growth and yield tables in Finland, and III Other research on forest types.  

The first lecture is a follow-up of the Cajander’s 1909 published article on forest types. It deepens the theory on forest types. The classification into forest types represents primarily different plant communities of ground cover. The types are named after the characteristic plant species, indicator plants, however, many other species appear in different abundance.

The second lecture represents the research proceedings of mensuration of forest stands of different types to compile yield tables for pine.  The forest types differ from each other distinctly on their growing preconditions, but inside one class the variation of the growing conditions is so small, that the classification can be used for yield tables, determining the basis of taxation and for classification of forest based on height over age.

The third lecture is a summary of other studies about forest type classification.  They confirm the results presented in earlier lectures. 

• Cajander, E-mail: ac@mm.unknown
• Ilvessalo, E-mail: yi@mm.unknown

The first proper growth and yield tables were prepared in Finland already in 1872, but they have been used little as the needs of forestry and forest sciences increased. One of the problems of the old yield tables was how the site quality classes are determined. The new growth and yield tables use the forest site type classification, which enables the use of same site types for all tree species. This makes it possible to compare the growth of different tree species in same kind of sites. The tables also use stem frequency distribution series. In the first stage, the tables were prepared for Southern and Central Finland.

The PDF includes a summary in German.

• Ilvessalo, E-mail: yi@mm.unknown

New growth and yield tables were prepared for Southern Finland. To finalize the tables, it had to be determined whether the forest site types developed by Cajanus could be used in mensurational research.

Comparative study was performed in 1916-1919 to study the growth of the trees in different forest site types. Total of 467 sample sites were measured in Southern and Central Finland. All the forest site types were found to have a distinctive vegetation typical to the site. It can be concluded that the ground vegetation can be used to determine the forest site type. The growth of trees was different in different forest site types, yet similar within each site type. The forest site types are uniform, natural and easy to determine, and can thus be used to classify the forest stands and used in mensurational research and a basis to growth and yield tables.

The PDF includes a summary in German.

• Ilvessalo, E-mail: yi@mm.unknown

Annual variations in wood utilization makes it complicated to estimate the balance between wood utilization and wood production of forests. According to the article, the balance is unsustainable especially in the private forests in the southern part of Finland. The annual wood utilization of the country was 37.3 million m³ in 1913, and the annual wood production 35.2 million m³, according to a report of a committee that was appointed to find methods to prevent overcutting. The committee suggested legislation to forbid forest devastation. Also the growth of the forests could be increased, if the forests are well managed, the article argues. To prove this, the potential wood production capacity is estimated for the municipalities of Viipuri, Mikkeli and Kuopio, and compared to the present wood production and wood utilization of the area.

The PDF includes a German summary.

• Ilvessalo, E-mail: yi@mm.unknown

Tree growth is one of the factors that have been used to determine the site quality. The aim of the study was to show that growth of single trees growing on a same forest site class are similar, but differ from trees growing on a different site type. To compare the tree growth, a stem analysis was performed to dominant trees in Scots pine (Pinus sylvestris L.) stands, measured in 15 Myrtillus type sample plots and in 15 Calluna type sample plots in state forests in Salmi, situated in north side of Lake Ladoga. The height growth when the tree was young was higher in the trees growing in the Myrtillus type than in the Calluna type. Also, the trees of same age are higher in Myrtillus type stand than in the Calluna type. In Calluna type, the height growth, however, evens out later in age than in the Myrtillus type. The volume growth of the trees begins to increase earlier in Myrtillus type, and is higher than in Calluna type. Similarly, the diameter growth in breast height is higher in the Myrtillus type.

The PDF includes a summary in German.

• Ilvessalo, E-mail: yi@mm.unknown

The aim of the present study was to describe the forest types of Finnish mineral forest lands as a uniform whole in the light of stand development and wood production.

The study shows that it has been possible to work out uniform age-based development series for different stand characteristics for forest types on mineral forest lands in Finland. There is generally a clear difference in the development series of various stand characteristics and their average values between different forest types. The exceptions in a few places have been explained as depending on certain factors. The differences between adjacent forest types in order of their quality are of varying magnitude, thus differing from a schematic site quality classification obtained through calculation. Consequently, each forest type has its own development series with regard to the stand characteristics.

The number of forest types in the whole country is rather high. However, the different forest types are limited to different parts cf the country in such a way that there is no need for more than 5–6 forest types and 4 northerly sub-forms (-types) in each region, except in the border areas between the regions. In Finland the forest types have been the basis of forest site classification in forest research and practical forestry over a period of half a century. In pointing out the necessity of further study of forest types, Cajander has stressed the examination of differences in the compositions of vegetation between different classes of density of tree-stand and building up average descriptions of vegetation in such classes in young, middle-age and old stands. The same may be caused by some other factors which also are of essential influence to the composition of the vegetation.

The PDF includes a summary in English.

• Ilvessalo, E-mail: yi@mm.unknown
• Ilvessalo, E-mail: mi@mm.unknown

The article is fifth part of a series of papers on fully stocked natural normal stands on mineral soils in Finland. This part studies the stands in Northern Lapland, dominated by Scots pine (Pinus sylvestris L.). This investigation was concerned mainly with Scotch pine stands, using Norway spruce (Picea abies (L.) H. Karst.) and birch (Betula sp.) stands for comparison only. 107 sample plots were measured.

The most common forest types in the area are Empetrum-Myrtillus-(Cladina) type, EM(C1), Ericacea-Cladinae type, ErCIT, P-L, and Cladina type, C1T. Stand development is more rapid and wood production greater in EM(C1) type than ErCIT, while the C1T stands are further behind in all respects. The average differences in stand characteristics between forest types are roughly similar, but for cubic volume and total production less, than between the more southerly forest types. Measurements made from increment cores taken at breast height have confirmed that variation of the pine annual ring width has on average been very considerable, in accordance with the climatic, mainly temperature, variations, in the investigation area close to the north pine forest limit.

The few plots from birch and spruce stands measured as samples in the northern Lapland investigation area indicate the generally poor development and wood production of these stands by comparison with pine stands.

The PDF includes a summary in English.

• Ilvessalo, E-mail: yi@mm.unknown

The article is third part of a series of papers on fully stocked natural normal stands on mineral soils in Finland. This part studies area between the ca. 62nd and 66nd parallels of the strip of land on the Gulf of Bothnia stretching from the coast to an altitude of 150 m above the sea level. The material consists of 121 sample plots in Scots pine (Pinus sylvestris L.) stands, 36 sample plots in Norway spruce (Picea abies (L.) H. Karst.) and 22 sample plots in birch (Betula sp.) stands.

Since the vegetation gradually changes from south to north, it was considered necessary to separate sub-types (marked s.) for certain southern-central forest types; these are poorer in vegetation but obviously more generally found than the main types. The Myrtillus s. sub-type shows slower development of pine stands than the Myrtillus type. The number of stems on the former is greater, owing to the slow initial development, but the mean diameter and height are smaller than on the latter. The difference in volume and growth increases with age. The slower the rate of self-thinning on the sub-type has the effect that the differences in total production are small.

The Vaccinium sub-type s. (VTs.) is poorer in vegetation than the southern-central type, differs from VT less than was the difference in the MT sub-types. The Empetrum-Vaccinium type (EVT) in general differs considerably from the VT but less from the VTs., in relation to which the difference shows mainly in the volume and total production. The EVT differs from the Calluna type as regards in all stand characteristics.

The results of this study suggest that the s.c. sub-type MT could be placed between the types MT and VT. This has significance especially in forest mensuration. However, in practical forest inventories it would seem possible to combine MT and MTs. to avoid having too many site classes. The types VT and VTs. can generally be considered nearly as one type. Similarly, CT and ECT (Empetrum-Calluna type) may be regarded as one site group. The differences may also partly be due to differences in early treatment of the forests.

The PDF includes a summary in English.

• Ilvessalo, E-mail: yi@mm.unknown