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Silva Fennica 1926-1997
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Acta Forestalia Fennica
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Articles containing the keyword 'sample plot'.

Category: Review article

article id 1095, category Review article
Jonas Fridman, Sören Holm, Mats Nilsson, Per Nilsson, Anna Hedström Ringvall, Göran Ståhl. (2014). Adapting National Forest Inventories to changing requirements – the case of the Swedish National Forest Inventory at the turn of the 20th century. Silva Fennica vol. 48 no. 3 article id 1095. https://doi.org/10.14214/sf.1095
Highlights: National Forest Inventories supply invaluable long term time series of forest state. Recent developments and international harmonization of modern NFIs widen the scope to even include ecosystem goods, e.g. biodiversity and carbon sequestration. The combination of NFI field data with remote sensing techniques can give good estimates for areas smaller than national and regional level.
National Forest Inventories (NFIs) are becoming increasingly important worldwide in order to provide information about the multiple functions of forests, e.g. their provision of raw materials to industry, biodiversity and their capacity to store carbon for mitigating climate change. In several countries the history of NFIs is very long. For these countries a specific challenge is to keep the inventories up-to-date without sacrificing the advantages associated with long time series. At the turn of the 20th century European NFIs faced some major challenges. In this article we describe the history and the recent developments of the Swedish NFI as an example from which general observations are made and discussed. The Swedish NFI started in 1923 and has evolved from an inventory with a narrow focus on wood resources to an inventory today which aims to provide information about all major forest ecosystem services. It can be concluded that the traditional approaches of most European NFIs, e.g. to collect data through sample plot field inventories, has proved to be applicable even for a wide range of new information requirements. Specifically, detailed data about land use, trees, vegetation, and soils has found new important uses in connection with biodiversity assessments and the estimation of greenhouse gas emissions. Though time-consuming and difficult, making NFI information comparable across countries through harmonization appears to be a useful approach. The European National Forest Inventory Network (ENFIN) was formed in 2003 and has been successful in pan-European NFI harmonization.
  • Fridman, Swedish University of Agricultural Sciences (SLU), SE-901 83 Umeå, Sweden ORCID ID:E-mail: jonas.fridman@slu.se (email)
  • Holm, Swedish University of Agricultural Sciences (SLU), SE-901 83 Umeå, Sweden ORCID ID:E-mail: soren.holm@slu.se
  • Nilsson, Swedish University of Agricultural Sciences (SLU), SE-901 83 Umeå, Sweden ORCID ID:E-mail: mats.nilsson@slu.se
  • Nilsson, Swedish University of Agricultural Sciences (SLU), SE-901 83 Umeå, Sweden ORCID ID:E-mail: per.nilsson@slu.se
  • Ringvall, Swedish University of Agricultural Sciences (SLU), SE-901 83 Umeå, Sweden ORCID ID:E-mail: Anna.Ringvall@slu.se
  • Ståhl, Swedish University of Agricultural Sciences (SLU), SE-901 83 Umeå, Sweden ORCID ID:E-mail: goran.stahl@slu.se

Category: Article

article id 7162, category Article
Aarne Nyyssönen, Pekka Kilkki. (1965). Sampling a stand in forest survey. Acta Forestalia Fennica vol. 79 no. 4 article id 7162. https://doi.org/10.14214/aff.7162

The purpose of this paper is to review tests made on the basis of Finnish material with regard to the efficiency of the 10-point cluster in sampling a stand in forest inventory. Currently, this system is applied in field work in the national forest surveys in the United States of America. The paper reports on tests, made on the basis of Finnish material, for comparison of the 10-point cluster of variable plots with 13 other designs in sampling a stand in forest survey. The research material consists of 12 stands, with Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) H. Karst.) as the main species.

The main results are concerned with the ability of different designs to provide gross volume estimates. As a measure of efficiency, three alternative series of variances were used, adjusted by three alternatives of time. The results are applicable, for instance, in double-sampling with photo and field classifications. In the comparisons, no attention was paid to the possibility of systematic errors in various designs.

For inventory volume, the 10-point cluster proved to be about 10 per cent less efficient than the best design of each alternative. The use of a single circular plot of 1,000 m2 can be recommended under the conditions of this test; furthermore, one or two 500 m2 plots were more efficient than any combination of variable plots.

The reason for the use of the 10-point cluster in forest surveying has been the ability of the design to provide simultaneous information on area condition classes. Among the designs tested, the 10-point cluster seems to be the only one capable of application in the estimation of condition classes.

Most of the information obtained by means of the 10-point cluster can be gained through ocular estimation, and from the sample trees to be measured in any design, but a cluster of several points appears to offer good means of estimation, for instance, of the presence of clumps and gasps in a stand.

  • Nyyssönen, ORCID ID:E-mail:
  • Kilkki, ORCID ID:E-mail:
article id 7136, category Article
Aarne Nyyssönen, Yrjö Vuokila. (1963). The effect of stratification on the number of sample plots of different sizes. Acta Forestalia Fennica vol. 75 no. 2 article id 7136. https://doi.org/10.14214/aff.7136

It is necessary to study the problems related to the size, number and location of sample plots as well as to the effect of stratification. This paper, mainly concerned with the volume of the growing stock based on measurements, comprises a part of the research in progress related to the issue.

The study contains a discussion of certain problems relevant to the planning of a forest inventory on the basis of variation in the volume of the growing stock. In particular, the aim has been to give data for selection of the size and number of sample plots, and to illustrate the importance of stratification, here based principally on dominant height.

The research material comprised two forest areas of 10 ha each; measurement of the growing stock was made in units of 49 m2. Based on the data was constructed a model area embracing 4 forested strata and one non-forested stratum. The mean and standard deviations of the volumes was calculated for the forest area as a whole and for the different strata. On studying stratification, two approaches were employed to distribute the sample plots among the strata: optimum allocation and proportional allocation. The latter is simple in application, and gave for forested areas number of sample plots which did not exceed by more than 10% those obtained by optimum allocation. It is obvious that the application of stratification is worthy of consideration within forest areas which comprise parts with distinct differences. The decrease in number of plots with increasing plot size is considerably more marked within a stratified area. Thus, larger sample plots should be used in the former case than in the later. The investigations give hints on how forest inventories should be carried out. However, it has some limitations, which are discussed in the paper.

The PDF includes a summary in English.

  • Nyyssönen, ORCID ID:E-mail:
  • Vuokila, ORCID ID:E-mail:
article id 7122, category Article
Kullervo Kuusela. (1960). Pinotavaraleimikon taksatoriset tunnukset ja niiden vaikutus leimikkoarvioinnin tarkkuuteen. Acta Forestalia Fennica vol. 72 no. 5 article id 7122. https://doi.org/10.14214/aff.7122
English title: Mensurational characteristics of cordwood stock market for felling and their effect on the precision of stock estimation.

The annual fellings and sales of pulpwood from the State Forests of Finland comprised 4.0–4.6 million m3 in 1955–1959. In order to improve the accuracy of the methods used in estimating the pulpwood stocks marked for felling, a pilot survey of 18 marked stocks was carried out in 1959. The stock area, average plot volume, variation of the plot volumes, size and shape of the plot and the distribution of the trees by diameter classes as factors affecting the precision have been studied in this paper.

The greater the mean volume of a plot the more homogenous is the structure of the marked stock. The same number of plots gives a better relative precision for the south Finnish marked stock than for the north Finnish ones, which are heterogenous and less valuable. Stocks smaller than 50 ha can often be estimated more advantageously by the strip method or visually than by the plot method. The proper size of plot in Southern Finland is 0.02–0.03 ha. In Northern Finland the plots should be larger due to the heterogenous stocks, about 0.05 ha. The shape can be either circular or rectangular. The former may be more practical and reliable in the field. The minimum number of sample trees is considered to be about 200 per 100 sample plots 0.03 ha in size.

The PDF includes a summary in English.

  • Kuusela, ORCID ID:E-mail:
article id 7115, category Article
Kullervo Kuusela. (1960). Volume and increment calculation of a sample plot determined with the relascope. Acta Forestalia Fennica vol. 71 no. 6 article id 7115. https://doi.org/10.14214/aff.7115

The relascope method, introduced by Bitterlich, has been mostly used in estimating the basal area of tree stands or growing stock. Volume estimation requires, in addition, mean height and form. The purpose of this study is to work out a method for calculating the volume, bark and increment of the stand from the measurements of sample trees taken on a plot determined with the relascope. All trees of the same diameter have their own plot size and the stand characteristics are the sum of all tree characteristics multiplied by a blow-up factor which is a function of the diameter.

Accurate determination of a sample plot with the relascope requires checking the boundary trees with a tape. In an average forest there are 10 to 20 unit trees on each plot if the opening of the relascope is 2 cm. Because all trees of equal diameter to be tallied on a sample plot represent an equal share of the total basal area, the number of trees to be tallied is very economical from the stand point of volume estimation. Objective selection of the sample trees can easily be done. The unit volume per hectare represented by each tallied tree, or by each sample tree, is directly proportional to the tree height. Thus, the estimates of the stock characteristics can be calculated as arithmetic means from the sample tree characteristics. The calculation procedure which gives the ordinary stock table, volume, bark and increment is also easily carried out with punched cards.

The PDF includes a summary in Finnish.

  • Kuusela, ORCID ID:E-mail:
article id 7115, category Article
Kullervo Kuusela. (1960). Volume and increment calculation of a sample plot determined with the relascope. Acta Forestalia Fennica vol. 71 no. 6 article id 7115. https://doi.org/10.14214/aff.7115

The relascope method, introduced by Bitterlich, has been mostly used in estimating the basal area of tree stands or growing stock. Volume estimation requires, in addition, mean height and form. The purpose of this study is to work out a method for calculating the volume, bark and increment of the stand from the measurements of sample trees taken on a plot determined with the relascope. All trees of the same diameter have their own plot size and the stand characteristics are the sum of all tree characteristics multiplied by a blow-up factor which is a function of the diameter.

Accurate determination of a sample plot with the relascope requires checking the boundary trees with a tape. In an average forest there are 10 to 20 unit trees on each plot if the opening of the relascope is 2 cm. Because all trees of equal diameter to be tallied on a sample plot represent an equal share of the total basal area, the number of trees to be tallied is very economical from the stand point of volume estimation. Objective selection of the sample trees can easily be done. The unit volume per hectare represented by each tallied tree, or by each sample tree, is directly proportional to the tree height. Thus, the estimates of the stock characteristics can be calculated as arithmetic means from the sample tree characteristics. The calculation procedure which gives the ordinary stock table, volume, bark and increment is also easily carried out with punched cards.

The PDF includes a summary in Finnish.

  • Kuusela, ORCID ID:E-mail:
article id 7485, category Article
Paavo Yli-Vakkuri. (1959). A method for establishing small permanent sample plots for ecological studies. Acta Forestalia Fennica vol. 68 no. 3 article id 7485. https://doi.org/10.14214/aff.7485

Especially in experimantal ecological research it is used small sample plots that are inventoried consequently. The paper describes a method for establishing small sample plots, developed by the writer in 1956. In the method, the central point of the sample plot is marked with an iron skewer, and the marking of the area to be inventoried was accomplished with a circular frame that is movable. The frame was fitted to the skewer with an aperture that indicated the central point. The area of the frame was relatively small, 0,25 m2. The sample plots were arbitarily placed at intervals from one another.

The PDF includes a summary in Finnish.

  • Yli-Vakkuri, ORCID ID:E-mail:
article id 5386, category Article
Risto Päivinen, Hannu Yli-Kojola. (1989). Permanent sample plots in large-area forest inventory. Silva Fennica vol. 23 no. 3 article id 5386. https://doi.org/10.14214/sf.a15544

Theoretical and practical aspects of permanent sample plots are discussed in this paper. A study material of 6,871 permanent sample plots was generated using increment sample plots of the 7th National Forest Inventory of Finland. The effect of measurement errors and use of increment functions as ”a priori” information was studied via simulation experiments. The change in the growing stock volume between two consecutive measurement rounds was divided into the components drain, growth and mortality. Finally, a hypothetical inventory design using permanent sample plots was evaluated.

The PDF includes an abstract in Finnish.

  • Päivinen, ORCID ID:E-mail:
  • Yli-Kojola, ORCID ID:E-mail:
article id 5270, category Article
Pekka Kilkki, Risto Päivinen. (1986). Weibull function in the estimation of the basal area dbh-distribution. Silva Fennica vol. 20 no. 2 article id 5270. https://doi.org/10.14214/sf.a15449

The paper demonstrates the possibility of using data from small relascope sample plots in the derivation of the regression models which predict the Weibull function parameters for the dbh-distribution. The Weibull parameters describing the basal area dbh-distribution were estimated for relascope sample plots from the Finnish National Forest Inventory. In the first stage of the estimation nonlinear regression analysis was employed to derive initial parameter estimates for the second stage, in which the maximum likelihood method was used. The parameter estimates were employed as dependent variables for the derivation of the regression models; the independent variables comprised of the compartment-wise stand variables generally estimated in ocular inventories.

The PDF includes an abstract in Finnish.

  • Kilkki, ORCID ID:E-mail:
  • Päivinen, ORCID ID:E-mail:
article id 4776, category Article
K. Stern. (1968). Überlegungen zur optimalen Teilstückgrösse in Feldversuchen mit Waldbäumen. Silva Fennica vol. 2 no. 4 article id 4776. https://doi.org/10.14214/sf.a14561
English title: Some considerations on optimal plot size in field experiments with forest trees.

18 permanent sample subplots of the Swedish and the Hassian Forestry Institute, each measured in equal intervals for several decades, were divided into subplots of different size. An analysis of variance was calculated for every set of subplot size. The development of intraclass-correlations over years and over different sizes of subplots could be explained if three different correlations were assumed: soil-correlation, correlations from irregular distribution of the trees, and correlation resulting from competition. Intraclass-correlations were positive or negative depending on dominance of one or two of these correlations.

An explanatory simultation study of competitional variance showed the effect of the degree of competitional correlations on the variance of means of subplots of different sizes. If this coefficient was small, all variances of subplots means within the range investigated became larger than expected in experiments without competition, with larger coefficients the variances of means of the smaller subplots became smaller, those of larger subplots larger than expected.

Plots of medium or large size are probably optimal for long term experiments with forest trees, if all sources of costs in such experiments are taken into account.

The PDF includes a summary in English and Finnish.

  • Stern, ORCID ID:E-mail:
article id 4776, category Article
K. Stern. (1968). Überlegungen zur optimalen Teilstückgrösse in Feldversuchen mit Waldbäumen. Silva Fennica vol. 2 no. 4 article id 4776. https://doi.org/10.14214/sf.a14561
English title: Some considerations on optimal plot size in field experiments with forest trees.

18 permanent sample subplots of the Swedish and the Hassian Forestry Institute, each measured in equal intervals for several decades, were divided into subplots of different size. An analysis of variance was calculated for every set of subplot size. The development of intraclass-correlations over years and over different sizes of subplots could be explained if three different correlations were assumed: soil-correlation, correlations from irregular distribution of the trees, and correlation resulting from competition. Intraclass-correlations were positive or negative depending on dominance of one or two of these correlations.

An explanatory simultation study of competitional variance showed the effect of the degree of competitional correlations on the variance of means of subplots of different sizes. If this coefficient was small, all variances of subplots means within the range investigated became larger than expected in experiments without competition, with larger coefficients the variances of means of the smaller subplots became smaller, those of larger subplots larger than expected.

Plots of medium or large size are probably optimal for long term experiments with forest trees, if all sources of costs in such experiments are taken into account.

The PDF includes a summary in English and Finnish.

  • Stern, ORCID ID:E-mail:
article id 7550, category Article
Aarne Nyyssönen, Pentti Roiko-Jokela, Pekka Kilkki. (1971). Studies on improvement of the efficiency of systematic sampling in forest inventory. Acta Forestalia Fennica no. 116 article id 7550. https://doi.org/10.14214/aff.7550

Emphasis was laid on the finding of regression equations to indicate the dependence of standard error upon various variables in systematic sampling. As a result, the size of sample for a given precision could be computed, under varying alternatives of sample plot size and type. Another task was that of examining inventory costs by means of time studies. On combination of the results in regard to the sample size and survey time, the relative efficiency of different alternatives could be discussed, with a view to the precision of the total volume of growing stock.

The PDF includes a summary in Finnish.

  • Nyyssönen, ORCID ID:E-mail:
  • Roiko-Jokela, ORCID ID:E-mail:
  • Kilkki, ORCID ID:E-mail:
article id 7550, category Article
Aarne Nyyssönen, Pentti Roiko-Jokela, Pekka Kilkki. (1971). Studies on improvement of the efficiency of systematic sampling in forest inventory. Acta Forestalia Fennica no. 116 article id 7550. https://doi.org/10.14214/aff.7550

Emphasis was laid on the finding of regression equations to indicate the dependence of standard error upon various variables in systematic sampling. As a result, the size of sample for a given precision could be computed, under varying alternatives of sample plot size and type. Another task was that of examining inventory costs by means of time studies. On combination of the results in regard to the sample size and survey time, the relative efficiency of different alternatives could be discussed, with a view to the precision of the total volume of growing stock.

The PDF includes a summary in Finnish.

  • Nyyssönen, ORCID ID:E-mail:
  • Roiko-Jokela, ORCID ID:E-mail:
  • Kilkki, ORCID ID:E-mail:

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