Category: Research article
article id 10347, category Research article
Assessing local trends in indicators of ecosystem services with a time series of forest resource maps. Silva Fennica vol. 54 no. 4 article id 10347. https://doi.org/10.14214/sf.10347
Contextual Mann-Kendall test detects significant trends in time-series of forest maps; Trends become more consistent as the areal unit size used for test input increases; Changes in different scales reflect different phenomena in forests; Significant trends were detected even after multiple testing correction.
Since the 1990’s, forest resource maps and small area estimates have been produced by combining national forest inventory (NFI) field plot data, optical satellite images and numerical map data using a non-parametric k-nearest neighbour method. In Finland, thematic maps of forest variables have been produced by the means of multi-source NFI (MS-NFI) for eight to ten times depending on the geographical area, but the resulting time series have not been systematically utilized. The objective of this study was to explore the possibilities of the time series for monitoring the key ecosystem condition indicators for forests. To this end, a contextual Mann-Kendall (CMK) test was applied to detect trends in time-series of two decades of thematic maps. The usefulness of the observed trends may depend both on the scale of the phenomena themselves and the uncertainties involved in the maps. Thus, several spatial scales were tested: the MS-NFI maps at 16 × 16 m2 pixel size and units of 240 × 240 m2, 1200 × 1200 m2 and 12 000 × 12 000 m2 aggregated from the MS-NFI map data. The CMK test detected areas of significant increasing trends of mean volume on both study sites and at various unit sizes except for the original thematic map pixel size. For other variables such as the mean volume of tree species groups, the proportion of broadleaved tree species and the stand age, significant trends were mostly found only for the largest unit size, 12 000 × 12 000 m2. The multiple testing corrections decreased the amount of significant p-values from the CMK test strongly. The study showed that significant trends can be detected enabling indicators of ecosystem services to be monitored from a time-series of satellite image-based thematic forest maps.
article id 2021, category Research article
Mapping forest attributes using data from stereophotogrammetry of aerial images and field data from the national forest inventory. Silva Fennica vol. 51 no. 2 article id 2021. https://doi.org/10.14214/sf.2021
Highlights: Image based forest attribute map generated using NFI plots show similar accuracy as currently used LiDAR based forest attribute map; Also similar accuracies were found for different forest types; Aerial images from leaf-off season is not recommended.
Exploring the possibility to produce nation-wide forest attribute maps using stereophotogrammetry of aerial images, the national terrain model and data from the National Forest Inventory (NFI). The study areas are four image acquisition blocks in mid- and south Sweden. Regression models were developed and applied to 12.5 m × 12.5 m raster cells for each block and validation was done with an independent dataset of forest stands. Model performance was compared for eight different forest types separately and the accuracies between forest types clearly differs for both image- and LiDAR methods, but between methods the difference in accuracy is small at plot level. At stand level, the root mean square error in percent of the mean (RMSE%) were ranging: from 7.7% to 10.5% for mean height; from 12.0% to 17.8% for mean diameter; from 21.8% to 22.8% for stem volume; and from 17.7% to 21.1% for basal area. This study clearly shows that aerial images from the national image program together with field sample plots from the NFI can be used for large area forest attribute mapping.
article id 983, category Research article
NFI plots as complementary reference data in forest inventory based on airborne laser scanning and aerial photography in Finland. Silva Fennica vol. 48 no. 2 article id 983. https://doi.org/10.14214/sf.983
Highlights: Using NFI plots in forest management inventories could provide a way for rationalising forest inventory data acquisition; NFI plots were used as additional reference data in laser scanning and aerial image based forest inventory; NFI plots improved the estimates of some forest variables; There are differences between the two inventory types that cause difficulties in combining the data.
In Finland, there are currently two, parallel sample-plot-based forest inventory systems, which differ in their methodologies, sampling designs, and objectives. One is the National Forest Inventory (NFI), aimed at unbiased inventory results at national and regional level. The other is the Forest Centre’s management-oriented forest inventory based on interpretation of airborne laser scanning and aerial images, with the aim of locally accurate stand-level forest estimates. The National Forest Inventory utilises relascope sample plots with systematic cluster sampling. This inventory method is optimised for accuracy of regional volume estimates. In contrast, the management-oriented forest inventory utilises circular sample plots with an allocation system covering certain pre-defined forest classes in the inventory area. This method is optimised to produce reference data for interpretation of the remote-sensing materials in use. In this study, we tested the feasibility of the National Forest Inventory sample plots in provision of additional reference data for the management-oriented inventory. Various combinations of NFI plots and management inventory plots were tested in the interpretation of the laser and aerial-image data. Adding NFI plots in the reference data generally improved the accuracy of the volume estimates by tree species but not the estimates of total volume or stand mean height and diameter. The difference between the plot types in the NFI and management inventories causes difficulties in combination of the two datasets.
article id 133, category Research article
Effects of training for inexperienced surveyors on data quality of tree diameter and height measurements. Silva Fennica vol. 44 no. 4 article id 133. https://doi.org/10.14214/sf.133
Due to the large number of sample plots and variables to be measured, inexperienced surveyors are expected to take field measurements in National Forest Inventories (NFIs). However, very little information exists on the data quality that can be expected from inexperienced surveyors given different levels of training. We evaluated the quality of data produced by inexperienced undergraduate students when measuring the most fundamental variables: tree diameter using a diameter tape and height using an ultrasonic Vertex III hypsometer. We found that a single training session on how to use the instruments and how to reduce measurement errors was insufficient for inexperienced surveyors to achieve measurement quality objectives (MQOs). Providing a single feedback of control team measurements significantly improved data quality, except in the measurements of tree height of broad-leaved trees, but additional feedback did not contribute to further improvement. We propose that field training courses for inexperienced surveyors incorporate a one-day exercise with feedback instruction.
article id 458, category Research article
Mapping biomass variables with a multi-source forest inventory technique. Silva Fennica vol. 44 no. 1 article id 458. https://doi.org/10.14214/sf.458
Map form information on forest biomass is required for estimating bioenergy potentials and monitoring carbon stocks. In Finland, the growing stock of forests is monitored using multi-source forest inventory, where variables are estimated in the form of thematic maps and area statistics by combining information of field measurements, satellite images and other digital map data. In this study, we used the multi-source forest inventory methodology for estimating forest biomass characteristics. The biomass variables were estimated for national forest inventory field plots on the basis of measured tree variables. The plot-level biomass estimates were used as reference data for satellite image interpretation. The estimates produced by satellite image interpretation were tested by cross-validation. The results indicate that the method for producing biomass maps on the basis of biomass models and satellite image interpretation is operationally feasible. Furthermore, the accuracy of the estimates of biomass variables is similar or even higher than that of traditional growing stock volume estimates. The technique presented here can be applied, for example, in estimating biomass resources or in the inventory of greenhouse gases.
article id 202, category Research article
Future wood and fibre sources – case North Karelia in eastern Finland. Silva Fennica vol. 43 no. 3 article id 202. https://doi.org/10.14214/sf.202
Information on the potential wood supply is important for the wood industry. In this study, the future development of growing stock, cutting potential and wood properties corresponding to the regional scenario of North Karelian Forest Programme 2006–2010 was analysed. The simulations were performed by employing the Finnish MELA system together with the sample plot and tree data of the 9th Finnish National Forest Inventory (NFI9) as initial data for the simulations. Disc-based models for basic wood density, proportion of latewood and fibre length of Norway spruce and Scots pine in Sweden were calibrated and integrated into the MELA system. The wood properties at breast height of both harvested and standing trees were analysed in different strata (age, site type and cutting method) during the scenario period of 50 years (2002–2052). The average wood properties within the same strata varied only slightly over time. However, the results for different strata differed considerably. In general, wood density, fibre length and proportion of latewood increased, on average, as a function of tree age and along with a decrease in site fertility (excl. wood density and proportion of latewood in harvested Norway spruce in the first case and fibre length in the latter case for both species). For trees less than 80 years, properties in harvested trees were equal to or slightly greater than those of standing trees. The values for clear-cuttings were greater or equal to those of thinnings (excl. wood density and proportion of latewood in Norway spruce). The study demonstrates the value of model-based analyses utilising NFI tree measurements in regions that are considered to be sources of raw material.
article id 563, category Research article
Spatial ecology of the three-toed woodpecker in managed forest landscapes. Silva Fennica vol. 36 no. 1 article id 563. https://doi.org/10.14214/sf.563
The effects of landscape structure and forestry on the abundance and dynamics of boreal forest bird species have been studied widely, but there are relatively few studies in which the spatial structure and quality of the landscape have been related to the spatial ecology of bird species. In this paper, we present methods to measure territory and landscape quality for the three-toed woodpecker (Picoides tridactylus) and similar territorial forest bird species based on data from the Finnish multi-source national forest inventory and metapopulation theory. The three-toed woodpecker was studied with territory mapping within an area of 340 square km in southern Finland in 1987–2000. Altogether 195 breeding territory sites were observed. The spatial occurrence of the territories was aggregated, and the highest densities were observed in spruce-dominated old-growth forest areas. Both territory and landscape quality had significant consequences for the occurrence of the three-toed woodpecker. The spatial patterning and permanence of breeding and non-breeding territories were influenced by a combination of spatial dynamics of the species and the quality of the landscape, the latter being much influenced by forestry. The landscape-level spatial occurrence of the three-toed woodpecker in the study area may represent source-sink dynamics. The results of this paper suggest the presence of threshold values at different spatial scales, which may determine the occurrence of the three-toed woodpecker and similar species in managed forest landscapes.
article id 593, category Research article
The probability of moose damage at the stand level in southern Finland. Silva Fennica vol. 35 no. 2 article id 593. https://doi.org/10.14214/sf.593
The probability of moose damage was studied in sapling stands and young thinning stands in southern Finland. Data from the eighth National Forest Inventory in 1986–92 were used for modelling. The frequency of damage was highest at the height of two to five meters and at the age of ten to twenty years (at the time of measurement). Moose preferred aspen stands the most and least preferred Norway spruce stands. Scots pine and silver birch were also susceptible to damage. Logistic regression models were developed for predicting the probability that moose damage is the most important damaging agent in a forest stand. The best predictive variables were the age and dominant species of the stand. Variables describing the site were significant as cluster averages, possibly characterizing the area as a food source (fertility and organic soil), as well as the lack of shelter (wall stand). When sample plot, cluster and municipality levels were compared, it was found that most of the unexplained variance was at the cluster level. To improve the model, more information should be obtained from that level. The regression coefficients for aspen as supplementary species, and for pine as dominant species, had significant variance from cluster to cluster (area to area). It was also shown that the occurrence of aspen is closely connected to the occurrence of moose damage in pine sapling stands.
article id 692, category Research article
Use of satellite and field information in a forest damage survey of eastern Finnish Lapland in 1993. Silva Fennica vol. 32 no. 2 article id 692. https://doi.org/10.14214/sf.692
The study area consists of the Finnish part of a Landsat 5 TM image from 1990. Three independent field samples were measured during 1991–93 in the study area. The first sample was used to compile training areas for supervised maximum likelihood classification of the image. Classification accuracy was studied in the second sample. The spectral separability of the forest strata usable in practical forestry was poor. The extent of the damage area was estimated by the principle of stratified sampling. The estimate included considerable bias because the field sample had not been objectively selected from the image classes. The third field sample was measured as part of the National Forest Inventory of Finland. It is wholly objective, and about ten times larger than the two earlier field samples. The poor spectral separability of the forest strata was confirmed by the NFI sample. However, this sample could be used in stratified sampling with little or no bias in the estimation of the damage area estimate. 14 different damage types were separated according to specific damaging agent. A thematic map was produced which presents the spatial distribution of two damage-rich image classes. The study area comprises 18 300 sq.km, of which 38% were damaged. At first sight it would appear that the proportion of damaged forest has tripled in ten years. However, this is not the case because now special attention was paid to forest health in the field work. Despite this, it is possible that some damage caused by unfavourable climatic phenomena in the ’80s was still perceptible in 1993. No damage caused directly by air pollution has yet been verified in the study area.
Category: Research note
article id 9986, category Research note
Landsat archive holdings for Finland: opportunities for forest monitoring. Silva Fennica vol. 52 no. 3 article id 9986. https://doi.org/10.14214/sf.9986
Highlights: The 45-year Landsat archive contained 30 076 images for Finland by December 31, 2017; 16.3% of these were acquired within ±30 days of August 1 (northern hemisphere summer), have <70% cloud cover, and a 30 m spatial resolution; Using time series analyses, these data provide unique information that complements other datasets available for forest monitoring and assessment in Finland.
There is growing interest in the use of Landsat data to enable forest monitoring over large areas. Free and open data access combined with high performance computing have enabled new approaches to Landsat data analysis that use the best observation for any given pixel to generate an annual, cloud-free, gap-free, surface reflectance image composite. Finland has a long history of incorporating Landsat data into its National Forest Inventory to produce forest information in the form of thematic maps and small area statistics on a variety of forest attributes. Herein we explore the spatial and temporal characteristics of the Landsat archive in the context of forest monitoring in Finland. The United States Geological Survey Landsat archive holds a total of 30 076 images (1972–2017) for 66 scenes (each 185 km by 185 km in size) representing the terrestrial area of Finland, of which 93.6% were acquired since 1984 with a spatial resolution of 30 m. Approximately 16.3% of the archived images have desired compositing characteristics (acquired within August 1 ±30 days, <70% cloud cover, 30 m spatial resolution). Data from the Landsat archive can augment forest monitoring efforts in Finland, provide new information for science and applications, and enable retrospective, systematic analyses to characterize the development of Finnish forests over the past three decades. The capacity to monitor trends based upon this multi-decadal record with the addition of new measurements is of benefit to multisource inventories and offers nationally comprehensive spatially-explicit datasets for a wide range of stakeholders and applications.
article id 9901, category Research note
Statistics of ash dieback in Latvia. Silva Fennica vol. 52 no. 1 article id 9901. https://doi.org/10.14214/sf.9901
Highlights: Dynamics of ash dieback during 2005–2015 were summarized; The area of ash dominated stands decreased twofold; The number of mature ash trees and their standing volume decreased by 53.1 and 69.9%, compared to 2005, respectively; The mortality of trees was higher during the first part of the survey, the decrease of standing volume culminated later.
Dieback of the common ash (Fraxinus excelsior L.) has been spreading throughout Europe since the 1990s, causing severe ecological and economical consequences; however, detailed statistics on its dynamics have been published rarely. This paper presents the dynamics of mature ash-dominated stands in Latvia for the period 2005–2015. Data from the national forest inventory and a permanent sampling plot network were summarised. According to the official statistics, the dieback has caused a twofold decrease in area of the ash stands (from 21 891 to 13 011 ha, which respectively comprised ca. 0.8 to ca. 0.4% of the total forest area). The official statistics on standing volume appeared biased, as they did not account for increased mortality. According to the permanent sampling plots, standing volume and stand density have been affected even more, having decreased by 53.1 and 69.9%, respectively, compared to 2005 (the stand density and standing volume of ash in 2015 was 77 individuals ha–1 and 151 m3 ha–1, respectively). The mortality of the trees has not been stable. Stand density decreased faster during 2005–2009 compared to 2010–2015, with mortality rates of 9.6 and 8.2% year–1, respectively. In contrast, the decrease in standing volume in 2005–2009 was slower than in 2010–2015 (mortality rates were 4.7 and 7.7% year–1, respectively) because trees with smaller dimensions were more susceptible to the dieback. Nevertheless, the observed mortality rates clearly indicate negative prospects for ash stands in Latvia.
article id 7146, category Article
Analysis of two alternative methods for national forest inventories in northern Europe. Acta Forestalia Fennica vol. 76 no. 6 article id 7146. https://doi.org/10.14214/aff.7146
A comparison was made between two alternative methods of continuous national forest inventory. In method 1, samples measured annually are taken throughout the country, in method 2 samples are confined to one section of the country each year. The figures are derived from national forest inventories carried out in the North-European countries Finland, Norway and Sweden. Systematic sampling on the ground has been employed without remeasured sample plots. Field work consisted of survey tracts.
For the whole country, method 1 gives results, which are continuously up-to-date, although detailed information requires observation over a period of several years. On an average, the results obtained from method 2 area at least n/2 years old (survey cycle n years). For a specific section of the country, method 1 gives preliminary results already in 1-2 years, but more accurate results are at least n/2 years old. Method 2 gives accurate results every nth year. Thus, method 2 is not always to be recommended, even if the emphasis is laid on regional information and planning.
To gain knowledge of annual timber removals, often necessary in assessing the forest resource situation, stump measurements can be used, either exclusively or by way of control. The corresponding sampling must be affected throughout the whole country, and this can be done only when method 1 is used. Other information required annually, such as estimates of seed crops, occurrence of pests or annual variation of growth due to the climate, favour method 1.
It can be concluded that method 1 has important advantages, although these must be bought at higher costs. A comparison of inventory costs shows, assuming the same degree of accuracy, that the total expenditure for method 2 is 7-8% lower than that for method 1, owing to the difference in transport requirements. Also, other aspects may affect the choice of method, for example, the use of aerial photographs may be arranged more efficiently in method 2.
article id 7487, category Article
Valtion metsät sekä niiden hoidon ja käytön yleissuunnitelma. Acta Forestalia Fennica vol. 68 no. 5 article id 7487. https://doi.org/10.14214/aff.7487
English title: (1959). The state forests of Finland and a general management plan for them based on an inventory made in 1951-1955.
The distances between the lines in the line survey in the first two National Inventories of Finland were too long to supply data for every State Forest district. Consequently, the Third National Forest Inventory offered an opportunity to supplement the inventory for State Forests in 1954 and 1955, and to gather data on forest resources of the State Fforests. On the basis of the results, a management plan for the State Forests was drafted. The first part of the paper describes the inventory procedure and results of the inventory, the second deduces future cuttings and a forest management programme.
In 1955 the total land area of the State Forests was 9.49 million ha. Drained peatlands cover 126,000 ha, drainable peatlands 798,000 ha and undrainable peatlands 2,621,000 ha. The average volume of growing stock in all State Forests was 55.2 m3/ha, including productive and unproductive forest land. The average increment in all State Forests was 1,39 m3/ha on productive land and in all lands in average 1,14 m3/ha.
Cutting budgets for the progressive yield were prepared by checking the silvicultural cut and estimating the allowable cut. They were made by age classes, developmental stages and for each region. The stock development was forecasted for a period of 40 years. In average the allowable cut was larger during the first decade than during the second. Allowable cut was estimated by the tree species and by timber assortments. The management plan included future forest management work, such as intermediate fellings, regeneration fellings, site preparation, artificial regenereation, tending of seedling stands, and draining of peatland.
The PDF includes a summary in English.
article id 7433, category Article
Nationwide surveys of forest resources and wood utilization in Finland. Acta Forestalia Fennica vol. 61 no. 21 article id 7433. https://doi.org/10.14214/aff.7433
The first estimates on the forest resources of Finland were presented in the middle of the 1900th 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.
Category: Special section
article id 290, category Special section
Models in country scale carbon accounting of forest soils. Silva Fennica vol. 41 no. 3 article id 290. https://doi.org/10.14214/sf.290
Countries need to assess changes in the carbon stocks of forest soils as a part of national greenhouse gas (GHG) inventories under the United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol (KP). Since measuring these changes is expensive, it is likely that many countries will use alternative methods to prepare these estimates. We reviewed seven well-known soil carbon models from the point of view of preparing country-scale soil C change estimates. We first introduced the models and explained how they incorporated the most important input variables. Second, we evaluated their applicability at regional scale considering commonly available data sources. Third, we compiled references to data that exist for evaluation of model performance in forest soils. A range of process-based soil carbon models differing in input data requirements exist, allowing some flexibility to forest soil C accounting. Simple models may be the only reasonable option to estimate soil C changes if available resources are limited. More complex models may be used as integral parts of sophisticated inventories assimilating several data sources. Currently, measurement data for model evaluation are common for agricultural soils, but less data have been collected in forest soils. Definitions of model and measured soil pools often differ, ancillary model inputs require scaling of data, and soil C measurements are uncertain. These issues complicate the preparation of model estimates and their evaluation with empirical data, at large scale. Assessment of uncertainties that accounts for the effect of model choice is important part of inventories estimating large-scale soil C changes. Joint development of models and large-scale soil measurement campaigns could reduce the inconsistencies between models and empirical data, and eventually also the uncertainties of model predictions.
article id 7666, category Article
Suomen metsävarat 1977-1984 ja niiden kehittyminen 1952-1980. Acta Forestalia Fennica no. 220 article id 7666. https://doi.org/10.14214/aff.7666
English title: (1991). Forest resources of Finland in 1977–1984 and their development in 1952–1980.
The field of work of the 7th National Forest Inventory was carried out during 1977–84. This report consists of the analysis of the forest resources, long-term development of forests and the results by ownership categories in Finland.
The area of forestry land, 26.4 million ha, has decreased slightly because of the increase of build-up areas and communication routes. Forest land, which is suitable to growing wood profitably, amounted 20.1 million ha. It has increased, although not as fast as earlier, due to drainage and fertilization of scrub and waste land swamps and the afforestation of agricultural land.
The growing stock volume was 1,660 million m3 and the estimated gross annual increment 68.4 million m3. A large quantity of young, rapidly growing stands, and fellings markedly below the increment, are the principal factors increasing the growing stock. The volume of Scots pine (Pinus sylvestris L.) has increased most but the greatest proportional increase has been in the volume of broadleaved trees.
The silvicultural quality of stands has improved and the increase in saw log tree volume has resulted in an increase in the total growing stock volume. The proportional volume of saw logs, however, has decreased. Both aging mature stands and postponed thinnings increase the risk of losses due to mortality and decay. Too dense stands retard the diameter growth of trees. The proportion of unsuccessful artificial regeneration has increased.
The area of private forests has slightly decreased, while companies and collective bodies have increased their ownership. Non-farmer private ownership already accounts for one half of the area of private forests. The silvicultural quality of company forests is best and the increase of the growing stock and its increment is proportionally greatest in these forests.
The PDF includes a summary in English.
article id 4494, category Article
English title: (1937). Forestry statistics.
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.
This presentation lists statistics available on forestry.