The National Forest Inventory of Finland
Erkki Tomppo and Markku Siitonen, The Finnish Forest Research Institute
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- Established almost 70 years ago, the Finnish National Forest Inventory
gives a firm foundation for planning Finland's forest industries and
the utilization and management of forests.
The Firs serious attempt to estimate the forest resources of Finland was
made by
Edmund von Berg, the leader of the Forest Academy of Tharandt,
in 1858. After his tour through Finland, von Berg presented an assessment
of the state of Finnish Forests.
The rapid growth of the forest industry since the 1870s and the felling
of trees deeper in wilderness forests increased the interest in forest
resources. Funds for estimating the yeld and consumption of forests were
granted in 1911 and pilot work was started the next year. The work was
completed by Yrjö Ilvessalo, later professor at the Finnish
Forest Research Institute and a fellow of the Academy of Finland.
Ilvessalo was also the leader of the first National Forest Inventory.
The field measurements were completed in 1924. The areas of site and stand
classes were estimated by line measurements. The lines ran from south-west
to north-east 26 kilometres apart. Growing stock characteristics were
estimated from sample plots lying on these lines.
Publication of the inventory results in 1927 was a historic moment.
For the first time in the world forest resources based on a national inventory
with a sound statistical framework had been collected into a single volume
/I/.
The first inventory showed the forest resources to be greater than assumed.
However, the rapid increase in the pulp industry posed a new threat to
the country's forest resources. The second inventory was carried out in
1936-1938. The line directions were the same as in the first inventory
but the sampling density in South Finland was doubled. The assessment
method was a combination of visual assessments and measurements on circle
sample plots. The results showed that the forest resources had more than
endured the demands imposed by the forest industries, see Fig. 1.
The method in the third inventory, carried out in 19541-1953, was almost
the same as in the second. One surprising finding was that the forest
resources were almost as large as before the war, in spite of the 10%
decrease in the forest area in 1945. The main reason was the fact that
less cutting was carried out.
Further substantial growth in the forest industry in the 1950s and the
export of timber produced a new threat to the sufficiency of forest resources.
The fourth inventory, the last one by Yrjö Ilvessalo, was carried
out in 1960-1963. The results were based on measurements from the lines
and sample plots.
A new cluster sampling method was developed by Kullervo Kuusela
in 1963. Measurements were made on temporary sample plots, and trees were
selected with relascope. The inventory organization led by Kuusela became
permanent. The fifth inventory moved yearly from the south to the north
by forestry borad districts. The method has remained almost the same since
1964 except for the launch of aerial photographs in north Finland in the
sixth inventory (1971-1976). The eighth inventory started in 1986 and
progressed into central Finland in 1990. A new feature is the small number
of permanent sample plots with detailed measurements.
Forest resource information can be updated computationally from field
measurements, cutting statistics and increment variation measurements.
The first updating concering the whole country was completed in spring
1990, givin up-to-date estimates of the growing stock in 1990 and the
increment in 1985-1990, see Figs. 1 and 2. Data from the seventh and eighth
inventories were used. The computing system applied (MELA) was originally
designed for long-term timber production planning on the regional and
national levels /3/,
Forest resources
Finland's forest resources have been fairly stable from the early 1920s
until the 1970s. The total growing stock varied between 1,500 and 1,600
million cubic metres, in spite of the 10% loss of forest area after the
second world war.
The effects of intensified forest management and silviculture started
to show at the end of the 1960s in the shape of greater growth and volume
of the growing stock. This trend has continued to the present day. The
updated estimate of growing stock is 1,880 million cubic metres in 1990.
The annual increment estimate for 1985-1989 is 79 million cubic metres.
During the 1990s the growing stock is expected to exceed 2,000 million
cubic metres. The 40-year trend in the mean volume of the grownig stock
since the 1950s is presented in Fig. 2 /1, 2/.
The proportion of the three main tree species pine, spruce and birch
have also been fairly constant, being pine 45% and spruce 37% of the growing
stock in 1990.
Figure 1 shows the time series of the total growing stock and total
increment by tree species. The land areas in the first, third and seventh
inventories are given in Table 1. The increase in forest land area is
due mainly to the drainage of peatlands. This has increased the total
growing stock, too.
Table 1. Land area according to the first (1921-1924), third
(1951-1953) and seventh (1977-1984) inventories. Note the 10% area loss
in 1945.
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1921-1924 1951-1953 1977-1984
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Mill. hectares
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Forest and other wooded land 25.3 21.9 23.2
Other land 9.1 8.6 7.3
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Total 34.4 30.5 30.5
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Alternatives for development of forests
Since the beginning of the 1970s annual cuttings have been lower than the
annual increment. By and large, cuttings have stayed constant while the
increment has started to increase. The reasons for this trend are the regeneration
of forests and silvicultural work carried out since the 1950s.
The average annual drain in 1985-1989 was 55 million cubic metres. During
the same period the annual increment was 24 million cubic metres higher
than the annual drain.
The cutting potential and the development of the growing stock are presented
in Fig. 3. The alternative 50-year predictions are based on the general
assumption that growth factors, response of trees and natural losses will
stay at their present levels. The trend in the increment is caused by
the increase of the growing stock and its more favorable structure in
the future.
Starting from the assumption that the total annual drain, including
fellings and natural losses, will stay at 55 million cubic metres (alternative
1) the growing stock will double in 40 to 50 years.
In the 1990s more than 100 million cubic metres could be cut annually
according to the present silvicultural regimes (Fig. 4). As a consequence,
the growing stock and the cuttings would decrease markedly in the next
few decades compared with the 1990s (alternative 2).
The third alternative indicates that the annual cutting removal could
be increased to 80 million cubic metres on a sustained basis.
The prospects for increasing cuttings during the next 30 years are dominated
by regeneration of old spruce stands and thinning cuttings of young pine
stands in southern Finland. In consequence, spruce will account for less
of the growing stock and pine for more in the next few decades. According
to the seventh inventory, 62% of forest are is pine dominated.
The total forest increment is predicted to increase still further due
to the age structure and silvicultural condition of the forest. Future
increment estimates are highly dependent on fures cuttings, as can be
seen in Figure 3.
Timber supply and consumption are not likely to reach the full potential
of the forests in the near future. The first consequences will be an increase
in both the size and the age of the growing stock, which will gradually
become a deterioration in productivity and increasing damage over the
next few decades.
New inventory system
The traditional role of the National Forest Inventory in Finland is to produce
objective and up-to-date information on forest resources and their development
for national and regional decision making.
Rapid changes in forests in the 1980s and the important role of the
forest sector in the Finnish economy were the main reasons behind the
further development of the inventory method. The public have been worried
about the environment and the degree of the utilization of forests. The
mass media have been keeping up fears of wide forest damage. Advances
in long-term forest management planning have made possible a wide analysis
of timber production potential and the setting of more accurate goals
for forest production based on inventory data. On the other hand, new
technologyu has given new sources of forest information and has made it
possible to increase the cost efficiency of an inventory and to get better
localized information for smaller areas.
Because of the low sampling density of the field inventory, reliable
results could be computed for farly large ares only, 150,000 ha and larger.
The latest inventories for the whole contry have taken almost 10 years.
Further, changes cannod be properly estimated by temporary sample plots.
To overcome these drawbacks and to get better localized and more up-to-date
information, the Forest Research Institute started to develop a new inventory
system in 1989. The method exploits satellite image data and digital map
data as well as other geographical data in addition to ground measurements
and their model-based updating.
The satellite information aided method in the National Forest Inventory
is expected to make it possible to:
- Estimate all the variables of the National Forest Inventory for each
point in the country. The variables include the properties of site type,
soil, growing stock, mortality, cutting, damage and diseases. Some improvement
in estimates of all varialbles can be expected over the current situation.
The estimates of variables concerning single pixels may be unreliable.
However, the communal level estimates, and in the case of some variables
also the forest holding and stand estimates, have turned out to be applicable.
- Assist in keeping the forest data up-to-date in the whole country.
Clouds prevent images covering the whole country every year. Model-based
simulation can be used to update the data between two image acquisition
dates. Other remote sensing data such as radar data or airborne data
can be utilized in the future.
- Keep the geographically localized data in digital form and to transfer
it easily into users' databases.
- Estimate the time and spatial variation of variables more reliably
than before with support from the new ground sampling design, which
includes permanent sample plots.
The remote sensing aided method already works with old temporary sample
plots; results are computed with the traditional system for large areas
and with the new one for small subareas. The full advantage of the system
will be obtained with the new field sampling method.
The feasible satellite image data at this moment are Landsat
TM and Spot images. In the forest phase TM images have been applied, and
Spot images will also be utilized later. At the moment, the spectral resolution
of TM image is better, while Spot has a better spatial resolution. One
TM image covers a larger area than one Spot image, making it more likely
to yield cloud-free images covering the whole country. Figure 5A shows
an example of a TM colour composition.
Digital map data produced by the National Board of Survey will
be used for improving the accuracy of land classification and to separate
forest and non-forest land from each other. The spectral response of peatlands
differs from that of mineral soils with the same growing stock. Further,
some peatlands cannot be separated from mineral soils. Therefore, digital
peatland information will be used to improve the accuracy of estimates.
Agricultural areas and roads will be digitized from base maps having
a scale of 1:50,000. A combination of a numerical interpretation and digital
map information will be used in classifying agricultural areas, because
the map data are not necessarily up-to-date.
Urban areas can be obtained from the house register provided by the
Statistical Centre of Finland. The coordinates of each house in Finland
are known. A digital urban area mask can be produced from this information.
Water area could be obtained from base maps but they can also be obtained
relatively reliably from satellite images.
Some administrative information such as community boundaries and, in
the future, boundaries of forest holdings will also be used in digital
form in order to differentiate between computation units.
Digital terrain models have been tested for correcting original spectral
values in order to avoid confusion in image analysis coused by slopes
of hills. Figure 5B shos an example of digital map data in analog form.
Conclusions
Established almost 70 years ago, the Finnish National Forest Inventory produced
time series of forest resources on the regional and national levels. The
information has given a firm foundation for planning Finland's forest industries
and the utilization and management of the forests.
The inventory method is now changing from repeated temporary field inventories
into an up-to-date, multi-source forest resource monitorin and forest
management planning system. In addtion to the traditional written publications,
the inventory results will be supplied as theme maps (Figs. 5C,5D,5E)
and in digital form for further processing by the users. The field sample
of the inventory will server as a general sampling framework for forest
research. The utilization of the inventory results is creating ne co-operation
between practical forestry and forest research.
The sound statistical basis will guarantee the reliability and generalizability
of the inventory information and keep up the status of the National Forest
Inventory as a standard for Finnish forest knowledge.
References
- Ilvessalo, Yrjö 1927. The forests of Suomi (Finland).
Results of the general survey of the forests of the country carried
out during the years 1921-1924. Communicationes Ex Instituto Quaestionum
Forestalium Finlandiae. Editae 11.
- Kuusela, Kullervo and Salminen, S. 1991. Suomen metsävarat
1977-1984 ja niiden kehittyminen 1952-1980. (in Finnish). English summary:
Forest resources of Finland in 1977-1984 and their development in 1952-1980.
Acta Forestalia Fennica.
- Siitonen, Markku. 1983. A long term forestry planning system
based on data from the Finnish national forest inventory. Proceedings
of the IUFRO subject group 4.02 meeting in Finland, September 5-9. 1983.
University of Helsinki, Department of Forest Mensuration and Management.
- Tomppo, Erkki. 1990. Satellite Image-Based National Forest
Inventory of Finland. In: Proceedings of ISPRS. COMISSION VII. Mid-Term
Symposium Global and Environmental Monitoring, Techniques and Impacts.
September 17-21. 1990 Victoria, British Columbia, Canada.
- Fig. a. Cutting potential in the 1990s according to present silvicultural
regimes.
- Fig. b. Inventory group measuring the trees of a relascope sample
plot. The data are recorded and checked on field computers and transmitted
daily via mobile phones for further processing.
- Fig. 1. Total volume and annual increment of the growing stock by
main tree species in 1921-1990 on forest and otehr wooded land.
The figures in 1921-1984 are results of the National Forest Inventories
for the area of the inventory moment. The total volume in 1990 and the
total increment on 1985-1998 have been gained by model-based updating
of the data of the seventh and eighth inventories.
- Fig 2. Mean volume of growing stock in 1951-1953 and in 1990 on forest
and other wooded land. The present growing stock is 22% bigger than
in early 1950s. According to cutting statistics, total cutting during
the period 1951-1989 exceeded the volume of the present growing stock.
- Fig. 3. Comparison of three extreme cutting options and their consequences
in 1990-2040. In addition to the absolute levels, the figures show the
strong interdependence of cuttings, increment and volume of growing
stock with time.
- Fig. 4. Cutting potential in the 1990s by main tree species (pine,
spruce, birch) according to present silvicultural regimes (see alternative
2 in the text and in Fig. 3). The maps have been processed from updated
data of the inventory.
- Fig. 5. Elements of a multi-source forest inventory. The test area
consists of the communes of Tohmajärvi and Värtsilä in
North Karelia with an area of 84,000 hectares.
- Fig. 5A. Colour composition of a Landsat TM image bands 2 (blue),
3 (green) and 4 (red).
- Fig. 5B. Composition of digital map data (mineral soils, swamps, arable
land, roads, buildings) and image analysis (waters).
- Fig. 5C. Dominant treee species based on image analysis.
- Fig. 5D. Volume of growing stock bsed on image analysis.
- Fig. 5E. A zoom of Fig. 5C aea 4,100 hectares.
