Forests make up a large part of the Swiss National Park (SNP). According to the SNP homepage 28% of the park is at present covered with forest. Research into natural forest development in the National Park started early. However, there is still much to be learnt. Why? We may think that we know a lot after 80 years of observation, but a generation of mountain trees can live between 300 and 600 years.
Fig. 1 - Spruce forest with larches in
the National Park: "Praspöl area".
Photo: Ulrich Wasem (WSL)
Forests are generally perceived as being something static. This is especially true of mountain forests. Only non-frequent visitors with good memories will notice that an unbelievable dynamic exists: not only are the animals and annual plants constantly changing, but also the seemingly static trees can also be seen to be developing if they are observed using the proper tools. Such tools are forest yield or forest growth research as well as forest inventories and modelling.
Forest growth research was put into practice in the National Park as early as 1926. The Federal Research Institute for Forest, Snow and Landscape WSL (the then Swiss Central Institution for Experimental Forestry) set up five research plots of 0.25 hectares in size. The first compilation, which is still kept up to date, was limited to a description and a photographic documentation. In 1934 the diameter of all trees and the height of some trees were measured and in 1947 all trees which were taller than 1.3 meters were marked with a number. In 1950 Burger published the first results of this survey. Measurements taken in 1963, 1977, 1991 and 2003 also included the social position of the trees in the stand and any damage, therefore allowing the development of every tree to be followed in detail.
During and after the Second World War – when timber prices were high – many of the communes, to whom the forest still belonged, wanted to know whether a profit could be made out of the timber in the National Park forests. That is why in 1957 an inventory, using random sample surveying, was made of the whole of the forest area. (KURTH 1960), a survey which unfortunately has never been repeated, apart from a few chosen follow up measurements taken in 2002 and 2003 (RISCH 2004).
Fig. 2 - Mountain pine forest in the
National Park: "Stabelchod area".
Photo: Ulrich Wasem (WSL)
In 1977, under the supervision of Prof. Hans Leibundgut, the ETH’s Institute for Silviculture set up twelve observation areas in different parts of the Park on which two stand inventories have since been carried out. In 1984 a country wide forest inventory, which included around 55 research plots in the National Park, delivered further forest data. However, a survey was not carried out in the dwarf pine forest. In the country wide forest inventory 2, which took place between 1993 and 1995, some of the research plots were once again surveyed. At the beginning of the 1990’s a further research plot for a long term forest ecosystem research project (LWF) of the WSL was established in the mountain pine stands below the Stabelchod Alp. Up to present, in spite of these various research activities, no total overall, reliable picture of development in the National Park forest exists.
The five research plots, known as the "Burger" areas, can be used as an example to show how dynamically the forest in the National Park is actually developing. However, these plots only represent approximately a half of the species actually present in the National Forest.
Near to Praspöl is a former pasture forest made up of Norway spruce, larch and "Engadin" Scots pine trees. The trees are standing very close to each other in small groups which is typical for this type of mountain forest.
Fig. 3 - Research plot Präspol 05-001: Former pasture forest of Norway spruce, European larch and "Engadine" Scots pine trees containing loosly grouped trees of all age groups. "Groups of various tree species live together as families so to speak". In the series of pictures the only noticeable changes are that single trees have fallen down and the trunk has rotted. Looking at the diameter distribution it can clearly be seen that in 1946 there were many trees present with a small diameter, including larches and mountain pines. In 1991 the trees with a diameter of up to 20 cm were all spruce trees. The mountain pines had totally disappeared and of the larch trees there remained only thick old trees.
The 5 pictures taken between 1946 and 2003 seem to show
the same scene. However, when looking at the number of trees in the various
diameter classes a large change can be noticed. From 1977 onwards the mountain
pine has disappeared. In 2003 larch and Scots pine trees are only present amongst
the thicker trees. Amongst the small trees with a diameter of up to 20cm there
are only spruce trees present. Why is this so? As trees grow it becomes darker
in a forest and spruce trees can endure this better than mountain pines or even
larches, which are considered to be a light demanding pioneer tree species, which first settle and then allow the development
of other tree species such as spruce which are more shade tolerant.
In God dal Fuorn there are two further research plots.
In the more easterly plot there has been a similar development to that in Praspöl, except that
here Swiss stone pines are present amongst the middle diameter class, but are
disappearing amongst young growth. The small trees are only spruce. Approximately
50 meters away there is an old mountain pine forest containing Swiss stone pine
trees which is approximately 240 years old. Using available data it can be seen
that here the old trees are more loosely grouped and as they eventually
disappear more light becomes available allowing mountain pines to once again "grow
in" amongst the smaller diameter classes.
In Stabelchod there are two pure mountain pine stands: the older one is approx. 90 years old and the younger one approx.. 100 years old. Both of these areas were once used for grazing. Both of these stands could provide possible clues to the dynamic of mountain pine forests. In the older, more southerly stand the trees are dying and falling down and therefore making room for a new generation of trees. The younger more northerly stand has developed out of natural mountain pine regeneration on a redundant pasture where an older stand once existed about 80 years ago. In both of these research plots Swiss stone pines can be found in the ground and brushwood layer, however not one of them has managed to reach a height of 1.3 meters.
Fig. 4 - Research plot Stabelchod sid 05-004: Pure mountain pine stand, today around 190 years old. "Groups…., as if they had grown out of the groups of grazing cattle …". The trees in the stand are growing very close together and the stem count is high.. The maximum diameter is 32 cm. Over the years the number of stems has decreased due to natural mortality. By 2003 so many pines had died off that in the lowest diameter class (0-4 cm) young trees of the next generation have been able to establish themselves.
A general picture of forest development in the National Forest can be drawn from the follow on surveys carried out during the Forest Inventory KURTH (1960) which were compiled in RISCH (2004). Young tree growth, that is to say trees which have not yet reached a height of 1.3 m is especially interesting for the further development of a stand; our observations will be restricted to these trees. In general the developments which were observed in the "Burger" areas have been confirmed.
The percentage of mountain pines amongst young tree growth reduces in progression to forest development. Whilst in earlier stages of forest development the mountain pine was the dominating species at a later stage of development only about a fifth of all young trees are mountain pines. The frequency of all other tree species amongst young growth is however increasing. The increase of forest Scots pine and European larch trees is very slight., whilst Norway spruce and Swiss stone pines, the two species which tolerate shade best, show a marked increase. Apart from shade tolerance the selective browsing of young trees by game animals, of which there is an abundance in the National Forest, could be expected to play a large role. But this does not seem to be the case. The mountain pine is by far the least browsed: on 18% of the young trees could browsing be observed. Swiss stone pines are browsed twice as much (36%). In spite of this the importance of the mountain pine is declining and that of the Swiss stone pine is increasing. More astonishing is the noticeable increase of spruce trees amongst young growth, because this is the most browsed tree in the park; browsing can be observed on 83% of young trees.
Fig. 5 - Development of young tree growth (tree height < 130 cm) in the National Park forests. Data from KURTH et al. (1960) and RISCH (2004).
The question still remains as to why forest research should be carried out in the National Park. The locations are very special when compared to the rest of the Swiss Alpine area and the results therefore cannot be transferred. It should also be taken into account that research itself could have an influence on this unique undisturbed development. On the other hand nowhere else in Switzerland are such observations possible. And last but not least the forest is a fundamental part of the National Park. These considerations speak in favour of long term forest research in the National Park being continued. The various continual observations should be better coordinated and selectively added to. A representative forest inventory, which could give information about the state and development of the whole of the forest is also desirable.