Establishment and Tending of Subalpine Forest: Research and Management.
H. Turner and W. Tranquillini, eds.
Proc. 3rd IUFRO Workshop P 1.07-00, 1984. Eidg. Anst. forstl. Versuchswes., Ber. 270 (1985): 7-10.
CONTRIBUTIONS OF SUBALPINE ECOLOGIC RESEARCH TO THE EXPLORATION OF THE PRESENT LARGE-SCALE FOREST DECAY
F.H. Schwarzenbach
Swiss Federal Institute of Forestry Research Birmensdorf, Switzerland
ABSTRACT
The survey of the development of for- est decline in Switzerland given in the introductory paragraphs shows that the forests of the subalpine zone are increas- ingly threatened. Observations made in spring and summer 1984 confirm that the destruction of the forests is continuing with undiminished intensity even on medium and high altitude sites.
The alarming thinning of the forests has lead foresters and scientists to join forces in seeking ways and means of ensur- ing the future of the mountain forests and of closing new gaps as quickly as possi- ble.
Research on the ecology of subalpine forests can make the following contribu- tions to research on forest damage:
- determination of the effects of the pollution of the air with anthropogenic harmful substances on the long-, medi- um-, and short-term development of sub- alpine forest communities;
- elucidation of those chain processes leading to the premature death of trees affected by forest decline and governing the course of the disease;
- determination of the effects of the progressive thinning of the mountain forests on the ecosystem;
- development of suitable measures for the reforestation of damaged mountain forest sites in the face of the additional stress caused by anthropogenic emis- sions;
- development of suitable measures for soil stabilisation using shrubs and fast-growing trees on slopes threatened by erosion and landslips after deforest- ation.
THE SITUATION REGARDING DEVELOPMENT OF FOREST DAMAGE IN THE MOUNTAIN REGIONS
As shown by the latest reports on the development of forest decline in Europe, the syndrome has now spread to all Alpine countries; observations made during the past few months indicate that forest de- cline is continuing its rapid spread, particularly in the mountain forests of the subalpine zone, and becoming more intensive within the areas already affect- ed. In Switzerland, both the results of a survey carried out in 1983 within the framework of the emergency programme SANA-
SILVA (Bucher, J., Kaufmann, E. and Lan- dolt, W., 1984), and the results for eastern and western Switzerland of the National Forest Inventory (Mahrer, F., Brassel, P. and Stierlin, H.R., 1984) show that forest decline is spreading in- to the subalpine zone. In September-Octo- ber of last year, the proportion of ail- ing trees in the mountain regions on the north slopes of the Alps was still gener- ally low. With the exception of the Val Poschiavo and the Munster Valley, the mountain forests on the southern slopes seemed mostly unaffected. In very general terms, forest damage was more apparent in the eastern and central parts of Switzerland than in the west. At the time of the survey, the worst hit species were silver fir (Abies alba Mill.), spruce
(Picea abies Karst.), and Scots pine (Pinus sylvestris L.), while European larch (Larix decidua Mill.) and cembran pine (Pinus cembra L.) showed only slight or negligible damage.
In the late autumn of 1983, a heavy needle fall began in spruces (Picea abies Karst.) in different localities in the mountain region and the Mittelland; this needle fall lead to the premature loss of older generations of needles. This insidious death of needles has continued through the present year with undiminished intensity and has resulted in a clearly perceptible thinning of the crowns of the affected trees. Observations made during the summer of 1984 show that spruces in all parts of Switzerland are now consider- ably affected by forest decline.
Furthermore, damage to Scots pine (Pinus syZvestris L.) and silver fir (Abies alba Mill.) has greatly increased since autumn 1983. Individual observations of the past few weeks suggest that coni- fers growing on high altitude sites (Pinus mugo Turra, Pinus cembra L., and Larix decidua Mill.) are now also suffering from the forest decline syndrome.
The condition of broadleaf trees has deteriorated very rapidly during the past few months. Where reports of damage last year were concentrated in north-west Switzerland, those received in the last few weeks show that practically all broad- leaf species - including fruit and orna- mental trees - are affected by forest de- cline, with beech (Fagus syZvatica L.), ash (Fraxinus excelsior L.), and birch
(Betula spp.) giving cause for particular concern.
Mass multiplication of parasitic in- sects has aggravated the damage to the forest. Mass attack on spruce by the spruce bark beetle (Ips typographus L.), for instance, caused substantial damage in eastern and northern Switzerland in autumn 1983.
In view of developments of the past few months, forestry officers and research cientists are giving a gloomy prognosis:
- Forest decline is continuing to spread with undiminished rapidity through all parts and all altitudinal zones of Switzerland.
The condition of the affected trees is deteriorating progressively.
- The weakened trees are increasingly sub- ject to attack by secondary parasites.
Forest decline is now affecting even those conifers and broadleaf trees which as recently as last summer seemed in little danger.
EFFECTS ON THE SUBALPINE FORESTS Although research has only the expe- rience of a very few years to depend on in analysing forest decline, certain conclu- sions significant for the assessment of
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its effects on subalpine forests can be reached on the basis of its pattern of spread and its temporal development. As far as our knowledge extends as present, the following findings are regarded as im- portant:
Forest decline can be considered as an insidious process of destruction result- ing in the premature death of the af- fected trees.
Terrestrial surveys and infra-red aeri- al photography both reveal that, during the initial phase of forest decline, only isolated trees are affected. At a
later stage, larger or smaller patches of damage become apparent within stands, and these often occur at forest edges or on sites ·which are exposed because of the terrain. Mature, solitary trees and tree groups in exposed positions seem to be especially endangered.
- Local mapping confirms that the degree of damage often varies considerably within small areas.
- During the initial phase, i t is mostly medium-aged and old trees that are af- fected; later, younger trees also begin to suffer.
In terms of its temporal sequence, the death process appears to follow a sig- moid curve (Figure 1) which probably
90
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increasing percentage of spruceswith growth impairments since about 1950 80
70 60
50 40
30 20 10
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Figure 1. Temporal Sequence of forest decay with respect to spruce (Picea abies)
corresponds to what is termed the 'logi- stic distribution function' (Linder, A.
and Berchtold,
w.,
1976). comparison of the curve functions reveals that the length of the initial, latent phase varies from species to species and also that there are substantial differences between species in the steepness of the curve. The fatal process is particularly rapid in spruce (Picea abies Karst.), where i t often progresses from an outwardly incon-spicuous growth reduction to a phase of disintegration; this in turn often begins with a rapidly progressive loss of nee- dles.
- The course of the process of destruction may be influenced by a variety of exo- genous factors such as drought, frost, or wind; furthermore, the symptoms may be obscured by the effects of attack by parasitic insects, wood-decomposing fun- gi or diseases.
- Observations to date suggest that forest decline is now affecting all indigenous conifers and broadleaf trees; in addi- tion, there are increasing indications that exotic and ornamental species as well as fruit trees are beginning to fall victim.
The consequences of a progressive thinning of the mountain forests are known from past experience:
- development of new avalanche starting zones on formerly forested sites
- increased danger from mountain torrents - increase in the number of landslips
increased risk of rock-falls more intensive erosion
- erosion of forest, meadow and arable soils
- flooding of valley floors.
In order to avert these disastrous consequences of the insidious destruction of the mountain forests, or at least to mitigate their effects, forestry must in- stitute all suitable measures to preserve the total area and spatial distribution of the forest; to close new openings by means of natural regeneration or artifi- cial planting; and to protect the forest soil on endangered sites from being erod- ed away or covered by debris or rubble.
The silvicultural and technical measures necessary for the maintenance of mountain forest are in themselves well-known and have long since been put into practice.
The only question is whether the personnel and materials available are at all suffi- cient to keep pace with the additional work necessitated by the rapid development of forest decline. If the destruction of the forests continues with its present in- tensity, the forest service in Switzer- land will soon no longer be in a position to ensure the maintenance of the protec- tion forests in the Alps. Having realised that their own resources are thus limited, the authorities concerned are now doing their utmost to press for an immediate and drastic reduction in air pollution, which, in the light of our present knowledge, is regarded as the primary cause of forest decline.
THE TASKS CONFRONTING ECOLOGICAL RESEARCH Forest decline has confronted forest- ry research with a demanding and compli- cated task. Switzerland, as a small coun- try, must concentrate all its energies on research in those fields which are of most importance and highest priority for the maintenance of its forests (Swiss National Foundation for Scientific Research: Execu- tion Plan NFP 14+). In applied research the main concern is to provide a scientif- ically sound basis for political decisions on environment, forestry and the timber industry. In basic research, the main em- phasis is on those areas in which experi- enced research groups of high repute are active, where research results promise significant progress towards the solution of the accumulated problems.
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The promotion of ecological research is necessary from the viewpoints of both practical forestry and basis research, though decisive advances can only be a- chieved through interdisciplinary coopera- tion. The major tasks in research on the ecology of the subalpine forests are:
- To determine the effects of atmospheric pollution by harmful substances from present-day civilisation on the develop- ment of subalpine forests on a long-, medium-, and short-term basis.
- To elucidate the chain processes leading to the premature death of trees affected by forest decline and governing the course of the disease.
To investigate the effects of the progressive thinning of the mountain forests on the ecosystem.
- To develop suitable measures for the reforestation of mountain areas with forest damage in the face of the addi- tional stress caused by anthropogenic emissions.
- To develop suitable measures for soil stabilisation using shrubs and fast- growing trees on slopes threatened by erosion and landslips after deforesta- tion.
Research on the relationship between air pollution and forest damage in the subalpine zone aims mainly at providing a basis for the implementation of appropri- ate and effective measures for the protec- tion of the environment. The other re- search goals are important for the forest service, which is responsible for the maintenance of the protection forests in the mountain regions.
OUTLOOK
The rapid development of forest de- cline in the alpine area is endangering the systematic maintenance of protection forests stipulated by the Forestry Bill of 1876. The situation caused by the un- expected and rapidly advancing process of destruction is giving cause for serious alarm. If forest decline continues with undiminished intensity, i t will pose a grave threat to the mountain population.
With such far-reaching consequences of the insidious process of destruction in mind, forestry is using all appropriate measures in environmental protection, traffic regu- lation and energy policy; in short i t is doing everything in its power to reduce overall air pollution to the levels of the post-war years as quickly as possible, and thus to improve the chances of surviv- al for the protection forests. In trying to provide practicable solutions to the most urgent problems, research scientists and practical foresters must work hand in hand. Cooperation is also desperately called for between the scientists, partic- ularly the ecologists of all nations. The maintenance and restoration of endangered protection forests throughout the world is at stake.
LITERATURE CITED
Bucher, J.B., Kaufmann, E., Landolt, W.:
Waldsterben in der Schweiz - 1983, 1. Teil, Interpretation der SANASILVA- Umfrage und der Fichtennadelanalysen aus der Sicht des forstlichen Immissi- onsschutzes. Schweiz.Z.Forstwes. 135, 1984, 4: 271-287.
Linder, A., Berchtold, W.: Auswertung von Prozentzahlen; Probit-Logitanalyse mit EDV, Uni Taschenbuch 522, Basel &
Stuttgart: Birkhauser, 1976; 232
s.
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Mahrer, F., Brassel, P., Stierlin, H.R.:
Erste Ergebnisse zum Waldsterben aus dem Schweizerischen Landesforstinven- tar (LFI). Schweiz.Z.Forstwes. 135, 1984, 4: 299-306.
Waldschaden und Luftverschmutzung in der Schweiz. Ausflihrungsplan flir ein Zu- satzprogramm im Rahmen des Nationalen Forschungsprogrammes 14: Lufthaushalt und Luftverschmutzung in der Schweiz.
Schweizerischer Nationalfonds Bern, September 1983, 16 S.
