[WSL] research department Landscape
paper presented at the conference 'Large Herbivore Initiative' in Lelyststad, the Netherlands, organized by WWF International grazing deer 50 K

Wild ungulates as a management tool:
long-term experiences from the Swiss National Park with red deer
Bertil O. Krüsi, Martin Schütz, C. Bigler, Helena Grämiger, G. Achermann
Swiss Federal Institute for Forest, Snow and Landscape Research, CH-8903 Birmensdorf, Switzerland.
For additional information please contact Martin Schütz: phone: ++41-1-739 25 26, fax: ++41-1-737 40 80, e-mail: martin.schuetz@wsl.ch,
The work was supported by the Swiss National Science Foundation (Projects 3100-39484.93 B. Nievergelt and 3100-045944.95 O. Wildi)

Kann mit wilden Huftieren die Biodiversität in Nationalparks erhalten werden?
Can we use wild ungulates to manage biodiversity in national parks?

Study Area

The Swiss National Park is located in the south-eastern corner of Switzerland, ranges in altitude from 1500 to 3170 m a.s.l. and encompasses an area of 170 km2. 50 km2 (29%) are occupied by forests (mainly dominated by Pinus montana), 36 km2 (21%) by grasslands (mainly alpine) and 84 km2 (50%) are without vegetation. In 1914, the year the park was founded, all the traditional activities by man and his cattle such as logging, hunting and grazing were stopped. In 1917 the first of more than 100 permanent plots was established in order to monitor the development of the vegetation, which has been done ever since at intervals of 5 to 10 years. Since 1920 the maximum number of wild ungulates (red deer, chamois, ibex, roe deer) present in the park during the summer months has been recorded every year. Between 1920 and today their number has tripled, primarily due to a steady increase in the number red deer from practically nil to 2000. During the summer of 1998, in the park the following numbers of wild ungulates were recorded: 1957 red deer (Cervus elaphus), 1599 chamois (Rupicapra rupicapra), 438 ibex (Capra ibex) and less than 100 roe deer (Capreolus capreolus). In contrast to the other wild ungulates, most of the red deer leave the park during the winter months, i.e. from early October until late May.

Wild ungulates and tree establishment

The impact of the increasing numbers of wild ungulates, in particular red deer, on the establishment of trees in the abandoned subalpine pastures was studied in the first 25m of grassland immediately adjacent to the forest edge. The study was carried out on the three major subalpine pastures of the park. On the whole, the age of more than 300 systematically selected trees was determined, using dendrochronological methods. All the trees germinated between 1915 and 1989 were age-standardised, i.e. transformed into 10-year old standard trees (using the calibration curve for Pinus silvestris, yield class 2), averaged per 5-year periods and compared with the 5-year averages of the maximum number of red deer present in the park during July and August. Between 1915 and 1989, high rates of tree establishment coincided with moderate densities of red deer (6-9 animals per 100 hectare of vegetation covered area) whereas low rates coincided with both periods of very low (0-2 red deer per 100 hectare) and very high (22-25 red deer per 100 hectare) densities. On the whole, the relationship between the number of red deer and the number of age-standardised trees established per hectare and year follows a slightly skewed bell shaped curve.

A bell shaped curve is exactly what one would expect if one assumes (i) that wild ungulates have both positive and negative effects on germination, establishment, growth and survival of trees, and (ii) that at moderate population densities the positive effects prevail and at high densities the negative. Among the positive effects, undoubtedly, most important is that wild ungulates create gaps in the otherwise closed herb layer, i.e. low-competition micro-sites, crucial for the germination of the seeds of all (Pinus montana, Picea abies and Larix decidua) but one (Pinus cembra) of the tree species frequent in the area. In a systematic sample taken in the three subalpine grasslands at a distance of 10 m from the forest edge, 68% of the tree seedlings (mostly Pinus montana) were found in gaps even though gaps occupied only 10% of the surface area. On the other hand, wild ungulates may also substantially hamper establishment, growth and survival of young trees through trampling, browsing, bark stripping and fraying. On the whole, however, most of the trees damaged by wild ungulates, would probably not exist in the first place were it not for the germination sites created by the very same ungulates.

During the period with moderate densities of red deer (1940-1960) the rate of tree establishment was with 85 age-standardised trees per hectare and year three to four times higher than during periods with very low (1915-1930; 20 trees/ha) or very high (1970-1989; 30 trees/ha) numbers of red deer. Consequently, it should be possible to use the red deer as a tool to control the encroaching of the forests onto the subalpine grasslands. Simulation models showed, however, (i) that the impact of wildlife management on the development of the forested area will become visible at the landscape level only after hundreds of years and (ii) that the number of red deer would have to be increased substantially beyond the present levels in order to protect the existing subalpine grasslands effectively against the encroaching forests. In the case of Alp Stabelchod, a subalpine pasture of 10 hectares, for instance, the simulation models showed that it would take between 400 years (6-9 red deer per 100 hectare of vegetation covered area in the park) and 1600 years (0-2 or 22-25 red deer per 100 hectare) until the forest would have reclaimed 50% of the pasture abandoned in 1914. Those periods of time result (i) if it is assumed that the number of successfully established trees depends solely on the number of wild ungulates and (ii) if trees that bifurcate at the soil surface are counted as one tree.

Climate and tree establishment

Between 1915 and 1989, the number of age-standardised trees (yield class 2) established per hectare and year correlated, however, not only significantly with the maximum numbers of red deer and wild ungulates (rs= 0.64 and 0.58, respectively; p<0.05; numbers of red deer and wild ungulates were transformed to fit a bell-shaped curve) but also with climatic factors such as "precipitation during the summer months" (rs= 0.78; p<0.01) and "length of the vegetation period" (rs= 0.67; p<0.05). Apparently, the particularly favourable density of wild ungulates was not the only reason for the high rates of tree establishment observed between 1940 and 1960. Rather, there is strong evidence that it resulted from the simultaneous occurrence of both (i) optimal densities of wild ungulates and (ii) ideal climatic conditions. It should be noted, however, that such favourable climatic conditions occurred only during 20 years, i.e. approximately 25% of the period studied.

Wildlife as a tool to manage the landscape

Within the range of population densities observed in the park so far, therefore, wildlife management would allow to change the rate of tree establishment in the order of magnitude of four only during periods with particularly favourable climatic conditions, i.e. during approximately 25% of the time. During the remaining 75%, it is safe to assume that the order of magnitude would be around two rather than four. In the case of Alp Stabelchod, therefore, wildlife management would allow to speed-up the period of time needed until the forest had reclaimed 50% of the grassland from 1600 years to 700 years rather than 400 years as previously estimated. 1600 years would be needed if no red deer but only chamois and ibex were present and if it is assumed that under those circumstances the number of germination sites rather than climatic conditions would limit the number of trees established. If today’s number of wild ungulates, in particular red deer, were maintained it would take approximately 930 years until the forest would have reclaimed 50% of the 10 hectares of Alp Stabelchod.

Under the conditions given in the Swiss National Park and remaining within the range of population densities observed in the park so far, wildlife management is definitely not an effective tool to steer the development of the landscape during the next couple of hundred years. In particular, it does not allow to stop or slow down significantly the advancing of the forests onto the subalpine grasslands. The latter could only be achieved if the number of red deer would be allowed to increase substantially beyond the levels observed so far, which at present is politically not feasible.

Wildlife as a tool to manage subalpine grasslands

On the abandoned subalpine pastures, on the other hand, the impact of red deer on structure and composition is obvious. How quickly and profoundly red deer are able to affect those grasslands illustrates the development of the vegetation during the past 80 years on permanent plot, 120 m2 in size, established by Braun-Blanquet back in 1917 on Alp La Schera at 2100 m a.s.l. Between 1917 and 1996 two major changes occurred: around 1940 Phleum pratense and other tall-growing species were outcompeted by Festuca rubra and other low-growing species adapted to grazing which around 1980 were, in turn, outcompeted by Nardus stricta. Both the changes coincided with changes in the number of red deer present in the area. In 1939 a licking stone was installed which resulted in a marked increase in the number of red deer from practically zero to between 60 and 100. In 1975 a special reduction hunt, carried out outside of the park, diminished the population of red deer from Alp La Schera by half. The remaining animals needed less food and did no longer graze the area with the permanent plot.

The transition from the ungrazed, tall growing meadows to heavily grazed, low growing swards dominated by Festuca rubra was accompanied by a marked increase in the number of plant species. On 15 permanent plots, located in areas heavily grazed by red deer and ranging in size from 1 m2 to 3055 m2, the number of plant species doubled on average between 1940 and 1990 (+98%). In contrast, the number of plant species did practically not change (-6%) during this period of time on 15 "control" plots, located in areas presently not grazed by red deer and ranging in size from 1 m2 to 250 m2.

In conclusion, wild ungulates in general and red deer in particular seem to represent an effective tool to maintain and/or increase locally the floristic and structural diversity of subalpine grasslands. However, the present numbers of wild ungulates allow to manage only approximately 30% of the subalpine grasslands in the Swiss National Park.

Further information on the topic is available on the Internet site Our Topics under the heading Herbivores and Vegetation Change in the National Park In the near future, the present state of research will be summarised in a volume entitled "Ungulates and Vegetation Change in the Swiss National Park", which will be published in English and German towards the End of 1999 in the Series "Nationalparkforschung in der Schweiz". The volume will be available at: Nationalparkhaus, CH-7530 Zernez, Switzerland, fax ++41-81-856 17 40.
Copyright WSL/FNP 1999 / Peter Longatti / e-mail: peter.longatti@wsl.ch / Last Update: 7.6.00