The Yahudia Forest is a nature reserve situated in the central part of the Golan, north-east of Lake Tiberias. The reserve, which extends over some 6600 ha, is located mostly 0-300 m above sea level. Level in its greater part, the reserve is cleft by deep canyons of perennial streams. Its soil, mostly basaltic-montmorilonitic, overlies mother rock of cover basalt which erupted in the Upper Pliocene and the Pleistocene epochs. A few limestone exposures from the Neogene can be found in the southern part. The climate is mediterranean, with annual precipitation of about 500 m.
In our survey of vertebrates we found 172 species. A more detailed survey was made of rodents and birds. As for mammals, our main interest was centred on wild boar, gazelles and rodents in context with their impact on vegetation in general and on Quercus ithaburensis in particular.
The vegetation survey was analysed by the nodal ordination method, and vegetation units were established accordingly. The central vegetation unit is the Quercus ithaburensis formation whose principal alliance of associations is that of a Quercus ithaburensis park forest, with grasslands of Avena sterilis and Hordeum bulbosum occupying the greater part of the plane areas. The higher areas of the Quercus ithaburensis Park Forest contain a unit of Ziziphus lotus savannoid vegetation, which appears to be a secondary vegetation following deforestation. In the low-lying regions of the forest park we have a unit of Ziziphus spinachristii savannoid vegetation. On the steep declivities grows an alliance of Styrax officinalis and Ferula tingitana associations which creates a denser forest. The aquatic vegetation is represented by the Salix acmophylla-Nerium oleander formation, and on the limestone exposures we have the Salsola vermiculata - Salvia dominica formation.
The phenology of Quercus ithaburensis has been researched and described, and the formation of cambial rings examined. It was found that normally me annual ring is formed, and that a direct connection exists between the quantity of annual precipitation and ring-width. On the basis of this connection and correlation between surface of sections and ages of trees, we drew up a diagram of distribution of tree ages which shows a high frequency of 40-60 years old trees and a low frequency of trees over 100 years old. On the basis of this diagram and historical evidence, we cam to the conclusion that most fellings of trees in the forest occurred in the periods of Circassian settlement during the latter half of the 19th Century and during the period of the First World War. The relatively high frequency of seedlings and mature trees, and the low frequency of middle-aged trees, led us to a deeper research of the subject of seedling germination, establishement and survival.
We examined the fertility of Quercus ithaburensis trees and the extent of acorn consumption by animals, and found great variability in acorn production, though the average yield per tree was 800 acorns. The greater part of the acorns are consumed by wild boar, and the smaller part by cattle and rodents. Acorns have a high germination potential, but lose it within a few days of having been exposed to dry weather conditions.
Over a period of 5 years observations were made of natural, hand-sown and transplanted seedlings under different grazing regimes (without wild boar or cattle; with wild boar and without cattle; with wild boar and cattle), and in different habitats connected with cairns on which grow most of the trees in the forest (top of cairn; slope of cairn; slope of cairn within tree's shade zone; bottom of cairn; open space outside cairn).
We found that there was more germination in open habitats, though only in the absence of wild boar. Where wild boar are present cairns have the advantage because not only are they more difficult of access to wild boar but desiccation of acorns is avoided there.
The positive reactions to irrigation and weeding have proved that water and competition are limiting factors in seedling establishment. It was found that acorns survive better in cairns where they are shielded from desiccation, competition with grasses, and to a relative extent also from fires. Satisfactory establishment was found under cattle-grazing regimes, where seedlings have less competition with herbaceous vegetation and fact lower fire frequency and intensity.
An analysis was made of the fire incidents in the Yahudia Forest - all of which man-made. In the southern part of the reserve which contains military training areas, a high frequency of fires was recorded in May. Here, a small number of fires consume large areas. In the northern part, which is under grazing, more fires occur although they are of lower intensity and consume smaller areas, and frequency is highest in June-July. A fire-frequency map was drawn up, enabling forecasts to be made of fire-prone areas, and accordingly a policy of fire-break spraying and control was recommended. It was found that notwithstanding the relative fire resistance of the adult tree, the impact of fire on seedlings and acorns is of tremendous significance for the forest's existence.
Cattle-grazing in the reserve has been examined with regard to its effects on herbaceous vegetation and on Quercus ithaburensis. A quantitative analysis of forage composition and cattle behaviour m pasture was made. It was found that only heavy grazing affects the composition of herbaceous vegetation and causes a relative rise in the growth of ruderal species. Quercus ithaburensis was found to form an important component of the cattle's diet, with leaves being consumed in summer, and acorns in winter. The quantity and nutritional value of acorns consumed made them a factor that should be taken into account in pasture planning.
A theoretical model describing the processes of germination, establishment and survival of Quercus ithaburensis has been brought, as have the various factors affecting the two main inhibition periods in the life of the seedling The main factors were found to be fire, water regime, and competition with grasses and adult trees, whereas rodents and wild boar have positive as well as negative effects, particularly during the germination period.
We have recommended that reserve management be based on programmed cattlegrazing of about 1200 mother cows in the northern part of the reserve, and on a fire-prevention regime with emphasis on the self-same area.
We have worked out a policy of regulating visitor intensity in accordance with the vulnerabilities of the various reserve areas, based on strict zones in the cental part of the reserve; zones for walking tours, and intensive development zones. Recommendation has been made to concentrate wildlife and reintroduce wild animal species that existed in the region in the past into the central area of the reserve's southern part, and to afford the public limited access to this area.
As far as vegetation is concerned, no intervention appears to be necessary, with the exception of afforestation of Quercus ithaburensis and Pistacia atlantica in the high-lying, unforested parts, and to extend such afforestation also to regions outside the reserve that were covered with forest in the past. A technique for planting Quercus ithaburensis trees has been recommended.
In this paper, we have dealt with the processes and main problems of the reserve, with a view to gaining tools for its management and with the intention that it my also serve as a model for researches in other nature reserves in Israel and comparable areas elsewhere. We are aware that there is still much room for research and accomplishment in spheres which have not found expression in this paper.
|Qualification||Doctor of Philosophy|
|Award date||29 Feb 1984|
|Place of Publication||S.l.|
|Publication status||Published - 1984|
- national parks
- nature conservation
- nature reserves
- plant ecology
- savanna woodlands
- seed germination
- seedling growth
- quercus ithaburensis