DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 3-4/2013 str. 43 <-- 43 --> PDF |
of the total area. So, in Prespa National Park the low portion of open areas is not the factor that does not allow the domination of seedlings that have been established and growing in canopy gaps (G). In Cyprus, according to Milios et al. (2011) it is possible that in some areas of J. excelsa formations seedlings growing in open areas do not dominate as a result of a low portion of gaps (open areas) that is available for their establishment. In the areas where facilitation is the crucial factor determining J. excelsa regeneration facilitation is related to protection against grazing as is observed in the central part of the Nestos valley in Greece (Milios et al. 2007) and possibly in the Balouchistan of Pakistan (Ahmed et al. 1989, 1990) and to improvement of harsh climatic conditions by partial shade as probably happened in the valley of Hayl Juwary in Oman (Fisher and Gardner 1995). In Africa, Hall (1984) mentions that in areas where precipitation is lower than 850 mm the regeneration of the species is closely related to the mother plants. Moreover, Milios et al. (2007) refer that plant litter under the nurse plants (that belong to the same species) is another factor that together with protection against grazing create a facilitation mechanism for the J. excelsa regeneration in the Nestos valley in Greece. In areas where there are not stressful factors J. excelsa regeneration is established in open places as observed in Africa, after a disturbance like fire, in locations where precipitation is of between 1000–1200 mm (Hall 1984). In Cyprus in the J. excelsa formations, where there is no grazing, even though the soils are shallow and rocky the regeneration in gaps is the dominant form of regeneration if there are enough open areas. Even in areas where there are not adequate free from shade areas the facilitation does not dominate in the regeneration process (Milios et al. 2011). In the present study grazing is the decisive factor which determines the regeneration process of J. excelsa. Even though grazed seedlings were not found trampling probably destroys regeneration plants. The heavily grazed broadleaved species in the nearby mixed species stands possibly explain the absence of grazing marks in J. excelsa seedlings, since the goats, sheep and cattle prefer the broadleaves. According to Ahmed et al. (1989) J. excelsa seedlings and smaller juveniles can be damaged or killed by trampling or animal tread. On the other hand Milios et al. (2007) found grazed J. excelsa seedlings in the central part of Nestos valley. It seems that the process of grazing through trampling and animal tread reduces the seedling density in gaps preventing the domination of regeneration plants growing in full light even in two of the three structural types where the areas without canopy cover of trees and shrubs is about 60 to 70 % of the total area. On the other hand if the number of grazing animals were a lot more probably facilitation of nurse plants through the protection of seedlings from trampling and tread would have been the dominant regeneration process. Herbivory affects population dynamics of plants (Gomez 2005), furthermore grazing affects negatively plant growth (Julien et al. 2006; McEvoy et al. 2006). Even though facilitation is not the dominant process in the regeneration of J. excelsa in Prespa National Park, a significant number of regeneration plants have been established under the facilitation. Site productivity seems to affect the process of facilitation, while the living foliage appearance does not influence it. In site type A, the density of F seedlings in dense J. excelsa formations is greater (p<0.05) than that of dense formations of site type B (where in a significant number of trees the height where the living foliage appears is 50–60 cm above the ground) (Table 2). In the case of the corresponding sparse formations of the two site types, the same pattern is observed (Table 2). On the other hand, in site type B, a difference between the densities of F seedlings in areas where in a significant number of trees the |