Επιδράσεις της βόσκησης βούβαλων στα υγρά ποολίβαδα του Εθνικού Δρυμού Πρεσπών

Abstract

Grazing in wetlands is considered as one of the most effective methods for the creation and maintenance of wet grasslands on areas that under no management interventions would be dominated by dense and often mono-specific stands of high emergent helophytes, such as reed beds of Phragmites australis. The purpose of the present research was to collect original data on the characteristics of the littoral vegetation and to study the effects of water buffalo (Bubalus bubalis) grazing on the littoral plant communities in order to formulate scientifically-based management recommendations for the restoration of wet grasslands at Lake Mikri Prespa. The research was conducted during 1997-2002 on a surface of 4.5 ha at the west shore of Lake Mikri Prespa, in the core area of Prespa National Park. Depending on the influence of the fluctuating water levels, four vegetation zones were identified in the study area. From the higher to the lower locations, the zones were: a) dry grassland, b) temporarily flooded zone, c) reedbed fringe, and d) reedbed proper. Water buffalo grazing was applied at a mean stocking rate of 1.5 Animal Units per ha per year. Additional treatments, namely summer cutting and winter burning, were applied in combination with water buffalo grazing. In each of the four vegetation zones, measurements of cover, vegetation composition and production in fixed and portable plots were performed. At the two lower zones, additional measurements were held on the cover and composition of vegetation in plots treated by yearly summer cutting and winter burning of the vegetation, as well as on the structural characteristics of the reed at all treatments. Vegetation in the first two zones included grasses, graminoids, legumes and forbs. From these, the vegetation in the reedbed fringe did not include legumes, while in the reedbed proper there were only grasses, graminoids and litter. The nutritional value (total protein, ligno-cellulose, lignin and cell wall content) presented significant differences between the four vegetation zones during spring, summer and autumn for two years (1998-1999). The maximum production by month at the fixed plots was found in May for the dry grassland and in April, May and June at the lower zones, depending on the rate of water level decrease after its maximum late spring values. The maximum seasonal production at the dry grassland was recorded in spring, while at the wetter zones in spring and in summer. The above-ground/ emergent seasonal production at the portable plots was found maximum in spring at the first zone (3899 kgr/ha), in spring and summer at the second (5413 kgr/ha), in summer at the third (8646 kgr/ha) and in summer and autumn at the fourth zone (10580 kgr/ha). Water buffalo grazing caused a substantial reduction in the cover of high emergent helophytes (by 29%) and increase of wet grassland species cover (by 32%), thus creating a wet grassland habitat type on a surface previously dominated by reeds. Additionally, grazing significantly affected reed structure by reducing the densities of fresh and dry stems, their height and diameter (by 69%, 58%, 84% and 26% respectively, compared to the control plots). Grazing was also very effective in maintaining low values for these parameters, thus preventing the re-establishment of reeds on the grazed plots. The effects of summer cutting were similar to those of grazing during three years of systematic performance, but immediately after it was ceased, reeds re-appeared with substantially increased density and height values. Winter burning temporarily favored the cover of wet grassland species and reduced litter compared to the control plots. As a conclusion, water buffalo grazing can be used as a management practice for the restoration and maintenance of wet grasslands at the littoral zone of Lake Mikri Prespa in the framework of a long-term management plan.

Η βόσκηση αγροτικών ζώων στους υγροτόπους είναι μια από τις αποτελεσματικότερες μεθόδους για τη δημιουργία και τη διατήρηση υγρών ποολίβαδων σε επιφάνειες, που υπό καθεστώς μη διαχείρισης, καταλαμβάνονται από πυκνές και συχνά αμιγείς διαπλάσεις υψηλών ελόφυτων. Δεν υπάρχει όμως τεκμηριωμένη γνώση σχετικά με το ρόλο του βούβαλου (Bubalus bubalis), ενός κατ’ εξοχήν ζώου των υγροτόπων. Σκοπός της παρούσας έρευνας ήταν η μελέτη των χαρακτηριστικών της παραλίμνιας βλάστησης και των επιδράσεων της βόσκησης βούβαλων στις παραλίμνιες φυτοκοινότητες με στόχο την επιστημονική τεκμηρίωση διαχειριστικών προτάσεων σχετικών με την αποκατάσταση και διαχείριση υγρών ποολίβαδων. Η έρευνα πραγματοποιήθηκε σε τέσσερις ζώνες βλάστησης στη δυτική όχθη της λίμνης Μικρή Πρέσπα κατά τα έτη 1997-2002 και σε έκταση 45 στρεμμάτων. Στις ζώνες εφαρμόστηκε βόσκηση βούβαλων και εν μέρη θερινή κοπή και χειμερινή καύση. Σε κάθε μία από τις ζώνες έγιναν μετρήσεις κάλυψης, σύνθεσης της βλάστησης, λιβαδικής παραγωγής, θρεπτικής αξίας καθώς και των δοκιμών παραμέτρων του καλαμιού (στις παρυφές του καλαμιώνα και στον αμιγή καλαμιώνα). Βρέθηκε ότι η βόσκηση βούβαλων επηρεάζει σημαντικά τα ποσοτικά και ποιοτικά χαρακτηριστικά της παραλίμνιας βλάστησης εγκαθιστώντας τύπο υγρού ποολίβαδου. Συμπεραίνεται, ότι η βόσκηση βούβαλων μπορεί να χρησιμοποιηθεί ως διαχειριστική πρακτική για την αποκατάσταση και διατήρηση των υγρών ποολίβαδων στη λίμνη Μικρή Πρέσπα στα πλαίσια ενός μακροχρόνιου σχεδίου διαχείρισης της βλάστησης της παραλίμνιας ζώνης.