Prilog fitocenološkim istraživanjima šuma crne johe (Alnus glutinosa Geartn) u Podravini

Crna joha (Alnus glutinosa) raste u okolici Đurđevca u Podravini u čistim i mješovitim sastojinama na približno 2000 ha i važna je gospodarska vrsta drveća. Podravske sastojine nadaleko su poznate po bujnom uzrastu, visokovrijednom drvu, a s fitocenološkoga stajališta po prirodnom, raznovrsnom i bogatom sastavu. U svojoj disertaciji Glavač (1960) je detaljno istražio i opisao dvije asocijacije u kojima prevladava crna joha: na staništima koja su poplavljena stajaćom vodom utvrđena je fitocenoza crne johe s dugoklasim šašem (Carici elongatae-Alnetum glutinosae), a na nju se sukcesivno nadovezuje mnogo suša zajednica crne johe i poljskoga jasena sa sremzom (Pruno-Fraxinetum). Obje su asocijacije bile prije toga istražene i opisane u Europi. Glavač je fitocenoze prikazao u sintetskim tablicama s 28 snimaka, utvrdio je njihov florni sastav, sistematsku pripadnost, sindinamiku, raščlanjenost i ostale značajke. Od Glavačevih istraživanja u proteklih pedesetak godina izgrađene su hidrocentrale na rijeci Dravi, promijenjeni ostali ekološki uvjeti i obnovljena većina crnojohovih šuma. To nas je ponukalo da recentnim fitocenološkim istraživanjima pokušamo utvrditi posljedice promjena na građu, dinamiku i strukturu sastojina u dvjema spomenutim asocijacijama. Na temelju 26 fitocenoloških snimaka i ostalih relevantnih podataka općenito smo utvrdili promjene u flornom sastavu u smjeru nestajanja hidrofita i higrofita i proširenju vrsta suših staništa, sukladno tomu znatnu promjenu odnosa površina istraživanih zajednica, njihova sindinamskoga razvoja i raščlanjenosti. U članku se govori i o problematici i potrebama detaljne fitocenološke razrade ostalih crnojohovih šuma u Hrvatskoj koje su istraživane relativno ekstenzivno i opisane u četiri asocijacije. U tom smislu obrazlaže se potreba šire analize i nastavka istraživanja.
Forests of common alder in Croatia cover approximately 8000 ha (Prpić and Milković 2005). The most valuable stands are found in the management unit Đurđevačke nizinske šume in Podravina. In this area common alder forms pure or mixed stand extending over about 2000 ha. The stands manifest distinctly regular growth of good quality. From a phytocoenological aspect they are characterized by a natural, diverse and rich composition. The two associations dominated by common alder were studied and described in detail by M. Glavač in his dissertation of 1960. These associations include the phytocoenosis of common alder and elongated sedge (Carici elongatae-Alnetum glutinosae) growing in floodplain sites with stagnant water and micro-depressions, and a much drier community of common alder and narrow-leaved ash with birdcherry (Pruno-Fraxinetum) continuing onto the former community. There have been many changes in the past fifty years elapsing since the research by Glavač, including the construction of hydropower stations on the river Drava, drastic ecological transformations and regeneration of the majority of common alder forests. We have undertaken phytocoenological research in order to assess the consequences of the changes on the structure, dynamics and composition of these two associations. The planned field research was carried out in the vegetation period of 2006 using the standard method of the Braun-Blanquet school. In doing so, we were able to analyze and compare the findings, since former research was also conducted using the same method. Stands with a stable floral composition aged 50 and over were used for relevés. The relevés were sized 20 × 20 m on average. A total of 28 relevés were made: 7 in the forest of common alder with elongated sedge and the rest in the association Pruno-Fraxinetum. Mosses were not considered. The forest of common alder with elongated sedge (Carici elongatae-Alnetum glutinosae W. Koch 1926) in Podravina grows on peat and base-rich, humu