Rastne in vegetacijske značilnosti evropskega črnega topola (Populus nigra L.) v poplavnem gozdu ob reki Savi in temperaturne razlike med izbranimi rastišči / Growth and vegetation characteristics of European Black Poplar (Populus nigra L.) in a …

Abstract

V raziskavi smo preučevali rastne, vegetacijske in temperaturne značilnosti avtohtonega črnega topola (Populus nigra L.) v izbranih sestojih na rastiščih ob reki Savi, kjer smo na rečnem otoku in v poplavnem logu pri Ljubljani izbrali odraslo in mlado razvojno fazo gozdnih sestojev na naravnih rastiščih črnega topola, vključujoč travnik. Ugotavljamo, da imajo črni topoli na rečnem otoku manjše premere in višine kot na rečni terasi ter da je na rečnem otoku variabilnost v višini in prsnem premeru dreves bistveno večja kot na rečni terasi. Osutost krošenj dreves je večja na rečni terasi, kjer je sestoj v razvojni fazi debeljaka, kot na rečnem otoku, kjer je sestoj v razvojni fazi drogovnjaka. Na preučevanem območju lahko opazimo zonacijo vegetacije, ki je značilna za zgornje in delno srednje tokove rek in se bistveno razlikuje od spodnjih tokov. Sestoje neposredno ob reki Savi uvrščamo v asociacijo Salicetum incano-purpuraea, ki jo uvrščamo v zvezo Salicion eleagno-daphnoidis, red Salicetalia purpureae in razred Salicetea purpureae. Sestoje na rečni terasi pa uvrščamo v asociacijo Lamio orvalae-Alnetum incanae ter višje v sintaksonomiji v zvezo Alnion incanae, red Fraxinetalia in razred Populetea albae. Na podlagi naših raziskav ugotavljamo, da so obravnavani gozdovi dobro ohranjeni in se vanje v zadnjem obdobju ni bistveno posegalo. Raziskave temperaturnih razmer kažejo, da se izmerjene temperature in kazalniki temperaturnega stresa v poplavnih gozdovih precej razlikujejo glede na mesto meritve (rečna terasa oziroma otok) ter glede na tip vegetacije (poplavni gozd oziroma travnik). Med posameznimi ploskvami smo ugotovili razlike v temperaturnih razmerah, kljub temu da ležijo v neposredni bližini na isti rečni terasi. Ugotavljamo tudi, da temperaturne razmere na Klimatološki postaji Ljubljana, ki je najbližja obravnavanim poplavnim gozdovom, ne odsevajo temperaturnih razmer za poplavne gozdove ob reki Savi. Glede na to, da se črni topol pomlajuje le neposredno ob reki, v starejših sestojih pa ne, bi veljalo v obravnavnih poplavnih gozdovih preiti k aktivnemu varovanju posameznih odraslih dreves, ki so poleg poplavnega rečnega režima pomembna za uspešno naravno obnovo črnega topola.

Ključne besede: Populus nigra L., poplavni gozd, rastiščne razmere, temperatura, rast, osutost krošnje, reka Sava, Slovenija

In this study we investigate the growth, vegetation and temperature characteristics of the native black poplar (Populus nigra L.) stands on the selected sites along the Sava River in Ljubljana vicinity. Mature and young regeneration stage of cottonwood forest stands were selected along the river Sava on the island and on the floodplain terrace in natural habitats of black poplar, including a meadow. Stands closer to the river Sava banks belong to the association Salicetum incano-purpuraea, which is affiliated to the alliance Salicion eleagno-daphnoidis, order Salicetalia purpureae and class Salicetea purpureae. Stands on the river terrace belong to the association Lamio orvalae-Alnetum incanae, alliance Alnion incanae, order Fraxinetalia and class Populetea albae. Based on our results, the selected forest stands are well preserved and have lately not been significantly exposed to negative human impact. Black poplar trees on the river island differ from the trees growing on river terraces in their horizontal stand structure. The tree height and diameter variability was significantly greater for black poplar trees on the river island compared to the river terrace. Furthermore, crown defoliation of trees is higher on the river terrace with the mature forest stand compared to the river island with younger stand. The measured temperature indicators and temperature stress in the flooded forests vary considerably, depending on the location of measurement (river terrace or river island) and on the type of vegetation (floodplain forest or meadow). We found differences in temperature conditions between the research plots, although they are located in the immediate vicinity and on the same river terrace. We also noted that the temperature conditions at the Ljubljana Climatological Station, which is the closest to the considered flood forests, do not reflect the temperature conditions of floodplain forests along the river Sava. Given that the black poplar naturally regenerates only directly on the river banks but not in older floodplain forest stands we would recommend active protection of individual adult trees that are, apart from the river flood regime, important for the black poplar’s successful natural regeneration.

Key words: Populus nigra L, floodplain forest, forest site conditions, temperature, growth, crown defoliation, river Sava, Slovenia