Biomass in Strawberry Tree Coppice Forests (Arbutus unedo L.) on Island Brač

U radu su prikazani rezultati izmjera zelene drvne i lisne mase iznad površine tla u panjačama planike (Arbutus unedo L.). Važan dio ovih istraživanja obuhvaća i prikaz modela za brzu i pouzdanu procjenu biomase u ovim šumskim ekosustavima. Opće linearno modeliranje korišteno je za razvoj modela. Istraživanja su obavljena i uzorci prikupljeni na trajnim eksperimentalnim plohama na otoku Braču, na podplohama 19 i 20. Biomasa drva i lišća odvojeno je mjerena kao težina i volumen. Nezavisni procjenitelji u panjačama planike bili su promjer izbojka na visini od 50 i 130 cm iznad površine tla, visina izbojka i promjer krošnje izbojka. Težina drva i lista mjereni su u kg, vo lu men u m3, promjer izbojka u cm, visina izbojka i promjer krošnje u metrima. Volumen drva u istraživanim panjačama, na površini od 25 m2 varira od 0,276 do 0,405 m3, a volumen lista od 0,044 do 0,0661 m3. Volumen ovisi o degradacijskom stadiju panjače, odnosno dimenzijama pojedinih jedinki koji ih sači nja vaju, njihovom broju po jedinici površine, sklopu i načinu grupira nja po površini te bonitetu staništa. Rezultati istraživanja pokazali su kako je drvna i lisna masa u panjačama planike u jakoj, vrlo jakoj i izuzetno jakoj linearnoj ovisnosti o promjeru izbojka, visini izbojka i promjeru krošnje izbojka. Koeficijenti korelacije kreću se od 0,599 do 0,961. Najveći koeficijent ko relacije ima odnos težine drva i promjera izbojka na visini od 50 cm iznad povr šine tla (r = 0,961). Univarijantnom regresijskom analizom biomasu iz nad površine tla, u panjačama planike, najbolje možemo procijeniti na osnovi pro mje ra izbojka, iako objašnjenju ovog regresijskog modela značajno pridonose i ostale nezavisne varijable. Promjer izbojka planike na visini od 50 cm iznad površine tla objašnjava 92,3 % varijabilnosti težine drva, a 72,6 % težine lista. Multivarijantni regresijski modeli ne daju znatno bolje rezultate od univarijantnih, posebno kod promjera izbojka kao najboljeg nezavisnog procjenitelja, gdje su vrijednosti izjednačene.The authors have collected and partly published the data about biomass for some important species on the Mediterranean karst area of Croatia during their research on projects. In this paper the data for strawberry tree (Arbutus unedo L.), whith together wit holm oak (Quercus ilex L.), laurestine (Viburnum tinus L.), crack phyllirea (Phillyrea latifolia L.), white heath (Erica arborea L.) and other maquis elements are published, which are found in Mediterranean littoral vegetation area of forest vegetation of holm oak (Quercion ilicis). This vegetation is spread from Istra to the Albanian border, especially on the middle and south Dalmatian islands: Brač, Korčula, Mljet, Lokrum and others. The vegetation develops in the form of closed maquis, rarely small forest (coppice). It grows till 10 m high and has a strong sprout strenght. It is completely adapted to ecologic situation of Adriatic forest, to draught, salt and cold, if it does not last long. Its fruit is edible and is used for making jam, spirit or liquer. It is also important as decorative plant in horticulture. It is especially nice in autumn, when the flowers and fruit are on the same branch. Research on strawberry coppice trees are done on experimental plots in Gornji Humac on the northeast part of the island Brač, dominated by un mi x ed and mixed evergreen oak forests. The plots have an area of 1 ha, the subplots 19 and 20, 25 m2 (table 1). The canopy on subplots amounts to 84,79 % (subplots 19), to 98,41 % (subplots 20), the medium height of sprout of strawberry tree is 3,60, that is 4,01 m (maximum 4,50 m). Biomass of wood and foliage on experimental plots was measured separately for every sprout as weight and volume, the independable estimatiors were the diameter od sprout on the height of 50 and 130 cm above ground, height of sprout and diameter of crown of the sprout. The weight of wood and leaves were measured in kg, volume in m3, diameter of sprout in cm, height of sprout and diameter of crown in m. Wood volume in coppice forests, on the area of 25 m2, varies from 0,276 to 0,405 m3, the leaf volume from 0,044 to 0,066 m3. The volume depends on the degradation stadium of coppice, that is on the dimension of species they consist of, their number on the unit of area, the way of grouping and the stand. The important part of the research is the model for quick and reliable estimation of biomass is forest ecosystems. General linear modelling is used for the development of the model. The research results showed that the wood and foliage volume in strawberry tree coppice is in strong, very strong and extremely strong linear dependance on the diameter of sprout, height of sprout and crown diameter of sprout. The correlation coefficients are between 0,599 and 0,961. The greatest correlation ceofficient has the relation of wood weight and sprout diameter at 50 cm height above ground level (r = 0,961). By univariate regression analyisis biomass above soil level in coppice strawberry trees can at best be estimated on the basis of sprout diameter, although the other independable variables also explain this regression model (table 4, figure 1). Diameter of sprout at 50 cm above ground explains 92,3 % of variability of wood weight, 72,6 % of leaf weight, while the crown diameter of the sprout explain 76,7 % of variability of wood weight and 75,9 % of weight and leaf volume. Multivariate regression models do not give much better results than univariate, especially at sprout diameter, as the best independable estimator, where values are equal. The diameter of sprout, its height and crown diameter of the sprout explain 87,9 % of variability of wood weight, 76,9 % of weight and leaf volume. Diameter of the sprout explains best this regression model for weight and wood volume, by weight and leaf volume of the crown diameter (table 5). All models can be used for quick and reliable estimation of biomass of each unit (wood and leaf) in strawberry tree coppice, especially with variable of sprout diameter