engleski

Biomass production of the common alder (Alnus glutinosa (L.) Gaertn.) in pure plantations and mixed plantations with the willow clones (Salix sp.) in Croatia

In the two decades, Croatian energy policy was directed towards the increase of renewable energy sources in the total balance. It resulted in an increased interest for breeding fast-growing hardwoods in short rotations. Although common alder is not so productive in short rotations as some willows and poplars, insufficient development of the biomass market and increased awareness for conservation of domestic forest tree species, makes it favorable for raising plantations as it is the indigenous forest tree species which can be grown in longer rotations, if needed. The estimate of above-ground dry biomass per tree (trunk and branches up to 7 cm in diameter) as well as production of biomass per hectare was done on 4 experimental plantations. The research included two mixed plantations of common alder open-pollinated families with willow clones (Salix sp.) and two pure common alder plantations. Experimental plantations at age of 14 and 16 years are located in two different sites. The estimated family mean values for dry biomass varied between 12.5 and 70.9 kg per tree. The results showed considerable differences between families as well as between different silvicultural treatments. The estimated production of the common alder dry biomass varied between 27.4 and 87.5 t/ha with mean annual increments (MAI) between 1.9 and 6.3 t ha -1 year -1. It was shown that willow clones have a negative influence on the alder biomass in mixed plantations, at studied age of plantations. Willow clones have shown greater biomass production, compared with common alder, in spite the fact that planting density is far lower. Although the planting density of common alder trees was lower compared to other studies, the average biomass production is within the frame of other results, which indicates significant potential of biomass production in local conditions. The additive variance was not statistically significant for the biomass trait, which was probably caused by the dominant influence of microenvironmental factors (weed, game) during the growth, but also by a small number of studied families. Statistically significant interactions of investigated families with silvicultural treatments and sites have been shown, which directs to the genetically caused differences in the adaptability of families on studied site and growth differences.

open-pollinated families; genetic test; variation; genotype × environment interactions

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