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Tree species composition 

Featuring:Matti Maajärvi, UPM

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Tree species composition 

sustainable forestry

Native tree species grow well and maintain biodiversity.

Native tree species are the basis for forest ecosystems. Due to their adaptation to climate and light conditions in their distribution area over the past millenia, native tree species are well-growing and resistant to forest damages. Other forest species have adapted to live with native tree species. That’s why they are significant for biodiversity.

Domestic main tree species for Finland include Norway spruce (Picea abies), Scotch pine (Pinus sylvestris) and two birch species, Silver birch (Betula pendula) and Downy birch (Betula pubescens). These are most important tree species commercially as well. 50 % share of the total volume of Finnish forests is pine, 30 % spruce and 17 % birch. Proportion of other tree species is fairly marginal 3 %. This figure consists of other broadleaved trees such as Aspen (Populus tremula), Grey and Black alder (Alnus incana and Alnus glutinosa), Rowan (Sorbus aucuparia) and Goat willow (Salix caprea). In the southernmost parts of Finland, in hemiboreal forest vegetation zone also hardwood tree species like Oak (Quercus robur) and Maple (Acer platanoides) exists. In other parts of the country hardwood species occur as single trees or small tree groups.

In forestry main tree species is selected based on fertility and water conditions of the forest soil. Dry heath forests and peatlands low in nutrients are usually pine-dominated. Spruce is dominant in more fertile mineral soils and nutrient-rich mires. Deciduous forests are present in fertile sites and at waterfronts. Selecting the right tree species according to site properties is crucial for wood production capacity of the forest.

Even though main tree species is selected according to site, forests are grown as mixed stands. Compared to single species monoculture, mixed tree species composition comes with several advantages: positive effect on forest soil nutrient balance and productivity, better resistance to forest damages, increased adaptation ability to changing conditions and higher biodiversity values. These advantages are targeted in conifer-dominated stands by having at least 10 % share of broadleaved trees throughout the forest rotation cycle.

Birch is most common broadleaved tree species in mixed conifer stands. Besides birch, other more infrequent broadleaves are saved for biodiversity in forestry operations. These tree species support other species specialized to live in connection with them. Infrequent species are therefore good choices for retention trees too.

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