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COMPARISON OF THE ABOVEGROUND BIOMASS OF BIRCH TREES BETWEEN NATURAL STANDS AND PLANTATIONS WITH LOW INITIAL DENSITY

Linards Sisenis

Abstract

Birch, primarily silver birch, is used in afforestation of marginal agricultural lands. Natural regeneration on fertile soils most of the cases happens with birch, if no specific management is applied. Therefore share of birch is increasing in hemiboreal forests Previously, target species of forest management had been coniferous trees. Thus the information on the growth and revenue from birch plantations is limited. Moreover, there the minimums density is set to 2000 trees ha-1 in regeneration and 800 trees ha-1 in plantations, that are established on former agricultural land (such plantations currently can?t be established on forest land). There is a limited information on low-density birch plantations, therefore aim of our study is to assess the aboveground biomass of birch in stands and plantations with low initial density and its impact to the revenues for the forest owner. Tree height and diameter at breast height was measured in plantation at the age of 40 years, established, using grafted material (clones) of Latvian plus-trees on former agricultural land with spacing 5x5 m (400 trees ha-1). Plantation was compared to the mean of birch stands on similar growing conditions (fertile mineral soils with normal moisture regime), obtained from National forest inventory sample plots. Biomass assessment was made for set of sample trees without stem defects or edge effect, selected from different diameter groups. Mean tree height in low density birch plantation ranging from 22.3 to 27.3 m between clones, but in birch stands at similar age it was 22.7±1.3 m. Thus, the height difference on average is 10% that can be explained primarily by selection effect ? plantation was established with plus tree clones. Mean diameter in plantation was 27.6 cm, in stands ? 21.3±1.7 cm. The differences in this parameter is 30%, arising both form selection effect and spacing. Using the actual survival, yield in plantation was 252±27 m3ha-1, but in forest stands at harvest age 30 years later (71 year) ? 286±48.5 m3ha-1. Low density plantation at the age of 40 years had similar biomass, than mature stands and ensured significantly higher revenues for forest owner.

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DOI resolver: doi.org/10.5593/sgem2019/3.2/s14.085

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