Growth, biomass and stem volume models for downy birch in Iceland

Downy birch (Betula pubescens Ehrh) is the only native tree species forming woodland in Iceland and covers around 1.5% of the land area. Historically, birch woodlands have been an important source of fuel, building material and animal fodder. Currently, birch wood production is not economically important, but the species provides other valuable ecosystem services, such as soil conservation and carbon sequestration. Planting of birch increased in the 1990´s, and from 2000 onwards the share of birch has been around 30% of the total annual tree planting. Growth models are essential tools for simulating forest development over time and are widely used in forest management, research, and policymaking. This study presents site index, individual-tree diameter (dbh 1.3 m) increment, and tree height models for even-aged stands of cultivated downy birch in Iceland. The data were collected from the Icelandic National Forest Inventory (NFI) plots measured between 2005 and 2024. In addition, models for aboveground biomass and stem volume were developed using dbh as a predictor. The models can be used in forestry practice and the management optimization of downy birch stands.