Metla Project 3279

Effect of structural complexity on growth and yield of forest stands

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Duration: 2000-2007   Keywords: advance growth, growth, models, retention, stand edge, stand structure, tree groups, uneven-aged stands, yield
Research Programme: Alternatives of silvicultural practices in forest management and their effects on forest production

Objectives

The purpose of the project is to acquire quantitative information and readily applicable knowledge and on the effect of structural complexity on growth and yield of forest stands, and the profitability of forest management. Empirical models will be constructed and incorporated in a decision support tool and utilized in the development of the MELA stand projection and optimization system. The objects of modelling activities will include · growth of released advance growth trees, resulting stand structure, and yield potential compared with plantation stands · effect of solitary and group retention of trees on the development of the next generation and its yield potential · yield, quality and economic potential in a birch or aspen overstory in a young spruce stand · early development of conifers subject to substantial competition from broadleave admixtures · height growth of sprouts subject to height and density variation of the crop tree stand · regeneration, mortality and growth and resulting stand dynamics in spruce stands managed with single tree selection, stands, and in stands with irregular structures and structural retention in terms of age-class management systems

Results

 The effect of retained Scots pine trees on height, diameter growth, and branching of individual Scots pine seedlings and seedling stands in Southern Finland was studied. Results indicated that Scots pine trees retained in Scots pine seedling stands had not brought about poorly stocked patches around their bases in the study stands. Each retained tree of 25–40 cm in diameter reduces the height growth potential of Scots pine seedlings about 9–17% within a circle of 10 m radius. Retained tree competition did not result in reduced tree diameter for a given height. Retained tree influence on the sum of branch cross-sectional area was substantial, especially on fertile sites. In stand level simulations, the retention of 48 ha-1 trees of 25 cm average diameter and 21 m height on a rather poor site resulted in about 5–7% decrease in seedling height, 6–8% decrease in diameter, and 2–5% decrease in maximum branch diameter compared to no retention. The effect of the spatial pattern of retention in random, regular, or clustered structures on seedling growth was marginal.  The adverse effects of retained birch and aspen trees on the development of pine saplings are somewhat smaller than those of retained pines of equal size. Retained aspen induce prolific sprouting up to about 10 m distance, which tends to cause problems (Valkonen, Miettinen & Ruuska 2003 (in press)).  The effects of a birch admixture on the height and diameter growth and maximum branch diameter in planted Scots pine stands was studied on average sites on mineral soils in southern Finland. Results indicated that the pines were capable of keeping up in height growth with birches that had originated from seed. Even a very high number of birches (10000 stems ha-1) had virtually no effect on the height growth of the pines. The number of birches had a pronounced effect on the diameter growth and the maximum branch diameter in pine. Retention of a temporary birch component in young pine stands seems a feasible way of mitigating the adverse effects of low planting densities on the external quality of pine (Valkonen & Ruuska 2003).  The influence of edge stands on the development of young pine stands was examined. Models were constructed in a data set from temporary plots, and typical cases were simulated. Results indicated that a mature pine-dominated edge stands has a substantial effect on the growth of the sapling stand. At a distance of 3 m from the edge, mean height of the saplings was only 42 % of the mean height (7.2 m) without the edge effect. Dividing a single 2-hectare regeneration block into 4 units of 0.5 ha each increased the proportion of area subject to a significant edge influence from 41 % to 72 %.

Project leader: Valkonen, Sauli
The Finnish Forest Research Institute, Vantaa Unit, PL 18, FI-01301 VANTAA, FINLAND
Phone: +358 29 532 5507
E-mail: sauli.valkonen@metla.fi

Other researchers: Eerikäinen, Kalle, JO (2004-07), Hökkä, Hannu, RO (2003), Kukko-oja, Kari, MU (2004-05), Niemistö, Pentti, PA (2003-05), Piri, Tuula, VA (2007), Päätalo, Marja-Leena, MU (2003-06), Saksa, Timo, SU (2003-05), Siipilehto, Jouni, VA (2003,2005-06), Siren, Matti, VA (2003,2006-07), Tolvanen, Anne, MU (2005), Varmola, Martti, RO (2007)


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Updated 12.06.2012
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