Effect of stand edge on the natural regeneration of spruce, beech and Douglas-fir

DOBROVOLNÝ, L. , STĚRBA, T. , KODES, J.: Eff ect of stand edge on the natural regeneration of spruce, beech and Douglas-fi r. Acta univ. agric. et silvic. Mendel. Brun. , 2012, LX, No. 6, pp. 49–56 Our work aimed at studying the strategy of woody plants regeneration during the regeneration of a spruce stand with the admixture of beech and Douglas-fi r by border cutting (NW-SE aspect) on acidic sites of higher elevations in the Bohemian-Moravian Upland. Spruce is better adapted to bear shade than Douglas-fi r. Nevertheless, in optimal light conditions up to a distance of ca. 35 m (about 16% DIFFSF) from the stand edge, the Douglas-fi r can put the spruce into danger as to height growth. By contrast to beech, the density of spruce is signifi cantly higher within the distance of 45 m (about 15% DIFFSF) from the stand edge but further on the situation would change to the benefi t of beech. The density of Douglas-fi r signifi cantly dominates over beech within a distance of 35 m from the stand edge; from 55 m (less than 15% DIFFSF), the situation changes in favour of beech. Beech can survive in full shade deep in the stand core waiting for its opportunity to come. As compared to spruce and Douglas-fi r, the height growth of beech was at all times signifi cantly greater at a distance of 25 m from the stand edge. Converted to practical conditions, spruce and Douglas-fi r with individually admixed beech seedlings showed good prosperity approximately up to a distance of one stand height from the edge. A mixture of spruce and beech did well at a greater distance but good prosperity at a distance of 2–3 stand heights was shown only by beech. Thus, border regeneration eliminates disadvantages of the climatic extremes of clear-cutting and specifi cs of shelterwood felling during which one – usually shade-tolerant tree species dominates in the natural regeneration (e.g. beech). edge eff ect, natural regeneration, spruce, beech, Douglas-fi r General mission of sustainable forestry is to achieve mixed stands with the site-corresponding composition of woody species, optimally developed through natural regeneration. However, the purposeful control of the regeneration of existing parent stands is diffi cult without the knowledge of the regeneration and growth strategy of individual species in the target mixture. Our work aimed at studying the strategy of woody plants regeneration during the border regeneration of a spruce stand with the admixture of beech and Douglas-fi r by border cutting. Key data for our study were those on light requirements and competitive relations among naturally regenerated target species, i.e. spruce, beech and Douglas-fi r. A method of regenerating spruce stands with the admixture of other tree species on natural fi r-beech sites increasingly used in the Czech forest practice is border regeneration. The specifi c variegated mosaic of ecological conditions on the outer (clearcut or shelterwood strip sized 0.5–1.0 of the height of the exploited stand) and inner (shelter up to 1.0– 1.5 of the height of the exploited stand) stand edges is favourable for many woody plants with diff erent light requirements to strike roots (Korpeľ, 1995). On the outer, optimally northern edge, Poleno and Vacek (2009) distinguish 3 zones of light conditions: a) along the stand wall where the shade duration and intensity are considerably long – suitable for shade-bearing woody plants; b) middle zone – root 50 L. Dobrovolný, T. Stěrba, J. Kodes competition and shade diminish – suitable for halfshade bearing woody plants; c) the zone that is most remote from the stand wall, whose ecological conditions partly near a clear-cut area – suitable for sun-tolerant woody plants. In terms of light requirements, spruce belongs in the category of shade-tolerant tree species, i.e. it is a half-shade bearing woody plant. This characteristic ranks the spruce with the climax species, i.e. species occurring at the end of the forest development stage (Poleno and Vacek, 2007). Beech is a shade-bearing climax woody plant (Mracek, 1989). Douglasfi r is characterized as a light-demanding species, which is tolerant to lateral shade only at young age (Uradnicek and Chmelař, 1995). Beech can survive up to several years at extremely low radiation values 3–5%; however, its growth would be very slow and the growth response to release very instant (e.g. Collet et al., 2001; Wagner et al., 2010). Assessing the competitive relations of beech and spruce regeneration in relation to light and/or other stand characteristics, a majority of works arrive at a similar value of relative radiation (ca. 15%) or basal area (ca. 30–35 m2) as a certain threshold of the two species. Below this limit, beech would maintain its advantage and above this limit, the height growth of spruce would begin to catch up with the beech. Above 20%, beech would loose the advantage and would be surmounted by spruce as to height growth (e.g. Leder and Wagner, 1996; Unkrig, 1997; Kuhne and Bartsch, 2003; Stancioiu and O’Hara, 2006). According to Saniga (1990), the degree of shelter at ≤ 62.5% (in beech stands) creates lower prerequisites for the growth competitiveness of spruce if admixed in clumps. With the basal area reduced to about 60% of the fully stocked stand, the spruce regeneration would start to overtake the beech (Leder et al., 2003). Busina (2006) claims that a decisive condition for Douglas-fi r germinate and further grow is light accessing the stand from above or from belowside. Insuffi cient or excessive light is considered an unfavourable condition. Regeneration of Douglasfi r on stand edges is therefore more certain and more abundant than regeneration under the stand; this is why various methods of border and strip felling and/or group felling are recommended. According to Kinský and Sika (1987), Douglas-fi r regenerates only with diffi culties under closed canopy; selfseeded plants soon die due to shade and root competition. Similarly, Malinova (2003) points out a conclusive infl uence of light in the development of natural regeneration. If the shelter stand density is high, the Douglas-fi r either would not strike roots at all or would disappear within a short time. According to Blascak (2003), the Douglas-fi r is more lightintensive at regeneration than the spruce. By contrast, Busina (2006) observed that the self-seeded spruce has higher light requirements in the fi rst years than the Douglas-fi r and can do better against weed competition, too.