ROOT DENSITY AND ROOT BIOMASS IN PURE AND MIXED FOREST STANDS OF DONGLAS-FIR AND BEECH

Belowground interactions possibly play an important role in the succes s of mixed forests. Therefore. root density, root length: root biomass and rooting pattern were surveyed in pure and mixed forest stands of Douglas-fir and Beech. Each type of stand was represented by ones appr oximately 40- and 70-year-old. The study was restricted to fine roots (< 2 mm). The highest root length, 184 x 10(6) m ha(-1), was found in a 64-year-old pure Beech stand. The smallest root length was 67 x 10(6 ) m ha(-1) found in a 60-year-old pure Douglas-fir stand. In the mixed stands, the soil layers at 0.15-0.30 m and 0.30-0.45 m were more inte nsively rooted than in the pure stands. In the mixed stands, Beech was strongly suppressed by Douglas-fir, although Beech managed to develop an equal or even larger root length than Douglas-fir. In the mixed st ands the specific root lengths of the fine roots of Douglas-fir and Be ech were higher than in the pure stands, which may indicate below-grou nd competition. In the mixed stands the below-ground competition betwe en the different species leads to a different use of soil resources by fine roots. Furthermore, there are indications that in the mixed stan ds, as a reaction to the strong above-ground domination of Douglas-fir , Beech develops a rooting strategy which ensures the possibility of a bove-ground expansion when the growth of Douglas-fir declines.