Náttúrufræðingurinn

Volume

Náttúrufræðingurinn - 1992, Page 30

Náttúrufræðingurinn - 1992, Page 30
Whittaker, R.H. 1975. Communities and ecosystems. Macmillan Publishing Co., Inc., New York. 385 bls. SUMMARY Effect of willow (Salix) on the establishment of birch (Betula pubescens) from seeds by Sigurður H. Magnússon and Borgþór Magnússon Agricultural Research Institute Keldnaholt 112 REYKJA VÍK Iceland In recent years experiments to introduce birch (Betula pubescens) by seeding into areas under reclamation have been carried out in Southern Iceland. Most of these ar- eas, which have lost their former top-soil and vegetation, are sparsely vegetated witli self-established willow species (Salix callicarpaea, S. lanata, S. phylicifolia and S. herbacea) and other early colonizers of barren areas. In one of these experiments it was noted that birch seedlings growing in the immediate vicinity of willow plants were considerably larger in size and of healthier appearance than seedlings of the same age distanced further away from the willow. In order to investigate this rela- tionship in a greater detail a special study was carricd out at one experimental site where willow plants are relatively abun- dant. Contparisons were made of the size of birch seedlings in relation to their distance front the nearest willow plant. The experi- mental plots had received the following treatments: a) seeding in fall, b) seeding in spring, c) seeding in fall, fertilized the following spring, d) seeding in spring, coated seeds. Measurements of seedlings which germinated during the suntmers of 1989 and 1990 were made in the autumn of 1990. A similar pattern of size distribution of birch seedlings was found for all treat- ments (Fig. 3 and 4). The seedlings within 70 cm of willow plants were larger than those distanced further away from them. This growth pattern was already establish- ed at the end of one growing season when seedlings near the willow had on the aver- age more than 1.7 times wider crown than seedlings further away. After two growing seasons the birch seedlings close to the willow plants had at least two times wider crown than seedlings growing further away from the willow. The enhanced growth of birch seedlings near the willow plants can amongst other things be related to shelter, improved nu- trient status of the soil and development of mycorrhiza. In the paper it is argued, however, that mycorrhizal infection was the main reason for the improved growth of birch seedlings near the willow. At the study site fruitbodies of the i'ungal species Laccaria laccata were very common around willow plants in the area of en- hanced birch growth. Fruitbodies of In- ocybe, Galerina, Hebelonui, Cortinarius and Psilocyhe were also found near the willow. Examination of the roots of the willow plants and the birch seedlings next to them revealed that they were all infect- ed with mycorrhiza. This relationship between willow plants and birch seedlings does not appear to have been previously described. The rela- tionship may be of considerable intpor- tance in the colonization and establish- ment of birch in riew areas and in plant succession, in particular in areas of low soil fertility. Further studies are needed on this relationship, especially on the role played by ntycorrhiza. 108

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