Seedling growth characteristics in three birches originating from different environments

The mountain birch (Betula pubescens ssp. czerepanovii) is considered to ha ve originated through introgressive hybridization between B. pubescens and B. nana. It is intermediate between the putative parent species in terms of growth Form and distribution. Consequently, we hypothesized that the mount ain birch should have growth characteristics intermediate between the other two birch forms. This hypothesis was tested in an experiment using first-y ear seedlings. Only in three out of 15 characteristics studied were mountai n birch characteristics clearly intermediate between B. pubescens and B. na na. In some casts the mountain birch was most similar to B. pubescens, whil e in others it resembled B. nana most closely. In certain other respects, B . pubescens and B. nana were more similar to each other than to mountain bi rch. In three measures of plant productivity, i.e., relative growth rate, l eaf area productivity, and plant nitrogen productivity, mountain birch show ed the highest values. Cluster analyses of thirteen growth-related characte ristics indicate that at a low fertilizer supply, B. pubescens and B. nana are more similar to each other than to the mountain birch. At a high fertil izer supply, mountain birch was more similar to B. pubescens. The results i ndicate that the growth characteristics of mountain birch seedlings are not inherited from its two "parent" species in any simple way.