Comparison of growth, structure and production in stands of naturally regenerated Betula pendula and Populus tremula

In Central Europe, the most important pioneer species are silver birch and European aspen. Changes in disturbance regime and an economic interest for this species have led to studies on this species and stands. Two naturally regenerated dense stands of birch (Betula pendula Roth - silver birch monoculture) and aspen (Populus tremula L. - European aspen monoculture) were selected from a Querceto - Fagetum mesotrophicum site to observe responses under the same conditions in Central Europe. Both stands regenerated after the allochthonous Norway spruce stands dieback at the site in 1999. Within a 10 m × 25 m transect established in both stands, the diameter at breast height (DBH) of all the trees was measured between 2015 and 2020. In addition, the height and position were recorded for all trees, and sample trees of both species were felled for biomass measurement. A higher volume production of aspen at the beginning (107.48/96.80 m3) and at the end of the experiment (178.32/143.08 m3) was accompanied with a lower above-ground wood biomass (WAB). The WAB of birch increased from 81.9 t.ha-1 to 103.3 t.ha-1 and aspen allocated 79.5 t.ha-1 to 94.8 t.ha-1 of biomass. The current annual increment of biomass for these stands was 4.3 t.ha-1 and 3.1 t.ha-1 in the age range of 17 to 22 years. The culmination of the volume increment has not yet occurred in any of the stands, but the mean annual increment of wood biomass has already been reached for both stands. Furthermore, the aspen stand tended to be more dynamic in terms of biomass allocation and mortality. Also, the lower self-tolerance of aspen confirmed our hypothesis: the two native pioneer species differ in their social behaviour within monospecific stands.