Ice break within a beech forest - Investigations on vegetation dynamics in the strict forest reserve "Ochsenberg"-(Eggegebirge/North Rhine-Westphalia)

On December 1st 1988 an ice break caused severe disturbances in beech forests of eastern Westphalia. Within the strict forest reserve Ochsenberg (Eggegebirge/North Rhine-Westphalia) two permanent plots (fenced and unfenced core areas) were established on an eastern slope covered with beech forest on limestone, to document the natural forest regeneration after the ice break. The tree population (1989, 1999, 2009), the tree regeneration (1989, 1993, 1997, 2011), and the understorey vegetation (1989, 1993, 1994, 2011) were repeatedly recorded. A comparison of earlier and current data showed an establishment of Urtica dioica and Rubus idaeus in the first years after the ice break. These species benefitted from improved light and nutrient conditions. Species typical for closed forests were nearly unaffected by the disturbance. They persisted under remaining old beech trees, within dead wood structures, and beneath establishing natural regeneration. 20 years after the ice break the tree layer has regenerated. The differences in vegetation composition depending on slope position (upper, middle and lower slope) and fencing variants (fenced and unfenced) that were detected in former investigations decreased. Especially the reduced light availability led to a decline in light-demanding disturbance indicators and in the coverage of the herb layer in general. Only the spring geophytes A Ilium ursinum and Cardamine bulbifera were recorded with constant cover values, They benefitted from a darker and moister microclimate within the regenerated forest. Pioneer tree species established rarely after disturbance, as beech dominated the natural regeneration at all times. This beech regeneration consisted of re-sprouting of overthrown beeches, but especially of seedlings from nuts produced by remaining old beech trees, which offered shelter for the developing seedlings as well. Due to the low light availability, a current regeneration of shade-tolerant beech was not observed. The present analysis documents the great regeneration ability of beech forests on limestone after large-scale disturbance. Due to the windward position and the high precipitation in the Eggegebirge, the local forests are susceptible to ice and snow break. Further disturbance within the strict forest reserve Ochsenberg is likely. Thus, we recommend a regular record of forest and vegetation data within the core area and the additional establishment of permanent plots across the whole forest reserve to be able to document future disturbance and different successional communities. In combination with data from other strict forest reserves the results can be useful in analyzing natural regeneration processes after large-scale disturbance. Furthermore conclusions for a close-to-nature forestry can be drawn.