Four decades of forest succession in the oak-dominated forest reserves in Slovakia

Abstract

Abstract: The study analyzes biodiversity, production and recovery processes in the natural oak-dominated forests in three protected areas in time span of four decades after the cessation of human impact. In each forest reserve, we established three permanent research plots of 0.5 ha, which were monitored regularly every 10 years. The obtained results confirmed an expected decrease of oak in all investigated areas, regardless of the level of past human intervention. Growth rates of oak stem density were negative in all reserves and ranged from -0.7% yr-1 (Kasivarova) to -2.1% yr-1 (Bujanov). A typical rotated-sigmoid diameter structure was confirmed during the whole observed period only in the reserve Boky. The moderate affected reserve (Kasivarova) showed a bimodal pattern and the most affected reserve (Bujanov) revealed the typical unimodal distribution. Considering spatial diversity, the recorded structure of investigated forests closely corresponds with the relative level of past intervention. In Boky, the most differentiated structure was reflected in the highest long-term mean stem density (890 ± 151 ha-1) and the lowest basal area and growing stock (36.5 ± 1.4 m2 ha-1 and 284 ± 22 m3 ha-1, respectively). The past-affected reserves reached higher values of basic stand parameters. In Kasivarova and Bujanov, the average basal area (36.5 and 44 m2 ha-1, respectively) and growing stock (284 and 518 m3 ha-1, respectively) correlated negatively with the level of structural heterogeneity, while the stem number revealed a positive correlation. We observed a continuous increase of deadwood volume and dead to live wood ratio. The recorded long-term volume of deadwood (43-128 m3 ha-1) and deadwood proportion (151-28%) tended to be higher in the past-affected reserves. The convergence towards the rotated-sigmoid distribution in both reserves with past human impact was recorded. Considering the vertical structure, the most dynamic changes were observed in the lower and middle layer. Moreover, the substitution of the light-demanding oak by shade-tolerant species (beech, hornbeam) was recorded. The intensity of substitution directly reflected the intensity of structure modification in the past. Our results suggest that the process of forest recovery and oak loss significantly depends on the level of past human intervention.