Naturalness of Quercus robur stands in Latvia, estimated by structure, species, and processes

Abstract

In seven Quercus robur stands in Latvia, the past history of stand development was determined by size and age structure of trees, dead wood amounts, cut stumps, and by forest inventory records and maps. All the stands met the criteria of Woodland Key Habitats. Quercus robur was the main canopy species in all stands. Since the time of the recruitment of canopy trees, there has been minimal release of the Q. robur in the > 1-m height class, at least among those that have survived until today. One stand lacked evidence of natural successional processes, while the others were naturally regenerating with Picea abies or deciduous tree species, such as Fraxinus excelsior, Ulmus glabra, Alnus glutinosa, and Tilia cordata. The dead wood amounts in plots suggest a high level of naturalness. However, the ages of the canopy oaks (up to 226 years) indicate lack of long-term natural development. Also, the presence of cut stumps in three plots and lack of standing dead wood in four plots are signs of the impact of human disturbance on natural processes. Since the 1920s, one of the stands had converted from a Populus tremula and Betula pendula to a Q. robur canopy. Even though the studied stands can be considered as having low naturalness based on age structure and past management history, they each supported two to eight Woodland Key Habitat indicator species, including one to six protected species.