Ecological restoration by canopy thinning in a Quercus robur forest can cause development of a dense shrub layer

The area of Quercus robur forest stands in Northern Europe is extremely low due to the legacies of forest management targeted on coniferous tree species and past land conversion on rich soils to agriculture. These stands are characterized by a unique flora and fauna and therefore they are important in the network of protected areas. It is well known that Q. robur will not regenerate under a closed canopy. Thus, these stands are being gradually replaced in succession by shade-tolerant species like Picea abies, which can alter soil conditions. Removal of encroaching trees around Q. robur to maintain the typical habitat conditions is commonly practiced in Northern Europe, but the results of these restoration activities are inconclusive, and not always published when conducted in a practical conservation framework. In Latvia, such restoration of Q. robur stands has commonly been implemented in protected areas, but no publications are available on achieved results. In a restoration project setting, we determined effects of removal of P. abies in the subcanopy and canopy around old Q. robur on tree regeneration and composition of the herb layer. Within a five-year period after management, the created openings were invaded first by generalist species common in open habitats. There was a continuous increase in abundance of the shrub Rubus idaeus, which reached 100% in all plots. There was minimal regeneration of Q. robur, while establishment of Populus tremula occurred. Development of a herb layer was inhibited. However, it is expected that this shrub phase will end in the short-to long-term priod of time.