Genetic diversity and differentiation of even-aged Norway spruce stands in Latvia
Norway spruce (Picea abies L. Karst.) is an important species in Latvia both ecologically and economically, and has been subjected to silvicultural management in Latvia since at least the middle of the 19th century. Forest regeneration activities starting in the 1960s resulted in the establishment of spruce stands with uncertified and often undocumented reproductive material. These spruce stands were often established by sowing, and no research or clear guidelines regarding the optimal density were available. As a result, many spruce stands were established and maintained at a high density. The growth of young spruce stands is initially slow, with annual height increment of 10-20 cm until the trees reach height of approximately two meters and in favourable growth conditions this stage is followed by a rapid increase in all stand parameters. However, the growth of some even-aged pure spruce stands abruptly declines at the age of approximately 40 years, while in other stands of similar age and composition this decrease or collapse is not observed. A comprehensive survey of even-aged spruce stands in Latvia has been undertaken, and factors influencing this decline in the growth potential of even-aged spruce stands have also been investigated, however, the genetic diversity and differentiation of even-aged spruce stands has not been investigated. A total of 19 SSR markers were utilised to genotype the 7 even aged spruce stands with differing growth potential. The genetic analysis and comparison of the perspective and non-perspective even-aged spruce stands indicated that the genetic diversity was not decreased in the non-perspective stands, and that genetic differentiation between stands and groups with differing growth potential assessments was low. The results obtained in this study suggest that the growth potential of even-aged Norway spruce stands is more dependent on the influence of environmental factors and management regime than genetic factors. This is a positive message, as in this case the conditions may be changed by the application of suitable management regime.