Structural diversity and production of alder stands on former agricultural land at high altitudes

The paper deals with the structural diversity and production of a less frequently studied type of alder stands originated on former agricultural lands in the 1950s, established partly by plantation and partly by natural succession in the area of the Krkonose Mts. and the Orlicke hory Mts. (Czech Republic). Four permanent research plots (PRP) were established at sites where Black alder (Alnus glutinosa L. Gaertn.) and Grey alder (Alnus incana L. Moench.) naturally occurs, each plot of 0.25 ha in size. The aim of the study was to evaluate the structure and development of the alder stands with respect to biodiversity, horizontal, vertical and species structure, diameter increment with emphasis on climate factors, and the quantity and quality of timber production. The results document low diversification of the studied stands in the PRPs. The horizontal structure is defined as random and clumped at sites at the highest altitude with high water table. The number of living trees with DBH >= 4 cm ranges between 556 to 828 trees ha(-1) with the relative stand density index (SDI) 0.67-0.77. The stand volume ranges from 247 to 393 m(3) ha(-1), and decreases with higher altitudes. Low temperatures is limiting factor for radial growth in the high mountain areas, respectively low precipitation in the middle lands. Owing to a rather specific site character, as especially the spring area, the stands exhibit only average production, but the production quality is generally high. The quality timber is suitable for industrial use; the rot-affected trunk base parts usable for fuel represent only approximately 16%.