Natural Regeneration Establishment of Norway Spruce (Picea abies L.) in Austria : Modelling Regeneration Success and Early Growth of Forest Stands. Proceedings from the IUFRO Conference held in Copenhagen, 10-13 June 1996

Horsholm

1996

S. 155-164

27 Lit. Ang.

Bandaufführung

78857

In the absence of reliable and representative data on the frequency of seed years, seed amounts, germination and survival of seeds, the data of the observation period 1992-1996 of the permanent national forest inventory of Austria are used to develop a model describing the probability for the occurrence, density and height of Norway spruce (Picea abies L. Karst.) natural regeneration in the forests of Austria. The forest inventory provided data on natural regeneration (saplings between 10 and 130 cm height) on clusters within a 3.89 km square sammpling grid. A logistic equation is used to predict to probability for natural regeneration occurrence. Input parameters for this equation are the variables that describe the site, with slope and azimuth as continous variables, and growth districts and vegetation types as discrete variables; the crown competition factor describes density and the quadratic mean diameter describes the stage of development of the stand. The same equation type is used to predict the conditional probability for the occurence of Norway spruce within the regeneration. An additional variable in this species specific model is a dummy variable wihich is set to 1 if Norway spruce occurs in the overstory and otherwise zero. Additional site variables entering this model are elevation and vegetation types characterising soil fertility and moisture. Because the density and height of spruce regeneration depends on the stand's susceptibility to browsing, the probability for browsing is also modelled as a logistic equation depending on elevation, vegetation type, stand density and disturbances (removal of trees from the overstory). Finally the probability for height and density of the regeneration is decribed by two bivariate Weibull-distributions, each one decribing browsed and unbrowsed Norway spruce regeneration respectively.