Time filter

Source Type

Breitenfurt bei Wien, Austria

On the way of including temperature and precipitation into an existing basal area increment model the definition of the competition index basal area of larger trees (BAL) has been refined to work independently from plot size of the input data and also for long time model runs. It has also been investigated in examining the effect of using different methods to estimate regression coefficients for exponential models. Linearisation causes a trend in the prediction. This is also true for mixed effect regression models which have been brought to linear form. Generalised linear mixed effect models show strongly skewed residuals. Estimates with non-linear regression have not shown too bad results. The use of generalised linear models (GLM) shows the best results and bias-free estimates can be expected by weighting the observations with their represented stem number. The inclusion of weather data required to change from five year estimates to one year estimates. This did not increase the prediction error during a 15 year model run. Temperature and precipitation describe much of the observed increment but estimates near the limits of the data or extrapolation beyond the observed weather conditions will be tentative. Source

Kristofel F.,Institute For Waldwachstum Und Waldbau
Austrian Journal of Forest Science | Year: 2010

In the year 1987 Professor P. ABETZ proposed the "Solitary program 1987" and in the same year the conversion of this program was implemented in Austria by the Institute for Forest Growth and Economics at the former Federal Forest Research Institute (FBVA). In the years 1987 and 1988 on the following places experiments were established into Norway spruce stands: Haid-Kogl near Frankenmarkt in Upper Austria (351), Prössing near Wolfsberg in Carinthia (352), Weitra in Lower Austria (353), Königswiesen in Upper Austria (354) and Maria Lankowitz in Styria (355).ABETZ proposed two variants of stem numbers (variant A and B). In 3 to 5 m high stands the stem numbers are reduced immediately for variant A to the final number of 350 stems ha -1. For variant B the stem numbers are reduced to 700 stems ha -1 at the beginning of the experiment and finally to 350 stems ha -1 when a dominant height of 20 m is reached. In addition he suggested establishing one plot with "conventional" stem numbers for comparison (variant C). The diameters in the variants A, B and C are developing clearly apart. After 20 years the mean diameter on variant B on the sites 351-354 are approximately 10-20% and on variant C around approximately 30-40% smaller than on variant A. With the mean height no clear differences arise between the three variants. The dominant heights develop on all variants as expected to a large extent independently from treatment. On site 355 not so pronounced differences were found, due to the differing age of the trees. The crowns of the variant A developed relatively rapidly into the width, at the third revision assessment they are approximately twice as with at the first assessment. After 20 observation years only few crowns show dimensions as expected for solitary trees. The branch diameters, were measured once on four of the five the sites. The variant A shows the highest branch diameters on the sites 352, 353 and 354, variant C however the lowest. Source

Kristofel F.,Institute For Waldwachstum Und Waldbau
Austrian Journal of Forest Science | Year: 2011

At the beginning of the 1980ies by the Sektion Ertragskunde des Deutschen Verbandes Forstlicher Forschungsanstalten was agreed upon the implementation of trials on the growth of individual trees under defined neighbourhood conditions. A substantial question was in which way the central trees could be released evenly and objectively by all participanting institutions. Upon this question K. Johann developed the "A-Wert" (A-Value) as an objective parameter for the determination of the release of central trees. By the former Forstlichen Bundesversuchsanstalt two experimental sites with spruce were installed after the recommendations for thinning trials, whereby the release of the central trees takes place in accordance with the programme after A-Values 4, 5 and 6. After approximately 20 years of observation clear diameter differences between the three treatment variants show up, gradated according to A-Value. The trees released after A-Value 4, achieve the largest diameters; the smallest diameters the ones released after A-Value 6. Source

Discover hidden collaborations