DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 1-2/1972 str. 61 <-- 61 --> PDF |
If we compare data about the reduction of assimilating surface in 1969 with those of 1971, we see that the differences are not significant. Accordingly we may say that the state in the management unit of »Belevine« did not worsen, or that the dieback of Fir there did not have a progressive character. Nevertheless, we are dealing with a forest where the assimilating surface of Fir — taken on an average — was reduced by about 8—9%. Having thus determined the state or the area in question and taken a considerable number of representative samples, there exists a possibility for different analyses and considerations. I restricted myself to the following problems: 1. How do healthy and infested trees put on their increment? 2. When did the diameter increment of Fir begin to fall off? 3. How does the reduction of assimilating apparatus affect the tree increment? To this purpose the increment cores were analysed in different ways. First, on each core was measured the individual recruitment time (t) for 5 cm. — diameter sub-classes (see Fig. 1). Second, on each core was measured the diameter increment for the past 10 years, i. e. from 1961—1970 (see Fig. 2). Third, on each core was measured the diameter increment for the past 5 years, i. e. from 1966—1970 (see Fig. 3). Fourth, on each core was measured the diameter increment during the previous past years, i. e. from 1961—1965 (see Fig. 3). After a fourfold analysis of cores a sorting of cores was carried out and the resulting data smoothed according to the theory of least squares. Recruitment time In the course of the summer of 1959 I worked out together with my students — during the field teaching — a working plan for the forest of »Belevine« (1959—1968). On this occasion we extracted in the mentioned management unit 1,225 increment cores from as many Fir trees. The volume increment was computed according to the method of »Increment percentage tables« with the help of the median of individual recruitment times (see Šumarski list, Zagreb 1954). At the beginning of July, 1971, students of the Zagreb Forestry Faculty extracted repeatedly in the same forest a considerable number of increment cores, viz. 695 from 695 Fir trees. On this occasion took part aslo my collaborators Šime Meštrović, M. F. and graduate engineer, and Radovan Križance , graduate engineer of forestry, both of them University assistants. Like 11 years ago, so this time the median of individual recruitment times was computed. It is interesting to compare the data from 1959 with data obtained 11 years later (see Tab. 1). What catches our eye immediately is that there are no great differences, which would mean that the diameter increment and the increment percent remained almost the same. But it is not so! The reason lies in the median of individual recruitment times. Although the median has its great adventages when calculating the increment, in this case it is not suitable, because the 57 |