DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 3-4/1965 str. 9 <-- 9 --> PDF |
EFFECT OF SOME LEPIDOPTEROUS DEFOLIATORS ON THE DIAMETER INCREMENT OF PEDUNCULATE OAK By Dr. Dušan Klepac and Dr. Ivan Spaić In Šumarski List (»Forestry Review«) 1949, pp. 280—290 there was described a method for determining the loss of increment brought about in stands attacked by the Gipsy Moth (Lymantria dispar L.). In one experimental area (sub-compartment No. 150a, management unit »Josip Kozarac«, forest district Lipovljani) it was established that the annual volume increment of Pedunculate Oak in 1956 dropped by ca. 30´Vo after an attack of the Gipsy Moth (Klepa c 1959). One year later, i.e. in 1957, the volume increment of Pedunculate Oak dropped by even more. This can be explained by the fact that for the building up of increment in one year the reserve substances which were formed in the preceding year are decisive. But as regards the above-mentioned case one should not forget that in 1957 Gipsy Moth caterpillars continued defoliating Oak tree crowns in the investigated stand because the control operation was performed a little too late Besides the Gipsy Moth there were noticed in the same year also the Lackey Moth (Malacosoma neustria) and the Oak Processionary Moth (Thaumetopoea processionea). There have passed 6 years from the first experiment ,and we would like to know how Pedunculate Oak reacted in the years folowing, i. e. from 1957 to 1963. In this paper we would like to give an answer to this question. For the mentioned purpose we extracted in spring 1964 by means of an increment borer 100 cores from 100 Oak trees from different sites and of different diameters b. h. These trees were chosen in the sub-compartment No. 150a, menagemen! unit »Josip Kozarac«, i. e. in the same stand where the first experiment was carried out 6 years ago. Each increment core was analysed, so that we measured the growth- ring width in the following years: 1958, 1959, 1960, 1961, 1962, and 1963. On sorting out the measured data we computed the arithmetic mean of the growth-ring width (g) in individual years and its standard deviation (a). These data are presented in Tab 1. It should be stated that we had measured the data for 1955, 1956, and 1957 at an earlier date, i. e. during the first experiment. Tab. 1 Mean width of growth ring (g) of Pedunculate Oak from sub-compartment No. 150a, management unit »Josip Kozarac«, for individual years Year 1955 1956 1957 1958 1959 1960 1961 1962 1963 g in m. m. 2.52 1.63 1.43 2.07 1.92 1.41 1.79 1.66 1.49 a in m. m. ±1.03 ±0.75 ±0.75 ±0.94 ±0.85 ±0.67 ±0.96 ±1.00 ±0.84 What do the measured data concerning the mean growth-ring width in the investigated stand show us? Conspicuous is the drop in the ring width in 1956, 1957, 1960, and 1963. The drop in the diameter increment in 1956 and 1957 was caused by the Gipsy Moth, which in 1956 defoliated completely the investegated stands, while in 1957 it did not appear in any greater numbers until 1964. The stand recovered, which manifested itself in the diameter increment in 1958 and 1959. But in 1960 we again noticed a drcip in the diameter increment. Whereas in 1958 the average growth-ring width was ca. 2 m. m., it dropped in 1960 to 1.41 m. m., i. e. by 30!:Vo. Which would mean that the volume increment in that year also decreased by ca. 3Ö´/o. In the following two years the diameter increment increased only slightly, and in 1963 it dropped again, although not so appreciably as in 1960. What would account for the drop in the increment in 1960 and 1963? This refers us to the climatic factors, which were probably not the cause of the drop in the increment of Pedunculate Oak in 1960 and 1963. That this is actually so, is borne out by data on the precipitation and temperatures, which in these and the preceding years (i.e.: 1959, 1960, 1962, and 1963) were not less unfavourable than in other years. Besides, in 1950, 1960, 1962, and 1963 were recorded no special weather inclemencies; in those years there occurred no full Oak masts. 9!) |