M. Galli (1), G. Longo (1-2), R. Serra (1) and S. Cecchini (3)
(1) Dipartimento di Fisica dell Università di Bologna, Via Irnerio 46, I-40126 Bologna, Italy
(2) Istituto Nazionale di Fisica Nucleare, Sezione di Bologna, Via Irnerio 46, I-40126 Bologna, Italy
(3) Istituto di Studio e Tecnologie delle Radiazioni Extraterrestri, CNR, Via Gobetti 101, I-40129 Bologna, Italy.

We have described in previous papers [1-2] our search for microsized particles trapped in the resin of trees that survived the Tunguska catastrophe. Here some biological effects of the Tunguska impact, observed during our examination of the wood of surviving conifers, are reported. No doubt some of these phenomena are direct consequences of mechanical and thermal effects of the 1908 explosion. Among them the traumas in the 1908 growth rings of trunks and branches and a kind of internal haemorrhage, i. e. an emission of resin, in the rings grown before 1908. The 1908 ring itself generally has a normal width showing that its growth was practically complete on 30 June, 1908. This ring, however, has an anomalously clear late wood, characterized by narrower cells with thinner walls, indicating not only a reduced cambium activity, but also a reduced lignification. The reduced photosynthetic activity, due to defoliation, is responsible for the minimum (often about 0.1 mm) reached by the ring width in 1909. In 1910-1913, some rings of different trees have a very irregular shape, due to a possible compression by the bark damaged in 1908. Finally, an observation of the tree section as a whole indicates that trees not overthrown by the explosion were left leaning in the leeward side of the shock wave, thus causing an eccentricity in the tree section corresponding to the direction of the shock wave.

The cause of the anomalous growth of tree rings after 1909 is more controversial. We collected tree ring data for 9 spruces, 1 larch and 1 Siberian pine. A comparison of the average tree ring width over about 30 years before 1907 and exactly the same period after 1909 has confirmed the width increase for all the 11 trees examined.

From these data no correlation with the tree position has been found. The trees were divided into two groups: 5 trees with an average ring width before 1907 equal to about 0.4 mm and a second group with a ring width of about 1 mm. After 1909 both groups reach approximately the same ring width of about 1.2-1.5 mm with an increase for the first group by a factor 3-4, as against a factor 1.2-1.5 for the second group.

1. Longo G., Serra R., Cecchini S. and Galli M. (1994) Planetary and Space Science, n. 2, 163--177.
2. Serra R., Cecchini S., Galli M. and Longo G. (1994) Planetary and Space Science, n. 9, 777--783.