Sphaeropsis sapinea Diplodia sapinea Pinus sylvestris S. sapinea S. sapinea S. sapinea S. sapinea

Summary Snow‐packing, a combination of ice, hoarfrost and snow on trees, and the subsequent tree damage by snow, were estimated on Norway spruce (Picea abies), Scots pine (Pinus sylvestris), and pubescent birch (Betula pubescens) in the winter of 1993‐94 in southern Lapland, northern Finland, near the local alpine timberline around 400 m a.s.l. Snow‐packing on each fully sized tree increased from a few hundred kilograms at 150–250 m a.s.l. to a maximum of 3290 kg at 300–350 m a.s.l. At 300 m a.s.l., snow‐packing per metre of stem increased from 30 to 50 kg on trees < 5 m in height up to 180–200 kg on 20‐m trees. There was 300 000‐480 000 kg/ha of snow accumulated on tree crowns. No stem breakage by snow‐packing occurred at or below 250 m a.s.l., whereas at 290–350 m a.s.l., 0‐46%, 39‐100%, and 0–33% of the spruce, pine and birch trees, respectively, had broken tops. Birch appeared to be the most resistant and pine the most susceptible to snow breakage.

AbstraetA new method has been developed for studying the history of Gremtneniella abietina infeetion in Seots pine {Pitius sylvestris) stands. The braneh analysis method is based mainly on the oeeurrenee of neerotie eankers and sears caused by C. abietina in annual shoots of branches. The supporting factors are the number of leader ehanges of branehes and branch death model.

The effects of excess nitrogen fertilization on tbe structure of Scots-pine needles {Pinus sylvestris) were examined in Finnish Lapland. Tbe trees were fertilized witb calcium ammonium-nitrate, and tbe levels of nitrogen applied were 0, 75, 150, 250, 500 and 1000 kg N/ba, respectively. Tbe thickness and widtb of the needle and thicknesses of tbe tissues were measured, and the conditions of various celltypes were classified at the light-microscopy level. In addition, tbe areas of the cell organdies were measured and tbe conditions of tbe cbloroplasts and otber cell compartments observed at tbe ultrastructural level. Larger needles and a thicker adaxial mcsopbyll were observed following excess N application (250-1000 kg N/ha). Tbe natural xcromorphic structure of tbe conifer needles became more mesomorphic, possibly influencing tbe protection afforded against environmental stresses. A bigli level of nitrogen fertilization caused changes in tbe central cylinder, especially in tbe vascular bundle and tbe sclerencbyma. Tbe needle nitrogen concentration was bigh in the highly fertilized trees and tbe boron concentration was simultaneously extremely low. As a consequence of tbe cbanges in tbe central cylinder, pbotoassimilate transport from tbe mesopbyll to tbe pbloem may be disturbed at bigb fertilization levels. Tbe cbanges at the ultrastructural level, i.e. injuries to the cbloioplast tbylakoids and tbe plasma membrane, and tbe formation of lipid accumulations, were indicators of tbe adverse effects of excess nitrogen. Witb an increasing atmospheric-nitrogen load, lower nitrogen fertilization levels in pine forests naturally adapted to low soil N sbould be considered in forest management.U. S.

The recently developed needle-trace method (NTM) was sueeessfully used to verify retrospectively the oecurrence of a well-documented needle-east epidemic caused by Lopbodermetta suteigena in the 5-year period of 1977-1981 in a stand oi Pinus sytvestris.