OCR Text |
Show 5 research to date has concentrated on the upper part of the sub- alpine zone, for it is here that reforestating is most difficult. Two research areas were selected at the Obergurgl site. One was a 1- hectare* clearing in a forest of Siberian pine ( Pinus cembra), mean altitude 1920 meters, located in order to study edge effects in the forest. The other was an area of 12.5 hectares in the transition zone from 2,070 to 2,225 meters. Several wooden huts were built to house instrumentation. The following brief summary of results from the research program to 1963 have been drawn from the two comprehensive volumes published by the Federal Forest 2/ Research Center at Mariabrunn-. Solar radiation is much stronger at 2,000 meters than at low elevations. This is particularly true with an overcast sky. for the clouds are not so thick. Snow cover on surrounding slopes can reflect enough sunlight to double radiation intensity. Scattered radiation from summer clouds can briefly raise intensity to levels greater than the solar constant. This intensive radiation in winter causes chlorophyll destruction and damage to tree crowns in the native pines. By contrast, the understory of pine forests in some places is so dark that this is a factor in suppressing reproduction. Warm zones develop on the slopes in contrast to cold air which forms pools in the valley. In summer these warm zones are in the wooded parts of the slopes, but in winter they lie higher up. Differences of air temperature and humidity are less in a sub- alpine forest than in stands of lower altitudes. Siberian pine needle temperatures oscillate daily with an amplitude about twice that of air temperature changes. Sub- cooling is severest in winter, the heating greatest in summer; extremes range from - 40 C to + 40 C. Needle * 1 Hectare = about 2i acres |