OCR Text |
Show lee ones. Wind is the dominant factor in determining evaporation. Technical problems limited measurements of soil moisture, but the few observations showed that wind is a more important determining agent than solar radi at i on. Plant communities, soil types, micro- organisms, animal life, and the ecological relation of wind, snow and thaw patterns all show definite inter-relat i onsh i ps. Natural reproduction of Siberian pine depends on relation of available seed quantity to the activity of its only natural disseminating agent, the thick- billed nutcracker ( Nucifraga carupcatactes). It also depends on certain plant types which provide suitable seed beds, and on the depth and duration of the snow cover. Artificial introduction of Siberian pine should be by transplanting nursery-grown seedlings at least four years old. Planting has to be done in holes or mounds. The planting holes are dug the previous summer to improve the soil, the trees are planted 5000 to the hectare, and the losses are made up after the first year. Losses up to 50% are expected for the first year, but this figure drops to 1- 5% for trees five to eight years old. Ultimate density of 3000 trees per hectare is sought. It is not yet known whether this density will suppress all avalanches. Measurements of assimilation and respiration of young Siberian pines show a strong annual variation in these quantities. Autumn assimilation is only half that of spring for similar amounts of solar radiation, and drops much lower prior to formation- of winter ground frost. The carbon dioxide balance is negative |