| Summary: | Dissertation (Ph.D.) University of Alaska Fairbanks, 1986 The purpose of this study was to determine the major factors which affect tree and moss productivity in a black spruce (Picea mariana Mill. B.S.P.) forest ecosystem, occurring on permafrost dominated soil. The cold, shallow rooting zone was heated 8(DEGREES) - 10(DEGREES)C above ambient which resulted in increased forest floor nutrient cycling and increased productivity in black spruce. The soil heat sum increased from 563 to 1133 soil degree days and the depth of thaw increased from 57 to 115 cm. Heating increased tree ring radius by 33% relative to the control. Foliar analysis showed significant increases in nitrogen (25%), phosphorus (73%) and potassium (14%), indicating that heating increased nutrient availability to the spruce trees. This resulted in a 22% increase in the maximum photosynthetic rates over the control. The 1 year old tissue had the highest photosynthetic rates, whereas the oldest needles maintained 40% of the maximum photosynthetic rates after 13 seasons. The highest levels of nitrogen and phosphorus were measured in the current tissue and declined with age. Nutrient use efficiency was highest in the 1 year old tissue and declined with needle age. Studies on microclimatic limitations to moss production on the forest floor indicated that water content was the most variable and potentially the most limiting factor. Light was also very limiting, but the range of limitation was small between different day types, demonstrating the moderating influence of the spruce canopy. Temperature was not as limiting a factor during the summer growing season. Limitation by microclimate allowed only 1% of maximum photosynthesis by mosses on dry, clear days and 9% on wet overcast days, with a potential of 20% under sunny and wet conditions. When data was combined for all days, moss photosynthesis ranged from 8 - 14% of maximum, similar to the low 13% efficiency of production calculated from biomass studies.
|
|---|