Browsing by Author "Jacobs, J."

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Effects of temperature and temperature preconditioning on seedling performance of whitebark pine
(1990) Jacobs, J.; Weaver, T.
Four experiments explored the effects of temperature on the germination and seedling performance of whitebark pine (Pinus albicaulis). While 1 month of stratification increased germination from 5 percent to about 40 percent, longer stratification periods (to 8 months) did not improve germination. Germination occurred throughout the 10 to 40 °C range with a broad optimum near 30 °C. Root growth occurred throughout the 10 to 45 °C range with an optimum near 30 °C. Long exposure (5 months) to low temperature (1.5 °C) lowered the temperature threshold for both germination and root growth. The apparent temperature range (perhaps 0 to 35 °C) and optimum (20 °C) for net photosynthesis at light saturation were lower than for germination and growth. While no preconditioning effect of light level (200 to 800 uE I M2*S) on the photosynthetic capacities of mature leaves was seen, photosynthesis increased progressively from needles preconditioned with winter, spring (5 °C day to 5 °C night), summer (15 °C day to 5 °C night), and abnormally warm (25 °C day to 15 °C night) temperatures.
Occurrence of Multiple Stems in Whitepark Pine
(1990) Weaver, T.; Jacobs, J.
Depending on the stand, Montana-Wyoming whitebark pines (Pinus albicaulis) may have multiple stems in 8 to 79 percent of the trees. The clumps had one to 11 stems with stand medians between two and three. Multiple stems may arise from several seeds germinating together. from basal branching, or both. Median. stem number and mm• mum stem number per clump decrease with stand age, probably due to both within-clump and between-clump competition. While declines are slight in open woodlands, clumps almost disappear in closed forests. The presence of clumps is correlated with stand density in other conifers as well.