Search

Factors affecting seed germination, seedling establishment and growth to reproductive maturity in Eucalyptus pauciflora Sieb. ex Spreng. at the tree line in southeastern Australia were investigated. Timing of germination was determined principally by temperature but could be strongly modified by soil water. Mortality of germinants was heaviest during the first growing season (dependent on soil water) and the first winter (dependent on the depth and duration of snow cover). Neither plant nor soil treatments with insecticide or fungicide had an overriding or consistent effect on germination or seedling establishment. The probability of reaching the sapling stage was greater for planted seedlings than for plants germinated on site, indicating the dependence of survival on accumulated reserves. There was no clear indication of a general decrease in survival with increasing altitude, because of an interplay between elevation and site factors including competing vegetation, snow depth and period of snow cover. Five-year-old saplings planted up to 200 m above the tree line produced reproductive structures and viable seed between the ages of 13 and 18 years. The relevance of the results to an understanding of the location of the present tree line is discussed.

Water potential measurements were made, over three winter seasons, on Eucalyptus pauciflora Sieb. ex Spreng. at four elevations extending up to 200 m above the natural tree line in the Snowy Mountains area of southeastern Australia. Shoot water potentials were lowest in winter but never approached lethal levels. Contrary to expectations, there was no gradient of water potential with elevation. This was attributed primarily to the absence of a gradient of soil temperatures once snowpack had developed. Lowest water potentials were observed at air temperatures several degrees above zero, suggesting that transpiration and absorption may be differently affected, with temperatures above and below these values causing higher water potentials. The results suggest that shoot dieback in winter, which is a common phenomenon at alpine tree lines, is not caused by low water potentials in southeastern Australia.