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LARCH SAWFLY SURVIVAL IN RELATION TO WATER LEVELS AND MICROTOPOGRAPHY IN TAMARACK BOGS

Published online by Cambridge University Press:  31 May 2012

W. G. H. Ives
W. G. H. Ives
Affiliation:
Forest Research Laboratory, Department of Forestry and Rural Development, Winnipeg, Manitoba
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Abstract

The microtopography of a small area of tamarack bog was examined in detail and related to the distribution of cocoons of the larch sawfly Pristiphora erichsonii (Hartig). The relief of the ground surface under tree crowns was very similar to the surface not under crowns, although the whole profile was slightly higher. Cocoons were found down to the limnic peat, corresponding to the level of the lowest depressions, with the greatest numbers per unit area in the hummocks.

The microtopographies in six tamarack bogs were sampled systematically and related to water levels, and an expression combining these two factors was related to larch sawfly survival. The microtopography in each bog did not change appreciably over a period of several years, but differences between bogs were pronounced and had a marked influence on the degree of flooding caused by equal changes in water tables. Excessive moisture during the period 1955–1966 was the prevalent condition in most of the bogs and extreme drought occurred only in 1961. There appeared to be a linear relationship between sawfly survival and an expression rating the favorableness of the cocoon environment in relation to excess moisture, but four divergent observations occurred among the data for 32 plot-years. It was postulated that these divergences were due to high mortality caused by a factor other than excess moisture.

Type
Articles
Information
The Canadian Entomologist , Volume 100 , Issue 4 , April 1968 , pp. 373 - 385
Copyright
Copyright © Entomological Society of Canada 1968

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