The centroid of tree crowns as an indicator of abiotic processes in a balsam fir wave forest

Abstract

Wave forests are rare and were previously known only in high altitude Abiesbalsamea forests in northeastern U.S.A. and in subalpine A. veitchii – A. mariesii forests in Japan. Wave forests have been discovered at several locations in Newfoundland, including a very large and unique wave forest extending over 100–150 km2 on the coastal plain of northwestern Newfoundland. The wave fronts, characterized by dead tree strips, are mostly sinusoidal with an axis aligned in the direction of the prevailing wind, are spaced 100–150 m apart, and move in 55-year cycles. Crest-shaped wave fronts are concave on the windward side, occur as random events, and leave a trailing edge to the right of the prevailing wind that becomes a sinusoidal wave front. Two types of wave cycles, uniformcycle and brokencycle, have been identified as regular and random events, respectively. This paper reports the initial results of a detailed study on the impact of wind on the dynamics of a wave forest and concentrates on the centroid as a measure of crown asymmetry useful for distinguishing between purely biotic (mainly competition) and abiotic (mainly wind) processes as the primary cause of crown asymmetry. The development of wave forests at Spirity Cove is described based on the hypothesis that longitudinal helical roll vortices are primarily responsible for their formation.