Proposed Scenario for Dieback and Decline of Acer Saccharum in Northeastern U. S. A. and Southeastern Canada

A sequence of events is presented that may explain the reported decline of sugar maple trees in the Northeastern United States and Southeastern Canada. The primary factor, caused by defoliation, is a severe reduction in reserve carbohydrates, especially in roots, at the beginning of the leafless period. In this respect, la te defoliators - those that defoliate in late July and early August - are much more destructive than those that defoliate in J une because it appears that carbon is being utilised in July and August by one or more sinks about as fast as it is being assimilated photosynthetically. This, in conjunction with a loss of foliage for an extended period and limited refoliation, could result in severe carbohydrate dcpletion. Limited carbohydrate reserves may not be sufficient for normal respiratory activity during the Ieafless period, or for vernal outgrowth of embryonie shoots. Late defoliation and low carbohydrate reserves also appear to reduce the ability of the trees to acclimate to low winter temperatures; hence, cold winters could result in additional shoot die back and mortality. Other factors such as drought, atmospheric pollutants, and numerous pathogens mayaiso influence carbohydrate reserves, thus contributing to decline.