GRAVES : HURRICANE DAMAGE 73 



when blown over to an angle, let us say, of 45°, the sheer weight of this butt 

 as well as of the upper parts pulled up the roots or broke them off like a power- 

 ful lever and thus completed the destruction which the wind started. 



Another point, brought out by several of the City park authorities, is that 

 of resisting leaf surface. Trees with a thick crop of leaves, as in the Norway 

 Maple (Acer platanoides) , were more subject to windthrow. 



Also trees affected with heart rot were ill prepared for the test. Many were 

 snapped off at some distance from the ground — a practical illustration of the 

 function of heartwood — to support the tree. 



From the above account it will be clear, I think, that the causes of wind- 

 throw in hurricanes are often complex. Each tree presents a problem by itself. 

 In the following table I have summarized the main causes. 



Causes of Hurricane Windthrow 



I. Shallow Root System 



A. Natural : Poplars, Willows. 



B. Acquired : 



1. Due to shallow soil, underlaid with clay, hardpan, or bedrock. 



2. Due to shallow original planting. 



II. Soil Watersoaked and hence offering little resistance to uprooting. 



III. Trunks with Heavy Butts, making recovery impossible when blown beyond 

 critical' angle, e.g. London Planes. 



IV. Large Leaf Surface, offering resistance, e.g. Norway Maples, some Oaks, Ailan- 

 thus. 



V. Trunks Weakened by heart rot. 



VI. Roots Weakened, partially rotted, or cut off in grading operations. 



VII. Position of Tree, facing an open exposure as in streets in or at end of "canyon" 

 between houses. 



VIII. Position of Tree in Path of Tornadic Current. 



I can not end this account without a few words from an entirely different 

 angle. One can not pass a tree day after day for several years and become ac- 

 quainted with its various moods throughout the seasons without acquiring a 

 sense of companionship — for here is a living being — of another kind of life, it 

 is true — and yet an individual which one knows and loves. And when it is sud- 

 denly uprooted, as many fine specimens were last September, one feels a sense 

 of loss, akin to the loss of an old friend. A year or two hence, a stranger visiting 

 our city may think the damage from the hurricane could not have been as bad 

 as described, because the streets and parks will appear quite normal. But certain 

 individual trees, well-known to the passer-by, will be missed for years to come. 



Brooklyn Botanic Garden 

 Brooklyn, New York 



