FACTORS INFLUKNCIXG REPRODUCTION 837 



forest association of the island. It occupies the rocky, dry, warm sites, 

 apparently confined to them by the competition of other trees on the 

 better sites. Strangely enough, it occurs also on granite ledges just 

 above the sea, exposed to the full sweep of the east wind, probably be- 

 cause these ledges, in spite of the proximity of the sea, are dry and 

 fairly warm. On the whole, owing to the unfavorable sites on which 

 it grows, this pitch pine is too short, limby, and small to be of com- 

 mercial value, running only about 15 to 20 feet in height by about 6 to 

 10 inches in diameter. It has nevertheless, especially where it is twisted 

 by the wind, a picturesque charm. 



Distribution of Age Classes. — The stand grows in even-aged groups, 

 composed of from one to many trees, as the result of the way in which 

 it originates. On the worst sites it starts as scattered trees or clumps 

 of trees here and there, giving small, even-aged groups. In a less un- 

 favorable place, as on a rocky fiat, a group of considerable size may 

 come in, forming an approximately even-aged forest. 



Reproduction. — The reproduction in this association consists of scat- 

 tered pitch pines of various ages in most of the openings. Where it is 

 nearly fully stocked, scattered seedlings occur under the light shade of 

 the parent trees, but are not abundant. In some of the better sites 

 there are seedlings of white pine and a few clumps of small fir and 

 spruce, indicating that here the pitch pine is a pioneer association which 

 sooner or later will probably give way to spruce. 



Gray Birch-Aspen Association 



Gray birch and aspen, the former predominating, make a temporary 

 cover after the destruction of the forest by fire. Both trees are short, 

 seldom reaching more than 15 feet in height, grow close together, and 

 often form dense thickets. On the moist and cool sites gray birch is 

 replaced by paper birch (Betula papyrifera) and yellow birch {B. 

 lutea), which grow to be fair-sized trees. 



The reproduction is seldom of birch or aspen, but of the conifers 

 which formed the original forest, and the abundance of this coniferous 

 reproduction depends largely on the number and distribution of seed- 

 bearing trees which have escaped fire. In a few places the reproduction 

 is abundant enough to give a fully stocked stand after it has crowded 

 out the birch and aspen ; more frequently it is sparse and will give an 

 open stand, which will gradually fill in from the seed of the trees which 

 are now only seedlings. In some places there have been second fires 

 which, destroying the coniferous reproduction, enable the birch and 

 aspen to maintain possession for a considerably longer tirtie, until grad- 

 ually crowded out by encroachment from the edges. 



