BARRIERS TO FOREST EXTENSION 87 
tough cone. The fire may kill the tree, but the seeds 
are often uninjured. This pine is thus reproduced in 
spite of fire. It is this peculiarity which, in part at 
least, accounts for its wide distribution over areas 
subject to frequent fires. 
The Indian set fire to improve the berry-crop, a 
common practise still in many parts of this country. 
He desired open places and pasture to furnish food 
for game and to facilitate hunting. Fires are com- 
monly set to-day in the forest throughout our South 
to improve the pasturage. 
Constant burning has tended to reduce the num- 
ber of species, and produce many open pure woods. 
Some trees are, however, gregarious. This flocking 
together is probably due, in part at least, to the fact 
that some species produce much more seed than oth- 
ers, and that this seed is produced in immense quan- 
tities, not every year, but every now and then, in 
what are called seed-years. These seed-years occur 
with more or less regularity, and the seeds sprout 
and mature together. In this way one species may 
often gain complete possession of the soil. 
Browsing animals, such as cattle and sheep, are, of 
course, more or less destructive to forests. Young 
trees of good flavor are soon devoured, while others 
are injured by trampling. A camel will eat a canvas 
tent, a giraffe can reach with its long neck the most 
