falls in an opening produce a seedling which 

 thrives in the sun-glare, — which grows without 

 shade. The seedlings of our great oaks and most 

 strong and long-lived trees cannot thrive unless 

 shielded from the sun, sheltered from the wind, 

 and protected from the sudden temperature- 

 changes which so often afHict openings. While 

 these maintain the forest areas, they extend it 

 but little. Only a small number of trees have 

 the peculiar frontier characteristics. Young 

 trees which cannot live in the sun are called 

 tolerant, — they tolerate shade and need it. 

 Species which conquer sunny territory are called 

 intolerant, — they cannot stand shade and 

 need sunlight. It will thus be seen that the ac- 

 quirement of treeless territory by any species 

 of tree demands not only that the tree get its 

 seeds upon the earth in that territory, but also 

 that the seeds, once there, have the ability to 

 survive in the sunlight and endure the sudden 

 changes of the shelterless opening. Most species 

 of oaks, elms, firs, and spruces require shade 

 during their first few years, and though they 

 steadfastly defend possessions, they can do but 



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