ECOLOGICAL SUCCESSION 31 



18. One more example may be given of the way in which 

 animals and plants are intimately bound up together in 

 ecological succession. Cooper ^^ has studied the relation of 

 the white pine blister rust to succession in the New England 

 and the Adirondacks. This disease is a very important one, 

 and the most critical point in its Hfe-history^ from the point of 

 view of controlling it, is its occurrence at one stage on the 

 various species of wild gooseberries (Ribes), Cooper found 

 that the distribution of Ribes was to an important extent 

 affected by the distribution of fruit-eating birds, and that 

 changes in the character of the birds during ecological suc- 

 cession resulted in a failure of the gooseberry seeds to spread 

 in sufficient numbers to establish many new plants, after a 

 certain stage in succession had been reached. The normal 

 succession in places where the original forest had been cleared 

 and then allowed to grow up again is as follows : first a stage 

 with rank grass and weeds ; this is followed by a shrub 

 stage, in which plants like raspberry, blackberry, juniper, etc., 

 are important. At this point the species of RibeSy though 

 relatively unimportant, reach their maximum abundance. 

 The shrub stage is followed by one with trees, of which the 

 most important are white pine, aspen, birch, and maple. 

 Finally a climax of other species may be reached. But the 

 important point is the appearance of the first trees, for at this 

 stage the bird fauna changes considerably and the number of 

 fruit-eating, or at any rate gooseberry- eating, birds diminishes 

 suddenly. The Ribes is able to exist in the shade of these 

 later forest stages of succession, but cannot produce fruit in 

 any quantity, and so, unless birds bring in new seeds from out- 

 side, the Ribes is bound to die out ultimately. As we have seen, 

 the corresponding changes in the bird species prevent any 

 large amount of seed getting into the forest after these stages, 

 and this reacts upon the rust. 



19. It is obvious that a knowledge of animals may be of 

 enormous value to botanists working on plant succession. 

 At the same time it is necessary for the animal ecologist to 

 have a good general knowledge of plant succession in the 

 region where he is working. It enables him to classify and 



