88 STRUGGLE FOR EXISTENCE. [Chap. IIL 



were not to be seen on the heath; and the heath was 

 frequented by two or three distinct insectivorous birds. 

 Here we see how potent has been the effect of the in- 

 troduction of a single tree, nothing whatever else having 

 been done, with the exception of the land having been 

 enclosed, so that cattle could not enter. But how im- 

 portant an element enclosure is, I plainly saw near 

 Farnham, in Surrey. Here there are extensive heaths, 

 with a few clumps of old Scotch firs on the distant hill- 

 tops: within the last ten years large spaces have been 

 enclosed, and self-sown firs are now springing up in 

 multitudes, so close together that all cannot live. 

 When I ascertained that these young trees had not 

 been sown or planted, I was so much surprised at their 

 numbers that I went to several points of view, whence 

 I could examine hundreds of acres of the unenclosed 

 heath, and literally I could not see a single Scotch fir, 

 except the old planted clumps. But on looking closely 

 between the stems of the heath, I found a multitude 

 of seedlings and little trees which had been perpet- 

 ually browsed down by the cattle. In one square yard, 

 at a point some hundred yards distant from one of 

 the old clumps, I counted thirty-two little trees; 

 and one of them, with twenty-six rings of growth, 

 had, during many years tried to raise its head above 

 the stems of the heath, and had failed. No wonder 

 that, as soon as the land was enclosed, it became 

 thickly clothed with vigorously growing young filrs. 

 Yet the heath was so extremely barren and so ext(to- 

 sive that no one would ever have imagined tliiat 

 cattle would have so closely and effectually searched it 

 for food. 



Here we see that cattle absolutely determine tfhe 



