66 ON THE ORIGIN OF SPECIES 



country. I will give only a single instance, which, 

 though a simple one, has interested me. In Stafford- 

 shire, on the estate of a relation, where I had ample 

 means of investigation, there was a large and extremely 

 barren heath, which had never been touched by the 

 hand of man ; but several hundred acres of exactly 

 the same nature had been enclosed twenty-five years 

 previously and planted with Scotch fir. The change in 

 the native vegetation of the planted part of the heath 

 was most remarkable, more than is generally seen in 

 passing from one quite different soil to another : not 

 only the proportional numbers of the heath-plants were 

 wholly changed, but twelve species of plants (not 

 counting grasses and carices) flourished in the planta- 

 tions, which could not be found on the heath. The 

 effect on the insects must have been still greater, for 

 six insectivorous birds were very common in the planta- 

 tions, which 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 introduction of a single tree, nothing 

 whatever else having been done, with the exception 

 that the land had been enclosed, so that cattle could 

 not enter. But how important 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 perpetually 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 



