i88s.] 



AND HORTICULTURIST. 



305 



Forestry. 



COMMUNICATIONS. 



SUCCESSION OF FOREST GROWTHS. 



I!Y ROBERT DOUGLAS. 



Three years ago I published my observations 

 on the succession of forest growths in the Rocky 

 Mountains and all the forests in the Northwest. 

 Since that time it has been observed that the same 

 rule applies to Europe. In the Gardeners' 

 Monthly for July an article on the same subject 

 copied from the [ndependent and headed " Suc- 

 cession of Forest Growths," names the very same 

 trees that I referred to, but in a way which shows 

 that the writer did not understand my meaning. 

 He says, '• In the Rocky Mountains of Colorado 

 the first tree to take possession of the rocky 

 heights is the Aspen Poplar. No other tree at- 

 tempts to take possession of the sterile soil." 



Now my observations have extended over many 

 years, and long journeys in the mountains, yet I 

 fail to bring to mind a single instance where the 

 aspen has taken possession of the sterile soil on 

 the rocky heights, except where the land had pre- 

 viously been burned over; and where the land 

 had been burned over, it is proof positive that 

 timber had already grown there ; so this does not 

 prove that it was the first tree to take possession. 



The natural place for the aspen is in moist soil, 

 and there it will be found making its best growth'. 

 It was an interesting fact for me to notice that 

 this tree, or its seeds rather, are so dtlicate that 

 they will not germinate even on land slides, but 

 newly burned land is in the best condition possi- 

 ble for delicate seeds ; and this tree has a better 

 opportunity than any other I know of for reaching 

 the burned land. Its seeds ripen in spring ; they 

 are produced in incalculable numbers, and so 

 small that a million would not weigh a pound ; 

 they are floated in the air on wings of down, so 

 that they are the only seeds which can reach the 

 mountain tops, but they cannot germinate so well 

 on ordinary dry land as many other trees; and 

 undoubtedly if the seeds of pines could reach the 

 sterile soils and rocky heights, they would be 

 more at home than the aspen. 



The writer, still speaking of the aspen, says : 

 "No sooner, however, does it spread over the wide 

 acres, than the twisted pine (Pinus contorta) rushes 

 in, contests the ground, and finally conquers." 



Now, in what way can the Pinus contorta "rush 

 in " on these rocky heights of sterile soil ? Its 

 seeds are not light like the seeds of the aspen. 

 They could not cross the valleys from another 

 mountain, and the trees, each one of them must 

 have a seed to start from. In cases where Pinus 

 contorta " rushes in " as soon as the aspen has 

 spread over the wide acres, it will be found that it 

 started from the seeds at the same time the 

 aspen did, but in four years it would not be so lall 

 as the aspen grew the first season. 



Pinus contorta (it is now called Murryana) has 

 very persistent cones. I have seen trees that have 

 held their cones sixteen years, very many if not 

 all of them still enclosing the seeds. Heat is the 

 best and almost the only instrument that will open 

 these cones ; hence when a fire destroys the forest 

 many of these seeds are just in the right condition 

 to germinate, and they can be seen springing up 

 in countless thousands, and by counting their 

 annual growths in the older burnings, you may tell 

 quite accurately in many instances, the year when 

 the forest was burned. 



It is quite possible that the aspen may antedate 

 all others of our forest trees, indeed it has been 

 found imbedded in the fens in Northern Europe, 

 deeper than almost any others of our commonest 

 forest trees, but this is no reason why we should 

 jump to the conclusion that its growing on the 

 Rocky Mountains at high elevations proves it. It 

 only grows on burned lands and on moist places, 

 and its seeds give it that advantage. 



I do nor see a particle of evidence in any of the 

 mountains and forests, to prove that there is a 

 succession of forest growths at all, except where 

 the lands have been burned over, or where the 

 conditions have been changed by being flooded, 

 or by being changed by some convulsion of 

 nature ; and these instances are so rare as hardly 

 to need a passing notice. The writer goes on to 

 quote Hansen's observations on the same subject, 

 but in this case also he neglects to state that the 

 aspen is the first tree to appear on burnt lands, 

 and the birch the next, just as I reported of the 

 burnt lands in Northern 'Wisconsin, and the Black 

 Hills of Dakota. It seems to me that any man 

 who will take time to look into this matter will see 

 plainly that the birch must follow the aspen, and 

 see just as plainly that it must drive the aspen out 



