FOREST WEEDS. 393 



by the locality, the prevailing system of forest management, 

 and the state of the weather during the growing season. In 

 the second place, by the species of tree and age of crop. 



Weeds are disseminated chiefly by winds which carry light 

 seeds and fruits by millions, as, for instance, the fruits of 

 ComjwsiUe ; many birds, especially thrushes and blackbirds, 

 disseminate seeds either by pecking at the ripe fruit-heads and 

 causing the wind to disperse the seeds, or by eating the fruits 

 and voiding the indigestible seeds. This is especially the case 

 with hawthorn. Other birds, such as finches, eat the seeds of 

 many weeds and are so far serviceable. Hares, deer, and other 

 animals also carry seeds about in their fur. The seeds of many 

 riparian plants are carried down by streams and inundations, 

 i. Damage according to Species of Tiiek. 



Slowly growing species are more easily injured by the 

 growth of weeds than fast-growing ones, and of these, light- 

 demanding species suffer most. The vigour of the weeds is 

 greatest on the most fertile soils. 



The following scale shows the degree in which the different 

 trees suffer from a strong growth of herbage. 



Suffer most: — Osier- willows, elm, ash, maples, sweet chest- 

 nut, silver-fir, and spruce. 



Suffer less: — Beech, hornbeam, and lime. 



Suffer still less : — Oaks, alder, tree-willows, Scots and Black 

 pines, and larch. 



Suffer least: — Birch, aspen, poplars, sallows, robinia, species 

 of Sorbus, Pyrus, Pruuus, and Weymouth pine. 



This scale, of course, will vary for different localities which 

 suit certain trees better than others. 



ii. Systems of Management. 



In high forests with natural regeneration, or artificially 

 planted under cover, the soil is not so liable to become covered 

 with weeds as in the clear-cutting system, which favours the 

 spread of weeds in the highest degree. The shelterwood 

 comimrtment system, also, if not very carefully managed, 

 sometimes gives rise to masses of weeds on the felling-areas. 



On fresh, and 'especially damp, rich soils, after a clear- 

 cutting, a dense growth of grass and weeds springs up in a 



