390 PROTECTION AGAINST PLANTS. 



3. Utility of Certain Weeds. 



Some weeds are directly or indirectly useful in woods. 



Many weeds, such as grasses, are directly useful for fodder, 

 thatch, or litter, or may be used by manufacturers, or for 

 medicine. A full account of such plants is given under 

 Forest Utilisation. The fruits of many shrubs afford useful 

 food for men, mammals, and birds. 



Weeds may also be indirectly useful in the following 

 ways : 



(a) Soil-indicators. Giving evidence of certain physical or 

 chemical qualities of soils. 



(b) Soil-fixers. Binding the soil on steep slopes, or on 

 shifting sands (sand-fixing grasses). 



(c) Soil-improvers. Enriching the soil with their detritus, 

 and maintaining its moisture, reducing radiation, and 

 especially by preventing extremes of temperature in the 

 surface soil (mosses), other than Polytrichum and Sphagnum. 



(d) Nui'ses, for young tender species in localities exposed to 

 frost, dry winds, or insolation. Thorny bushes and weeds of 

 an erect habit, such as the broom, are most useful in this 

 respect. Thorny bushes also protect all kinds of forest 

 plants against grazing animals or deer, and afford shelter 

 to useful birds. 



On these grounds forest weeds should not always be 

 extirpated, but only when they do more harm than good. 



4. Damage done by Forest Weeds. 

 A. General Nature of Damage. 



The damage done by forest weeds is either direct or indirect, 

 many weeds being hurtful in both ways. 



Directly injurious are poisonous plants, such as Daphne 

 Mezereum, L., nightshade, or belladonna, which are hurtful to 

 animals grazing in the forests. A dense growth of black- 

 thorn, roses, brambles, etc., is also a great hindrance to 

 fellings, and may therefore be considered directly hurtful. 



The indirect Jiurtfulness of weeds is due to the following 

 causes : 



