482 REARING OP THE ESTRBLISHED CROP. 



or in groups, their number and distribution being dependent en- 

 tirely on the number of really promising timber-yielding stems 

 present in the original crop. In the case of shade-avoiding 

 species on good soil, the number of stems may aggregate from 24 

 to 32, and even more, per acre ; with shade-enduring broad- 

 crowned species the number would obviously be less. The rege- 

 neration fellings or, in other words, the plenary thinnings are 

 begun early, in order that the whole series may be carried out 

 while the crop is still young and the trees are in their full vigour of 

 growth. Homburg's measurements, in forests of beech and oak 

 with a slight admixture of ash, maple, elms and other species, 

 give 1'4 per cent as the mean annual increment at the time of the 

 first preparatory felling (age of crop about 70 years) and 4'8 per 

 cent, or an increase of 3*4, for the following period of 17 years. 

 These figures prove the necessity and advantage of beginning 

 regeneration, if it is to be effected under cover, as early as possible. 



2. The young undercrop raised in groups by spontaneous solving. 



As in Homburg's method the regular regeneration fellings on 

 the uniform system fulfil the object of plenary thinnings, so in this 

 method the regular regeneration fellings in groups, begun early 

 and carried through slowly, do the work of the same thinnings. 

 The extent to which the period covered by the fellings should be 

 prolonged beyond the time absolutely necessary for regeneration will 

 depend on the suitability of the soil for the species to be fostered, 

 being comparatively slight on dry poor soils. 



In forests worked by jardinage also the regeneration fellings and 

 plenary thinnings must be combined into one and the same ope- 

 ration, the area worked over at each point being somewhat larger 

 than in the case of regeneration pure and simple. But jardinage 

 itself procures the same results as plenary thinnings, and indeed 

 jardinage and plenary thinnings combined really constitute only 

 an intensive system of jardinage. 



3. The young crop raised artificially. 



In this case the commencement of the plenary thinnings is not 

 limited by the age at which the crop would become fully fertile, 

 but may be undertaken as soon as the crop can be safely opened 

 out sufficiently for sowing or planting under it. For this reason, 

 instead cf making only a single plenary thinning, as in the case of 

 natural regeneration by seed, the desired ultimate isolation of the 

 timber trees of the crop should be effected step by step, as the 



