RELATION OF LIGHT-INTENSITY TO ADVANCE GROWTH. 147 



14. On the Relation of Light-Intensity to Advance 

 Growth in Oak and Beech Forests. 



{IVM Plate.) 

 By (t. p. Gordon, B.Sc. 



" Advance growth " is defined as including trees, from the 

 seedling to the pole stage, which have sprung up in openings 

 in the forest, or under the forest canopy, before regeneration 

 fellings were commenced ; it is perhaps most typical of forests 

 worked under the Selection system and of primeval forests. 

 Its presence in the forest is usually associated with the 

 approaching maturity of the trees forming the canopy over 

 that part in which it occurs. Observations made in the above 

 types of forest in Britain and on the Continent indicate that light 

 is an important factor in the formation of this advance growth. 



At the outset, the effects of an increase in the light-intensity 

 would seem to be rather varied. Of primary importance perhaps 

 is the effect on the forest soil, which is one tending towards 

 increased evaporation, while it also allows of increased deposi- 

 tion of moisture; the resultant action, however, is probably a 

 desiccating one. Correlated with this there would come about 

 ameliorating changes in the texture of the soil, as a result of 

 increased capillary and percolating actions. Again the gaseous 

 exchange in the humus-forming layer on the forest floor becomes 

 intensified, and so organic metabolic agents at work in the soil 

 are probably stimulated to increased activity. On the other 

 hand, a diminution in the light-intensity may be considered to 

 have, in general, effects opposite to those already described. 

 Now it is fairly evident that these factors will largely influence 

 the appearance and persistence of advance growth in a forest. 



Moreover, it will be admitted that the variation in the actual 

 chemical intensity of light has also a considerable physiological 

 effect on all plant forms. Illustrations of this are obtained in 

 the general habit of growth, the structure of leaf and bud, as 

 well as in other features of the seedlings forming the advance 

 growth. Indeed the type of the individual corresponds almost 

 exactly to Engler's Schattenbuchen (shade-beech).^ In Plate I. 



^ See Mittcilimgen der Schzveizerischen Centralanstalt fiir das forstliche 

 Versiichswesen, Band x., 191 1, p. 120, Tafel i. Quarterly Journal of 

 Forestry^ igi2, vol. vi. pp. 64-69. 



