280 PLANT SOCIOLOGY 



In the heath regions of the European-Atlantic province, where 

 heath burning is carried out periodically for the renewal and refreshing 

 of worn-out heaths, the natural revegetation, unaffected by man, has 

 been studied in a careful fashion by Fritsch, Parker, and Salisbury 

 {New Phytologist, 1913, 1915). Callwia reappears very quickly. A 

 test quadrat of 25 sq. ft. showed 2 years 8 months after the fire, 4,641 

 Calluna seedlings in addition to 11,513 seedlings of Erica cinerea. 

 The revegetation here passes through six stages: the first stage is 

 characterized by algae (Cystococcus humicola, Gloeocystis, Trochiscia, 

 Dadylococcus) together with the fungus Ascoholus atrofuscus and 

 sparse shoots from surviving roots of Ulex. The mosses Ceratodon 

 and Funaria appear in the second stage, together with a number of 

 grasses and herbs, such as Aira, Carex pilulifera, and Rumex acetosella. 

 The third stage comprises the algae of the first, along with Mesotaenium 

 violescens and numerous lichens, such as the Cladonias. The flowering 

 plants increase. The fourth and fifth stages are marked by the final 

 predominance of the heath with Calluna, Ulex, and Erica. In the 

 region investigated (Hindhead Common) a sixth and final stage follows, 

 consisting of such trees as Pinus, Betula, and Pirus, a proof that here 

 the heath cannot maintain itself without the aid of man. Aside from 

 the conditions of competition, the changes in humus content and 

 water supply of the upper soil horizon play a great role in the revegeta- 

 tion of a region. Parallel to the accumulation of humus runs the 

 increase in the water content. Thus the bare soil of a burned surface 

 after eight days of rain contained 11.19 per cent; the soil of the Calluna 

 heath, 31.39 per cent, and the Vaccinium myrtillus heath, almost 

 70 per cent of water by weight. 



The revegetation of a heath surface following the removal of the 

 upper surface of the soil, in the northwest German heath region near 

 Hanover, is shown in Fig. 145. The field represents a sheep pasture 

 no longer used, sprinkled with Juniperus in which Pinus silvestris has 

 naturally established itself and increased since cessation of pasturing. 



In the Mediterranean region, in western North America, and in 

 South Africa periodic bush fires are the regular method for the improve- 

 ment of pastures. Continuous repetition of bush fires in southern 

 Europe produces special communities rich in geophytes and thero- 

 phytes which attain widest distribution in southern France and 

 northern Spain. Species of Cistus are the first shrubby pioneers on 

 the burnt places (Fig. 146). They soon collect in extensive clumps 

 but die out after ten to fifteen years if not burned again and are 

 succeeded by other shrubs: upon silicious soils by species of the 

 Lavandula stoechas- Erica scoparia association; and upon soils with 



