ECOLOGY 



32 



dunes and bad lands, on the exfoliating sedges, which in their turn yield to 

 domes of Yoscmite and in the sinter grasses and afterwards to shrubs, or in 

 and diatom basins of Yellowstone gey- some cases to the latter directly. 

 5gfs When the ruling caste of woody 



Wherever an area is bare or is de- plants is once established in a forest 

 nuded by natural agencies or by man climate, trees of small demands and 

 and his animals, development begins, rapid growth overshadow the shrub 

 progressing slowlv or rapidlv in accord- stage, and later yield to the invadmg 

 ance as the site is water, rock or actual phalanx of climax trees of slower 

 soil, and passing through a series of growth but greater permanence. In the 

 communities to end finally in the cli- prairie region, the succession termmates 

 max proper to each climate. with a community of drouth-resisting 



Primary successions on granite may grasses, since the rainfall is not suffi- 

 require a thousand years or more be- cient to permit the development to 

 tween the pioneering erustlike lichens continue to forest, 

 and the climax forest of oak or pine, On rocky ridges, mountain peaks, 



and hundreds of years to fill a lakelet lava fields and boulders everywhere, 

 to the point where meadow or wood- the course of succession is quite dif- 

 land can flourish on the humus soil, ferent. By contrast with water plants. 

 By contrast, secondary successions fol- the chief task of the pioneers is to con- 

 lowing fire or cultivation mav take no vert rock into soil and to increase the 

 more than a half-century for' the com- water rather than diminish it. In the 

 plete cycle, and an abandoned field in miniature deserts of rock-surfaces only 

 the prairie may be reclaimed by the the humblest plants can thrive, such as 

 grasses in a decade or two. lichens and mosses which are capable 



of enduring desiccation for months. 

 The first settlers are crustlike 

 SUCCESSION IN WATER AND ON ROCK lichcns, which ctch the surface and 



slowly produce a thin layer of dust. 

 Probably the most familiar kind of After many years leafy species gradu- 

 succession is that found in standing ally invade and carry the task forward, 

 water, with its communities of pond- yielding to mosses as a thin soil appears 

 lilies, cat-tails, bulrushes and sedges, in crack and crevice. As the soil in- 

 The pioneer colony of this series is creases in depth, tiny saxifrages and 

 founded by submerged stoneworts, other "rock-bearing" herbs enter, and 

 pondweeds, hornworts and the like in these are followed after an interval by 

 water up to about 20 feet. grasses. From this stage, the general 



As these grow and decay, the pond course is the same as that in succession 

 is gradually filled to the level at which from water, inasmuch as grasses are 

 floating plants can push in and take followed by shrubs and these by trees 

 possession. These then rule as con- in the case of a forest climate, 

 querors for a while, but likewise bring 



about their own downfall by shallow- succession in soils 



ing the water so that bulrushes, cat- 

 tails, wild rice and reed-grass can in- Succession on sand dunes takes 

 vade, usually in this order. The remains place more rapidly and dramatically 

 of these accumulate even more rapidly since soil of a sort is already present 

 and in a few decades the pool may be- and the major problem is to fix the 

 come a wet meadow covered with shifting sand and enrich it with plant 



