392 Forestry Quarterly 



of plant formations and it might be well worth the forest investi- 

 gator's attention to study this phenomenon more closely. Perhaps 

 one of the most recent, and at the same time most interesting, 

 studies in plant succession is that conducted by Cooper (90) in 

 the Palo Alto region of California. On the alluvial deposits near 

 the bay he finds : 1. algae in the shallow water of the bay ; 2. salt 

 marsh; 3. composite-willow formation; 4. oak forest of Quercus 

 lobata and agrifolia; 5. chaparral. His investigations show that 

 the salt marsh replaces the algae soon after the soil surface 

 emerges at low tide. The willow formation follows with the 

 elimination of salt from the soil. The oak forest appears when 

 there is sufficient soil depth for the tree roots above the water 

 table. The chaparral follows when the distance to the water 

 table becomes so great that the oaks cannot obtain sufficient soil 

 moisture. The chaparral formation is permanent because it 

 flourishes independently of moisture supply from the ground 

 water. This succession progresses from halophytic to mesophytic 

 and thence to xerophytic. 



Many recent studies in plant succession, as will be noted from 

 the above discussion, are in reality investigations in forest suc- 

 cession. Plant ecologists evidently find in the forest a fruitful 

 field for study. On the other hand, I know of no foresters en- 

 gaged in such studies. Probably the reason for this is that 

 these studies are too purely scientific for the forester who is 

 in a good position to look at such investigations only in the light 

 of their application to silvics or silvicultural practice. Here, as 

 elsewhere, the forest investigator would do well to follow the 

 plant ecologist. He should adopt his methods of studying and of 

 gathering data so that the results secured by plant ecologists and 

 forest ecologists will be mutually helpful. 



The phenomenon known as zonation is perhaps the oldest one 

 recognized by phytogeographers. Zones may he due either to 

 some growth character of the plant or to one or more of the 

 physical factors of the habitat. The latter is by far the more 

 common and more obvious cause. It has long been recognized 

 that vegetaional zones based upon moisture parallel great bodies 

 of water, while zones based upon temperature parallel the equator. 

 The zones found on mountain slopes, which are essentially due 

 to a combination of these two factors, follow the contours of the 

 topography. 



