NO. 3 dunkle: plant ecology, channel islands 281 



climates are on such a small scale that but few typical canyon commun- 

 ities occur. Species typical of canyon habitats on other islands are either 

 absent or very restricted in number. Coreopsis and Convolvulus grow 

 luxuriantly in all parts of the canyons. 



Opuntia littoralis is a co-dominant with Coreopsis and Convolvulus 

 on southern slopes. Among other species are Lotus argophyllus orni- 

 thopus, Eschscholzia, Muhlenbergia micros per Tua, Hemizonia fascicu- 

 lata ramosissima, and Amhlyopappus pusillus. On the canyon bottoms 

 and the lower, northern exposures grow several grasses which are 

 apparently limited to these areas such as Melica imperjecta, Bromus 

 ruhens, and B, vulgaris. In such localities will also be found Phacelia 

 floribunda. Plants that seem limited to the north exposures of the 

 canyons include GUia gilioides, Nemophila racemosa, Aphanis?na bli- 

 toideSj and Polypodium californicum Kaulfusii. Additional plants found 

 on other northern slopes as well as on those of the canyons include 

 Trifolium gracilentu7n, Pterostegia drymarioides_, and Eriogonum 

 giganteum compactum. 



The soils on both slopes of the canyons are very coarse with those 

 of the northern exposure slightly finer and with a larger content of 

 humus. On these steep canyon slopes the run-ofiF of storm water has 

 carried away many of the finer and lighter constituents of the soil, 

 though this surface erosion has been somewhat checked by the heavier 

 plant cover of the northern exposures. Thus the northern exposure had 

 36.2 per cent of gravel and 3.6 per cent of silt and clay, while the 

 southern exposure had 43.1 per cent and 4.2 per cent respectively. 



Since observations on other Channel Islands have shown that 

 similarly oriented, but larger, canyons possess much greater differences 

 between the plant communities of their northern and southern exposures 

 than do the small Santa Barbara canyons, it is apparent that even greater 

 enviormental differences must be found on the opposite slopes of these 

 larger canyons. These differences must exist in their evaporation rates, 

 their temperatures, and their soils. 



Sea Bluffs 



The sea bluffs, cliffs, and headlands possess much the same soil 

 composition as do the canyon slopes, i.e., a coarse soil containing less 

 than 10 per cent of silt and clay. They present various exposures and 

 slope angles, and differ greatly in their exposure to wind. The sea winds, 

 coming from great ocean distances and cooled by their contact with 

 the water, possess a greater relative humidity than they maintain after 



