456 



ZOOLOGY 



Practical 

 value of 

 study of 

 life zones 



The zones 

 defined 



Boreal 



Mount Tamalpais is drier and warmer than the Muir 

 Woods immediately below, and the normal relation- 

 ship of the zones is reversed. 



3. From the above considerations it may well ap- 

 pear that the whole subject is so complex as to make the 

 definition of zones impossible. We are, indeed, warned 

 against a too rigid application of Dr. Merriam's prin- 

 ciples ; but the experience of years has shown that the 

 life-zone theory is not only essentially sound, but of 

 very great practical importance. Nature has been 

 experimenting for ages past; her records are far more 

 complete than those of the meteorologists, and she has 

 determined by severe processes of selection what life 

 may exist in each locality. Consequently, if we study 

 the native biota, - - that is, the wild life of a region, - 

 and determine that it exists under a given set of con- 

 ditions, then the appearance elsewhere of the same 

 biota comes to be an indicator of climate. Such an 

 indicator does not take account of single factors alone, 

 such as temperature, but includes everything which 

 is significant. Reasoning in such ways, we are able 

 broadly to indicate in advance what crops will be 

 likely to succeed in new localities, - - something of 

 peculiar importance in a country like ours, where 

 agriculture and horticulture are continually extending 

 their boundaries. 



4. The life zones in North America may be defined 

 as follows, beginning with the northernmost : 



A. BOREAL (borealis, northern). This may be 

 divided into three zones, as follows : 



(a) Arctic-alpine Zone. In the arctic regions, beyond 

 the limit of trees, and on mountains above 

 timber line. The arctic and alpine parts differ 

 in one important particular. Arctic regions 



