For April, 1922 



121 



Arctic and Alpine Vegetation 



WILLARD N. CLUTE 



THE tilt given to the axis of our planet when it began 

 its everlasting spin about the sun is responsible for 

 a great deal of that variety with which life is said 

 to be spiced. Among other things it gave us our sea- 

 sons and incidentally that succession of storms and calms 

 that we call the weather. On a globe with its axis per- 

 pendicular to the plane of its orbit, every place on its 

 surface would receive the same length of daylight in the 

 twenty-four hours, but the greatest intensity of light and 

 heat would be at the equator from whence it would de- 

 crease regularly to the poles. Tlit- inclined axis of our 

 own globe, however, makes the sun appear to travel north 

 and south with the seasons over a region forty-seven 

 degrees wide, at one time carrying Summer conditions 

 far northward and at another leaving a vast region about 

 the pole in cold and darkness while it advances Summer 

 toward the opposite pole. 



Under these conditions the vegetation near the equator 

 enjoys perpetual Summer, interrupted only by wet and 

 dry seasons as the sun passes with its belt of clouds, while 

 the plants nearer the poles must adjust themselves to 

 great changes, now exposed to the terrible cold and dark- 

 ness of the long arctic night and now bathed in sunlight 

 for weeks at a time. In latitude 70° the sun in Summer 

 is above the horizon continuously for sixty-five davs and 

 in latitude 80^ it shines iminterruptedly for one hundred 

 and thirty-four days. The decrease in the heat and light 

 intensity in high latitudes is compensated for, in some 

 degree, by the greater length of daylight. At mid-Sum- 

 mer more heat falls on the polar regions in twenty-four 

 hours than falls on the equator in the same time, but in 

 spite of this the lower layers" of the soil remain in the 

 condition they were left in after the last glaciation and 

 have never thawed out. Much of the heat that reaches 

 the earth is used in thawing the upper layers of soil, in 

 melting the ice and snow and in evaporating the water, 

 so that the soil is never really warm. Evaporation, how- 

 ever, is not rapid and in spite of a reduced rainfall the soil 

 over vast areas is wet or boggy. Where drainage is poor, 

 the water stands in puddles between peaty hillocks on 

 which the scanty vegetation grows. 



A broad belt of this nature forms the northern limit 

 of vegetation in both hemispheres and is known as tundra. 

 In its more favorable sections it may support a plant cov- 

 ering of grasses and flowering plants, but elsewhere it is 

 covered with mosses, especially peat mosses, and lichens 

 like the "reindeer moss" (Cladonia) which afTords food 

 for musk oxen, reindeers and other herbivores. 



The most noticeable eiifect that cold produces on plants 

 is a reduction in size. The plants that inhabit cold re- 

 gions are always small and compact in comparison with 

 the same species from more hospitable lands. Great 

 numbers of "cushion-plants" with minute leaves and short 

 stems denselv matted together are found and these, grow- 

 ing in close little communities, form the bloom mats so 

 frequently mentioned in descriptions of northern coun- 

 tries. The flowers for the most part are large, brilliantlv 

 colored and abundant, and stem and leaves often have 

 considerable color also. Many forms are in demand for 

 the rock garden in milder regions. Most of the species 

 whose common names begin with "arctic" belong to this 

 class. 



Owing to the shortness of the Summer season in high 

 latitudes there is no succession of bloom such as we see 

 in milder regions. When Spring comes all vegetation 



Irishes forth with astonishing rapidity and is soon in full 

 leaf and flower. A remarkably small amount of heat is 

 able to induce growth, a few degrees above the freezing 

 point being sufficient. Frosts may occur at any time dur- 

 ing the Summer and the plants be frozen up again and 

 again, but such hardy specimens thaw out again and con- 

 tinue growth unharmed. The woody plants find it ex- 

 tremely difficult to survive such conditions and usually 

 drop out long before the limits of vegetation are reached. 

 Last to give up the struggle are the aspens, birches, 

 alders, and willows. Reduced in stature to the size of 

 small shrubs or undershrubs they make a brave stand 

 but finally only the willows are left and these literally 

 digging themselves in, with trunks under the surface, 

 send up tiny branches with two or three leaves and a 

 few minute flowers. In more favorable conditions large 

 areas are covered with shrubs of the heath family, notably 

 the Labrador tea and huckleberry as well as the heath- 

 like crowberry. 



There are no plant families that are distinctly arctic. 

 All the species belong to families whose centers of distri- 

 bution are farther south. Large deposits of coal in lands 

 now covered with ice and snow, however, indicate that 

 at some distant day the climate must have been very nuich 

 warmer. 



In milder regions mountain tops of sufficient elevation 

 provide conditions for growth somewhat like those that 

 prevail in the arctic lowlands and when the mountain 

 ranges extend roughly north and south they may pro- 

 vide a highway over which northern plants can spread 

 far toward the equator. In many cases the identical 

 species that grow beyond the arctic circle may thus reach 

 nearly or quite to the Alexican boundary. Although 

 comparable to arctic regions as regards temperature, 

 there are various other features of elevated regions that 

 combine to make conditions quite difl:'erent from those 

 near the poles, and this has resulted in a number of forms 

 that resemble northern forms but are better classed as 

 alpine than arctic. Contrasted with arctic regions the 

 mountain tops have a regular succession of day and night 

 and a greater amount of light during the day. Owing 

 to the elevation there is greatly reduced air pressure and 

 less carbon dioxide as well as a marked change of tem- 

 perature daily. The rainfall is often scanty and the ab- 

 sence of cliiuds allows a greater amount of ultra-violet 

 light to penetrate to the earth. In spite of these dififer- 

 ences, however, the mountain summits have much the 

 same general features as the arctic regions. At the 

 highest points are found mosses and lichens similar to 

 those of the tundra and below them are the grasses, 

 cushion-plants and bloom-mats which form the mountain 

 meadows. Still lower come the dwarf shrubs and stunted 

 trees known as the elfin wood close to what is called the 

 "timber line." Near the upper limits of tree growth the 

 vegetation consists of needle-leaved evergreen trees but 

 lower down deciduous broad-leaved trees are found and, 

 if in the tropics, these may merse into the broad-leaved 

 evergreens of the rain forest. Recalling the vegetation 

 of the earth as a whole we discover that it has manv 

 indications of zoning that .sucgest those of the mountains. 

 The principal diiTerence is that a thousand miles in lati- 

 tude corresponds to a few thousand feet in altitude. Be- 

 ginning with the broad-leaved forest at the equator we 

 pass through a zone of deciduous forest to a needle-leaved 

 evergreen belt from which we emerge into a grassland 

 that vanishes far nothward in the arctic tundra. 



