LIFE-ZONES IN PENNSYLVANIA
The term Life-Zone is used by scientists in referring to a region where environmental conditions so react upon each other as to form a suitable home for certain plant and animal forms. A Life-Zone naturally has no hard and fast boundaries as does a geographical zone; its boundaries are determined by temperature, rainfall, soil, altitude, drainage, and innumerable other factors, which so create a certain average whole as to attract certain species of plants, birds, mammals, and so forth, which in turn themselves become part of the environment, and are responsible for the presence of certain forms. These Life-Zones are, then, associations which naturally develop in sections where similar conditions exist. In Pennsylvania there are three or four of these associations. One, noticeable in the southern and southwestern counties, has been called the Carolinian Life-Zone. Here such birds as the Carolina Wren, Cardinal, Tufted Tit, and Red-bellied Woodpecker live. In much of Pennsylvania the Alleghenian Life-Zone occurs, where the Least Flycatcher, Wilson’s Thrush, Swamp Sparrow, and Rose-breasted Grosbeak are to be found in summer. Higher in the mountains is the Canadian Life-Zone; here the Junco, Hermit Thrush, Red-breasted Nuthatch, Wilson’s Snipe, and Northern Water Thrush nest. As you read this book, you will notice that many birds are to be found in northern or mountainous counties; others in southern or less mountainous counties, and so forth. This is an indication of Life-Zone distribution.