CHAPTER XX 

 PHENOLOGY 



Phenology, the word being a shortened form of phenomenology, 

 is a branch of ecology that deals with the seasonal occurrence of the 

 various vital phenomena of plants, such as leafing, blooming, fruit- 

 ing, falling of leaves, etc. Interesting and valuable phenological 

 studies can be made anywhere without expensive equipment and 

 phenology thus lends itself well for field work for classes or for indi- 

 vidual students of ecology. Such studies are very valuable in con- 

 nection with work on plant communities since it is not possible to 

 understand the morphology of an association, nor the relations of the 

 component species to the environment, without knowing something 

 of the phenology of the plants concerned. The time of flowering of 

 any particular species of plants varies from year to year because of 

 varying climatic conditions but there is sufficient regularity so that 

 in periodic climates, such as are found throughout the United States, 

 rather definite seasonal aspects can be recognized in most associa- 

 tions. Only four will be discussed in this chapter. 



139. Seasonal Succession in a Deciduous Forest.— Considering a 

 deciduous forest in the east-central United States at about 40° north 

 latitude as an example, six seasons can be quite readily recognized. 

 These are as follows: 



■ A. Winter Season.— During the winter the trees are essentially 

 inactive and have dropped their leaves as a means of conserving 

 the water supply during a season when absorption is difficult or 

 impossible. Most other plants are also in a resting condition either 

 as rhizomes, corms, bulbs, tubers, wintergreen rosettes, or seeds. 

 There are a few algse and fungi, and perhaps a few mosses, that are 

 more or less active all winter but in general the forest is in an inactive 

 condition. 



B. Prevernal Season.— The prevernal season begins with the first 

 activity of the plants, usually late in March or early in April, and 

 lasts until the leaves of the trees are out, usually in early May, 

 Many trees bloom during this season as do also the early spring 

 flowers. These early spring flowers, such as hepatica, bloodroot 

 (Sanguinaria canadensis) (Fig. 104), spring beauty (Claytonia 

 virginica), dutchman's breeches {Dicentra cucularia), etc., all take 

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