194 P.J. Webber et al. 



GROWTH FORMS AND ENVIRONMENTAL CONTROL 

 Definition of Growth Forms 



The factors controlling the distribution of plant populations could 

 not be analyzed at the scale of resolution of individual species, however 

 desirable such analyses might be, because of the lack of complete data on 

 all species. Thus the plant species were grouped into growth forms based 

 on aboveground characteristics (Figure 6-2), Since the early work of 

 Raunkiaer (1934), the importance of plant growth forms as strategic 

 adaptations to the tundra environment has been emphasized (Bliss 

 1962a, Tikhomirov 1963, Chabot and Billings 1972). The evidence is that 

 growth forms are selected in different habitats, and therefore are a mean- 

 ingful basis on which to analyze different plant-environment interac- 

 tions. The growth form categories are based primarily on the nature of 

 the shoot habit, although some categories, such as bryophytes and 

 lichens, are systematic or phylogenetic in character. Nevertheless, bryo- 

 phytes and lichens seem to be valid growth forms in the tundra. 



Woody shrubs in the coastal tundra at Barrow are all of low stature 

 and many are prostrate. Shrubs are subdivided on the basis of being ever- 

 green or deciduous. The genus Salix is the principal representative of the 

 deciduous shrub while Cassiope tetragona and Vaccinium vitis-idaea 

 represent the evergreen shrub. Herbaceous plants with elongated, narrow 

 leaves are represented by the graminoids, i.e. grasses, sedges and rushes. 

 The graminoids are subdivided into those with crowded, bunched shoots, 

 here called caespitose graminoids, and those with well spaced individual 

 shoots, here called single graminoids. Luzula confusa and Eriophorum 

 vaginatum are examples of caespitose graminoids and Dupontia fisheri 

 and Carex aquatilis represent the single graminoids. 



Four growth forms are recognized for the broad-leaved herbs or 

 forbs. Acaulescent, or essentially stemless, plants with a rosette of radi- 

 cle leaves, such as Saxifraga nivalis and Pedicularis lanata, are called 

 rosette forbs. Broad-leaved herbs with erect leaves or leaves supported 

 into the canopy on long petioles or on an erect stem are called erect forbs 

 and are represented by Polygonum viviparum and Petasitesfrigidus. Mat 

 forbs such as Cerastium jenisejense and Stellaria humifusa have tightly 

 matted, often long, prostrate stems with leaves along the length of the 

 stems. Cushion forbs have short, crowded stems, often coming from a 

 single tap root, which give the plant a hemispherical shape illustrated by 

 Saxifraga caespitosa and Silene acaulis. 



