The Vegetation: Pattern and Succession 201 



photosynthetic rates (Tieszen and Wieland 1975). Reserve materials are 

 stored below ground (AUessio and Tieszen 1975a). The meristematic re- 

 gion that overwinters is either just below the moss or soil surface, or pro- 

 tected above ground by dead but persisting leaf sheaths. Forbs of the ros- 

 ette, erect, mat or cushion types have high leaf growth rates and syn- 

 chronous leaf production early in the season. The leaf duration is one 

 growing season. The respiration rate during leaf growth is high, but net 

 photosynthetic rates may be moderate (Tieszen 1973). Materials stored 

 below ground in rhizomes and roots are mobilized early in the season to 

 support the rapid growth (Mooney 1972). The perennating bud is located 

 below ground or at the soil surface. 



Deciduous shrubs have a high leaf growth rate and synchronous leaf 

 production early in the growing season. Respiration rates are high during 

 the leaf growth period, and photosynthesis rates are high; for example 

 photosynthesis rates of Salix are higher than those of the graminoids 

 (Chapter 4). The perennating buds are above ground and materials are 

 stored in stems through the winter. The aboveground location of the per- 

 ennating buds and stored materials makes the deciduous shrubs suscep- 

 tible to grazing and to loss of plant parts due to abrasion by wind. The 

 production of wood by the deciduous shrub involves a large biosynthetic 

 cost, since the efficiency of lignin synthesis is comparatively low (Table 

 5-5). The deciduous shrub also has a relatively low root biomass (Chap- 

 ter 3), which reduces the total maintenance cost. 



Evergreen shrubs usually have synchronous leaf growth (Johnson 

 and Tieszen 1976) with a low rate of leaf turnover, although some, e.g. 

 Dryas integrifolia, have sequential but low rates of leaf production (Svo- 

 boda 1977). The respiration rates of evergreen woody shrubs are rela- 

 tively low because of the low rates of growth. Photosynthesis rates based 

 on leaf dry weight are also low, about half those of the graminoid form, 

 but may be similar to the graminoid on a leaf area basis (Johnson and 

 Tieszen 1976). Leaf resistance to water loss may be low in spite of their 

 xerophytic appearance (Kedrowski 1976, Oberbauer 1978). Materials are 

 stored in the stems and leaves through the winter, perhaps in the form of 

 lipids. The perennating buds are located above ground. The evergreen 

 form is found on exposed locations that are snow-free early in the sea- 

 son. It can photosynthesize early when the surface is warm, even though 

 the soil and roots are frozen, since all the materials required for photo- 

 synthesis are stored in the leaf. It commonly survives desiccation and 

 grows late in the season. The form also occurs in late-lying snowbeds. 



The moss and lichen forms grow throughout the season whenever 

 moisture and temperature conditions permit photosynthesis. Respiration 

 and photosynthesis are low in relation to graminoids (Chapter 4). Mate- 

 rials are stored where they are formed; translocation is uncommon (Col- 

 lins and Oechel 1974). The intake of minerals by moss depends largely 



