The Vegetation: Pattern and Succession 195 



Distribution of Growth Forms 



An analysis of the distribution of plant growth forms along the en- 

 vironmental gradients shows that some growth forms have high fidelity 

 for a vegetation type, e.g. the evergreen shrub in the heaths, while other 

 growth forms are distributed through several vegetation types, e.g. the 

 single-stemmed graminoids and the mosses. 



The above- and belowground standing crops and foliage area indices 

 of the vascular plants form clear patterns along the complex environ- 

 mental gradients (Figure 6-5). A comparison of the patterns of foliage 

 area index and productivity shows a general correlation between these 

 two variables similar to that described by Miller et al. (1976). 



The principal factor controlling the distribution of bryophytes ap- 

 pears to be slight differences in microrelief which influence soil moisture 

 regimes. Bryophyte biomass is low on sites with high hydrogen sulfide 

 and highest in the presence of moderately low values for soil moisture 

 and soluble phosphate. The standing crop of forbs and woody dicoty- 

 ledons is highest in dry, well-aerated sites with moderate levels of phos- 

 phorus. 



Aboveground biomass of graminoids increases along the moisture 

 gradient from the Salix heath to the Arctophila pond margin. The Luzula 

 heath has a higher graminoid biomass than the Salix heath because of the 

 caespitose graminoids, such as Luzula confusa, which are abundant on 

 dry sites. In all types except the two heaths, which are relatively dry, the 

 aboveground standing dead is less than the aboveground live for both 

 graminoids and forbs. The decay index for litter and prostrate dead vas- 

 cular plant material, which is the ratio of net aboveground productivity 

 to litter and prostrate dead, is lower on dry sites than on wet sites, and 

 standing dead material is incorporated into prostrate dead and litter frac- 

 tions more easily on the wet sites. 



The distribution of belowground biomass in relation to environ- 

 mental factors differs from that of aboveground material. Belowground 

 biomass is greatest in the most anaerobic soils, and in soils with moderate 

 moisture and high concentrations of soluble phosphate (Figure 6-5). The 

 ratio of aboveground to belowground biomass presents yet another pic- 

 ture, with the lowest ratios (1:40) in moist, partly anaerobic soils with 

 low soluble phosphate concentrations. The ratio increases along the 

 moisture gradient and from anaerobic to aerobic soils. These patterns of 

 belowground biomass support the conclusion (Chapin 1974a, Wielgo- 

 laski 1975c, Chapter 5) that vascular plants develop greater amounts of 

 absorptive root tissue on anaerobic, phosphate-poor soils. But they are 

 also partly an artifact of the changing growth form spectrum along these 

 gradients, i.e. a shift from woody-stemmed species to rhizomatous spe- 



