The Vegetation: Pattern and Succession 193 



the gradient of increasing soluble phosphate, the sequence of vegetation 

 types runs from Carex-Eriophorum meadow, Carex-Oncophorus mea- 

 dow and Carex-Poa meadow to the heaths, Arctophila pond margin and 

 Dupontia meadow. The three vegetation types associated with the lowest 

 phosphate concentrations occur on sites that receive no drainage water or 

 influx of minerals, while the types associated with higher concentrations 

 are found on mineral soils on sites receiving an influx of drainage water. 



Turnover rates (grams incorporated annually per gram standing 

 crop) in a particular vegetation type depend on the species or growth 

 forms present (Table 6-2). Turnover rates for aboveground biomass are 

 about 1.0 yr"' for those vegetation types that are mainly composed of 

 graminoids and forbs. In the Salix heath and Carex-Poa meadow, 

 woody dicotyledons are common and biomass turnover rates are about 

 0.6 yr"'. The woody dicotyledons in these vegetation types have low turn- 

 over rates; several individuals of Salix pulchra were at least 20 years old, 

 as determined by counts of terminal bud scars on the branches. 



Turnover rates of standing dead range from 0.3 yr"' in the Luzula 

 heath to 3.2 yr"' in the Arctophila pond margin. The turnover rates for 

 standing dead in the Carex-Oncophorus, Dupontia and Carex-Erio- 

 phorum meadows are 1.0 yr"' to 1.3 yr"'. The turnover rate of standing 

 dead is affected by the rates at which standing dead is blown or washed 

 away from the site or pressed prostrate by snow and rain. 



Turnover rates of litter and prostrate dead are from about 0.2 yr"' in 

 the Salix heaths to 1.8 yr"' in the Arctophila pond margin. Turnover 

 rates are 0.6 to 0.9 yr"' in the Carex-Oncophorus, Dupontia and Carex- 

 Eriophorum meadows. These turnover rates are affected by the rates of 

 removal of material from the site, by rates of decomposition and by rates 

 of incorporation of the vascular material into belowground material, 

 which depends partly on the rate of vertical growth by moss. 



The turnover rates for all aboveground dead material are about 0.2 

 yr"' in the heaths, 0.4 yr"' in the Dupontia and Carex-Eriophorum mea- 

 dows, and 1.2 yr"' in the Arctophila pond margin. These turnover rates 

 imply residence times of dead material of less than a year in the Arcto- 

 phila pond margin, to 2 to 2.5 years in the meadows, to 6.3 years in the 

 heaths. Residence times of aboveground material in all vegetation types 

 are between 1.9 and 7.7 years, and are about 3.4 years in the Dupontia 

 and Carex-Eriophorum meadows. 



Belowground turnover rates are estimated from root longevity data 

 when available (Chapter 5). Root longevities are about 5 years in Dupon- 

 tia and 8 years in Carex aquatilis, giving turnover rates of 0.2 to 0. 12 yr"' 

 for the Dupontia and Carex-Eriophorum meadow types. Lower turn- 

 over rates are expected for the belowground parts of the woody dicoty- 

 ledons. 



