422 S. F. MacLean, Jr. 



E 6000 



E 



u 

 in 

 O 



E 

 o 



m 

 □ 



01 



4000- 



o 

 _ a. _ 



o 



o 

 o 

 o 



6000 



E 

 in 



S 4000 

 o 



CD 



^ 20001- ° -I o 2000 



0> 



k. 

 0) 



'0 20 40 60 « 20 30 40 50 



Current Year's Vascular Growth Accumulated Orgonic Motter 



b. 



o 

 o o 



o 

 o 



o 



° o ■ 



g m"^ 



I 60 

 o 



3 



kg m" 



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o 



0) 



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40- 



c 

 a> 



- O C. 



o 

 _ o 



o 

 o 





 20 30 40 50 



Accumulated Organic Matter 



kg m' 



,-2 



FIGURE 11-3. The relationship of invertebrate biomass to 

 current year's vascular plant growth (a) and total organic 

 matter to 20 cm (b), and of vascular plant growth to total or- 

 ganic matter to 20 cm (c). (After MacLean 1974a.) 



with depth than does biomass of microorganisms. 



Invertebrate abundance and biomass can also be compared to the 

 amount and distribution of net primary production, which represents in- 

 put of fresh substrate for heterotroph activity. Peak season aboveground 

 vascular plant biomass was used as an index of annual input into the var- 

 ious microtopographic units. This measure is available for five of the 

 study plots in which invertebrate populations were sampled. Total inver- 

 tebrate biomass shows a strong positive correlation with this index of pri- 

 mary production on these five plots (Figure 11 -3a). 



In many ecosystems concentration of invertebrates near the soil sur- 

 face maximizes their access to fresh substrate in the form of litter falling 

 from a plant canopy to the ground surface. In tundra plants, however, 

 the larger part of the annual primary production is invested in roots and 

 rhizomes (Chapter 3). Billings et al. (1978) estimated the annual root 

 turnover of the Carex-Oncophorus meadow as between 60 to 65 g m'^ 

 yr"' and 90 g m'^ yr"'. Even the minimum estimate is in excess of annual 



