Table 3 — Number and distribution of active ectomycorrhizal root tips in soil strata; 

 all samples taken during June to July peak activity period (Harvey and 

 others 1978) 



Percent distribution of 





Number 





ectomycorrhizal root tips in 





Site 



ectomycorrhizal 























number and 



roots (x) all 







Decayed 



Shallow 



Deep 



acronym 



strata combined 



Litter 



Humus 



wood 



mineral 



mineral 





No. /liter 







- - Percent 



















Old-growth' 















5(WWP-I) 



2120" 



3iQab 



57" 



26"" 



6= 



I'' 



4(WH-I) 



95*" 



gacde 



67" 



16"=" 



8" 



3^ 



1(WH-M) 



93*" 





32" 



51""= 



IQac 



1" 



7(SAF-WY) 



65" 





37" 



28" 



28" 



1" 



8(PP-W) 



60" 





gac 



yac 



74" 



lO'^ 



2(SAF-M) 



2V 







74a 



igbc 



6" 



1" 



6(GF-I) 







13" 



31" 



20" 



10" 



3(DF-M) 



11^ 



14a 



30" 



31" 



21" 



2" 



Second-growth 















9(MIX-i) 



49" 





47" 



35""" 



10"= 



2" 



lO(LPP-i) 



41" 





15" 



57"" 



15" 



2" 



13(PP-i) 



29" 







25" 



61" 



11" 



2" 



14(LPP-y) 



14^ 







36" 



40" 



21" 



3" 



ll(WL-y) 



7^ 



V 



23" 



yab 



57' 



11" 



12(DF-i) 



4^ 



20" 







46" 



33" 



1" 



iSee table 1 for explanation of abbreviations. 



^Differing letters indicate significant differences (o = 0.05) between sites, down column (w-z), 

 and within strata and site, across (a-e). based on two-sided t-test of numbers of short root 

 tips/liter. 



^Ectomycorrhizal distribution in individual strata shown as a percentage of the total to 

 facilitate between site comparisons. 



seasons. Also, many sites with limited organic matter pro- 

 duction have few substantial deposits accumulated, and 

 those that do are likely to be disrupted by harvesting- 

 related disturbances and natural wildfires. These results 

 appear to support a management recommendation to 

 maintain 2.4-3.6 tons/ha (10-15 tons/acre) (based on the 31 

 to 45 percent volume class) of woody residues to maintain 

 soil organic reserves (Harvey and others 1981). 



The concentration of ectomycorrhizal short root tips in 

 shallow organic horizons (table 5) makes them extremely 

 vulnerable to external perturbation. Even moderate 

 physical disturbance or heating is likely to produce high 

 mortality of short roots from nearby trees. Also, because 

 it is now apparent that moisture laden with air pollutants 

 (acid rain) can inhibit ectomycorrhizal activities (Reich and 

 others 1985), their concentration in shallow horizons of In- 

 land West forests may make them extremely vulnerable to 

 air pollution damage. A shallow distribution of feeder 

 roots from conifers has been noted (Fogel and Hunt 1979; 

 Maser and Trappe 1984; Mikola and others 1966; Vogt and 

 others 1981). 



In the two instances reported here where the most ecto- 

 mycorrhizal short root tips were not concentrated in the 

 organic horizons (table 5, sites 8— old-growth ponderosa 

 pine— and 11— second-growth western larch), they were 

 concentrated in the topmost mineral layer (table 4). In one 

 of these instances the dominant host (ponderosa pine) is a 

 relatively deep-rooted species (Steinbrenner and Rediske 



1964) growing on an extremely dry site where surface 

 moisture is episodic and rare during the growing season. 

 In the other instance, the dominant host was young 

 western larch, a well-adapted pioneer species growing on a 

 highly disturbed site with little surface organic matter 

 present. 



When soil organic matter content was grouped into 

 volume classes for each site, numbers of active short root 

 tips compared between classes showed no significant dif- 

 ferences in distribution (table 4). However, a strong trend 

 toward low numbers in the highest organic matter class 

 (> 45 percent of the core) was evident. Also evident was 

 the low percentage volume of the cores represented by 

 organic fractions in all but the most productive ecosystems 

 (table 2, table 4). When the comparison between organic 

 classes was made on a larger sample base (150 cores), sig- 

 nificant differences between classes within the Coram Ex- 

 perimental Forest sites in Montana for old-growth western 

 hemlock, subalpine fir, and Douglas-fir (sites 1, 2, 3) were 

 found (table 4). 



A comparison of the distribution of ectomycorrhizal 

 short root tips in all organic versus all mineral soil frac- 

 tions (combined) showed a strong, frequently significant 

 trend favoring organic fractions for all but the old-growth 

 ponderosa pine and second-growth western larch sites 

 (sites 8, 11) (table 5). A direct measurement of the depth 

 of organic horizons (litter, humus, and decayed wood com- 

 bined) showed the extreme shallow nature of organic 



5 



