Er. Ingham et Wg. Thies, RESPONSES OF SOIL FOODWEB ORGANISMS IN THE FIRST YEAR FOLLOWING CLEARCUTTING AND APPLICATION OF CHLOROPICRIN TO CONTROL LAMINATED ROOT-ROT, Agriculture, ecosystems & environment. Applied soil ecology, 3(1), 1996, pp. 35-47
Alteration in soil foodweb organism populations (numbers, biomass and
activity) were monitored following clearcutting of a mature 70-year ol
d Douglas-fir forest and compared with an uncut mature Douglas-fir sta
nd. Changes in soil foodweb organisms were assessed following applicat
ion of chloropicrin to stumps in the clearcut to reduce infection by P
hellinus weirii, which causes laminated root rot. The effect of chloro
picrin was measured using two different spatial scales: (1) around tre
ated stumps, and (2) within 0.2 ha areas where all stumps within the a
rea were treated with chloropicrin. A 10-fold decrease in total fungal
biomass, between 2- and 3-fold reductions in total bacterial biomass,
a 2-fold reduction in nematode numbers and a nearly 10-fold reduction
in the ratio of total fungal to total bacterial biomass were observed
between 9 months to a year following clearcutting. Active fungal biom
ass in the 20% chloropicrin treatment was reduced 1 year (October) aft
er application Reduction in amoebae numbers were observed between Apri
l and June in the 100% chloropicrin treatments, while no effects of ch
loropicrin on total fungal biomass, total bacterial biomass, flagellat
e, ciliate or nematode numbers were observed. The ratio of total funga
l to total bacterial biomass was reduced as compared to the control in
the 100% chloropicrin-treated infected areas in April following chlor
opicrin treatment. Chloropicrin decreased soil foodweb organisms in on
ly one out of 45 random soil samples from 0.2 ha areas. In samples col
lected from around stumps, three points out of 180 had significant dec
reases in all organism numbers as compared to non-chloropicrin treated
stumps. Chloropicrin-sensitive tomato and alfalfa seedlings, planted
at 2 m from stumps to monitor the release of chloropicrin from stumps,
indicated there was no significant release of chloropicrin in the fir
st year following clearcutting and chloropicrin application.