RESPONSES OF SOIL FOODWEB ORGANISMS IN THE FIRST YEAR FOLLOWING CLEARCUTTING AND APPLICATION OF CHLOROPICRIN TO CONTROL LAMINATED ROOT-ROT

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.