320 

 280 



1975 1976 



Figure 1 .--Available nitrogen levels in the humus layer (O2) after a pre- 

 scribed fire in a clearcut Douglas-fir/ western larch stand. 



Table 2.~Soil populations of autotrophic nitrifying bacteria 

 {NItrosomonas) before and after a prescribed fire 





Bacteria/g of dry soil 



Soil layer 



Before burn Six weeks after burn 



Humus (O2) 



800 3 280* 



Mineral (0-5 cm) 



240 960* 



* = significant difference 0.01 <p <0.05. 



Table 3.~Available soil nitrogen (NH^ and NO3) content as affected by prescribed fire 



After fire 



Soil layer Before fire 2 days 6 weeks 9 montfis 13 months 



Lb/acre(kg/ha)- 



0-1 + O2 



1.9 



(2.1) 



9.0 



(10.1) 



4.4 



(4.9) 



1.6 



(1 



8) 



0.7 



(0.8) 



Decayed wood (O3) 



1.8 



(2.0) 



6.5 



(7.3) 



6.2 



(6.9) 



5.2 



(5 



8) 



2.1 



(2.3) 



Mineral 

























- 5 cm 



1.2 



(1.3) 



2.9 



(3.3) 



5.1 



(5.7) 



2.1 



(2 



4) 



.7 



( .8) 



5 - 22 cm 



3.7 



(4.2) 



4.8 



(5.4) 



7.0 



(7.9) 



5.2 



(5 



8) 



2.4 



(2.7) 



All layers 



8.6 



(9.6) 



23.3 



(26.1) 



22.7 



(25.4) 



14.1 



(15 



8) 



5.9 



(6.6) 



3 



