ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

Table 6. --Average concentrations of nutrients in soi 1 solutions
Treatment
Pi 1 ed Piled
Broadcast burned burned Chipped Chipped
Nutrient Forest burned (under) (between) removed returned
Ni tra te-
ni trogen 0.1 1.5 4.4 1.2 1 .O 0.9
Potassium 0.6 1.6 2.0 1 .O 1 .O 1.6
Calcium 2.6 5.3 11.9 4.2 4.2 6.8
Magnesium 0.7 1.4 3.3 1 .I 1.1 1.6
Sodi um 1.4 1.1 2.2 1 .O 2.0 1.2
All residue disposal methods produced increased concentrations of nitrate-
nitrogen. The percent increase varied from 2- to 100-fold, over that found in soil
solutions under the undisturbed forest. Ten soil solution samples, eight of which
were taken from beneath burned piles, exceeded the maximum concentration of 10 mg/l
establ ished for pub1 i c water suppl ies.
Total phenol concentrations during the first year ranged from practically none
under undisturbed conditions to 0.622 mg/l under chipped-returned and to 0.188 mg/l
under the chipped-removed treatment, Thereafter phenol concentrations declined
markedly, reaching pretreatment values by 1975. The phenols came from a breakdown
and leaching of fresh organic debris--from the chip mulch and from the needles and
fine debris incorporated into the surface mineral soil on the "near complete''
utilization units.
DISCUSSION AND CONCLUSIONS
Growth rates of both planted and seeded lodgepole pine differed markedly among
the four clearcutting and slash disposal treatments. Hopefully, quantitative analysis
of soil and plant tissue would help explain some of this variation. But, despite
gathering a wealth of data that describe the trees and the sites upon which they
were growing, this primary objective was not met. There were no statistically valid
differences in nutrient concentrations within these trees that explain their differ-
ent growth rates. Admittedly, iron concentration in the above-ground portion,
especially in new foliage, was greatest on the piled-burned sites and least on the
chipped-returned sites. This correlates directly with tree growth. However, even
the lowest iron concentrations appear to be more than adequate for satisfactory
conifer nutrition (Leaf 1973).
Logging and slash disposal directly affect the surface (Ao) organic horizon
of forest soils. Most obvious are physical effects such as the disturbance of this
layer and its partial incorporation into the mineral soil beneath. Logging usually
adds fine debris to the Aq horizon. On one of the treatments in this study there
was an even greater addition by mulching with chips. Broadcast burning, in contrast,
often removes part or all of this horizon, and always deposits a layer of ash on the