and October respectively. As of early November the soil in the heated section remained essentially 

 unfrozen to the surface and was under 0.5 m of drifted snow. Biological sampling of this heated 

 experimental plot began in the fall and will continue throughout 1971. 



Primary producers 



The total above-ground production was reduced on the clip and clear plot, even though the 

 active layer depth was somewhat greater than that on the controls. Apparently the physical effects 

 of removing vegetation inhibit production, possibly by removing the insulating and protecting features 

 of the standing dead canopy. Reduced production has been observed by previous investigators in 

 the growing season following heavy grazing by lemmings. 



Reduced production was also seen on the plot subjected to heavy mulching. The effect on the 

 canopy was to increase light extinction simultaneously with an increase in air temperature. Depth 

 of thaw was reduced. The interaction of these factors resulted in a reduced production . 



Rather surprisingly, fertilization produced no measurable increase in above-ground production 

 in the year of application, although visible effects such as increased greenish color were discern- 

 ible. This result contrasts sharply with results obtained at another Barrow site (Fig. 2, site 10) 

 where fertilizer was applied between 1961 and 1964 



Site 10 

 1970 Fertilized Control 



Production, g/m^ 

 Standing dead, g/m^ 

 Depth of thaw, cm 



There, the residual effect of fertilization, six years after the last application, is still striking. The 

 difference in depth of thaw is probably related to the very thick layer of sphagnum moss which has 

 developed on the fertilized plot. The fact that high production is associated with a shallow depth 

 of thaw and, most likely, low soil temperatures argues against the importance of these factors in 

 inhibiting production on the mulched plot, discussed above. Results obtained on this previously 

 fertilized plot suggest that effects of fertilization on the site 2 plots may become more evident in 

 subsequent years. Alternately, the 1970 sampling intensity for the peak season sample may not 

 have been large enough to account for plot variability. 



Above-ground production was slightly greater on the site 1 control plots than on the site 2 

 control plots. At site 1 production was apparently reduced by oil treatment and by physical dis- 

 turbance. Again limited sample size precludes definitive conclusions. On both sites chlorophyll 

 m^ and leaf area index were closely correlated with production. The major deviation was the rela- 

 tively high chlorophyll value found in the greenhouse. This can probably be attributed to relatively 

 greater proportions of photosynthetic tissue in the plants exposed to slightly higher air temperatures 

 and slightly lower light intensity. Similarly, although peak season production was reduced in the 

 clip and clear and mulched plots, seiiescence and deterioration of chlorophyll occurred much 

 sooner on the cleared plots than on the mulched plots. 



Consumers 



The use of 6 x 6-m study plots was not suitable for the study of vertebrate consumers, since 

 each individual ordinarily moves over areas larger than the manipulated plots. Soil arthropod 

 populations were observed at 10-day intervals in the control plots and in the clip and clear, clip- 

 aiid uncleared, and lightly mulched plots. There was no detectable difference between populations 

 of the two species of Tipulidae on tiie control and nuinipulated plots. Because of the extended life 

 cycles of arctic Tipulidae the density of larvae on these plots resulted from eggs laid in previous 

 seasons, before the manipulations were imposed. The emergence of adult crane flies was also 



64 



