Tab le 2 . - - Average density and its variation for six particles 



comprising cheatgrass 



Average Number of Standard Coefficient 



density observations deviation of variation 



G . /cc . G. /cc. Percent 



Stalks 



0.36 



10 



0.03 



8.4 



Leaves 



.25 



10 



.02 



7.9 



Peduncles 



.51 



10 



.06 



12.0 



Spikelets 



.57 



5 



(^) 



(1/) 



Awns 



.59 



15 



.28 



46.6 



Glumes 



.21 



15 



.03 



12.7 



^Not calculated. 



Density 



Density of ponderosa pine needles free of decay averaged 0.51 gram per cubic 

 centimeter with a standard deviation of 0.046 gram per cubic centimeter for thirteen 

 10-needle samples. Decay of needles ordinarily reduces their density as was evidenced 

 in another sample of needles, some slightly gray in color and harboring incipient de- 

 cay. Density of this sample, determined for 620 needles from three stands, averaged 

 0.47 gram per cubic centimeter. 



Density for the entire cheatgrass plant averaged 0.34 gram per cubic centimeter 

 (table 2). Density of stalks is based on a volume figure containing some void space, 

 since the centers of the larger stalks are hollow. Consequently, density of stalk 

 material itself should be greater than density of the entire stalks. Density of awns 

 varied considerably, most likely because their shapes were assumed to be frustrums of 

 right cones; whereas in truth, they vary from elliptical to circular in cross section. 

 Their irregular shape and minute size made accurate determination of their volume 

 difficult. 



Table 3. -- Fuel properties of the forest floor L layer from 13 stands of 



ponderosa pine 



Fuel property 



Highest stand 



Lowest stand 



Average 



2/ 



S.E. 



Loading (g. /m. 2) ^ 

 X Ccc./cm. ) 

 Particle spacing (cm.) 

 Bulk density (g./cc.)^ 



oA 



601 

 1. 23 

 .90 

 .0429 

 58.5 



129 



.45 

 .44 

 .0049 

 20.0 



324 



.82 

 .66 

 .0158 

 37.5 



62 



.08 

 .04 

 .0033 

 4.9 



^Stand values are averages from five plots. 



2^^ J J J- J T / mean square tor error 



^Standard error of stand averages equals ■\/ — —. 



^ V treatment replications 



where values for this calculation are provided from an analysis of variance with stands 



as treatments (Steel and Torrie 1960, page 104). 



^Ovendry basis . 



9 



