Canopy Cover 



The plots located in the openings had the least canopy coverage, ranging from 2 

 to 6 percent. The natural and canopy plots had the greatest canopy influence, with 

 over 80 percent coverage. The canopy coverage on the other plots fell between these 

 two groups, ranging from 35 to 72 percent. 



Linear regression analyses comparing percentage of canopy cover to other physical 

 factors give the following correlation coefficients: litter depth, +0.85; total radia- 

 tion (9:30 a.m. - 3:30 p.m.), -0.91; maximum soil surface temperatures, -0.78; soil 

 moisture 2 days after a rainfall, -0.84. These correlations indicate that increased 

 canopy probably leads to greater amounts of organic matter, and decreased sunlight, 

 soil temperatures, and rainfall occurring on the forest floor. Other factors such as 

 vegetation and litter depth will also affect soil moisture, but the interception ability 

 of the pine canopy must be emphasized. 



Solar Radiation 



Total solar radiation amounts for 6 hours received on the opening and pine- 

 associated treatments ranged from 350 to 390 g-cal/cm^ (9 to 10 Btu/in^) and from 130 

 to 340 g-cal/cm^ (3 to 9 Btu/in^), respectively. The plots in the openings, having 

 little canopy influence, received the highest amounts of radiant energy. Some pine- 

 associated plots also received long periods of full sunlight because they were posi- 

 tioned with few or no potential shade trees to the south or overhead. Nearly all 

 variations of shading were encountered. 



Maximum Soil Surface Temperatures 



The range of maximum soil surface temperatures for the opening plots was 138° to 

 151°F (57°-66°C). This was similar to temperatures encountered on the pine-influenced 

 plots, 109° to 158°F (43° to 70°C) . Maximum temperatures were recorded where litter 

 and other organic matter were present; the litter, the opening-litter, the opening- 

 natural, and the fire treatments (due to the black surface). The removal of litter and 

 live vegetation in the openings resulted in lower surface temperatures as was observed 

 on the opening-cleared treatment. Heavy canopy reduced temperatures somewhat, but sur- 

 face temperatures were lowest on those treatments with the combined effects of bare 

 mineral soil and large amounts of canopy cover. This latter situation occurred on the 

 canopy and near treatments. 



Soil Nutrient Analysis 



Three of the eight exchangeable cations--iron, copper, and zinc--showed very little 

 variation between treatments throughout the summer. The iron averaged 2 to 4 yg/g of 

 soil, the copper averaged 2 to 3 vg/g, and the zinc averaged 1 to 2 vg/g- 



The amounts of calcium and sodium showed slightly greater treatment variation, but 

 seemingly not enough to cause growth differences. The calcium content in the opening 

 treatment soils averaged 2,300-1,800 vg/g of soil throughout the summer, whereas soil 

 from the pine-influenced plots averaged 2,200-1,600 yg/g over the same period. Sodium 

 from the pine-influenced plots averaged 11 yg/g of soil throughout the growing season. 

 The opening plots contained 2 to 3 yg/g less than these. 



The remaining three cations--manganese, potassium, and magnesium--were more vari- 

 able, but it is obvious that those treatments associated with the ponderosa pine stand 



8 



