Influence of Fire on Soil Nutrients in a Ponderosa Pine Type

Abstract

Plant bioassays, with lettuce and ponderosa pine seedlings as indicator plants, and chemical analyses were used to investigate differences in macronutrient availability in soils from areas of different wildfire burn histories. Soils originating from the same parent material were collected from unburned areas consisting of a large control area, having no known history of burning, and two small relict unburned areas, located within two large areas that had been burned over by a severe wildfire at different times in their history. The vegetation, litter, and soil profiles of the relict areas suggested that the soils of these areas were very similar to those of the control area, which indicated that the soils of all three areas were alike before the advent of wildfire into the two burned—over areas. The assays essentially substantiated this conclusion. Soils were collected from the same three areas, with the difference that two were from central locations in the large areas burned over by wildfire. Thus representative soils were obtained from areas with no known history of burning, an old burn (over 12 years old), and a recent burn (3 years old). Assays indicated that nutrient availablility in these soils was completely different, and this difference apparently was due to the effect of wildfire on the soils. Fire, through its effect on soil nutrients, could thus exert a profound effect on the nature and growth of the surface vegetation.