The Long-Term Effects of Wildfire and Post-Fire Vegetation On Sierra Nevada Forest Soils.

This paper compares carbon and nutrient contents in soils (Alfisols derived from andesite), forest floor and vegetation in a former fire (1961) and an adjacent forest in the Sagehen Watershed in the Sierra Nevada Mountains of California. Soils from the former fire (now occupied predominantly by Ceanothus velutinus, a nitrogen-fixing shrub) had significantly lower contents of extractable SO₄^2- and P (both Bray and bicarbonate) but significantly greater contents of exchangeable Ca²⁺ than the adjacent forested site (dominated by Pinus jeffreyii). ¹⁵N data suggested that N fixation had occurred in the former fire site, but N contents did not differ between the two sites. O horizon carbon and nutrient contents did not differ between the two sites, but vegetation C and nutrient contents were significantly greater in the forested than former fire site. These results contrast with those at Little Valley Nevada where soil (Entisols derived from granite) C, N, Ca, Mg, and K contents within the former fire (1981, now also occupied predominantly by Ceanothus velutinus) were greater than in the adjacent forest (Pinus jeffreyii) but extractable P contents either did not differ or were greater in the former fire. We conclude that the long-term effects of wildfire on soils are strongly influenced by post-fire vegetation and soil parent material.