Abstract
This paper compares carbon (C) and nutrient contents in soils (Alfisols derived from andesite), forest floor and vegetation in a former fire (1960) 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 SO42− 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 C 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 from a nearby, previous study at Little Valley Nevada, also dominated by P. jeffreyii growing on a different soil type (Entisols derived from granite). In the Little Valley study, soil C, N, Ca2+, Mg2+, 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 soil extractable P contents either did not differ or were greater in the former fire. We conclude that soil parent material is an indirect but strong mediator of the effects of post-fire vegetation on soils in this region, especially with respect to soil P changes, which vary substantially between andesite- and granite-derived soils.
Highlights
In forest ecosystem of the Sierra Nevada Mountains of Nevada and California, wildfire was a natural event prior to European settlement
We feel that some patterns in the long-term effects of fire on soils and ecosystem nutrient contents at these two sites can be observed
It appears that the long-term effects of wildfire at the Sagehen site are similar to those at the formerly investigated Little Valley site in that: (1) Soil total C and total N between former fire and forested sites are similar at both sites
Summary
In forest ecosystem of the Sierra Nevada Mountains of Nevada and California, wildfire was a natural event prior to European settlement. These fires were frequent, with a mean return interval ranging from 10–25 years [1], and for that reason, they often remained beneath the forest canopy because they kept so-called “ladder fuels” at a minimum. Fire has well-documented immediate effects on soils, including volatilization of nitrogen (N) from burned material, mobilization of NH4+ and SO42− from organic matter in mineral soils, and increases in ionic or otherwise labile fractions of less volatile nutrients (P, K, Ca, Mg) left in ash [3,4]. Changes in ortho-P availability vary considerably depending on the amount of mobilization by fire from organic matter and immobilization with increased Ca2+ [5,6,7]
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