Soil Carbon Dynamics after Forest Harvest: An Ecosystem Paradigm Reconsidered

Abstract

In one of the most influential studies in the recent history of forest ecology, W. W. Covington (1981) described a pattern in organic matter storage in the forest floors of northern hardwood stands as a function of date of harvest. We review the history of the use and misuse of Covington's curve, describe the studies that tested and failed to support early interpretations of the curve, and provide some alternate interpretations. The curve suggested that forest floor organic matter declines by 50% within 20 years after harvest, and this decline was attributed to accelerated decomposition and changes in litter inputs after harvest. Subsequent studies showed that decomposition rates of surface litter generally decrease after clear-cutting, but accelerated decomposition remains possible in the Oe and Oa horizons. Changes in litter inputs are still difficult to evaluate, because the rate at which woody debris enters the forest floor is unknown. Although Covington attempted to minimize variation due to mechanical disturbance during logging, a reasonable alternative explanation for low organic matter in the forest floor of young stands is that surface material is mixed into mineral soil during harvesting operations. The pattern of forest floor organic matter in stands of different ages may be partly due to changes over time in logging technology and the intensity of biomass removal, in addition to successional effects. It is important to distinguish between mechanisms that release carbon to the atmosphere and those that transfer it to the mineral soil before making inferences about nutrient cycling and carbon sequestration.

Temporal trends in the foliar nutritional status of the French, Walloon and Luxembourg broad-leaved plots of forest monitoring

“…Indeed, ground skidding has probably partially buried the forest floor into the mineral soil (Yanai et al, 2003) and the changes in ground climate resulting from canopy opening possibly accelerated litter decomposition (Prescott et al, 2000). The forest floor plays a major role in P nutrition (Jonard et al, submitted).…”

Life cycle impacts of forest management and wood utilization on carbon mitigation: knowns and unknowns

“…A competing theory by Yanai et al [44]) suggests that with careful management, SOC will not be reduced. The largest driver for these differing impacts is the level of soil disturbance, compaction and soil degradation, all of which can be managed with appropriate policies.…”

“…Yanai et al also suggest that SOC may actually be increased with appropriate management inputs [44], for example, an application of urea fertilization as part of the management regime has been shown to increase both forest productivity and soil carbon accumulation for some soils [17,18,47]. This result is consistent with the research on C:N:P ratios from Cleveland and Liptzin, which suggests that in nutrient-limited soils, increasing nitrogen content will result in more carbon retention in the soil to maintain the C:N:P ratios in dynamic equilibrium [38].…”

The legacy of forest management in tropical forests: analysis of its long-term influence with ecosystem models

“…Estas pérdidas aparentes de materia orgánica se atribuyen normalmente a una aceleración de la descomposición y al descenso de las entradas de hojarasca cuando el ecosistema se reorganiza tras la intervención humana (Yanai et al, 2003). Aunque el modelo simuló un aumento de las tasas de descomposición tras las talas (tal y como ha sido sugerido por Prescott et al, 2000), este efecto se mantuvo al mínimo, ya que los cambios en las tasas de descomposición tras las cortas no siempre siguen una pauta predecible (Yanai et al, 2003). Por lo tanto, la reducción de la masa de materia orgánica del suelo puede atribuirse principalmente a la reducción de producción de hojarasca.…”