Forest decomposition rate

A coincident effect on decomposers may be from the accumulation of heavy metals, such as lead, which is entrained in the photochemical-oxidant complex. In Sweden, Ruhling and Tyler have preliminaiy evidence that litter decomposition rate in a spruce forest was limited by increased concentration of heavy-metal ions, but only during times of the year when water and temperature were not limiting factors. 

Finally, processes operating at larger spatial scales may control the storage of C in soils. Fire, for example, is as important a loss mechanism as decomposition for organic C in thick detrital layers in boreal forests (Flarden et al., 2000). For fire-prone regions, the net status of the land surface as a C sink or source depends as much on the area burned in a given year as on the responses of decomposition rates to weather variability in unbumed areas. 

Production of roots on top of the mineral soil has been explained as a consequence of the low nutrient availability in Amazon forests (Herrera et al. 1978, Cuevas and Medina 1983, Medina and Cuevas 1989). Vertical root distribution results from differential nutrient availability in the soil profile (Berish 1982, Berish and Ewel 1988). Shallow rooted systems may be a result of litter and soil organic matter production and decomposition rates in systems where nutrient input from litter exceeds that of nutrient release by soil weathering, as is the case of Ca, Mg, and P in terra firme forests (Medina and Cuevas 1989). In the Middle Caqueta region of Colombia, for example, Ca and Mg concentrations in the L and F layers are between 15 and 20 times higher than in the mineral soil (Duivenvoorden and Lips 1995). 

Edmonds R. L. (1988) Decomposition rates and nutrient dynamics in smaU-diameter woody litter in four forest ecosystems in Washington, USA. Can. J. Forest Res. 17(6), 499-509. 

More recent data of R.Kuperman (1999) on interaction of biogeochemical cycles during litter decomposition have supported this trend. White oak (Quercus alba L.) leaf litter decomposition rates and patterns of N, S and P immobilization and release in decomposing litter were quantified in Oak-Hickory Forest ecosystems in the Ohio river valley for a long term (several decades) bulk atmospheric deposition gradient... 

The inventory in the terrestrial biosphere for the present day is summarized in Table II. Because of the heterogeneity of the landscape and the sparsity of measurements, the values in Table II are necessarily estimates. In general, above-ground carbon density is greatest in tropical rain forest where the temperature and abundant precipitation favor NPR By contrast, soil carbon is highest in the tundra where decomposition rates are slow. 

The mechanism of explosive desensitization by preshocking has been studied using a three-dimensional reactive hydrodynamic model of the process. With the mechanism determined, it was possible to modify the Forest Fire heterogeneous shock initiation decomposition rate to include both the desensitization and failure to desensitize effects as will be described in Chapter 4 and Chapter 6. 

A model, called Forest Fire after its originator, Charles Forest has been developed for describing the decomposition rates as a function of the experimentally measured distance of run to detonation vs. shock pressure (the Pop plot named after its originator, A. Popolato ) and the reactive and nonreactive Hugoniots. The model can be used to describe the decomposition from shocks formed either by external drivers or by internal pressure gradients formed by the propagation of a burning front. 

Figure 4.6 shows the decomposition rate calculated, using the Forest Fire model as a function of pressure. Forest Fire was incorporated in the SIN code, as shown in Appendix A, and the rate is fit as a function of pressure [In rate) = A + BP +. . . XP"]. 

To model desensitization by preshocking, the modification indicated by the three-dimensional study, described in Chapter 3, to the Forest Fire decomposition rate was to limit the rate by the initial shock pressure and to add the Arrhenius rate law to the limited Forest Fire rate. The Forest Fire rate for TATB is shown in Figure 4.21, along with the Arrhenius rate calculated using the temperatures from the HOM equation of state for the partially burned TATB associated with the pressure, as determined by Forest Fire. The multiple shock Forest Fire model (MSFF) uses a burn rate determined by Forest Fire, limited to the initial shock pressure, and the Arrhenius rate using local partially burned explosive temperature. 

To approximate this experimental observation and the results obtained from the three-dimensional numerical model study, the multiple shock Forest Fire model was used. The Forest Fire rate was determined by the first shock wave or the rates determined by any subsequent release waves that result in lower pressures and lower decomposition rates. As suggested by the three-dimensional study described in Chapter 3, the Arrhenius rate was added using the local partially burned explosive temperatures to the Forest Fire rate. 

Figure 4.29 The Forest Fire decomposition rates as a function of shock pressure.

As documented in Chapter 4, the build-up to detonation of heterogeneous explosives is described by the Forest Fire decomposition rate. The build-up of detonation process is described in Chapter 2. A technique was developed by Michael Gittings to include both build-up to detonation and build-up of detonation in the AMR (automatic mesh refinement) Eulerian hydrodynamic code, NOBEL. The NOBEL build-up models and computer movies of applications discussed in this section are described in a PowerPoint presentation on the CD-ROM in the /NOBEL/BUNOBEL directory. 

Numerical reactive hydrodynamic codes such as SIN, TDL or 2DE include the Forest Fire decomposition rate. For unresolved burns, it is necessary for the decomposition front of a detonation wave to occur over several computer meshes or cells so that the physics of the flow, the shock jump conditions, are properly described. Historically this was accomplished by adjusting the artificial viscosity so that the burn occurred over about 3 cells. If the mesh size changed, a new viscosity coefficient was determined empirically that would result in a realistic burn. As shown in the movie on the CD-ROM at /MOVIE/VISC.MVH, if there is insufficient viscosity, one obtains a reactive front with a peak that oscillates. If there was too much viscosity, a flat pressure profile occurs at the front. The problem is not unique to Forest Fire as other burn rates such as Arrhenius have the same numerical problems when numerically unresolved in reactive hydrodynamic codes. 

FIRE Code for computing Forest Fire rate of decomposition of... 

GeneL J-A. et al.. Response of termite eonunnnity and wood decomposition rates to habitat fragmentation in a subtropical dry forest. Trap. Ecol., 42, 35, 2001. 

An increase in the supply of fertilizer N can, in turn, result in an increase or decrease in below-ground C production, depending on the experimental conditions and plant species used. At high N rates, the decomposition of native. soil organic matter seemed lowered (conserving effect), as reflected by the decrease in the rate of respiration of unlabeled soil-C, both in crop (90) and forest soils (108,109). 

Pentachlorophenol applied to beech forest soils every 2 months for 2 years at the rate of 1.0 g/m2 markedly reduced populations of soil organisms. At 5.0 g/m2, it drastically reduced most of the soil animal species and also the microflora (Zietz et al. 1987). Reduction of the soil metabolism by PCP retards decomposition and affects the overall nutrient balance of forest ecosystems (Zietz et al. 1987). Pentachlorophenol is more toxic to earthworms in soils with comparatively low levels of organic materials. The LC50 (14-day) value for Lumbricus rubellus was 1094 mg PCP/kg DW soils with 6.1% organic matter, and 883 mg/kg DW soils with 3.7% organic matter (Van Gestel and Ma 1988). The earthworm Eisenia fetida andrei is more sensitive than Lumbricus rubellus ... 

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