Masters Degrees (Forest and Wood Science)

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Browsing Masters Degrees (Forest and Wood Science) by browse.metadata.advisor "David, Drew"

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    The longevity of decaying eucalyptus hybrid roots in sub-tropical plantation forests
    (Stellenbosch : Stellenbosch University, 2019-02) Stephan, Johan Carl Jacobus; Du Toit, Ben; David, Drew; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: The global threat posed by extreme climate change has led to an increase in the amount of climate change related research. It is now more important than ever before to accurately quantify the carbon pools in terrestrial ecosystems, in order to better understand how these pools might influence the carbon cycle. The residence time of carbon in dead coarse roots (i.e. roots greater than 2 mm diameter), an often-neglected carbon pool, are still not well understood. (Fine roots are known to have rapid turnover, rates and was not considered in this study). The decay rate constant of decomposing roots after clear felling in Eucalyptus hybrid stands was determined using a chronosequence sampling approach followed by analysis of the density and carbon contents. The results were subsequently modelled with single component negative exponential model (k = 0.1058). Eucalyptus hybrid root systems in sub-tropical plantations took on average 6.6 years to lose 50% density, 13.1 years to lose 75% density and 28.3 years to lose 95% density. The relationships between root decomposition and root size class (2-10 mm, 10-50 mm, >50 mm diameter roots and tree stump) as well as site productivity (in the form of mean annual increment) were also investigated. Neither root size nor site productivity had significant relationships with root decomposition rate. Coarse root carbon content did not vary with time after felling or site productivity, but rather with root size. The mean carbon concentration for each root size class was 46.8 ± 1.6% (2-10 mm), 48.6 ± 1.9% (10-50 mm), 48.8 ± 1.4% (>50 mm) and 48.6 ± 2.3% (stump). The results showed that Eucalyptus hybrid coarse roots in subtropical plantations in South Africa should be regarded as an important long-term pool of sequestered carbon. The decay model is earmarked for inclusion in a South African forestry carbon calculator that estimates the stock changes of various above- and below ground carbon pools in forest ecosystems over time.