Quantitative description of woody plant communities: Part I. An approach

Abstract

Various descriptive units for woody plant communities are proposed. These are the Evapotranspiration Tree Equivalent (ETTE), Browse Tree Equivalent (BTE) and Canopied Subhabitat Index (CSI), which describe the status of a woody community in terms of potential moisture use, value of the trees as food for browsers and subhabitat suitability for grass‐tree associations, respectively. A Quantitative Description Index (QDI) for woody plant communities, containing descriptive unit‐values, is proposed. The calculation of the various unit‐values, excluding the CSI, rests upon the relationship between spatial volume of a tree crown and its true leaf volume and true leaf dry matter, taking into account differences in leaf densities. These relationships, and the factors that influence the estimation of leaf densities, are discussed. Regression equations were developed from harvested Acacia karroo trees. Their applicability to other woody species was confirmed as predicted values differ non‐significantly from true values of two other species.

Verskeie beskrywingseenhede vir houtagtige plantgemeenskappe word voorgestel. Dit sluit in die Evapotranspirerende Boomekwivalent (ETBE), Wei Boomekwivalent (WBE) en Bedekte Subhabitat Indeks (BSI), wat onderskeidelik bedoel is om die status van ‘n houtagtige gemeenskap te beskryf in terme van: potensiele voggebruik; waarde van die bome as voer vir struikvreters en die subhabitat geskiktheid vir gras‐boom assosiasies. ‘n Kwantitatiewe Beskrywingsindeks (KBI) vir houtagtige plant gemeenskappe, wat beskrywings‐eenheid‐waardes bevat, is voorgestel. Die berekening van die onderskeie eenheid‐waardes, die BSI uitgesluit, berus op die verwantskap tussen die ruimtelike volume van ‘n boomkroon en sy werklike blaarvolume en werklike blaar droëmateriaal, met inagneming van verskille in blaardigthede. Hierdie verwantskappe, en die faktore wat die skatting van blaardigthede beïnvloed, word beskryf. Regressie vergelykings is vanaf geoeste Acacia karroo bome ontwikkel. Hul aanwendbaarheid na ander houtagtige spesies is bevestig deurdat voorspelde waardes nie‐betekenisvol van ware waardes van twee ander spesies verskil het.

Additional index words:

• Available browse
• competition for moisture
• grass‐tree associations
• predictions
• spatial tree volume