Relationships between soils and productivity of NSW blackbutt (Eucalyptus pilularis Sm.) forests

Abstract

Relationships between site factors, soil and foliage nutrients and growth using growth plots established in pure regrowth blackbutt (Eucalyptus pilularis) on the North Coast of NSW were analysed. The plots were located on five different soil parent materials and were part of research into Eucalyptus stand growth dynamics. When all the plots were combined growth (basal area and volume) were related to rainfall, and elevation. Growth was related to soil texture with lower growth on soils high in sand. Growth rate (periodic annual increment) was related to soil nutrients with the highest correlations with soil total phosphorus. The relationships between growth and growth rates and soil parameters differed with soil parent material with texture, soil rooting depth, total phosphorus concentration and exchangeable calcium important factors. The relationships between soil nutrient quantities (kg ha−1) to 40 cm soil depth and volume mean annual increment were analysed, this providing a method to quantitatively related nutrients in biomass or harvesting removals. There was a positive correlation between volume increment and soil nitrogen on soils derived from sands but not on other parent materials where phosphorus and calcium were positively correlated. It was estimated that if the quantity of P and Ca accumulated in stem biomass at age 50 years were removed it would only potentially affect growth by 0.48% on soils derived from sedimentary rocks but by 12% on granitic soils. The information may used to develop an estimate of sensitively to change in site as a result of management practices. Growth was analysed in relation to foliage nutrients and foliage phosphorus was the nutrient most significantly (positively) related to growth with nitrogen and cations positively related but to a lower level of significance. Manganese concentrations were negatively correlated with growth. There is no clear answer to what limits the spatial extent of blackbutt especially at the fertile end of the spectrum, that is, why is it not found on very fertile soils? The question also arises as to whether populations on different soil types, although in close proximity, are different provenances.