The estimation of carbon budgets of frequently burnt tree stands in savannas of northern Australia, using allometric analysis and isotopic discrimination

Abstract

The stock, rates of sequestration and allocation of carbon were estimated for trees in 14 0.1-ha plots at Kapalga in Kakadu National Park, Northern Territory, using new allometric relationships of carbon stock to stem cross-sectional area and measured growth rates of trees. Carbon stocks of trees ranged from 12 to 58 t ha–1, with sequestration representing ~9% of the total stocks. More than half of the sequestered carbon is allocated to leaves and twigs and ~20% to wood. Only ~25% is retained in the live trees with leaf and twig fall accounting for 80%–84% of the total transfers to the environment. An alternative method of calculating sequestration rates from consideration of water use and carbon-isotope discrimination data had a close to 1 : 1 match with estimates from allometric relationships. We developed and applied algorithms to predict the impacts of fire on carbon stocks of live trees. This showed that the reduction in live carbon stocks caused by single fires increased with increasing intensity, but the impact was highly dependent on the tree stand structure.

Environmental and allometric drivers of tree growth rates in a north Australian savanna

“…What is not generally appreciated is that a regime of annual early fires, while favouring growth and survival of adult trees, may reduce the growth and survival of juvenile trees, with consequent effects on recruitment of saplings and adult trees and thus the sustainability of tree populations in the longer-term. Cook et al (2005) have shown that repeated lowintensity fires would drive a stand towards a dominance of trees with stem diameters greater than 10-20 cm and towards greater dominance of eucalypts, trends that are consistent with our results. At Munmarlary, only fire protection was found to favour the recruitment of small stems: at the start of the experiment there were no mid-storey trees in any treatment, and after 23 years only a few stems had been recruited into the mid-storey of plots subject to any of the fire treatments (Russell-Smith et al, 2003;Fig.…”

Growth and survival of termite-piped Eucalyptus tetrodonta and E. miniata in northern Australia: Implications for harvest of trees for didgeridoos

“…Other studies of growth rates of Eucalyptus minata and E. tetrodonta all have reported that E. minata trees grew faster on average, than E. tetrodonta trees (Werner and Murphy, 2001;Cook et al, 2005;Werner, 2005;Prior et al, 2006). It is important to point out that these studies all measured trees without regard for termite piping.…”

Which trees dominate in savannas? The escape hypothesis and eucalypts in northern Australia

“…Growth rates of eucalypts are typically very low (generally <20 cm year -1 height growth and approx. 2 mm year -1 in diameter at breast height (DBH); Prior et al 2004Prior et al , 2006Prior et al , 2009Cook et al 2005a;Werner 2005;Murphy et al 2010). Werner (2005) reported mean eucalypt growth of 2.1 mm year -1 in DBH, which was not significantly different from non-eucalypts (collectively, 1.54 mm year -1 ) in unburnt situations.…”