Is decline in high altitude eucalypt forests related to rainforest understorey development and altered soil bacteria following the long absence of fire?

Abstract

The objective of this study was to identify attributes of the understorey vegetation, soil root biomass, soil chemistry and microbial community that may be associated with tree decline in high altitude eucalypt forests in Tasmania.The sites studied were in healthy eucalypt forest, forest in decline and forest containing dead eucalypts dominated by rainforest, in north-east (Eucalyptus delegatensis forest) and in north-west (Eucalyptus coccifera forest) Tasmania. In both regions bare ground, rock and shrubby species were associated with healthy sites whereas decline sites were associated with moss and a tall understorey with a high percentage cover of rainforest species. Healthy sites had low root biomass in the top 10 cm of the soil profile relative to decline and rainforest sites. Seedlings of high altitude species were grown in rainforest soil (0.314% N and 0.060% P) and healthy eucalypt soil (0.253% N and 0.018% P). The four eucalypt species studied had similar root to shoot ratio in the two soils, but the rainforest species, Nothofagus cunninghamii and Leptospermum lanigerum, had higher root to shoot ratio in the healthy eucalypt than in the rainforest soil. We produced three soil filtrates: (i) fungi and bacteria present; (ii) bacteria only present and; and (iii) sterile, from healthy, decline and rainforest sites in north-east and in north-west Tasmania and used linseed as a germination bioassay. Filtrates from the north-east decline and rainforest sites induced a significantly greater dysplastic germination response than healthy sites in (i) and (ii) filtrates, but this was not found in filtrates from sites in the north-west. We conclude that while the development of a rainforest understorey and elevated soil root biomass in the long absence of fire is generally associated with high altitude eucalypt decline, altered bacterial and/or chemical attributes of soil are not always associated with high altitude eucalypt decline.

Without management interventions, endemic wet‐sclerophyll forest is transitioning to rainforest in World Heritage listed K’gari (Fraser Island), Australia

“…Our study provides some insight into the fate of the two focus species over a 65‐year survey period and indicates that both species are unlikely to sustain their presence over time in an unmanaged forest, that is, in the absence of fire or other interventions. Our findings are in line with the observed decline in overstorey Eucalyptus species in unburnt wet‐sclerophyll forests (Ellis, ; Harvest, Davidson, & Close, ). In Tasmanian wet‐sclerophyll forests, the decline of Eucalyptus follows the change in burning regimes of Indigenous landowners from high frequency and low‐intensity fires, to infrequent, high‐intensity fires or fire exclusion.…”

“…In Tasmanian wet‐sclerophyll forests, the decline of Eucalyptus follows the change in burning regimes of Indigenous landowners from high frequency and low‐intensity fires, to infrequent, high‐intensity fires or fire exclusion. This shift has prompted the expansion of rainforest species, litter accumulation, changes to the soil environment, and decreased presence of Eucalyptus species (Harvest et al, ). In the same forest, removal of rainforest species (logging and burning) can reverse the deterioration of Eucalyptus species (Ellis, Mount, & Mattay, ).…”

Fire severity, feedback effects and resilience to alternative community states in forest assemblages

“…When high intensity fires burn into less flammable forests compositional change is thought to occur because; firstly the disturbance is large enough to remove species that perpetuate the exclusion of fire, and secondly space is opened up for the colonisation of more flammable species (Cochrane et al, 1999;Bowman, 2000;Hoffmann et al, 2009). Conversely, when fire is excluded from flammable vegetation, community dominants may not recruit and colonisers from non-flammable vegetation may suppress further fire (Ash, 1988;Banfai and Bowman, 2006;Harvest et al, 2008;Close et al, 2009). …”

Crown condition assessment: An accurate, precise and efficient method with broad applicability to Eucalyptus

“…Many types of eucalypt dieback have been reported from across Australia including regrowth dieback (Kile et al 1981;Wardlaw 1989), jarrah dieback (Podger 1968), bell-minor dieback (Stone 1996;Florence 2005;Stone et al 2008), rural dieback (Landsberg et al 1990;Close & Davidson 2004), high-altitude dieback (Ellis 1964;Harvest et al 2008) and limeinduced chlorosis dieback (see Parsons and Uren 2007 for review; Grigg et al 2009). …”

“…The aetiology of eucalypt dieback is often ecologically complex with multiple factors involved (Podger et al 1980;Granger et al 1994;Stone 1999;Jurskis & Turner 2002;Harvest et al 2008) and can result in ecosystem change and the disruption of ecosystem function ). General symptoms of dieback are observed despite the multiple causes that affect particular attributes.…”