Mortality of Eucalyptus marginata (jarrah) seedlings in Mediterranean‐climate forest in response to overstorey, site, seedbed, fertilizer application and grazing

Abstract

The effects of overstorey, site, seedbed, seedling density, application of fertilizer and grazing on mortality of Eucalyptus marginala (jarrah) seedlings were studied experimentally in the northern jarrah forest of Western Australia. Rainfall, soil temperature, soil water deficits, leaf water potentials and photosynthetically active radiation (PAR) were monitored. Seedlings on sites with the overstorey removed experienced significantly higher soil temperatures for 9 months of the year (of up to 6°C), smaller soil and leaf water deficits during the dry season (minimum predawn leaf water potentials of -0.5 MPa compared to -1.6 MPa) and higher intensities of PAR (maximum values of 1900 i^mol m"^ s"' compared to 900 |imol m~2 s~'), compared to seedlings on sites with the overstorey retained. Mortality of £. marginata seedlings was greater on sites where the overstorey was retained compared to where the overstorey was removed, on low quality sites than high quality sites, and on undisturbed and lightly disturbed seedbeds compared to heavily disturbed seedbeds. Seedling density, application of fertilizer and grazing by vertebrates did not have a significant effect on percentage mortality. Most ofthe mortality occurred as water deficits developed in late spring and summer and was attributed to these water deficits. Some mortality that occurred prior to the development of substantial water deficits was probably caused by pathogenic fungi. We conclude that mortality of .£", marginata seedlings in the northern jarrah forest of Western Australia can be minimized by reducing the density of the overstorey and by seeding into a seedbed that has had litter and groundcover removed and the soil disturbed,

Eucalyptus forest shows low structural resistance and resilience to climate change‐type drought

“…This is consistent with previous research in the NJF that has shown seedling mortality typically occurs from competition with overstorey trees for limited soil moisture (Stoneman et al. ). Thus, soil moisture competition from large overstorey trees represents one of the primary factors regulating stem density in the NJF.…”

Frequent wildfires erode tree persistence and alter stand structure and initial composition of a fire‐tolerant sub‐alpine forest

“…This suggests potential for on‐going self‐thinning of E. pauciflora forests decades after fire, which might be exacerbated by overstorey suppression of smaller size classes (Barker ; Stoneman et al. ). Other disturbances, such as drought (in particular, a ‘very long’ rainfall deficit from 1996 to 2010 in south‐east Australia; BOM 2010) could have contributed to seemingly high percentage clump mortalities and top‐killed stems (37%) at Unburned sites, as has been recently recorded for other resprouter forests in southern Australia (Prior et al.…”

Eucalyptus recruitment in degraded woodlands: no benefit from elevated soil fertility

“…Nutrient treatments were designed to increase and decrease the availability of the most commonly limiting macronutrients nitrogen and phosphorus, which are widely considered to influence pasture growth and have been shown to increase Eucalyptus establishment in Australian forests (Stoneman et al 1993).Treatments were as follows: high sugar (HS) application of 1.0 kg m -2 of granulated white sugar, shown to substantially reduce soil nitrate available for plant uptake (Prober et al 2005); low sugar (LS) application of 0.33 kg m -2 ; control (no additions); and di-ammonium phosphate (DAP; (NH 4 ) 2 HPO 4 ) fertiliser addition of 15 g m -2 (35.2 kg ha -1 of P). The first round of nutrient addition/depletion began in autumn (early May 2007, almost 5 months before planting, Fig.…”

“…Growth responses are primarily to N (Moore and Keraitis 1971;Cromer and Jarvis 1990;Kirschbaum et al 1992), P (Kirschbaum et al 1992), or both in interaction (Halsall et al 1983;Fabião et al 1995); the main effects being increased shoot to root ratio, specific leaf area (SLA) and photosynthetic rate (Stoneman 1994). Improved soil nutrition was also shown to reduce seedling mortality of Eucalyptus incrassata seedlings by about 30% (Stoneman et al 1993). The preferred form of N supply is also important and differs between species, with nitrate (NO 3 -)-N producing a stronger response than ammonium (NH 4 ?…”