Effects of forest soil desiccation on the growth of Eucalyptus regnans F. Muell. seedlings

Abstract

Abstract. The growth rate of Eucalyptus regnans seedlings in their first year can be much increased if the soil is first dried and then rewetted. The ratio of growth on predried soil to growth on undried soil (the Growth Ratio or GR) reaches a maximum at air‐dryness (pF 6.0–6.4). In E. regnans forest soil, GR is greatest in humus‐rich topsoil and declines with depth. The effect of air‐drying persists for several months after rewetting when soil is stored under glasshouse conditions. It is largely unaffected by repeated drying and wetting, by the rate of drying or by the season of collection. The mixing of dried and undried soil or the placement of a layer of dried soil above undried soil produces an enhancement of growth proportional to the amount of dried soil added. Firing of a litter layer above soil at wilting point increases subsequent seedling growth to that in air‐dried soil. The addition of ash from a litter fire to undried soil produces an increase in growth approximately equal to that caused by air‐drying The drying effect is most pronounced in soils from mature E. regnans forest and nearby brackenland and is less in dense younger forest, frost‐hollow grasslands and old grassy gaps in the mature forest. The effect is restored by the inoculation of E. regnans mycorrhizal roots from both dried and undried soil. The effect varies along an gradient from 500 to 1500 m a.s.l. and is a maximum in the wet E. regnans climatic zone and a minimum in zones or local aspects where forests are normally subject to frequent drying. The stimulatory effect on seedling growth in soils of the E. regnans zone may have an effect on the outcome of competition during regeneration in large gaps. Part of the growth responses previously ascribed to the ‘ash‐bed’ effect may be due to the desiccation effect in these soils.

Seedling growth in conifers and angiosperms: impacts of contrasting xylem structure

“…Flindersia is a more shade-tolerant primary forest tree common in tropical north-eastern Australia; its contrast with the pioneer status of Toona was desirable to provide some control for successional status. E. regnans derives from a temperate south-eastern Australia and exhibits high growth rates although it is described as shade intolerant (Ashton and Kelliher 1996). All three angiosperm species were vessel bearing, with vessels >17 cm long observed in the stems of each angiosperm seedling (T. J.…”

Arbuscular-Mycorrhizal Networks Inhibit Eucalyptus tetrodonta Seedlings in Rain Forest Soil Microcosms

“…Although the ashbed effect has been investigated for more than half a century, its mechanisms remain ambiguous because it likely involves multiple phenomena associated with fire and soil desiccation. Those phenomena may include at different times and places, direct fertilization by ash [7], soil physical and chemical changes that diminish P adsorption [7], [8], release of mineral nutrients from heat-killed soil microorganisms [8] (but see [9]), partial soil sterilization that eliminates pathogenic microbes [10] (but see [11]), or other alterations of the soil microflora, especially ectomycorrhizal fungi [12], [13]. Notwithstanding uncertainty about the mechanisms behind the ashbed effect, empirical evidence from across Australia shows that without fire, rain forest resists invasion by savanna plant species, just as fire contributes to savannas' resistance to replacement by rain forest [4].…”

Temporal patterns of forest seedling emergence across different disturbance histories

“…We predicted that environmental variability in the landscape would influence the abundance of emerging seedlings. Specifically, we predicted that emerging seedlings would be more abundant in areas located on a northerly aspect, which typically receive more solar radiation (Aguilera et al, 2015;Ashton & Kelliher, 1996;Petter et al, 2015). Furthermore, because of the well-known relationship between soil moisture and topography (Huggett & Cheeseman, 2002;Petter et al, 2015), we predicted that higher indices of topographical wetness would correlate to higher abundances of emerging seedlings.…”

“…Moreover, we found that early-successional sites on a northerly aspect were characterized by a high abundance of shrub seedlings, but a low abundance of Eucalyptus seedlings. These results are likely attributed to species-specific environmental preferences for germination (Ashton & Kelliher, 1996;Bell, 1994;Harper et al, 1965;Titus & del Moral, 1998). However, they also may reflect unmeasured variables associated with indices of topographical wetness and northerly aspects, such as temperature, solar radiation, and the density of surrounding vegetation (Aguilera et al, 2015;Ashton & Kelliher, 1996;Petter et al, 2015).…”

“…The emergence of seedlings post disturbance is a critical preliminary stage in the recovery of forest ecosystems and is triggered by several environmental and species-specific factors (Bell, 1999;Clarke et al, 2009;Ford & HilleRisLambers, 2020;Long et al, 2015;Walck et al, 2011;Wright et al, 2018). These include the following: (a) heat and smoke produced during wildfires (that can break seed dormancy) (Auld & Denham, 2006;Flematti et al, 2004;Long et al, 2015), (b) an increase in the availability of nutrients (Chambers & Attiwill, 1994), (c) the presence of soil symbionts (Jumpponen et al, 2012) or pathogens (Ashton & Chinner, 1999), (d) the presence of remnant vegetation (Kara & Topaçoğlu, 2018), and (e) climatic conditions such as an increase in solar radiation, water availability (Ashton & Kelliher, 1996;Bell, 1994;Harper et al, 1965;Titus & del Moral, 1998), and temperature (Ford & HilleRisLambers, 2020). The composition of emerging plant species post disturbance is also regulated by the distribution, longevity, and dormancy of reproductive propagules (Palmer et al, 2018) and dispersal mechanisms or barriers of dispersal such as habitat fragmentation or distance to source population, which may be species-specific (Primack & Miao, 1992;Tautenhahn et al, 2016).…”