Exotic grass invasion alters microsite conditions limiting woody recruitment potential in an Australian savanna

Abstract

Andropogon gayanus Kunth. is a large African tussock grass invading Australia’s tropical savannas. Invasion results in more intense fires which increases the mortality rate of adult woody plants. Invasion may also affect community structure by altering the recruitment potential of woody plants. We investigated the effects of A. gayanus invasion on ground-level microclimate, and the carbon assimilation potential and recruitment potential of two Eucalyptus species. We compared microclimatic variables from the early wet-season and into the mid-dry season to coincide with the period of growth of A. gayanus. We assessed Eucalyptus recruitment by monitoring seedling establishment, growth and survival of experimentally sown seed, and estimating seedling density resulting from natural recruitment. A. gayanus invasion was associated with increased grass canopy height, biomass and cover. Following invasion, the understorey microclimate had significantly reduced levels of photon flux density, increased air temperatures and vapour pressure deficit. The conditions were less favourable for woody seedling with aboveground biomass of seedlings reduced by 26% in invaded plots. We estimated that invasion reduced daily carbon assimilation of woody seedlings by ~30% and reduced survivorship of Eucalyptus seedlings. Therefore, A. gayanus invasion reduces recruitment potential, contributing to the transformation of savanna to a grassland ecosystem.

Moisture availability and ecological restoration limit fine fuels and modelled wildfire intensity following non‐native ungulate removal in Hawaii

“…Even in fenced exclosures free of non-native ungulates in a landscape that was once native wet forest, no woody establishment was detected. It is likely that established heavy non-native grass cover in these sites was effective at suppressing any woody recruitment, as seen in our control plots (Elgar et al, 2014;Setterfield et al, 2018).…”

Land transformation in tropical savannas preferentially decomposes newly added biomass, whether C3 or C4 derived

“…1B), as well as PyC that is dominated by C 4 ‐derived carbon. Such practices may also have increased or maintained relatively high woody cover and helped mitigate Gamba grass invasion (Rossiter et al 2003, Setterfield et al 2018).…”

Reply on RC1

“…In all simulations, no irrigation and fertilization were applied and tilling always occurred before the planting date, meaning that all straw and grasses that remained on the field were transferred to the soil and incorporated into the soil C and N pools. 2017), 13 Feng and Dietze (2013), 14 Ullmann (1989), 15 Simioni et al (2000), 16 Baldocchi et al (2004), 17 de Jong and Jetten (2007), 18 Running and Coughlan (1988), 19 Baldocchi and Meyers (1998), 20 Guenther et al (1996), 21 Chandra and Dubey (2008), 22 Setterfield et al (2018) https://doi.org/10.5194/gmd-2020-417 Preprint. Discussion started: 5 February 2021 c Author(s) 2021.…”