Drought affects the performance of native oak seedlings more strongly than competition with invasive crested wattle seedlings

Abstract

Two of the most important processes threatening vulnerable plant species are competitive displacement by invasive alien species and water stress due to global warming. Quercus lusitanica, an oak shrub species with remarkable conservation interest, could be threatened by the expansion of the invasive alien tree Paraserianthes lophantha. However, it is unclear how competition would interact with predicted reductions in water availability due to global climate change. We set up a full factorial experiment to examine the direct interspecific competition between P. lophantha and Q. lusitanica seedlings under control and water-limited conditions.• We measured seed biomass, germination, seedling emergence, leaf relative growth rate, biomass, root/shoot ratio, predawn shoot water potential and mortality to assess the individual and combined effects of water stress and interspecific competition on both species.• Our results indicate that, at seedling stage, both species experience competitive effects and responses. However, water stress exhibited a stronger overall effect than competition. Although both species responded strongly to water stress, the invasive P. lophantha exhibited significantly less drought stress than the native Q. lusitanica based on predawn shoot water potential measurements.• The findings of this study suggest that the competition with invasive P. lophantha in the short term must not be dismissed, but that the long-term conservation of the native shrub Q. lusitanica could be compromised by increased drought as a result of global change. Our work sheds light on the combined effects of biological invasions and climate change that can negatively affect vulnerable plant species.

Responses of European forests to global change‐type droughts

“…In another study by Santamarina et al . (2022) it has been shown that invasive species can threaten seedling establishment, particularly if drought stress intensifies. The competitive effect of an invasive shrub species ( Paraserianthes lophantha (Willd.)…”

“…In this special issue, a broad range of observational and experimental studies are provided that relate to tree health, drought and heat stress resistance and recovery at multiple levels, including causes and consequences of drought-induced tree mortality. The studies use a wealth of approaches, covering remote sensing West et al 2022), ground-based monitoring (Frei et al 2022;George et al 2022), different management regimes (Bose et al 2021;Meyer et al 2022), including species mixture effects Santamarina et al 2022), field studies on wood formation plasticity (Larysch et al 2022), acclimation potential at the leaf level (Weithmann et al 2021;Petrik et al 2022) and recovery potential at the tree level (Kn€ uver et al 2022). These are supported by field- (Guan et al 2022;Kahmen et al 2022;Kn€ uver et al 2022) and lab-based (Kunert et al 2021;Petruzzellis et al 2021;McAdam et al 2022) ecophysiological studies that will increase our understanding of the impacts and consequences of global change-type droughts.…”

Extreme droughts and heatwaves endanger temperate forests

“…For example, differences in drought vulnerability among co-existing species were strongly related to structural-morphological traits, in particular root water uptake depth (Kahmen et al 2022). Interactions between species can further enhance (or buffer) drought impacts, depending on the severity of the drought Santamarina et al 2022).…”

“…2022) and species interaction effects in mixtures (Haberstroh & Werner 2022; Santamarina et al . 2022), to results from remote sensing (Haberstroh et al . 2022; West et al .…”

“…Interactions between species can further enhance (or buffer) drought impacts, depending on the severity of the drought (Haberstroh & Werner 2022; Santamarina et al . 2022).…”