Functional traits of expanding, thicket‐forming shrubs: contrasting strategies between exotic and native species

Abstract

Abstract. Woody expansion has been documented for decades in many different systems globally, often yielding vast changes in ecosystem functioning. While causes and consequences of woody expansion have been well documented, few studies have addressed plant functional traits that promote dramatic and rapid expansion in range. Our objectives were to investigate plant functional traits that contribute to the colonization, rapid expansion, and thicket formation of an invasive, N-fixing shrub, Elaeagnus umbellata Thunb. (Elaeagnaceae), and a native, N-fixing shrub Morella cerifera (L.) Small (Myricaceae) and compare to native, sympatric, non-expanding shrub species. Quantified functional traits included morphological (e.g., specific leaf area, leaf area) and physiological characteristics (e.g., electron transport rate, hydraulic conductivity) and were linked to two primary resources: light and water, which directly influence plant growth. Elaeagnus umbellata and M. cerifera rely on different strategies to maximize carbon gain, yet resulting physiological efficiency is similar. Elaeagnus umbellata invests a substantial amount of energy into growth during a short amount of time (i.e., deciduous growing season), using an acquisitive trait strategy to outcompete cooccurring woody species, while M. cerifera is productive year-round and uses a combination of conservative and acquisitive traits to outcompete co-occurring woody species. The majority of quantified functional traits of E. umbellata and several of M. cerifera are indicative of efficient light capture, utilization, and internal water movement. These factors contribute to rapid range expansion and thicket formation by promoting enhanced productivity while simultaneously inhibiting colonization and expansion of co-occurring species. Suites of functional traits are important for expansive success and thicket formation, yet differences in functional traits represent alternative strategies for colonization, rapid expansion, and thicketization.

Plant functional traits reflect different dimensions of species invasiveness

“…3). This finding is consistent with the existence of a diversity of life histories and functional strategies that confer invasion success under different contexts and ecological conditions (Dawson et al 2009, Speek et al 2011, Lai et al 2015, Carboni et al 2016, Shiflett et al 2017, Catford et al 2019.…”

Native Woody Plants of the Southern United States with Weedy or Invasive Tendencies: A Review of Common Offenders

“…The species is opportunistic and will quickly dominate disturbed areas such as clear cuts and oil fields (Keener et al, 2019). Shiflett et al (2017) described southern waxmyrtle's ability to efficiently capture light and utilize internal water movement. These factors promote rapid thicket formation while simultaneously discouraging colonization and expansion of co-occurring species.…”

Temporal changes in the dominance of tree functional traits, but no changes in species diversity during woody plant encroachment in a Brazilian savanna

“…With increasing tree cover, Cerrado ground layer environments change, reducing both ground layer light availability and decomposition rates, consequently altering nutrient cycling (Throop & Archer, 2007; Leitner et al, 2018) via a reduction in the grass component and an increase in water and nutrients in deeper soil layers, altering the recruitment and reproduction of woody species (Pausas et al, 2004; de Dantas, Pausas, et al, 2013; Shiflett et al, 2017). Such local‐scale environmental change would likely increase the relative abundance of species with life‐history strategies centred around resource competition (light, water and nutrients) rather than life‐history strategies of stress and disturbance (higher temperatures and fire) (de Dantas, Pausas, et al, 2013).…”

“…With increasing tree cover, Cerrado ground layer environments change, reducing both ground layer light availability and decomposition rates, consequently altering nutrient cycling (Throop & Archer, 2007;Leitner et al, 2018) via a reduction in the grass component and an increase in water and nutrients in deeper soil layers, altering the recruitment and reproduction of woody species (Pausas et al, 2004;de Dantas, Pausas, et al, 2013;Shiflett et al, 2017).…”