Does a trade‐off between growth plasticity and resource conservatism mediate post‐fire shrubland responses to rainfall seasonality?

Abstract

Summary Growth plasticity may allow fire‐prone species to maximize their recovery rates during temporary, sporadic periods of rainfall availability in the post‐fire environment. However, moisture‐driven growth plasticity could be maladaptive in nutrient‐limited environments that require tighter control of growth and resource use. We investigated whether a trade‐off between plasticity and conservatism mediates growth responses to altered rainfall seasonality in neighbouring shrubland communities that occupy different soils. We monitored post‐fire vegetation regrowth in two structurally similar, Mediterranean‐type shrublands for 3 years. We investigated the effects of experimentally altered rainfall seasonality on post‐fire species’ growth rates. We found that moisture‐driven growth plasticity was higher among species occupying the fertile soils of the renosterveld site relative to those occupying the nutrient‐poor soils of the fynbos site. This resulted in higher overall responsiveness of post‐fire recovery patterns in renosterveld to experimental shifts in rainfall seasonality. In post‐fire shrubland communities, the trade‐off between moisture‐dependent growth plasticity and resource conservatism could be mediated by soil nutrient availability. Therefore, edaphic differences between structurally similar shrublands could lead to differences in their sensitivity to post‐fire rainfall seasonality.

Long-term vegetation response to rainfall seasonality and fire in the heathlands and shrublands of the Cape Floristic Region (SW South Africa)

“…During this phase, the parallel dynamics of Restionaceae, Ericaceae and Proteaceae, which shade and outcompete each other in post-fire fynbos succession (Hoffman et al, 1987;Rutherford et al, 2011) likely reflect a dynamic mosaic pattern at the landscape scale, as is observed at the site today. The expansion of fynbos under enhanced seasonality may suggest the retreat of renosterveld and its replacement by fynbos, in accordance with the findings of van Blerk et al (2021a).…”

“…At the research site, different post-fire responses to manipulated rainfall seasonality had differential impacts on renosterveld and fynbos communities (van Blerk et al, 2021b). Under accentuated summer drought tighter nutrient conservation strategies would afford fynbos taxa a competitive advantage over renosterveld at a community level (van Blerk et al, 2021a). Further mechanisms of post-fire competitive exclusion by seedling shading due to a more frequent fire regime probably explains fynbos resilience over 500 years.…”

“…In this context, palaeoecological data series are invaluable as they extend the timescales of observation and provide a centennial to millennial-scale framework against which patterns of vegetation change dynamics can be examined in relation to human, environmental or combined forcings. Such studies are particularly valuable at ecotones where ecological communities are at an environmental or ecological limit (Forbes et al, 2018a;MacPherson et al, 2018;Macpherson & Gillson, 2019;Gillson et al, 2020) To this end, we developed a palaeoecological study at a site where fynbos, renosterveld and succulent karoo vegetation was present, and that was adjacent to a multi-annual rainfall manipulation experiment designed to test plant population and community responses to altered seasonal regimes (van Blerk et al, 2021a(van Blerk et al, , 2021c. Here we present a high-resolution multi-proxy reconstruction of centennial palaeoecological change and results from the TraCE21ka climate model simulation (Liu et al, 2009;He et al, 2013) from the highly biodiverse Greater Cape Floristic Region (GCFR) of South Africa.…”

Globally important plant functional traits for coping with climate change

“…There is a body of work focusing on responses at the molecular level that are related to individual phenotypic plasticity, showing that changes in trait attributes within individuals occur in response to environmental changes (Nicotra et al 2010, Anderson 2016. This is a key point that is not addressed by our analysis but should be considered in future research as it may alter the relative abilities of different species responding positively to climate change where some species benefit from changing their traits (plasticity) (Nicotra et al 2010), and some cannot but benefit from resource conservatism (bet-hedging) (Power et al 2019). Another important consideration for future studies which is gaining momentum in the functional ecology community is that of intraspecific variation in traits.…”

Consistent responses to moisture stress despite diverse growth forms within mountain fynbos communities

“…Moll and Sommerville 1985 ; van der Heyden and Lewis 1989 ) and irrigation during summer has resulted in a 20–40% increase in net photosynthetic rate in one study species (van der Heyden and Lewis 1990 ). Furthermore, recent work has shown limited plasticity in response to experimental changes in seasonal moisture availability in fynbos, particularly in established shrubs (van Blerk et al 2021a , b ).…”