Crown defoliation decreases reproduction and wood growth in a marginal European beech population

Abstract

Abiotic and biotic stresses related to climate change have been associated to increased crown defoliation, decreased growth and a higher risk of mortality in many forest tree species, but the impact of stresses on tree reproduction and forest regeneration remains understudied. At dry, warm margin of species distributions, flowering, pollination and seed maturation processes are expected to be affected by drought, late frost and other stresses, eventually resulting in reproduction failure. Moreover, inter-individual variations in reproductive performances versus other performances (growth, survival) could have important consequences on population’s dynamics.We investigated the relationships between individual crown defoliation, growth and reproduction in a drought-prone population of European beech, Fagus sylvatica. We used a spatially explicit mating model and marker-based parentage analyses to estimate effective female and male fecundities of 432 reproductive trees, which were also monitored for basal area increment and crown defoliation over nine years.Female and male fecundities markedly varied among individuals, more than did growth. Both female fecundity and growth decreased with increasing crown defoliation and competition and increased with size. Male fecundity only responded to competition, and decreased with increasing competition. Moreover, the negative effect of defoliation on female fecundity was size-dependent, with a slower decline in female fecundity with increasing defoliation for the large individuals. Finally, a trade-off between growth and female fecundity was observed in response to defoliation: some large trees maintained significant female fecundity at the expense of reduced growth in response to defoliation, while some other defoliated trees rather maintained high growth at the expense of reduced female fecundity.Synthesis. Our results suggest that while decreasing their growth, some large defoliated trees still contribute to reproduction through seed production and pollination. This non-coordinated decline of growth and fecundity at individual-level in response to stress may compromise the evolution of stress-resistance traits at population level, and increase forest tree vulnerability.

MASTREE+: Time‐series of plant reproductive effort from six continents

“…In masting species, highly variable allocation to reproduction has wider effects on plant resource allocation, and carbon and nutrient cycling through ecosystems, but this remains poorly explored (Brumme et al, 2021; Khanna et al, 2009; Muller‐Haubold et al, 2015). Data in MASTREE+ can be combined with existing field and remote‐sensing data sets of plant growth or productivity, and with data sets of whole‐ecosystem or soil carbon and nutrient fluxes to understand how variable allocation to reproduction influences carbon sequestration above and belowground, and how this varies between species and across environmental gradients (Bajocco et al, 2021; Nussbaumer et al, 2021; Oddou‐Muratorio et al, 2021; Zhang et al, 2022). Related work can use MASTREE+ data combined with existing or retrospective sampling (e.g.…”

Individual reproductive success in Norway spruce natural populations depends on growth rate, age and sensitivity to temperature

“…From an evolutionary point of view, it is of the utmost importance to understand how different individuals cope with such reproductive costs not only in single reproductive seasons but throughout their lifetime to maximise their reproductive success (Barringer et al 2013). Our understanding of the link between individual growth and reproductive success is still limited and, to date, only a few studies have collected the genetic and dendrochronological data required to study this relationship through parentage analysis (González-Martínez et al 2006, Moran andClark 2012;Oddou-Muratorio et al 2018b). A hump-shaped relationship between growth rate and female reproductive success was observed in red oaks by Moran and Clark (2012), leading these authors to hypothesise the existence of a trade-off between growth rate and reproductive success.…”

“…They have been correlated to population genetic parameters calculated on neutral genetic markers (e.g., King et al 2013;Latutrie et al 2015;Babushkina et al 2016;Housset et al 2016;Avanzi et al 2019) and used in genotype-phenotype association studies (Heer et al 2018;Housset et al 2018;Trujillo-Moya et al 2018). So far, only a few studies included single dendrochronological traits in models describing parentage relationships (González-Martínez et al 2006;Moran and Clark 2012;Oddou-Muratorio et al 2018b). Although dendrochronological analyses permit to quantitatively describe a wide variety of functional traits (Fonti et al 2010;Housset et al 2018), a comprehensive evaluation of the role that different dendrophenotypic traits may play on individual reproductive success of forest trees has never been performed.…”