Is forest fecundity resistant to drought? Results from an 18‐yr rainfall‐reduction experiment

Abstract

Recruitment is a primary determinant of the long-term dynamics of plant populations in changing environments. However, little information is known about the effects of anthropogenic environmental changes on reproductive ecology of trees. We evaluated the impact of experimentally induced 18 yr of drought on reproduction of three contrasting forest trees: Quercus ilex, Phillyrea latifolia and Arbutus unedo. Rainfall reduction did not decrease tree fecundity. Drought, however, affected the allocation of resources in Q. ilex and A. unedo but not the more drought tolerant P. latifolia. Larger crop production by Q. ilex and A. unedo was associated with a stronger decrease in growth in the rainfall-reduction plots compared with the control plots, suggesting that these species were able to maintain their fecundity by shifting their allocation of resources away from growth. Our results indicated resistance to change in tree fecundity in Mediterranean-type forest subjected to an average 15% decrease in the amount of soil moisture, suggesting that these ecosystems may adapt to a progressive increase in arid conditions. However, the speciesspecific reductions in growth may indirectly affect future fecundity and ultimately shift community composition, even without immediate direct effects of drought on tree fecundity.

Climate change and plant reproduction: trends and drivers of mast seeding change

“…Across natural productivity gradients and in fertilisation experiments, more favourable growing conditions are generally associated with larger seed crops in mast years rather than more frequent masting [24,85]. Climate manipulation experiments have not revealed a consistent response of masting frequency to reduced precipitation in drought-limited ecosystems [25,94]. On the other hand, a geographical transition from 2-to 3-year masting cycle in Sorbus acuparia appeared follow the productivity gradient, with less frequent mast years where productivity was lower [91].…”

“…A small but growing number of studies have used experimental approaches in an attempt to isolate the effects of climate change on masting. In drought-limited ecosystems, long-term rainfall exclusion experiments indicate that increased drought stress does not result in strong effects on the interannual variability of seed or fruit production, even if mean seed production is reduced and the underlying mechanisms regulating reproduction are sensitive to reduced water availability [25,94]. Experimental studies manipulating climate in forest systems is logistically challenging, particularly over the time-scales required to characterise masting.…”

Measuring temporal patterns in ecology: The case of mast seeding

“…Crone et al (2011) had already warned the masting community about the potential of CV to be a poor metric for measuring the temporal variability of reproductive efforts and that interpreting CV should be considered in context. To date, only a few studies analyzed their data sets using D or PV (Bogdziewicz, Fernández-Martínez, et al, 2020;Fernández-Martínez et al, 2017Koenig et al, 2020;Vergotti et al, 2019) after our first warning about the problems linked to using CV for masting was Recurrent arguments for maintaining the use of CV are that CV is strongly correlated with the proportion of zeros in a time series and that masting is about skipping reproductive attempts (see the hypothesis of predator satiation (Espelta et al, 2008;Kelly & Sork, 2002)),…”

“…(2011) had already warned the masting community about the potential of CV to be a poor metric for measuring the temporal variability of reproductive efforts and that interpreting CV should be considered in context. To date, only a few studies analyzed their data sets using D or PV (Bogdziewicz, Fernández‐Martínez, et al., 2020; Fernández‐Martínez et al., 2017, 2019; Koenig et al., 2020; Pesendorfer et al., 2020; Vergotti et al., 2019) after our first warning about the problems linked to using CV for masting was published (Fernández‐Martínez et al., 2018). Ascari et al.…”

Resource manipulation through experimental defoliation has legacy effects on allocation to reproductive and vegetative organs inQuercus ilex

“…Climate change effects on tree growth can be either positive due to CO2 fertilization, nitrogen deposition (Fernández-Martínez et al 2017), and the lengthening of the growing season (Menzel and Fabian 1999;Piao et al 2007;Delpierre et al 2009), or negative because of more stressful conditions especially in water limited ecosystems where aggravated droughts are expected (IPCC 2013;Dai 2013). These climate change effects are likely to affect both the carbon source through photosynthesis (Luyssaert et al 2007;Biederman et al 2016) and the carbon sink through the cambial activity (Babst et al 2013;Lempereur et al 2017), and to modify carbon allocation to the different organs, especially the reproductive structures (Gavinet et al 2019;Bogdziewicz, Fernández-Martínez, et al 2020). Understanding strategies of resource allocation into reproductive functions versus other functions, as well as the environmental determinants of reproductive success is therefore essential to grasp and predict how the reproductive success of trees and regeneration will be affected by future climatic conditions.…”