Abstract
Anticipating the next generation of forests requires understanding of recruitment responses to habitat change. Tree distribution and abundance depend not only on climate, but also on habitat variables, such as soils and drainage, and on competition beneath a shaded canopy. Recent analyses show that North American tree species are migrating in response to climate change, which is exposing each population to novel climate-habitat interactions (CHI). Because CHI have not been estimated for either adult trees or regeneration (recruits per year per adult basal area), we cannot evaluate migration potential into the future. Using the Masting Inference and Forecasting (MASTIF) network of tree fecundity and new continent-wide observations of tree recruitment, we quantify impacts for redistribution across life stages from adults to fecundity to recruitment. We jointly modeled response of adult abundance and recruitment rate to climate/habitat conditions, combined with fecundity sensitivity, to evaluate if shifting CHI explain community reorganization. To compare climate effects with tree fecundity, which is estimated from trees and thus is "conditional" on tree presence, we demonstrate how to quantify this conditional status for regeneration. We found that fecundity was regulated by temperature to a greater degree than other stages, yet exhibited limited responses to moisture deficit. Recruitment rate expressed strong sensitivities to CHI, more like adults than fecundity, but still with substantial differences. Communities reorganized from adults to fecundity, but there was a re-coalescence of groups as seedling recruitment partially reverted to community structure similar to that of adults. Results provide the first estimates of continent-wide community sensitivity and their implications for reorganization across three life-history stages under climate change.
Highlights
Extensive climate changes in North America since forest stands established over the last few centuries may have changed where tree species can recruit in the aftermath of recent diebacks (Ibáñez et al, 2007; Woodall et al, 2009; Bell et al, 2014; Serra-Diaz et al, 2016; Davis et al, 2019)
This study examines how climate and habitat variables differ in their effects on seed production and seedling establishment and survival
Our goal is to jointly model recruits and adults of all species, thereby accommodating their mutual dependence structure, but to isolate the effects of adults from direct climate-habitat interactions (CHI) effects through conditioning
Summary
Extensive climate changes in North America since forest stands established over the last few centuries may have changed where tree species can recruit in the aftermath of recent diebacks (Ibáñez et al, 2007; Woodall et al, 2009; Bell et al, 2014; Serra-Diaz et al, 2016; Davis et al, 2019). Regeneration Niche Shifts for adult distribution and abundance explained by climate and habitat variables, may represent past conditions, when current stands were established. Related concepts like a species’ climate envelop (Pearson and Dawson, 2003; Thomas et al, 2004) or suitable habitat (Freckleton and Watkinson, 2002; Iverson et al, 2008), quantified with adult trees and current conditions, may not align with the conditions for seed production and seedling recruitment (Ibanez et al, 2006; Clark et al, 2011). In this paper we show that the differences in niche requirements quantified from adult distributions can diverge from those for fecundity and seedling recruitment, with important implications for responses to contemporary climate change
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