North American tree migration paced by climate in the West, lagging in the East

Abstract

Tree fecundity and recruitment have not yet been quantified at scales needed to anticipate biogeographic shifts in response to climate change. By separating their responses, this study shows coherence across species and communities, offering the strongest support to date that migration is in progress with regional limitations on rates. The southeastern continent emerges as a fecundity hotspot, but it is situated south of population centers where high seed production could contribute to poleward population spread. By contrast, seedling success is highest in the West and North, serving to partially offset limited seed production near poleward frontiers. The evidence of fecundity and recruitment control on tree migration can inform conservation planning for the expected long-term disequilibrium between climate and forest distribution.

Niche Shifts From Trees to Fecundity to Recruitment That Determine Species Response to Climate Change

“…The regeneration niche recognizes that conditions affecting fecundity and seedling establishment can differ from adults (Grubb, 1977;Clark et al, 1998;Ibanez et al, 2006;Engler et al, 2009;Swab et al, 2012). Accumulating climate changes can progressively distance the habitats where regeneration can occur from current distributions of mature trees (Sharma et al, 2021). If climate effects depend on soils, drainage, and biotic variables, then climate-habitat interactions (CHI) will complicate responses (Ibanez et al, 2009;Clark et al, 2016;Serra-Diaz et al, 2016).…”

“…If climate effects depend on soils, drainage, and biotic variables, then climate-habitat interactions (CHI) will complicate responses (Ibanez et al, 2009;Clark et al, 2016;Serra-Diaz et al, 2016). The emerging misalignment of adults and their recruits will be especially severe if recruitment stages are most sensitive to climate (Sharma et al, 2021). 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).…”

“…Comparing the habitat relationships for adults, seed production, and recruits requires comparable methods. Models for the biogeographic distribution of seeds (Clark et al, 2021;Sharma et al, 2021) are necessarily conditional on the abundance of trees that produce those seeds; we cannot know how much seed would be produced by a species where it does not grow. An unconditional estimate would require wide availability of trees planted throughout climate/habitat space.…”

“…Like fecundity, recruitment depends on the abundance of adults and thus must be modeled conditionally. Unlike fecundity, recruitment rates obtained from ingrowth to forest inventory plots are not explicitly referenced to adults (they are numbers per area per year) (Sharma et al, 2021), but they implicitly depend on adult presence.…”

Editorial: Predicting and Managing Climate-Driven Range Shifts in Plants

“…Plants face a number of challenges to tracking climate, including dispersal (e.g., seed number, dispersal distance, etc.) and establishment limitations (i.e., unsuitable soil or competition from existing vegetation) (Van Grunsven et al, 2010;Svenning et al, 2014;Lustenhouwer et al, 2017;Thuiller et al, 2019;Sharma et al, 2022). It is also challenging to predict where suitable future habitats will be, given uncertainties in biodiversity models (Thuiller et al, 2019) and climate projections (IPCC, 2013).…”