Flowering time responses to warming drive reproductive fitness in a changing Arctic

Courtney G Collins; Amy Angert; Karin Clark; Sarah Elmendorf; Cassandra Elphinstone; Greg Henry

doi:10.1093/aob/mcae007

Flowering time responses to warming drive reproductive fitness in a changing Arctic

Ann Bot. 2024 Jan 22:mcae007. doi: 10.1093/aob/mcae007. Online ahead of print.

Authors

Courtney G Collins^{1

2}, Amy Angert^{1

2}, Karin Clark³, Sarah Elmendorf⁴, Cassandra Elphinstone^{1

2

5}, Greg Henry^{1

5}

Affiliations

¹ Biodiversity Research Centre, The University of British Columbia, Vancouver BC, Canada.
² Department of Botany, The University of British Columbia, Vancouver BC, Canada.
³ Department of Environment and Natural Resources, Government of the Northwest Territories, Yellowknife, NT, Canada.
⁴ Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO, USA.
⁵ Department of Geography, The University of British Columbia, Vancouver BC, Canada.

PMID: 38252914
DOI: 10.1093/aob/mcae007

Abstract

Background and aims: The Arctic is warming at an alarming rate, leading to earlier spring conditions and plant phenology. It is often unclear to what degree changes in reproductive fitness (flower, fruit, seed production) are a direct response to warming versus an indirect response through shifting phenology. This study aims to quantify the relative importance of these direct and indirect pathways and project the net effects of warming on plant phenology and reproductive fitness under current and future climate scenarios.

Methods: We used two long-term datasets on twelve tundra species in the Canadian Arctic as part of the International Tundra Experiment (ITEX). Phenology and reproductive fitness were recorded annually on tagged individual plants at both Daring Lake, Northwest Territories (64.87, -111.58) and Alexandra Fiord, Nunavut (78.83, -75.80). Plant species encompass a wide taxonomic diversity across a range of plant functional types with circumpolar/boreal distributions. We use Hierarchical Bayesian Structural Equation models to compare the direct and indirect effects of climate warming on phenology and reproductive fitness across species, sites and years.

Key results: We find that warming, both experimental and ambient, drives earlier flowering across species, which leads to higher numbers of flowers and fruits produced, reflecting directional phenotypic selection for earlier flowering phenology. Furthermore, this indirect effect of climate warming mediated through phenology was generally ~2-3x stronger than the direct effect of climate on reproductive fitness. Under future climate predictions, individual plants showed a ~2 to 4.5-fold increase in their reproductive fitness (flower counts) with advanced flowering phenology.

Conclusions: Our results suggest that, on average, the benefits of early flowering, such as increased development time and subsequent enhanced reproductive fitness, may outweigh its risks. Overall, this work provides important insights into population-level consequences of phenological shifts in a warming Arctic over multi-decadal time scales.

Keywords: Arctic; International Tundra Experiment; Tundra; climate change; directional selection; flowering time; fruiting; phenology; reproductive fitness; warming.