Defining the role of fire in alleviating seed dormancy in a rare Mediterranean endemic subshrub.

Adam T Cross,Kingsley W Dixon,Maria Paniw,David J Merritt,Shane R Turner,Fernando Ojeda

doi:10.1093/aobpla/plx036

Abstract

Fire is a topical issue in the management of many ecosystems globally that face a drying climate. Understanding the role of fire in such ecosystems is critical to inform appropriate management practices, particularly in the case of rare and ecologically specialized species. The Mediterranean heathlands are highly fire-prone and occur in a biodiversity hotspot increasingly threatened by human activities, and determining the reproductive thresholds of at-risk heathland species is critical to ensuring the success of future conservation initiatives. This study examined the germination biology of the threatened carnivorous subshrub Drosophyllum lusitanicum, with specific focus on the role of fire-related cues (heat and smoke) in combination with seasonal temperatures and moisture conditions to determine how these factors regulate seed dormancy and germination. We found that D. lusitanicum produces water-permeable, physiologically dormant seeds with a fully developed, capitate embryo that when fresh (~1 month old) and without treatment germinate to 20-40 % within 4-8 weeks. Seeds possess a restricted thermal window (15-20 °C) for germination and a neutral photoblastic response. Seed dormancy was overcome through precision nicking of the seed coat (>90 % germination) or by short exposure to dry heat (80 or 100 °C) for 5-30 min (60-100 % germination). We propose seedling emergence from the soil seed bank may be cued by the passage of fire, or by soil disturbance from the movement and browsing of animals. Long-term population viability is likely to be contingent upon appropriate management of the persistent soil seed bank, as well as the adequate management of key ecological disturbances such as fire. Drosophyllum lusitanicum faces an increasingly bleak future in the absence of conservation and management initiatives aimed at reducing habitat fragmentation in heathlands and aligning fire management and livestock practices with biodiversity outcomes.

Highlights

Many terrestrial environments around the world are predicted to experience increasing pressure from a drying climate in coming decades (Dai 2011; Cook et al 2014; Fu and Feng 2014; McCabe and Wolock 2015)
This study represents the first detailed empirical assessment of seed dormancy, seed germination biology and the ecological drivers of germination in the rare Mediterranean endemic D. lusitanicum, and provides the first evidence of seed germination in a carnivorous plant being stimulated by exposure to high temperatures
We suggest that D. lusitanicum is a fire-adapted species reliant upon opportunistic recruitment following stochastic disturbance events, and that the long-term viability of natural populations is likely to be contingent upon the appropriate management of the long-lived soil seed bank and preservation of the functional integrity of key ecological disturbance processes in its heathland habitat such as fire (Paniw et al 2017b)

Summary

Introduction

Many terrestrial environments around the world are predicted to experience increasing pressure from a drying climate in coming decades (Dai 2011; Cook et al 2014; Fu and Feng 2014; McCabe and Wolock 2015) This climatic change is expected to increase the fire-risk and extend the length of the fire season in many regions (Flannigan et al 2000; Moriondo et al 2006), and may significantly affect the ecology of fire-prone ecosystems such as the Mediterranean heathlands (Mouillot et al 2002; Giannakopoulos et al 2009; Batllori et al 2013; Brotons et al 2013). Understanding the effects of fire suppression on individual species is constrained by a lack of detailed knowledge on the role fire and other disturbances play in maintaining population viability and in governing reproductive ecology (Paniw et al 2017b)

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Discussion

Conclusion