Position of cones within cone clusters determines seed survival in black spruce during wildfire

Abstract

It has recently become clear that the regeneration density of serotinous species within a burned area declines with local fire intensity. It is assumed that this occurs because variation in local fire intensity leads to variation in incident heat fluxes and, ultimately, seed necrosis. We argue here that this same relationship between incident heat flux and seed necrosis is important at the scale of individual plant crowns. Using Picea mariana (Mill.) B.S.P. (black spruce), we show that postfire seed viability increases with crown height, depth into the crown, and angle from wind direction (with the windward side enjoying greater viability). All three effects are what one would expect given the physics of buoyant plumes, interactions of moving fire lines with wake flow around cylinders, and heat transfer in porous bodies such as a tree crown. We conclude by discussing the broader consequences of cone cluster size and global change on regeneration in serotinous species.

Increasing fire and the decline of fire adapted black spruce in the boreal forest

“…To this end, we assessed the importance of fire return interval (18,43), prefire basal area of focal species (10,44), seedbed condition [represented by residual soil organic layer depth, which is influenced by soil combustion (25,45)], canopy combustion severity (44,46), and climate conditions following fire (7,19) in determining the postfire regeneration outcomes outlined in Fig. 1.…”

“…To evaluate whether the intensification of wildfire regimes will affect boreal North America in predictable ways, we must first understand whether there are consistent drivers of state change. To this end, we assessed the importance of fire return interval ( 18 , 43 ), prefire basal area of focal species ( 10 , 44 ), seedbed condition [represented by residual soil organic layer depth, which is influenced by soil combustion ( 25 , 45 )], canopy combustion severity ( 44 , 46 ), and climate conditions following fire ( 7 , 19 ) in determining the postfire regeneration outcomes outlined in Fig. 1 .…”

How climate change might affect tree regeneration following fire at northern latitudes: a review

“…The vulnerability maps that we produced are useful for identifying areas where species may be the most vulnerable to future climate conditions, where forest stands may be most at risk of regeneration failure, and where regeneration monitoring efforts should be prioritized. If recruitment proves to be deficient in these areas, adaptive silviculture practices such as the use of tree provenances adapted to future conditions (Nagel et al 2017;Splawinski et al 2019; Stevens-Rumann and Morgan 2019) could be used to mitigate the negative impacts of climate change on timber supply.…”

“…Reduction in postfire regeneration density has been already observed in southern forests, particularly in dry areas (Donato et al 2016;Rother and Veblen 2016;Stevens-Rumann et al 2017). A rise in fire frequency increases the probability that fires will occur before trees have reached their optimal seed production (Splawinski et al 2019). Yet, even when trees are sufficiently mature to produce seeds (or to reproduce vegetatively), future climate conditions are also expected to affect the recruitment process and increase the probability of post-fire regeneration failure.…”

Boreal tree regeneration after fire and fuelwood harvesting in coastal Nunatsiavut

“…B.S.P. and species of Pinus L.), and light, winddispersed seeds (species of Betula L. and Picea glauca (Moench) Voss) allow for quick post-fire germination and establishment on combusted organic layers that are warmer and higher in nutrient availability than pre-fire substrate (Certini 2005;Splawinski et al 2019). In addition to post-fire seed dispersal strategies, other species carry out vegetation resprouting from roots (Betula spp.…”