Fire-related cues improve germination and seedling vigor of the post-fire off-spring of Pinus radiata, a serotinous invader tree

Abstract

Germination rate and seedling establishment control post-fire regeneration of trees and may foster invasion of exotic species particularly of fire-adapted species as the serotinous Pinus radiata. We analyzed the influence of heat shock and the presence of ash as substrate on seed germination and early vigor of seedlings of distinct cohorts of P. radiata that developed under the influence of fire or in the absence of it, i.e. post-fire invasion and unburned plantation, respectively. Seeds were collected from the Reserva Forestal Lago Epuyén in Northern Patagonia, Argentina. The natural history of this region is characterized by the occurrence of extensive fires. Ten randomly selected trees from unburned plantations and post-fire invasion that occurred in 1987 of similar age were cut down and 10 serotinous cones by plant were collected without color or size bias. Seeds from both stand types were subjected to four treatments: ash solution (5 g/L) and two thermal shocks (90 and 120 °C for 5 min), and a control without thermal shock or ash presence. The number of germinated seeds was counted every 5 days during 30 days. Germination percentages observed were high (between 80 and 100%) for both seed sources and under all the fire-associated treatments. Post-fire invasion had longer radicles with ash and under the thermal shock at 90 °C, as well as a higher percentage of seedlings that developed cotyledons and with the highest survival. Recurrent fires exert a significant effect on germination and early growth of the exotic P. radiata which may foster invasion.