Contrasting Effects of Fire Severity on the Regeneration of Pinus halepensis Mill. and Resprouter Species in Recently Thinned Thickets

Ruth García‐Jiménez,Marina Palmero‐Iniesta,Josep Espelta

doi:10.3390/f8030055

Ruth García‐Jiménez, Marina Palmero‐Iniesta + Show 1 more

Open Access

https://doi.org/10.3390/f8030055

Copy DOI

Abstract

Many studies have outlined the benefits for growth and reproduction resulting from thinning extremely crowded young forests regenerating after stand replacing wildfires (“thickets”). However, scarce information is available on how thinning may influence fire severity and vegetation regeneration in case a new fire occurs. We investigated the relationship between thinning and fire severity in P. halepensis thickets, and the effects on the establishment of pine seedlings and resprouting vigour in resprouter species the year after the fire. Our results show a positive relationship between forest basal area and fire severity, and thus reserved pines in thinned stands suffered less fire damage than those in un‐thinned sites (respectively, 2.02 ± 0.13 vs. 2.93 ± 0.15 in a scale from 0 to 4). Ultimately, differences in fire severity influenced post‐fire regeneration. Resprouting vigour varied depending on the species and the size of individuals but it was consistently higher in thinned stands. Concerning P. halepensis, the proportion of cones surviving the fire decreased with fire severity. However, this could not compensate the much lower pine density in thinned stands and thus the overall seed crop was higher in un‐thinned areas. Establishment of pine seedlings was negatively affected by the slope and positively driven by the number of cones and thus it was higher in un‐thinned than in thinned stands (respectively, 2581 ± 649 vs. 898 ± 325 seedlings∙ha-1). Thinning decreases fire intensity, and thus it may facilitate fire suppression tasks, but retaining a higher density of pines would be necessary to ensure P. halepensis regeneration after a new fire event.

Highlights

Germination of seeds protected in a soil or canopy seed bank is one of the main regeneration mechanisms developed by plants to cope with fire, the most frequent disturbance in Mediterranean type ecosystems [1,2,3]
In comparison to the numerous studies that have stressed the benefits of early thinning for forest structure and stand development, little attention has been paid to the effects that a new fire event might produce in early thinned stands and how they might recover after this disturbance
Our results indicate that the areas that were thinned before the fire event presented less fire damage than un-thinned stands, where P. halepensis basal area was higher

Summary

Introduction

Germination of seeds protected in a soil or canopy seed bank is one of the main regeneration mechanisms developed by plants to cope with fire, the most frequent disturbance in Mediterranean type ecosystems [1,2,3]. Promotes the fast return of crucial ecosystem services [7,8] Notwithstanding these benefits, the too profuse establishment of tree seedlings (“thickets” or “dog hair stands”) entails some constrains concerning forest development, as competition precludes tree growth and reproduction [9,10] while increases the risk of new stand-replacing wildfires before a new seed bank has developed (“immaturity risk”, [11,12]). In comparison to the numerous studies that have stressed the benefits of early thinning for forest structure and stand development, little attention has been paid to the effects that a new fire event might produce in early thinned stands and how they might recover after this disturbance

Objectives

Methods

Results

Discussion

Conclusion