Leaf and bark functional traits predict resprouting strategies of understory woody species after prescribed fires

Abstract

In temperate forests, both deciduous and evergreen species with small or large leaves coexist in the understory and resprout after prescribed burnings. This diversity of traits suggests that there are different strategies operating after the initial resprout growth to re-acquire space, capture resources and resist additional stresses. This study aims to understand resprout vigor 3 years after burning of woody understory species with different leaf traits and bark investment (i.e., the ratio between bark thickness and basal stem diameter).In two temperate forests, we burned one stand in late spring and another in fall. After 3 years, we studied resprout number and resprout basal diameter and length of ten individuals of six species per stand. Three species were common in both forests and three were different. Therefore, species of both forests were grouped in three groups based on leaf traits and in three different groups according to their bark investment. Besides the expected positive effect of pre-fire plant size, resprout number and vigor were higher after burning in spring than in fall. The higher resprout volume in evergreens, with small specific leaf area (SLA), than in deciduous species, with large SLA, may be related to evergreens having a longer possible growing season than deciduous species. In addition, species in different leaf groups differed in the ratio of resprout length to diameter growth, suggesting that it is important for deciduous small-leaved species to grow tall rapidly before they are shaded by large leaved species. In contrast, no direct effect of light availability on resprout vigor was detected. Bark investment did not explain resprout vigor but did affect resprout number in the low bark investment group. In this group, resprout number decreased with increasing maximum fire temperature. Based on our results, burning in the fall is advisable when the management objective is to minimize the recovery of the understory. In addition, to reduce the dominance of understory woody species with low bark investment, our study suggests that understory fires must be performed with moderate to high intensity.