Fire tolerance strategies in woody species from Pantanal riparian forests involve phenolic compounds and structure of the inner bark

Abstract

Fire is common in seasonally dry areas in many parts of the world, and its effects on vegetation in these areas have been well studied. In riparian forests of the Pantanal, where fuel accumulation (dead plants) in the dry season can be a substantial driver of fire occurrence, little is known about the role of bark traits to fire protection in woody plants. Herein we evaluated some physical, chemical and anatomical bark traits to determine if they are associated with fire tolerance in tree riparian species of the Pantanal. To accomplish this, we selected three fire-sensitive species and seven fire-tolerant species in riparian forest of the Paraguay River. Bark samples were analyzed for relative total, outer and inner bark thickness, bark density, concentration of phenolic compounds and tannins, thermogravimetric behavior and their anatomical structure. We observed higher concentration of phenol and tannins and higher percentage of sclerenchyma in bark from fire-tolerant species than fire-sensitive species. Bark of fire-tolerant species also showed more sclerenchyma cells near vascular cambium and higher temperatures of thermal decomposition. In contrast, relative total, outer and inner bark thickness, and bark density did not differ between species groups. The high concentration of phenol and tannins, combined with higher percentage of sclerenchyma in secondary phloem, appear as the major bark traits that could mitigate fire damage in species from riparian forest of the Brazilian Pantanal.