Introduction

Wildfires pose a growing threat to tropical rain forests throughout the world, including Madagascar, an island nation that contains 5% of the world’s known species, roughly 90% of which are endemic. In January 2021, wildfires near the port city of Toamasina burned three 0.25-hectare forest restoration areas. These areas were part of an experiment manipulating density, composition, and size of restoration plantings. As such, the wildfires created a unique opportunity to study how basic properties of restored/regenerating forests affect fire intensity (i.e., heat production), severity (i.e., damage to vegetation), and resulting tree mortality.



Objectives

We compared fire intensity, severity, and native tree mortality to test four predictions about wildfire and restoration design. We predicted that fire damage would be lower in the interior of plantings compared to the edges, in larger plantings (625 m2) compared to smaller plantings (81 m2), in plantings with a border of species with fire-retardant adaptations, and in denser (1-m spacing) versus sparser (4.5-m spacing) plantings.



Methods

We measured fire intensity and severity using established indices based on damage to tree tags and planting posts (e.g., scorching, melting). Tree mortality was measured after several rain events to account for resprouting. We analyzed data using GLMER.



Results

82% of 756 planted trees were killed by wildfires. Fire intensity was typically great enough to melt plastic tree tags and sometimes to turn metal tree tags to cinder. Planted trees typically had charred leaves and scorched stems. Tree mortality varied among species (47-100%; p Implications

We demonstrate that densely-planted restorations were less fire-damaged than sparse plantings. This is probably because dense plantings better suppressed flammable ferns (Dicranopteris linearis) and palms (Ravenala madagascariensis). Also, planting a border of native, fire-retardant species (e.g., Intsia bijuga) decreased fire intensity and severity, though not tree mortality. The statistical power of these comparisons will increase as two additional sites burned in early 2022. Designing strategies to reduce wildfire damage will help Madagascar achieve its goal of restoring four million hectares by 2030.