A landscape assessment of frost damage in the northmost Neotropical dry forest

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Adrián Bojórquez Sr. and Angelina Martinez-Yrizar, Instituto de Ecologia, Universidad Nacional Autonoma de Mexico, Hermosillo, Mexico, Juan C. Alvarez-Yepiz, Instituto Tecnologico de Sonora, Mexico

Background/Question/Methods
Extreme climatic and weather events are inducing widespread tree mortality in many forested ecosystems worldwide. A severe frost related to the historic cold wave that affected much of North America in early February 2011 led to extensive tree mortality in the lowland tropical dry forest of northwestern Mexico. In this region, we assessed frost-induced vegetation damage using anomalies of the widely used NDVI spectral index. In addition, to confirm if forest greenness loss indicates a high degree of forest damage, NDVI anomalies were related to field measures of disturbance severity (density of frost-killed trees) and forest recovery (post-frost recruits and resprouting trees).
Results/Conclusions
Negative NDVI anomalies occurred in 84% of the lowland tropical dry forest landscape (100 – 600 m a.s.l.), suggesting widespread frost-induced vegetation damage. The most affected zones were located within the 300-400 elevation belt. These areas are dominated by concave land forms, where cold air can be trapped and remain longer than in nearby areas. The relationship between NDVI anomalies and density of frost-killed trees confirmed the high degree of frost damage across the lowland vegetation, highlighting the key role of elevation during advective frost. High frost-disturbance severity stimulated more recruitment and less tree resprouting. Our results demonstrate the reliability of spectral indices for rapid assessment of climate-induced vegetation change, the high vulnerability of tropical dry forests to extreme frost and the predominant mechanism of vegetation recovery after severe frost disturbance.