TGA/TDA and Analytical Pyrolysis (Py/GC-MS) of Two Mediterranean Forest Species with Distinctive Flammability Characteristics: Cupressus sempervirens L. and Quercus suber L.

Abstract

The frequencies of wildfires in the Mediterranean climate regions (MCRs) have amplified due to the increased temperatures and drought periods resulting from climate change. Vast areas of forests are consumed by wildfires and certain species are threatened by extinction due to their high flammability and weak thermotolerance to climate change whereas, other species with high thermotolerance are exploited as silviculture measures in forest management strategies. Canopy and litter foliage are the first ignitable structures in a forest fire. In this context, the foliar flammability characteristics of two fire resilient Mediterranean forest species are tested and compared on a laboratory scale; Quercus suber L. (Q.s.L.) and Cupressus sempervirens L (C.s.L). Thermo gravimetric/thermo differential analysis (TGA/TDA) and low- to high- temperature analytical pyrolysis tests and gas chromatography-mass spectrometry (GC-MS) were conducted on live and dry foliar samples of Lebanese C.s.L and Algerian Q.s.L. Branch and cork samples of Q.s.L were also pyrolyzed (Pyr/GC-MS) for their volatile content. The hemicellulose/cellulose degradation temperatures of C.s.L. were in the order of 30 to 50°C more than those of Q.s.L. Lignin degradation started later in the Q.s.L. and took place at temperatures higher than those of C.s.L. (>30°C), while the heat release rates (HRR) were greater for the latter than the former in both degradation phases. The pyrolysis tests showed higher volatile content of C.s.L compared to Q.s.L. The high thermotolerance characteristic of C.s.L may be referred to its high terpene content which was negligible in Q.s.L given the fact that it is a non-monoterpene emitter oak species with no terpene storage compartments. The use of C.s.L as a fire barrier could be justified given their thermotolerance characteristic. Q.s.L. fire resilience is justified for their bark characteristics however; their foliage fire resilience should be further experimented.