Abstract
To explore the possible relationship between diseased trees and wildfires, we assessed the flammability of canker-resistant and susceptible common cypress clones that were artificially infected with Seiridium cardinale compared to healthy trees. This study explored the effect of terpenoids produced by the host plant in response to infection and the presence of dead plant portions on flammability. Terpenoids were extracted and quantified in foliage and bark samples by gas chromatography–mass spectrometry (GC–MS). A Mass Loss Calorimeter was used to determine the main flammability descriptors. The concentration of terpenoids in bark and leaf samples and the flammability parameters were compared using a generalized linear mixed models (GLMM) model. A partial least square (PLS) model was generated to predict flammability based on the content of terpenoid, clone response to bark canker and the disease status of the plants. The total terpenoid content drastically increased in the bark of both cypress clones after infection, with a greater (7-fold) increase observed in the resistant clone. On the contrary, levels of terpenoids in leaves did not alter after infection. The GLMM model showed that after infection, plants of the susceptible clone appeared to be much more flammable in comparison to those of resistant clones, showing higher ignitability, combustibility, sustainability and consumability. This was mainly due to the presence of dried crown parts in the susceptible clone. The resistant clone showed a slightly higher ignitability after infection, while the other flammability parameters did not change. The PLS model (R2Y = 56%) supported these findings, indicating that dead crown parts and fuel moisture content accounted for most of the variation in flammability parameters and greatly prevailed on terpenoid accumulation after infection. The results of this study suggest that a disease can increase the flammability of trees. The deployment of canker-resistant cypress clones can reduce the flammability of cypress plantations in Mediterranean areas affected by bark canker. Epidemiological data of diseased tree distribution can be an important factor in the prediction of fire risk.
Highlights
The relationship between non-native plant disease and the frequency of wildfires, and the implications for fire management has become an increasing focus of research in recent years [1,2]
The interaction between wildfire and an emerging fungal forest disease was studied in Californian and Oregon forests affected by sudden oak death (SOD) [1,4,13]
At the beginning of June 2018, four ramets of each cypress clone were artificially inoculated with a standard isolate of S. cardinale (ATCC 38654) following the procedure described in Danti et al [48], while the other ramets were left intact
Summary
The relationship between non-native plant disease and the frequency of wildfires (the effect on fire regimes), and the implications for fire management has become an increasing focus of research in recent years [1,2] Both wildfires and disease caused by invasive pathogens (and insects) are key factors in determining tree mortality in forests worldwide and are linked to the global change context [3,4,5,6,7,8,9,10]. The interaction between wildfire and an emerging fungal forest disease was studied in Californian and Oregon forests affected by sudden oak death (SOD) (caused by Phytophthora ramorum) [1,4,13] This new disease altered the physical and biochemical characteristics of the ecosystem e.g., fuel load, increasing the surface fuel, restructuring the forest canopy, decreasing canopy continuity and increasing tree mortality
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