Fire survival traits of oaks in the Trans-Pecos Mountains
Gaetani, Maria S.
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Trees may survive fire through persistence of above or below ground structures; investment in bark aids in the first while investment in carbohydrate storage aids in the second. Investment in defense structures comes at a cost, necessitating tradeoffs. I hypothesized that relative investment in bark or carbohydrates changes with tree age and with fire regime: I predicted delayed investment in bark and early investment in carbohydrates under low frequency, high severity fire regimes. Common oaks of the Texas Trans-Pecos region (Quercus emoryi, Q. gambelii, Q. gravesii, Q. grisea, Q. hypoleucoides, Q. muehlenbergii, Q. pungens) were sampled at three sites with historically mixed fire regimes: the Chisos Mountains, the Davis Mountains and the Guadalupe Mountains. Bark thickness was measured on individuals representing the full span of sizes found in the three mountain ranges. Carbohydrate concentration in taproots was measured after initial leaf flush and before secondary shoot development. Investment in each trait was standardized by bole diameter and analyzed using major axis regression. Four species showed isometric investment through ontogeny: Q. gambelii, Q. gravesii, Q. muehlenbergii, Q. pungens. Q. grisea invests early in bark and reduces investment through time (allometric slope, alpha=0.75). In contrast, Q. hypoleucoides has thin bark in young stems and it accelerates investment over time (alpha=1.25) resulting in among the thickest bark when mature. Root carbohydrate concentrations were similar across all species and sizes, suggesting that any differences in below ground storage are likely to be in total volume of storage tissue rather than carbohydrate concentration. Investment patterns in bark were to habitat preference and by proxy to expected fire regime (p=0.07). Through expanding our understanding of fire survival traits we are better equipped to determine species success under novel disturbance regimes.