Are digestibility and flammability related? Two variables shaping landscape dynamics of Northwestern Patagonian forests

Abstract

Large herbivores prefer to consume plants with high concentration of digestible carbohydrates and protein, whereas fire spread is favored by foliage characteristics that induce rapid ignition and high radiant energy. We tested in eight Patagonian woody plants whether foliar traits that determine dry matter and nitrogen digestibility to browsing herbivores were related to four variables that determine their flammability. We found a negative relation between digestibility and flammability. Fiber content (i.e. Neutral and Acid Detergent Fiber), was positively related with heat emission, maximum temperature and flame duration, being negatively related to time to ignition. PCA indicated that digestibility was negatively related with all variables associated with flammability. Digestibility decreased throughout the growing season, whereas flammability showed no clear seasonal trend. Fiber content was correlated with time to ignition and maximum temperature during most of the growing season, except in late spring. We conclude that highly digestible plants are likely to be less flammable than fiber rich ones, and that fiber content may serve as an indicator of seasonal changes in flammability of foliage. Because leaf traits are likely to influence habitat selection and movement by herbivores as well as spread and severity of fires, further studies linking foliar shape variables and plant architecture with their chemical composition may improve current mechanistic models of herbivore and fire behavior.