부산대학교 도서관

Byline: Melisa Blackhall, Estela Raffaele, Juan Paritsis, Florencia Tiribelli, Juan M. Morales, Thomas Kitzberger, Juan H. Gowda, Thomas T. Veblen, Etienne Laliberte Keywords: ecological memory; livestock effects; non-resprouting species; Nothofagus spp.; plant population and community dynamics; plant-herbivore interactions; pyrophobic forests; pyrophytic shrublands; resprouting Summary Ecological memory, often determined by the extent and type of retained biological legacies present following disturbance, may produce persistent landscape patterns. However, after fire, the persistence or switch to an alternative state may depend on the complex interplay of ecological memory (biological legacies) and potential effects of new external factors influencing the post-fire environment. The current study assesses both the strength of ecological memory resulting from biological legacies of pre-burn vegetation types as well as post-fire effects of livestock. Following a severe fire in 1999, we set up a network of long-term exclosures to examine the effects of legacies and cumulative herbivory by cattle on fuel types, amounts, distribution, flammability and microenvironmental conditions in two post-fire communities representing alternative fire-driven states: pyrophobic Nothofagus pumilio subalpine forests and pyrophytic Nothofagus antarctica tall shrublands in northwestern Patagonia, Argentina. Our results show that the retained post-disturbance legacies of tall shrublands and subalpine forests largely determine fuel and flammability traits of the post-fire plant communities 16 years after fire. The importance of biological legacies retained from the unburned plant communities was reflected by the substantially higher amounts of total fine fuel, greater vertical and horizontal fuel continuity and the higher temperatures reached during experimental tissue combustion at post-fire shrubland compared to post-fire forest sites. We show that herbivores may produce antagonistic effects on flammability by decreasing tissue ignitability, total fine fuel and litter depth, and disrupting the vertical and horizontal fine fuel continuity, therefore reducing the probability of fire propagation. However, cattle can increase ratios of dead to live fine fuels, reduce soil moisture, and inhibit tree height growth to canopy size, consequently impeding the development of a closed pyrophobic forest canopy. Synthesis. Our results support the hypothesis that biological legacies, most importantly the dominance by pyrophytic woody plants that resprout vigorously vs. the dominance by pyrophobic obligate seeders, favour fuel and flammability characteristics at the community level which reinforce the mechanisms maintaining pyrophytic shrublands vs. pyrophobic forests. Herbivory by introduced cattle can partially blur sharp pyrophobic/pyrophytic state boundaries by promoting the development of novel post-fire transitional states. CAPTION(S): Table S1. Results of the general linear model considering the influence of two categorical predictors (cattle= fenced/unfenced plots; vegetation type (VG) = Nothofagus pumilio subalpine forest/N. antarctica tall shrubland) and their interaction, on fine fuel variables: total fine fuel, dead/total fine fuel and litter depth. Table S2. Results of the general linear model considering the influence of two categorical predictors (cattle= fenced/unfenced plots; vegetation type (VG) = Nothofagus pumilio subalpine forest/N. antarctica tall shrubland) and their interaction, on laboratory flammability variables: foliar moisture, time to ignition and flame duration. Table S3. Results the general linear mixed model with repeated measures, where between-subject factors were grazing treatments (cattle=fenced/unfenced plots) and vegetation type (VG= N. pumilio subalpine forest/N. antarctica tall shrubland) and we considered the flammability phase as the within-subject factor (with three levels: temperature needed to achieve flame appearance, maximum temperature reached and temperature during flame extinction). Table S4. Results of the general linear model considering the influence of two categorical predictors (cattle= fenced/unfenced plots; vegetation type (VG) = Nothofagus pumilio subalpine forest/N. antarctica tall shrubland) and their interaction, on microenvironmental conditions (mean maximum daily air temperature and mean minimum daily relative humidity for December 2014 and March 2015).