Fire feedbacks, alternative stable states and the role of livestock on post-fire subalpine N. pumilio forests. WildFIRE PIRE Workshop: Understanding climate-human-fire interactions at different temporal and spatial scales

PARITSIS, J; HOLZ, A; BLACKHALL, M; KITZBERGER, T; RAFFAELE, E; TIRIBELLI, F; MORALES, JM; GOWDA, J; VEBLEN, TT

Chico Springs

Workshop; WildFIRE PIRE Workshop: Understanding climate-human-fire interactions at different temporal and spatial scales; 2017

Montana State University

Fire feedback processes through which pyrophobicvegetation communities are replaced by alternative stable states dominated bypyrophytic vegetation have been increasingly documented in multiple communitiesand have profound implications in ecosystem functioning. A thoroughunderstanding of the mechanisms responsible for these feedbacks demands theevaluation of multiple processes, which may synergistically or antagonisticallyaffect the feedbacks. In the eastern slopes of the Patagonian Andes two woodycommunities grow in juxtaposition: pyrophobic forests dominated by thenon-resprouter tree Nothofagus pumilioand pyrophytic mixed shrublands. Our overall objective is to quantify fuelproperties (amount and vertical distribution), vegetation structure andmicroclimate in unburned forests and in post-fire plant communities asmechanisms that might explain flammability differences and fire vegetationfeedbacks involving these communities. Additionally, we experimentally evaluatedthe role of livestock on the transition and maintenance of the phyrophyticshrubland alternative stable state that results from the initial severe burningof pyrphobic tall N. pumilio forest. Fuelamount and arrangement in unburned N.pumilio forests are unfavourable for fire activity compared with post-fire N. pumilio forests and shrublands. Microclimaticconditions following burning of N.pumilio forests and shrublands were significantly warmer and drier than inthe unburned forest, and more frequently exceeded thresholds associated withfire activity in this region. These results suggest that once N. pumilio forests are transformed tothe alternative state of shrublands, return to a forest cover is unlikely dueto increased probability of burning in shrublands. Livestock presence generatedantagonistic effects on flammability.  Herbivoresdecreased tissue ignitability, total fine fuel and litter depth, and disrupted thevertical and horizontal fine fuel continuity, therefore reducing theprobability of fire propagation. However, livestock also increased ratios ofdead to live fine fuels, reduced soil moisture, and inhibited tree heightgrowth to canopy size, consequently impeding the development of a closedpyrophobic forest canopy, which may promote the development of novel post-firetransitional states.