Recent fire and livestock browsing enhance plant-level fuel flammability in northwestern Patagonian shrublands

BLACKHALL M. , VEBLEN T. RAFFAELE E.

JOURNAL OF VEGETATION SCIENCE

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2014

1100-9233

AbstractQuestion: Could disturbance by fire and ungulate herbivory alter fire regimesby increasing flammability in shrublands and early-successional forests?Location: Nahuel Huapi National Park, northwest Patagonia, Argentina.Methods: We compared four characteristics that influence fuel flammability ?fine fuel load, plant bulk density, percentage fine fuel, and percentage dead finefuel ? and the vertical distribution of live and dead fine fuel at recently burned(<15 yr) and unburned (>50 yr) sites, both in the presence and absence of cattle,for six resprouting species: non-palatable Lomatia hirsuta and Diostea juncea,moderately palatable Nothofagus antarctica and Schinus patagonicus, and highlypalatable Maytenus boaria and Ribes magellanicum.Results: Changes in flammability in response to recent fire, and to a lesserextent cattle browsing, were strongly dependent on species identity. Non-palatableL. hirsuta tended to increase in flammability following fire, whereas cattledid not affect its fuel properties. Nothofagus antarctica showed ambiguousresponses: plants had reduced plant bulk density at recently burned sites, implyingreduced flammability, but changes in percentage fine and dead fine fuelpoint to increasing flammability at burned sites with cattle. Diostea juncea andS. patagonicus showed increased plant bulk density at sites with cattle andincreased percentage fine fuel in response to fire. Cattle browsing was the maindriver of variability in flammability for highly palatable species, showingincreased plant bulk density and percentage fine fuel in response to cattle. Firehad a strong effect on the vertical distribution of live and dead fine fuel, showingan increase of burnable biomass in response to recent fire. The reduction of verticalfuel continuity was extreme on highly palatable species. In contrast,moderatelyand non-palatable species, which are abundant under herbivore pressure,were characterized by vertically well-distributed fine fuel biomass in the presenceof cattle.Conclusions: Responses of flammability traits to fire and cattle depended onspecies identity, but themajority of the species studied showed higher fuel flammabilityat recently burned sites affected by cattle. Domestic livestock, byincreasing the flammability of post-fire vegetation,may be key agents in alteringfire regimes in forest?shrublandmosaics.IntroductionHumans have long modified vegetation patterns intentionallyor accidentally by altering fire ignition rates and introducingdomestic livestock towildland landscapes (Bacheletet al. 2000; McWethy et al. 2013). However, there is relativelylittle research on how the combined influences ofincreased human-set fires and livestock