Pine Plantations and Invasion Alter Fuel Structure and Potential Fire Behavior in a Patagonian Forest-Steppe Ecotone

Abstract

Abstract:Planted and invading non-native plant species can alter fire regimes through changes in fuel loads and in the structure and continuity of fuels, potentially modifying the flammability of native plant communities. Such changes are not easily predicted and deserve system-specific studies. In several regions of the southern hemisphere, exotic pines have been extensively planted in native treeless areas for forestry purposes and have subsequently invaded the native environments. However, studies evaluating alterations in flammability caused by pines in Patagonia are scarce. In the forest-steppe ecotone of northwestern Patagonia, we evaluated fine fuels structure and simulated fire behavior in the native shrubby steppe, pine plantations, pine invasions, and mechanically removed invasions to establish the relative ecological vulnerability of these forestry and invasion scenarios to fire. We found that pine plantations and their subsequent invasion in the Patagonian shrubby steppe produced sharp changes in fine fuel amount and its vertical and horizontal continuity. These changes in fuel properties have the potential to affect fire behavior, increasing fire intensity by almost 30 times. Pruning of basal branches in plantations may substantially reduce fire hazard by lowering the probability of fire crowning, and mechanical removal of invasion seems effective in restoring original fuel structure in the native community. The current expansion of pine plantations and subsequent invasions acting synergistically with climate warming and increased human ignitions warrant a highly vulnerable landscape in the near future for northwestern Patagonia if no management actions are undertaken.

Towards a framework for understanding the context dependence of impacts of non‐native tree species

“…High threshold impacts occur when impacts ensue only once a critical density or biomass is reached (Figure c). For example, young or low‐density pine invasions do not significantly alter wildfire fuel loads; however, in older or denser invasions, fuel loads and fuel spatial continuity increase rapidly (Figure c, where there is a strong increase in total fuel in older invasions), which can result in altered fire behaviour and fire effects (Davis, Maxwell, Caplat, Pauchard, & Nuñez, ; Paritsis et al, ). High threshold impacts may also occur with litter accumulation, where large amounts of litter bury native vegetation (Brewer, Souza, Callaway, & Durigan, ).…”

Landscape characteristics of non‐native pine plantations and invasions in Southern Chile

“…These ranges are consistent with previous research, which reported pine plantations between 765 and 950 m (Paritsis et al . ). The high topographic relief in Chile creates strong temperature and moisture gradients which likely limit plant growth at high elevation (Veblen et al .…”

“…; Paritsis et al . ). Pines require substantially more water than vegetation that undergoes seasonal dormancy and thus can reduce water availability (Le Maitre et al .…”

Emergent freeze and fire disturbance dynamics in temperate rainforests

“…; Paritsis et al . ). While many historical and recent large fires in Chile occurred just north of the CTRF region in the more Mediterranean central valley, there are plantations of Eucalypts in the SPCTR as far south as 42 0 on Isla Chiloé, and at the Patagonian dry forest/steppe ecotone lodgepole pine ( Pinus contorta var.…”