Projections of fire probability and ecosystem vulnerability under 21st century climate across a trans-Andean productivity gradient in Patagonia.

Warming trends are altering fire regimes globally, potentially impacting on the long-term persistence of some ecosystems. However, we still lack clear understanding of how climatic stressors will alter fire regimes along productivity gradients. We trained a Random Forests model of fire probabilities across a 5°lat × 2° long trans-Andean rainfall gradient in northern Patagonia using a 23-year long fire record and biophysical, vegetation, human activity and seasonal fire weather predictors. The final model was projected onto mid- and late 21st century fire weather conditions predicted by an ensemble of GCMs using 4 emission scenarios. We finally assessed the vulnerability of different forest ecosystems by matching predicted fire return intervals with critical forest persistence fire return thresholds developed with landscape simulations. Modern fire activity showed the typical hump-shaped relationship with productivity and a negative distance relationship with human settlements. However, fire probabilities were far more sensitive to current season fire weather than to any other predictor. Sharp responsiveness of fire to the accelerating drier/warmer fire seasons predicted for the remainder of the 21st century in the region led to 2 to 3-fold (RCPs 4.5 and 8.5) and 3 to 8-fold increases in fire probabilities for the mid- and late 21st century, respectively. Contrary to current generalizations of larger impacts of warming on fire activity in fuel-rich ecosystems, our modeling results showed first an increase in predicted fire activity in less productive ecosystems (shrublands and steppes) and a later evenly amplified fire activity-productivity relationship with it shape resembling (at higher fire probabilities) the modern hump-shaped relationship. Despite this apparent homogeneous effect of warming on fire activity, vulnerability to predicted late 21st century shorter fire intervals were higher in most productive ecosystems (subalpine deciduous and evergreen Nothofagus-dominated rainforests) due to a general lack of fire-adapted traits in the dominant trees that compose these forests.

Patterns and drivers of recent disturbances across the temperate forest biome.

Increasing evidence indicates that forest disturbances are changing in response to global change, yet local variability in disturbance remains high. We quantified this considerable variability and analyzed whether recent disturbance episodes around the globe were consistently driven by climate, and if human influence modulates patterns of forest disturbance. We combined remote sensing data on recent (2001-2014) disturbances with in-depth local information for 50 protected landscapes and their surroundings across the temperate biome. Disturbance patterns are highly variable, and shaped by variation in disturbance agents and traits of prevailing tree species. However, high disturbance activity is consistently linked to warmer and drier than average conditions across the globe. Disturbances in protected areas are smaller and more complex in shape compared to their surroundings affected by human land use. This signal disappears in areas with high recent natural disturbance activity, underlining the potential of climate-mediated disturbance to transform forest landscapes.

How are monospecific stands of invasive trees formed? Spatio-temporal evidence from Douglas fir invasions.

Invasive plant species can produce many impacts on native communities. Impacts can be especially important when the non-natives reach high densities, producing monospecific stands where little grows besides the non-native species. We propose three basic pathways by which monospecific stands of invasive tree species are formed: (i) gradually from the propagule source, (ii) via synchronous establishment and (iii) following several pulses of synchronous establishment. Different patterns can produce different impacts through time and may require different management techniques. This study aims to further our understanding of how monotypic stands of invasive species arise. We documented how monospecific stands are formed during invasion processes by studying patterns of spatio-temporal establishment of several monospecific stands of Douglas fir in Patagonia. We obtained data on tree density, year of establishment, size, distance to the seed source and other related measurements for this tree species along transects from the original seed source (80-year-old plantations) to the edge of the monospecific stand. We found that these monospecific stands arose in a more complex way than expected. While individuals established on average simultaneously over all distances from the seed source, there was substantial variation in time of establishment at all distances. Also, tree density was higher near the source than far from it. Different factors can account for the observed pattern of tree establishment, including seed dispersal, mycorrhizal facilitation and herbivory. Our results elucidate the complexities of spatio-temporal pattern of formation in monospecific stands. This understanding can improve management strategies and techniques for this invasion and other plant invasions in different regions.

Southern Annular Mode drives multicentury wildfire activity in southern South America.

The Southern Annular Mode (SAM) is the main driver of climate variability at mid to high latitudes in the Southern Hemisphere, affecting wildfire activity, which in turn pollutes the air and contributes to human health problems and mortality, and potentially provides strong feedback to the climate system through emissions and land cover changes. Here we report the largest Southern Hemisphere network of annually resolved tree ring fire histories, consisting of 1,767 fire-scarred trees from 97 sites (from 22 °S to 54 °S) in southern South America (SAS), to quantify the coupling of SAM and regional wildfire variability using recently created multicentury proxy indices of SAM for the years 1531-2010 AD. We show that at interannual time scales, as well as at multidecadal time scales across 37-54 °S, latitudinal gradient elevated wildfire activity is synchronous with positive phases of the SAM over the years 1665-1995. Positive phases of the SAM are associated primarily with warm conditions in these biomass-rich forests, in which widespread fire activity depends on fuel desiccation. Climate modeling studies indicate that greenhouse gases will force SAM into its positive phase even if stratospheric ozone returns to normal levels, so that climate conditions conducive to widespread fire activity in SAS will continue throughout the 21st century.

New host-plant records for the defoliator Ormiscodes amphimone (Fabricius) (Lepidoptera: Saturniidae)

Ormiscodes amphimone (Fabricius) is a phytophagous moth species known to severely defoliate woody species in Chile and Argentina. Here we document new records of O. amphimonehost associations emphasizing the role of Nothofagus pumilio as its primary host in our study area. This new record for Argentina is highly significant given the economic importance of N. pumilio as a timber resource and the potential of O. amphimone to generate extensive outbreaks.

New host-plant records for the defoliator Ormiscodes amphimone (Fabricius) (Lepidoptera: Saturniidae).

Ormiscodes amphimone (Fabricius) is a phytophagous moth species known to severely defoliate woody species in Chile and Argentina. Here we document new records of O. amphimonehost associations emphasizing the role of Nothofagus pumilio as its primary host in our study area. This new record for Argentina is highly significant given the economic importance of N. pumilio as a timber resource and the potential of O. amphimone to generate extensive outbreaks.