Andrés Holz

Effects of High-Severity Fire Drove the Population Collapse of the Subalpine Tasmanian Endemic Conifer Athrotaxis Cupressoides

Athrotaxis cupressoides is a slow-growing and long-lived conifer that occurs in the subalpine temperate forests of Tasmania, a continental island to the south of Australia. In 1960-1961, human-ignited wildfires occurred during an extremely dry summer that killed many A. cupressoides stands on the high plateau in the center of Tasmania. That fire year, coupled with subsequent regeneration failure, caused a loss of ca. 10% of the geographic extent of this endemic Tasmanian forest type. To provide historical context for these large-scale fire events, we (i) collected dendroecological, floristic, and structural data, (ii) documented the postfire survival and regeneration of A. cupressoides and co-occurring understory species, and (iii) assessed postfire understory plant community composition and flammability. We found that fire frequency did not vary following the arrival of European settlers, and that A. cupressoides populations were able to persist under a regime of low-to-mid severity fires prior to the 1960 fires. Our data indicate that the 1960 fires were (i) of greater severity than previous fires, (ii) herbivory by native marsupials may limit seedling survival in both burned and unburned A. cupressoides stands, and (iii) the loss of A. cupressoides populations is largely irreversible given the relatively high fuel loads of postfire vegetation communities that are dominated by resprouting shrubs. We suggest that the feedback between regeneration failure and increased flammability will be further exacerbated by a warmer and drier climate causing A. cupressoides to contract to the most fire-proof landscape settings.

Fire-Vegetation Feedbacks and Alternative States: Common Mechanisms of Temperate Forest Vulnerability to Fire in Southern South America and New Zealand

ABSTRACT In the context of global warming and increasing impacts of invasive plants and animals, we examine how positive fire–vegetation feedbacks are increasing the vulnerability of pyrophobic temperate forests to conversion to pyrophytic non-forest vegetation in southern South America and New Zealand. We extensively review the relevant literature to reveal how these temperate southern hemisphere floras have generated similar positive fire–vegetation feedback mechanisms resulting in increased vulnerability to anthropogenically altered fire regimens. For the two regions, we address the following questions. 1. What are the major plant species, physiognomic types and functional types characteristic of pyrophytic versus pyrophobic vegetation types and how do their traits affect flammability, resistance to fire and recovery after fire? 2. What are the roles of herbivory and microclimate in enhancing fire–vegetation feedbacks? 3. Are there similarities in trends of cover type transitions in relation to altered fire regimens? 4. How are climate change, land-use trends and the effects of introduced plants and animals affecting the vulnerability of these ecosystems to fire-induced transitions to alternative stable states? Most temperate forests of New Zealand and southern South America evolved under conditions of low fire frequencies so few taxa became adapted to recurrent fire. Current dichotomous landscapes consisting of juxtaposed pyrophobic and pyrophytic vegetation types are the outcome of the expansion of fire-resilient and fire-promoting species associated with the arrival of humans. Despite considerable differences in human history and biogeographic history, the case studies presented here show remarkable parallels in life-history traits of the key pyrophobic taxa, fire–vegetation feedback mechanisms, overall ecosystem responses to anthropogenic alteration of fire regimens, and likely vulnerability to expected global change influences on future fire regimens.

ENSO controls interannual fire activity in southeast Australia

El Nino Southern Oscillation (ENSO) is the main mode controlling the variability in the ocean-atmosphere system in the South Pacific. While the ENSO influence on rainfall regimes in the South Pacific is well documented, its role in driving spatiotemporal trends in fire activity in this region has not been rigorously investigated. This is particularly the case for the highly flammable and densely populated southeast Australian sector, where ENSO is a major control over climatic variability. Here we conduct the first region-wide analysis of how ENSO controls fire activity in southeast Australia. We identify a significant relationship between ENSO and both fire frequency and area burnt. Critically, wavelet analyses reveal that, despite substantial temporal variability in the ENSO system, ENSO exerts a persistent and significant influence on southeast Australian fire activity. Our analysis has direct application for developing robust predictive capacity for the increasingly important efforts at fire management.

Southern Annular Mode drives multicentury wildfire activity in southern South America

Significance Fire is a key ecological process affecting ecosystem dynamics and services, driven primarily by variations in fuel amount and condition, ignition patterns, and climate. In the Southern Hemisphere, current warming conditions are linked to the upward trend in the Southern Annular Mode (SAM) due to ozone depletion. Here we use tree ring fire scar data obtained from diverse biomes ranging from subtropical dry woodlands to sub-Antarctic rainforests to assess the effect of the SAM on regional fire activity over the past several centuries. Our findings reveal a tight coupling between fire activity and the SAM at all temporal scales and in all biomes, with increased wildfire synchrony and activity during the 20th century compared with previous centuries. 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.

Influences of fire–vegetation feedbacks and post‐fire recovery rates on forest landscape vulnerability to altered fire regimes

1Smithsonian Conservation Biology Institute, Front Royal, VA, USA; 2Department of Mathematics, Oregon State University, Corvallis, OR, USA; 3Department of Geography, University of Colorado at Boulder, Boulder, CO, USA; 4School of Environment, University of Auckland, Auckland, New Zealand; 5Department of Geography, Portland State University, Portland, OR, USA; 6Laboratorio Ecotono, INIBIOMA, CONICET-Universidad Nacional del Comahue, Bariloche, Río Negro, Argentina; 7Departamento de Ecología, Universidad Nacional del Comahue, Bariloche, Río Negro, Argentina and 8Center for Tropical Forest Science– Forest Global Earth Observatory, Smithsonian Tropical Research Institute, Panama

Climate Change Amplifications of Climate‐Fire Teleconnections in the Southern Hemisphere

Recent changes in trend and variability of the main Southern Hemisphere climate modes are driven by a variety of factors, including increasing atmospheric greenhouse gases, changes in tropical sea-surface temperature and stratospheric ozone depletion and recovery. One of the most important implications for climatic change is its effect via climate teleconnections on natural ecosystems, water security and fire variability in proximity to populated areas, thus threatening human lives and properties. Only sparse and fragmentary knowledge of relationships between teleconnections, lightning strikes, and fire is available during the observed record within the Southern Hemisphere. This constitutes a major knowledge gap for undertaking suitable management and conservation plans. Our analysis of documentary fire records from Mediterranean and temperate regions across the Southern Hemisphere reveals a critical increased strength of climate-fire teleconnections during the onset of the 21st century including a tight coupling between lightning-ignited fire occurrences, the upward trend in the Southern Annular Mode and rising temperatures across the Southern Hemisphere.

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.Climate change may impact forest disturbances, though local variability is high. Here, Sommerfeld et al. show that disturbance patterns across the temperate biome vary with agents and tree traits, yet large disturbances are consistently linked to warmer and drier than average conditions.

Holocene Dynamics of Temperate Rainforests in West-Central Patagonia

Analysis of long-term ecosystem dynamics offer insights into the conditions that have led to stability versus rapid change in the past and the importance of disturbance in regulating community composition. In this study, we (1) used lithology, pollen and charcoal data from Mallin Casanova (47°S) to reconstruct the wetland, vegetation and fire history of west-central Patagonia; and (2) compared the records with independent paleoenvironmental and archeological information to assess the effects of past climate and human activity on ecosystem dynamics. Pollen data indicate that Nothofagus-Pilgerodendron forests were established by 9000 cal yr BP. Although the biodiversity of the understory increased between 8480 and 5630 cal yr BP, forests remained relatively unchanged from 9000 to 2000 cal yr BP. The charcoal record registers high fire-episode frequency in the early Holocene followed by low biomass burning between 6500 and 2000 cal yr BP. Covarying trends in charcoal, bog development and Neoglacial advances suggest that climate was the primary driver of these changes. After 2000 cal yr BP, the proxy data indicate (a) increased fire-episode frequency; (b) centennial-scale shifts in bog and forest composition; (c) the emergence of vegetation-fire linkages not recorded in previous times; and (d) paludification in the last 500 years possibly associated with forest loss. Our results therefore suggest that Nothofagus-Pilgerodendron dominance was maintained through much of the Holocene despite long-term changes in climate and fire. Unparalleled fluctuations in local ecosystems during the last two millennia were governed by disturbance-vegetation-hydrology feedbacks likely triggered by greater climate variability and deforestation.

Fire History and Fire Regimes Shifts in Patagonian Temperate Forests

Fire has been a frequent disturbance in Patagonia. The presence of charcoal in sedimentary records covering the last 44,000 years suggests that natural fires played a significant role in shaping the landscape before the arrival of Native Americans ca. 14,500–12,500 years ago. Dendrochronological studies focused on the reconstruction of fire histories have been conducted in the Patagonian forests on both sides of the Andes Cordillera, beginning in the late 1990s. Here, we review the present knowledge of the history of fires in temperate forests in Patagonia, their main drivers, and discuss the evidence and impacts of burns and reburns on post-fire response, as well as possible mechanisms to shift into alternative stable states. Dendrochronology was extremely useful to develop multi-century fire histories in Araucaria araucana, Pilgerodendron uviferum, Fitzroya cupressoides and Austrocedrus chilensis and mixed Austrocedrus-Nothofagus dombeyi forests in Patagonia. In the case of Araucaria, Austrocedrus and Pilgerodendron forests, dendrochronological reconstructions show diverse and heterogeneous patterns of fire frequency related to changes in human activities and settlement processes over the last centuries. Fire history reconstructions document infrequent events in the Fitzroya wet rainforests, with ca. 800-year old in the Costal Range in South-Central Chile and ca. 1000-year old chronologies in the Argentinean Andes. Climate variability has a significant influence on fire occurrence in these Patagonian forests. Fire events have been strongly associated with low moisture availability linked to El Nino – Southern Oscillation (ENSO) and the Southern Annular Mode (SAM), the major climate drivers promoting fire. Future directions and challenges for fire history studies in Patagonian forests are proposed at the end of this chapter.

Potencial de los anillos de crecimiento de Pilgerodendron uviferum para el estudio histórico de las Iglesias de Chiloé, Patrimonio de la Humanidad

Las iglesias de Chiloe son antiguas estructuras de madera reconocidas patrimonio de la humanidad por la UNESCO. Gran parte de su historia de construccion y reparaciones aun se desconoce. Considerando que muchas de las iglesias de Chiloe fueron construidas utilizando madera de Pilgerodendron uviferum, el objetivo de este trabajo fue evaluar el potencial de esta especie para datar piezas de madera de dos de estas historicas construcciones: las iglesias de Vilupulli e Ichuac. En Vilupulli se dataron piezas de 311 y 181 anos provenientes de los pilares de la torre. Estas piezas fueron fechadas con cronologias de ancho de anillos de P. uviferum cercanas a las dos iglesias. Tambien utilizando estas cronologias se dataron piezas de 79, 89, 97 y 135 anos obtenidas a partir de los pilotes que sostienen el piso de la iglesia de Ichuac. Considerando que Vilupulli fue construida a principios del siglo XX, es posible que las muestras de la torre que presentaron fechas cercanas a 1918, sean parte del proceso tardio de construccion de la iglesia o de una restauracion posterior. Por su parte, Ichuac fue construida a finales del siglo XIX, por lo que las piezas del piso que dataron entre 19201929, formarian parte de una posible restauracion no descrita previamente en archivos historicos, la cual pudo ocurrir incluso varios anos posterior a la fecha del anillo mas reciente encontrado en las piezas estudiadas. Se concluye que P. uviferum tiene alto potencial para estudios historicos en estructuras patrimoniales en el sur de Chile.