Local forest structure variability increases resilience to wildfire in dry western U.S. coniferous forests.

A 'resilient' forest endures disturbance and is likely to persist. Resilience to wildfire may arise from feedback between fire behaviour and forest structure in dry forest systems. Frequent fire creates fine-scale variability in forest structure, which may then interrupt fuel continuity and prevent future fires from killing overstorey trees. Testing the generality and scale of this phenomenon is challenging for vast, long-lived forest ecosystems. We quantify forest structural variability and fire severity across >30 years and >1000 wildfires in California's Sierra Nevada. We find that greater variability in forest structure increases resilience by reducing rates of fire-induced tree mortality and that the scale of this effect is local, manifesting at the smallest spatial extent of forest structure tested (90 × 90 m). Resilience of these forests is likely compromised by structural homogenisation from a century of fire suppression, but could be restored with management that increases forest structural variability

Ecological legacies of drought, fire, and insect disturbance in western North American forests, The

Includes bibliographical references.2015 Fall.Temperate forest ecosystems are subject to various disturbances including insect agents, drought and fire, which can have profound effects on the structure of the ecosystem for many years after the event. Impacts of disturbance can vary widely, therefore an understanding of the legacies of an event are critical in the interpretation of contemporary forest patterns and those of the near future. The primary objective of this dissertation was to investigate the ecological legacies of drought, beetle outbreak and ensuing wildfire in two different ecosystems. A secondary objective of my research, data development, was motivated by a lack of available data which precluded ecological investigation of each disturbance. I studied the effects of drought on deciduous and coniferous forest along a forest-shrubland ecotone in the southern portion of the Wyoming Basin Ecoregion. The results show that forests in the region have experienced high levels of cumulative drought related mortality over the last decade. Negative trends were not consistent across forest type or distributed randomly across the study area. The patterns of long-term trends highlight areas of forest that are resistant, persistent or vulnerable to severe drought. In the second thread of my dissertation, I used multiple lines of evidence to retrospectively characterize a landscape scale mountain pine beetle disturbance from the 1970s in Glacier National Park. The lack of spatially explicit data on this disturbance was a major data gap since wildfire had removed some of the evidence from the landscape. I used this information to assess the influence of beetle severity on the burn severity of subsequent wildfires in the decades after the outbreak. Although many factors contribute to burn severity, my results indicate that beetle severity can positively influence burn severity of wildfire. This is likely due to the change in forest structure in the decades after the outbreak and not as a direct result of tree mortality from the outbreak. The long-term perspective of this study suggests that ecological legacies of high severity disturbance may continue to influence subsequent disturbance for many years after the initial event. This work also provides insight on future disturbance interactions associated with the recent mountain pine beetle outbreak that has impacted tens of millions of hectares in western North America over the last two decades

Using Remote Sensing to Determine Riparian Resilience in Beaver Dammed Versus Un-Dammed Corridors Following Whiplash Weather

Beaver complexes slow and store water allowing for riparian growth which in turn fosters biodiversity, retains carbon, and enhances resistance to fires and drought. Given the benefits associated with beaver complexes and the potential they have for climate mitigation, California hopes to reintroduce beavers and restore their habitat throughout the state. However, the impact of high peak flow events on beaver complexes and their adjacent riparian corridors is less understood and requires more documentation at various spatial scales. To better understand the potential beavers may have as climate change mitigators it is important to understand beaver complex resiliency following a high peak flow event. This study used remotely sensed mean normalized difference vegetation index (NDVI) data, which is a measure of vegetative greenness, to serve as a primary indicator of resilience. Mean NDVI for riparian vegetation was collected in 5 beaver complexes and 5 non-beaver developed sections along the Salinas River in California. Both beaver sites and non-beaver sites were exposed to a multi-month flooding event after enduring several dry years. The term “whiplash weather” can be used to characterize the quick flip from dry conditions to flash floods. Each beaver complex contained multiple dams that were continually maintained by the residing beavers even following the high peak flow months which lasted from December 2022 until March 2023. We hypothesized that with the surge of water, the dams within each of the beaver complexes would fail and the exposure would also cause riparian loss thus revealing a lack of resistance; however, following the flood we assumed that beaver complexes would be able to rebuild their dams and recover back to their steady state implying resilience. We evaluated trends in mean NDVI to assess the influence of flooding, beaver influence, and seasonality on riparian resilience. Our study suggests that beaver complexes are capable of promoting a resilient ecosystem in the face of whiplash weather which is a growing threat in California

Chilean wildfires: probabilistic prediction, emergency response and public communication

The 2016/17 wildfire season in Chile was the worst on record, burning more than 600,000 hectares. Whilst wildfires are an important natural process in some areas of Chile supporting its diverse ecosystems, wildfires are also one of the biggest threats to Chile’s unique biodiversity and it’s timber and wine industries. They also pose a danger to human life and property due to the sharp wildland-urban interface that exists in many Chilean towns and cities. Wildfires are however difficult to predict due to the combination of physical (meteorology, vegetation and fuel condition), and human (population density and awareness level) factors. Most Chilean wildfires are started due to accidental ignition by humans. This accidental ignition could be minimized if an effective wildfire warning system alerted the population to the heightened danger of wildfires in certain locations and meteorological conditions. Here we demonstrate the design of a novel probabilistic wildfire prediction system. The system uses ensemble forecast meteorological data together with a longtime series of fire products derived from Earth Observation to predict not only fire occurrence, but in addition, how intense wildfires could be. The system provides wildfire risk estimation and associated uncertainty for up to 6 days in advance, and communicates it to a variety of end users. The advantage of this probabilistic wildfire warning system over deterministic systems is that it allows users to assess the confidence of a forecast and thus make more informed decisions regarding resource allocation and forest management. The approach used in this study could easily be adapted to communicate other probabilistic forecasts of natural hazards

The Fire in the Mediterranean Region: A Case Study of Forest Fires in Portugal

Forest fires are a common disturbance in many forest systems in the world and in particular in the Mediterranean region. Their origins can be either natural or anthropogenic. The effects in regard to the time trends, vegetation, and soil will be reflected in the species distribution, forest composition, and soil potential productivity. In general, it can be said that the larger the fire and the shorter the time between two consecutive occurrences, the higher the probability to originate shifts in vegetation and soil degradation. In the Mediterranean region, the number of fire ignitions does not reflect the burnt area due to the occurrence of very large fires. The latter occur in a very small proportion of the number of ignitions, but result in very large burnt areas. Also there seems to be an increasing trend toward larger fires in the Mediterranean region due mainly to climatic and land use changes. This case study highlights the importance of vegetation regrowth a short time after the fire to maintain both forest systems and soil conservation

Review of broad-scale drought monitoring of forests: Toward an integrated data mining approach

Efforts to monitor the broad-scale impacts of drought on forests often come up short. Drought is a direct stressor of forests as well as a driver of secondary disturbance agents, making a full accounting of drought impacts challenging. General impacts can be inferred from moisture deficits quantified using precipitation and temperature measurements. However, derived meteorological indices may not meaningfully capture drought impacts because drought responses can differ substantially among species, sites and regions. Meteorology-based approaches also require the characterization of current moisture conditions relative to some specified time and place, but defining baseline conditions over large, ecologically diverse regions can be as difficult as quantifying the moisture deficit itself. In contrast, remote sensing approaches attempt to observe immediate, secondary, and longer-term changes in vegetation response, yet they too are no panacea. Remote sensing methods integrate responses across entire mixed-vegetation pixels and rarely distinguish the effects of drought on a single species, nor can they disentangle drought effects from those caused by various other disturbance agents. Establishment of suitable baselines from remote sensing may be even more challenging than with meteorological data. Here we review broad-scale drought monitoring methods, and suggest that an integrated data-mining approach may hold the most promise for enhancing our ability to resolve drought impacts on forests. A big-data approach that integrates meteorological and remotely sensed data streams, together with other data sets such as vegetation type, wildfire occurrence and pest activity, can clarify direct drought effects while filtering indirect drought effects and consequences. This strategy leverages the strengths of meteorology-based and remote sensing approaches with the aid of ancillary data, such that they complement each other and lead toward a better understanding of drought impacts

Response of a Rocky Mountain forest system to a shifting disturbance regime, The

2019 Fall.Includes bibliographical references.Climate change is likely to drive widespread forest declines and transitions as temperatures shift beyond historic ranges of variability. Warming temperatures and shifting precipitation patterns may lead to increasing disturbances from wildfire, insect outbreaks, drought, and extreme weather events, which may greatly accelerate rates of ecosystem change. However, the role of disturbance in shaping forest response to climate change is not well understood. Better understanding the impacts of changing disturbance patterns on forest decline and recovery will allow us to better predict how forest ecosystems may adapt to a warming world. Severe wildfires and bark beetle outbreaks are currently affecting large areas of forest throughout western North America, and increasing disturbance size and severity will have uncertain impacts on forest persistence. The goal of my dissertation was to investigate the factors shaping disturbance response in a region of the San Juan Mountains, Colorado, which has undergone impacts from a high-severity spruce beetle outbreak and wildfire in the last 15 years. I conducted three separate studies in the burn area of the West Fork Complex wildfire, which burned in 2013, and in surrounding beetle-affected spruce-fir forests. The goals of each study were to 1) assess whether the severity of spruce beetle outbreaks occurring before wildfire resulted in compounded disturbance interactions affecting vegetation recovery, 2) determine how the severity of each disturbance type influenced fine-scale below-canopy temperature patterns across the landscape, and 3) assess how conifer seedling regeneration densities were influenced by effects of disturbance severity on seed dispersal, temperature, and vegetation structure. I found that disturbances influenced seedling regeneration and ecosystem resilience through several mechanisms. First, pre-fire beetle outbreak severity was negatively correlated with post-fire vegetation cover, indicating that the combined disturbances were inhibiting regeneration beyond what may have been expected with fire alone. Second, disturbances had significant effects on below-canopy temperatures, with burned areas ~0.5 °C warmer than unburned forest areas and differences in overnight minimum temperatures resulting from loss of live canopy in unburned, beetle-killed forests. Third, the large fire size and high severity resulted in very little spruce seed dispersal or conifer regeneration in most of the burned area, while spruce regeneration in unburned forest was negatively correlated with increasing overstory mortality from the spruce beetle. My results indicate that disturbance is playing an important role in determining the future trajectory of the forest in my study area. The West Fork Complex fire has caused a severe ecosystem transformation, has increased landscape exposure to warming temperatures, and is preventing forest re-establishment as a result of a lack of seed sources. The spruce beetle outbreak has not resulted in such a severe transformation, but is possibly leading to reduced forest resilience by reducing spruce seedling re-establishment and by altering fuel structures to make forests more prone to high soil burn severity if fire follows within ~10 years. Warming of below-canopy microclimates is not exacerbated by spruce beetle outbreak, and is rather partially offset by cooling of overnight temperatures. These findings provide insights into how forest responses to climate change may be shaped by disturbance processes, which are occurring with increasing severity and frequency worldwide

Agrometeorological forecasting

Agrometeorological forecasting covers all aspects of forecasting in agrometeorology. Therefore, the scope of agrometeorological forecasting very largely coincides with the scope of agrometeorology itself. All on-farm and regional agrometeorological planning implies some form of impact forecasting, at least implicitly, so that decision-support tools and forecasting tools largely overlap. In the current chapter, the focus is on crops, but attention is also be paid to sectors that are often neglected by the agrometeorologist, such as those occurring in plant and animal protection. In addition, the borders between meteorological forecasts for agriculture and agrometeorological forecasts are not always clear. Examples include the use of weather forecasts for farm operations such as spraying pesticides or deciding on trafficability in relation to adverse weather. Many forecast issues by various national institutions (weather, but also commodity prices or flood warnings) are vital to the farming community, but they do not constitute agrometeorological forecasts. (Modified From the introduction of the chapter: Scope of agrometeorological forecasting)JRC.H.4-Monitoring Agricultural Resource

The compound event that triggered the destructive fires of October 2017 in Portugal

Portugal is regularly affected by destructive wildfires that have severe social, economic, and ecological impacts. The total burnt area in 2017 (∼540,000 ha) marked the all-time record value since 1980 with a tragic toll of 114 fatalities that occurred in June and October events. The local insurance sector declared it was the costliest natural disaster in Portugal with payouts exceeding USD295 million. Here, the 2017 October event, responsible for more than 200,000 ha of burnt area and 50 fatalities is analyzed from a compound perspective. A prolonged drought led to preconditioned cumulative hydric stress of vegetation in October 2017. In addition, on 15 October 2017, two other major drivers played a critical role: 1) the passage of hurricane Ophelia off the Coast of Portugal, responsible for exceptional meteorological conditions and 2) the human agent, responsible for an extremely elevated number of negligent ignitions. This disastrous combination of natural and anthropogenic drivers led to the uncontrolled wildfires observed on 15 October

Assessment of the hydrological effect of drought and fire events on evapotranspiration at a regional scale

Doutoramento em Engenharia Florestal e dos Recursos Naturais - Instituto Superior de Agronomia / ULUntil today, there is only little knowledge about the behavior of actual evapotranspiration (ETa) before and after wildfires in Portugal, which can be estimated from remote sensing techniques. In this thesis, an existing Simplified Two-Source Energy Balance model (STSEB) was adapted, based on moderate resolution imagery to estimate ETa and its contributing parts of transpiration and evaporation. The study served to test the model and its precision. A bias of about 1 mm d1 for the estimated ETa was observed, where evaporation was regularly overestimated and transpiration underestimated. This error is acceptable for two-layer models based on satellite imagery, but estimates cannot be used for irrigation management. The evolution of the estimated ETa after wildfires (up to four years) was analyzed at eucalypt stands at the Caramulo mountain range in Portugal. By investigating the recovery of ETa after wildfire, the difference between burnt and unburnt stands was mainly related to fire severity and stand characteristics. Two to three years after the fire events, the difference between burnt and unburnt stands became nonsignificant for all severity classes. At the same region, the prediction of soil moisture deficit from drought indices was tested. The drought indices empirically estimate the dryness of an area and are directly related to fire danger. They are based on a simple water balance equation where effective rainfall and ETa are the only input and output, respectively. In this work the empirical equation of (ETa) was substituted by the estimated ETa from STSEB, which enhanced the spatial resolution of the drought indices, being regularly interpolated from point estimates. Spatial patterns of soil moisture deficit were predicted, which indicated a relationship to fire occurrences. To conclude, the ETa estimated by the remote sensing based STSEB model, was used to make observations of the water cycle on a regional scale. In contrast to other post-fire studies, eucalypt stands in Portugal were found to be subject to a smaller hydrological impact after wildfires. This implies a fast recovery and a smaller influence on streamflow and groundwater resources. Furthermore, the drought indices, using the ETa from STSEB, identified areas with higher proneness to drought, by improving the spatial resolution, using satellite imagery compared to traditional interpolation techniques. The results support fire danger rating and might help to improve fire regime and forest managementN/