Wildfire disturbance-recovery dynamics in Southern Siberia: feedbacks between climate change and ecosystem resilience

This project will result in methods to detect boreal recruitment failure (RF) due to fire, an explanatory model of RF, and quantification of climate feedbacks from RF that are not currently accounted for in any climate or vegetation model. The associated data collection and research outputs will benefit models of climate-fire-vegetation feedbacks. Presently all models that incorporate fire disturbance assume forest recovery.

Research Questions
1. When and where does boreal RF occur?
2. What are the factors that cause boreal RF?
3. What climate feedbacks are likely to result from boreal RF?

Forest loss due to the failure of new trees to survive (recruitment failure) post-fire occurs in boreal forests in Eurasia and North America. The existence of ecological thresholds, or "tipping points" that cause abrupt ecological shifts, is well-known in ecosystems theory but where and when ecosystems are approaching such dramatic changes is difficult to predict. One such extreme ecological shift has been observed in boreal forests that fail to recover after multiple fires within a short time interval (< 10 years). These areas are dominated by grass and are similar to steppe vegetation. Transition from forest to steppe is consistent with predicted changes in vegetation composition in response to regional climate change, and is consistent with global observations of forest loss in response to climate. Preliminary analyses of these sites indicate causes related to changing fire regimes effected by climate.

Firstly, although vegetation indices have been used to identify forest loss, there is currently no method to detect RF using remotely sensed data. We address here the likelihood that RF produces a unique signature that can be detected remotely. The total area affected by RF in Eurasia and North America is at present unknown. Using RF locations provided by the Sukachev Institute (see letter of support), we have developed preliminary methods to differentiate between successfully recovery from fire and RF using remotely-sensed vegetation indices. The proposed research would refine these methods and develop an automated approach to detect RF. The lengthening satellite data record permits a new focus on the impact of climate change on boreal forests (the largest terrestrial biome) and its potential consequences. Remotely sensed imagery to date have yielded "snapshots" of ecosystems and disturbance events. With more than a decade of daily imagery from the MODIS sensors, we can begin to monitor processes like disturbance-recovery cycles. This new focus is critically important to the study of climate-ecosystem interactions and climatic "tipping points".

Secondly, the causes of RF have not been identified. RF has been observed in areas of Siberia where the length of time between fire disturbances was extremely low. Initial field observations of RF sites indicate that high soil temperature and low moisture create a seedbed unsuitable for recruitment of trees following a fire. Additional field data will provide the inputs for an explanatory model of RF that includes characteristics of the fire (such as intensity and fire weather), pre-fire vegetation (e.g., stand age and density), and post-fire environment (e.g., soil temperature and moisture).

Thirdly, the effect of RF on carbon, water and energy fluxes that impact climate has not been quantified. The replacement of forests with steppe vegetation results in carbon losses to the atmosphere from combustion and post-fire decomposition. The net climate impact of RF is presently unknown. Albedo is initially low following a fire and then may become higher due to the higher albedo of replacement vegetation. Changes in evapotranspiration rates affect latent and sensible heat fluxes. The area of RF is likely to grow in response to increasing fire frequency and severity, but the dynamics of recovery from wildfire and RF have not been incorporated into any coupled climate-vegetation models.

The impact of the proposed research on economic and social well-being is highlighted by our project partners, the World Wildlife Fund for Nature (WWF) and Northern Eurasia's Future Initiative (NEFI). These groups have partnered with the research proposal team because of the effect of massive wildfire disturbances in Siberia and their impact on ecosystem services such as wildlife habitat, wood, and non-timber forest products. The potential for forest loss after repeated wildfire disturbance is a troubling one for agencies that promote conservation strategies in boreal Siberia, given how much these ecosystems provide to human societies and rare and threatened wildlife species such as the Siberian crane and the Siberian sturgeon. A spatial estimation of the areas where forests have been lost due to fire-driven recruitment failure is an early output of the proposed analysis. This information will be useful to agencies like WWF and NEFI to overlay with existing information on forest resources and wildlife habitat to determine what natural resources may be under threat.

After the areas of recruitment failure are mapped, we will look use an explanatory model to study the factors that cause post-fire recruitment failure in Siberia. Knowing what factors are associated with recruitment failure will allow conservation agencies and land managers to assess burned areas in terms of their vulnerability to recruitment failure. This information will aide in the strategic management of forest resources through fire exclusion in vulnerable regions, replanting in areas that have been affected, and afforestation to offset unrecoverable forest losses. These practices will directly benefit those who are dependent on forest products for their livelihood and wildlife species that rely on boreal forest stands for forage material and habitat.

We will engage with the project partners who support the impact of the proposed research via teleconferences throughout the course of the project. Initial products will be shared with project partners as well as preliminary results from a combination of field observations, remotely sensed data, and model outputs. Our conservation-oriented project partners will provide an assessment of the effect that recruitment failure is likely to have on economic and social well-being, and how our data products can be best suited to address these important questions.

With respect to engaging the public in the science of boreal disturbance-recovery cycles, we will reach out to schools and non-profit organizations in the UK and Russia that are interested in hosting all-ages activities developed by Dr Barrett and the proposal team. Dr Barrett has already developed two interactive group activities to teach the general public about feedbacks among climate change, fire and post-fire recovery.