Recovery - Biomass re-accumulation ... It is extremely hard for tundra to recover its nutrient budgets ... vegetation will become co-limited by multiple resources. 3.
Modeling the effects of fire disturbance and warming climate on carbon and nutrient budgets in the arctic tundra ecosystem Yueyang Jiang, Edward Rastetter, Adrian Rocha, Andrea Pearce, Gaius Shaver, Jessica Drysdale, and Bonnie Kwiatkowski
Fall ESA Meeting August 5, 2013
Background Arctic tundra is characterized by: Low primary productivity, low element inputs, and slow element cycling (e.g., nitrogen, phosphorus). Thin active layer, with permafrost impenetrable to plant roots. Long cold winter and short cool summer, low precipitation, and dry winds, low solar radiation, summer surface water pooling and moist soil.
Fire events are not frequent. (Hu et al. 2008)
Severe
Moderate
In 2007 1039 km2 of tundra burned near Anaktuvuk River on the North Slope of Alaska Unburned
We monitored recovery in 3 locations.
S* U*
*M
Recovery –
Biomass accumulates rapidly after fire
Severe Burn, 31 May
34 days
2008
2012
Recovery - Question What is the role of nutrient limitation in regulating the recovery of C balance following tundra fires?
Recovery - model simulation The multiple element limitation (MEL) model is a biogeochemical model that simulates ecosystem C, N, P and water cycles. The heart of the MEL model is an algorithm that allocates plant assets (e.g., biomass, enzymes, carbohydrate, etc.) toward the uptake of different resources. I will refer to these assets collectively as the “uptake effort”.
We ran MEL simulations at severe, moderate and unburned sites across the Anaktuvuk River Fire scar, to simulate the C and nutrient recovery.
Recovery - Net C exchange
Recovery - Biomass re-accumulation Following fire, Five surface years later, is “less tundra green” burns in the are burns. greener than the unburned site.
Recovery - Limitation during 1
st
5 years
Our simulations indicate: 1. Immediately following the fire, biomass is low and nutrients are readily available. Production is therefore limited mostly by the photosynthetic capacity of the vegetation and effort is allocated toward C, light, and water. 2. After about 3 years, plant nutrient demand exceeds net mineralization rates and production becomes nutrient limited and effort is reallocated toward N and P.
3 PO4
Response to Initial Nutrient Stocks
NH 4
Recovery - Nutrient budget N P
Soil released nutrient through mineralization, which Biomass continuously accumulated N and P through Total nutrient stocks declined over three years supported the plant regrowth. the first five post-fire years. after fire, then began to recover.
Recovery - Long-term projection Severe
Moderate
It is extremely hard forbiomass tundraand to recover its nutrientC After the early declines, SOM re-accumulate through next current 200 years, but cannotCtotally recover to budgetsthe under conditions; recovery is not the pre-fire level. possible until nutrients are recovered.
Combustion C loss was ~1.75 Tg over 1039 km2 burn scar.
Burn severity
Unburned Moderate Severe
% of 1039 km2
3%
34%
63%
(km2)
31
353
655
Area
Jones et al. 2009
Recovery - Fire importance The C released by ARF is approximately 8 times the annual C loss of the Kuparuk River watershed (0.218 Tg C, measured by Oechel et al. 2000), which is about 5 times larger than the ARF scar area. The C lost in the ARF could offset about 50% of the annual C sink of all pan-arctic tundra (3 - 4 Tg C/year) as modeled by McGuire et al. (2009).
Recovery - Under a warming climate Under elevated CO2 and warming: 1. The recovery of vegetation from fire is faster under elevated CO2 and warming. 2. The faster recovery is accompanied by a transfer of nutrients from soil to vegetation. 3. In our simulations, the enhanced vegetation growth produces enough litter to compensate for soil C losses.
Our simulations indicate tundra is even more resilient to fire under elevated CO2 and warming.
Recovery - Take home message 1. Burn severity dictates both short- and long-term succession of C and nutrient pools in plants and SOM. 2. The most limiting resource for regrowth varies at different stages of recovery. However, in the long term, tundra vegetation will become co-limited by multiple resources. 3. Under elevated CO2 and warming, nutrient limitation will be decreased by increasing mineralization of N and P from SOM. The stimulated plant growth will allow tundra to recover more rapidly from fire.
4. Small scale C response to fire disturbance ≈ the large-scale C response to climate change.
Recovery - Current work Quantify the potential nutrient pool in the soil organic matter. Compile daily climate data at 1×1 km grid cells for the whole North Slope (e.g., from SNAP, UAF). Conduct simulations for each 1×1 km grid cell using super computers.
July 2011
June 2008
