skip to main content


The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 5:00 PM ET until 11:00 PM ET on Friday, June 21 due to maintenance. We apologize for the inconvenience.

Title: Using Metabolic Energy Density Metrics to Understand Differences in Ecosystem Function During Drought

Terrestrial ecosystems obtain energy in the form of carbon‐containing molecules. Quantifying energy acquisition and dissipation throughout an ecosystem may be useful for describing their resistance and resilience to disturbances. Three longleaf pine savannas with different vegetation composition—a result of variation in soil moisture and land use legacy—were used as a case study to test energy‐based metrics of ecosystem metabolic function. Available energy from gross ecosystem exchange of CO2and its dissipation into metabolic energy density (EM) and energy storage were used to identify differences in drought recovery over an 8‐year period. Sites with higher plant functional diversity in the understory stored more energy and lowered their EMby ~20% when adapting to drought. In contrast, the site with greater abundance of woody understory and overstory species relied on stored energy twice as often as the more diverse sites. The absence of native understory species, due to anthropogenic legacy, prolonged ecosystem‐scale drought recovery by 1 year. This study provides the tools to understand differences in site metabolic energy dynamics and has the potential to identify site characteristics that indicate greater vulnerability to disturbances. Metabolic energy density can be applied to any global ecosystem and provides a first step to describe coupled carbon and energy allocation in ecosystems, which may be used to further refine ecological theory and its management implications.

more » « less
Award ID(s):
1702996 1702029
Author(s) / Creator(s):
 ;  ;  ;  
Publisher / Repository:
DOI PREFIX: 10.1029
Date Published:
Journal Name:
Journal of Geophysical Research: Biogeosciences
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract. Ecosystems are open systems that exchange matter and energy with theirenvironment. They differ in their efficiency in doing so as a result of theirlocation on Earth, structure and disturbance, including anthropogenic legacy.Entropy has been proposed to be an effective metric to describe thesedifferences as it relates energy use efficiencies of ecosystems to theirthermodynamic environment (i.e., temperature) but has rarely been studied tounderstand how ecosystems with different disturbance legacies respond whenconfronted with environmental variability. We studied three sites in alongleaf pine ecosystem with varying levels of anthropogenic legacy and plantfunctional diversity, all of which were exposed to extreme drought. Wequantified radiative (effrad), metabolic and overall entropychanges – as well as changes in exported to imported entropy(effflux) in response to drought disturbance and environmentalvariability using 24 total years of eddy covariance data (8 years per site).We show that structural and functional characteristics contribute todifferences in energy use efficiencies at the three study sites. Our resultsdemonstrate that ecosystem function during drought is modulated by decreasedabsorbed solar energy and variation in the partitioning of energy and entropyexports owing to differences in site enhanced vegetation index and/or soilwater content. Low effrad and metabolic entropy as well as slowadjustment of effflux at the anthropogenically altered siteprolonged its recovery from drought by approximately 1 year. In contrast,stands with greater plant functional diversity (i.e., the ones that includedboth C3 and C4 species) adjusted their entropy exports when facedwith drought, which accelerated their recovery. Our study provides a pathforward for using entropy to determine ecosystem function across differentglobal ecosystems.

    more » « less
  2. Abstract. Global ecosystems vary in their function, and therefore resilience to disturbance, as a result of their location on Earth, structure, and anthropogenic legacy. Resilience can therefore be difficult to describe solely based on energy partitioning, as it fails to effectively describe how ecosystems use available resources, such as soil moisture. Maximum entropy production (MEP) has been shown to be a better metric to describe these differences as it relates energy use efficiencies of ecosystems to the availability of resources. We studied three sites in a longleaf pine ecosystem with varying levels of anthropogenic legacy and biodiversity, all of which were exposed to extreme drought. We quantified their resilience from radiative, metabolic and overall MEP ratios. Sites with anthropogenic legacy had ~10% lower overall and metabolic energy use efficiency compared to more biodiverse sites. This resulted in lower resilience and a delay in recovery from drought by ~1 year. Additionally, a set of entropy ratios to determine metabolic and overall energy use efficiency explained more clearly site-specific ecosystem function, whereas the radiative entropy budget gave more insights about structural complexities at the sites. Our study provides foundational evidence of how MEP can be used to determine resiliency across ecosystems globally.

    more » « less
  3. Climate change is increasing the frequency and severity of short-term (~1 y) drought events—the most common duration of drought—globally. Yet the impact of this intensification of drought on ecosystem functioning remains poorly resolved. This is due in part to the widely disparate approaches ecologists have employed to study drought, variation in the severity and duration of drought studied, and differences among ecosystems in vegetation, edaphic and climatic attributes that can mediate drought impacts. To overcome these problems and better identify the factors that modulate drought responses, we used a coordinated distributed experiment to quantify the impact of short-term drought on grassland and shrubland ecosystems. With a standardized approach, we imposed ~a single year of drought at 100 sites on six continents. Here we show that loss of a foundational ecosystem function—aboveground net primary production (ANPP)—was 60% greater at sites that experienced statistically extreme drought (1-in-100-y event) vs. those sites where drought was nominal (historically more common) in magnitude (35% vs. 21%, respectively). This reduction in a key carbon cycle process with a single year of extreme drought greatly exceeds previously reported losses for grasslands and shrublands. Our global experiment also revealed high variability in drought response but that relative reductions in ANPP were greater in drier ecosystems and those with fewer plant species. Overall, our results demonstrate with unprecedented rigor that the global impacts of projected increases in drought severity have been significantly underestimated and that drier and less diverse sites are likely to be most vulnerable to extreme drought.

    more » « less
  4. Abstract

    Drought, fire, and windstorms can interact to degrade tropical forests and the ecosystem services they provide, but how these forests recover after catastrophic disturbance events remains relatively unknown. Here, we analyze multi‐year measurements of vegetation dynamics and function (fluxes of CO2and H2O) in forests recovering from 7 years of controlled burns, followed by wind disturbance. Located in southeast Amazonia, the experimental forest consists of three 50‐ha plots burned annually, triennially, or not at all from 2004 to 2010. During the subsequent 6‐year recovery period, postfire tree survivorship and biomass sharply declined, with aboveground C stocks decreasing by 70%–94% along forest edges (0–200 m into the forest) and 36%–40% in the forest interior. Vegetation regrowth in the forest understory triggered partial canopy closure (70%–80%) from 2010 to 2015. The composition and spatial distribution of grasses invading degraded forest evolved rapidly, likely because of the delayed mortality. Four years after the experimental fires ended (2014), the burned plots assimilated 36% less carbon than the Control, but net CO2exchange and evapotranspiration (ET) had fully recovered 7 years after the experimental fires ended (2017). Carbon uptake recovery occurred largely in response to increased light‐use efficiency and reduced postfire respiration, whereas increased water use associated with postfire growth of new recruits and remaining trees explained the recovery in ET. Although the effects of interacting disturbances (e.g., fires, forest fragmentation, and blowdown events) on mortality and biomass persist over many years, the rapid recovery of carbon and water fluxes can help stabilize local climate.

    more » « less
  5. Abstract

    Tropical cyclones can physically alter ecosystems, causing immediate and potentially long‐lasting effects on carbon dynamics. In 2018, Hurricane Michael hit the southeastern United States with category 5 winds at landfall and category 2 winds reaching over 100 miles inland, resulting in extensive damage. Longleaf pine woodlands in the path of the hurricane were damaged, but severity varied based on the storm track. We used a combination of eddy covariance measurements, airborne LiDAR, and forest inventory data to determine whether hurricane affects structure, function, and recovery of two longleaf pine woodlands at the ends of an edaphic gradient. We found that the carbon sink potentials in both sites were diminished following the storm, with reductions in net ecosystem exchange (NEE) primarily due to lower rates of photosynthesis, as respiration only increased marginally. The xeric site carbon losses and physiological reductions were smaller following the disturbance, which led to the recovery of ecosystem physiological activity to prestorm rates before that of the mesic site, as indicated by maximum ecosystem CO2uptake rates. Two years following the hurricane both stands continued to have reduced NEE, which signaled altered function. We expect both locations to recover their lost carbon stocks in ∼10–35 years; however, long‐term studies are needed to examine how longleaf woodlands respond to compounding disturbances, such as drought, fire, or other wind storms, which vary significantly across the ecosystem's range. Additionally, hurricanes are intensifying due to climate change, potentially amplifying the degree to which they will alter this ecosystem in the future.

    more » « less