NREM Banner                                                       UH Centennial


Impact of rising temperature on carbon input, partitioning, loss and storage in tropical wet forests

HETF Forest

 Figure 1a. One of nine permanent plots in tropical wet forest on the Island of Hawaii.


Plot Layout


Figure 1b. Location of nine permanent plots across a 5.2C mean annual temperature gradient.  Plots are located in The Hawaii Experimental Tropical Forest (Laupahoehoe Unit) of the USDA Forest Service, and the Hakalau Forest National Wildlife Refugee of the US Fish and Wildlife Service.

In collaboration with Dr. Christian Giardina of the Institute of Pacific Islands Forestry, we are conducting a study to examine how rising temperatures will impact carbon cycling in tropical wet forest ecosystems.  Terrestrial ecosystem carbon storage in soils and vegetation exceeds that in the atmosphere by a factor of four, and represents a dynamic balance among carbon input, partitioning, loss, and storage.  This balance is likely being altered by climate change, but the response of terrestrial carbon cycling to rising temperatures remains poorly quantified.  Importantly, temperature-induced changes in ecosystem carbon flux and storage have the potential to feedback into atmospheric CO2 levels and global climate.  In this study we are examining how tropical forest ecosystems will respond to rising temperature by examining ecosystem carbon storage (live biomass, coarse woody debris and soil organic matter); carbon input (gross primary production; GPP); carbon fluxes (litterfall, aboveground net primary productivity (ANPP), soil-surface CO2 efflux, and total belowground carbon flux (TBCF)); and carbon partitioning (fraction of GPP partitioned to aboveground vs. belowground) across a 5.2C mean annual temperature (MAT) gradient on the Island of Hawaii.  Along the MAT gradient, substrate
type and age, dominant overstory vegetation, disturbance history, and plant available water are constant, allowing us to isolate the impacts of temperature on ecosystem carbon cycling.  This work is funded by the National Science Foundation, the USDA Forest Service, and the College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa.

If you are interested in conducting research
utilizing our existing experimental design across the MAT gradient, please complete and email this form to

Publications to date
Bothwell L, Selmants, PC, Giardina, CP, Litton, CM (In review) Leaf litter decomposition rates increase with rising mean annual temperature in Hawaiian tropical montane wet forests. PeerJ.

Giardina CP, Litton CM, Crow SE,  Asner GP (2014) Increased total belowground carbon flux, and not soil carbon loss, drives temperature related increases in soil respiration. Nature Climate Change 4: 822-827. (PDF)

Selmants PC, Litton CM, Giardina CP, Asner, GP (2014) Ecosystem carbon storage does not vary with mean annual temperature in Hawaiian tropical montane wet forests. Global Change Biology 20: 2927-2937. (PDF)

Mascaro J, Litton CM, Hughes RF, Uowolo A, Schnitzer SA (2014) Is logarithmic transformation necessary in allometry? Ten, one-hundred, one-thousand-times yes. Biological Journal of the Linnean Society, 111, 230-233. (PDF)

Iwashita DK, Litton CM, Giardina CP (2013) Coarse woody debris carbon storage across a mean annual temperature gradient in tropical montane wet forest. Forest Ecology and Management, 291, 336-343. (PDF)

Litton CM
, Giardina CP, Albano JK, Long MS, Asner GP (2011) The magnitude and variability of soil-surface CO2 efflux increase with temperature in Hawaiian tropical montane wet forests. Soil Biology & Biochemistry, 43, 2315-2323. (PDF)

Mascaro J, Litton CM, Hughes RF, Uowolo A, Schnitzer SA (2011) Minimizing bias in biomass allometry: Model selection and log-transformation of data. Biotropica, 43, 649-653. (PDF)

Ise T, Litton CM, Giardina CP, Ito A (2010) Comparison of modeling approaches for carbon partitioning: Impact on estimates of global net primary production and equilibrium biomass of woody vegetation from MODIS GPP. Journal of Geophysical Research-Biogeosciences, 115, G04025, doi:10.1029/2010JG001326. (PDF)

Litton CM, Giardina CP (2008) Belowground carbon flux and partitioning: Global patterns and response to temperature (Invited article). Functional Ecology, 22, 941-954. (PDF)

Global patterns in carbon flux and partitioning

Belowgrounc C allocation with temperature

 Figure 2
. Hypothesized relationship between mean annual temperature and the partitioning of GPP (carbon flux as a fraction of GPP) to aboveground vs.  belowground (top panel).  While GPP, aboveground C flux, and belowground C flux all increase with MAT, the slopes of the aboveground and belowground  relationships differ because the factors constraining GPP change as MAT increases (bottom panel).  At colder sites, air temperature presents the strongest  limitation to GPP, and belowground resource supply (e.g., nutrients and water) is high by comparison.  Conversely, at warmer sites, air temperature constraints are  alleviated and belowground resource supply exerts a stronger limitation to GPP.  As a result, partitioning of GPP to belowground increases at higher MAT (from  Litton and Giardina 2008).

Carbon allocation plays a critical role in forest ecosystem carbon cycling by shifting the products of photosynthesis between respiration and biomass production, ephemeral and long-lived tissues, and aboveground and belowground components.  As a primary control on terrestrial carbon storage and forest ecosystem carbon dynamics, carbon allocation is a dynamic balance among total ecosystem carbon input (gross primary production), carbon fluxes and  partitioning of GPP to individual components, and carbon loss.  Some of our recent work on carbon allocation
has focused on global syntheses of available data in forest ecosystems. This work is designed to inform terrestrial ecosystem models by examining general patterns in carbon flux and partitioning, and their response to variables such as resource availability, stand age, competition, and climate change.

Publications to date
Ise T, Litton CM, Giardina CP, Ito A (2010) Comparison of modeling approaches for carbon partitioning: Impact on estimates of global net primary production and equilibrium biomass of woody vegetation from MODIS GPP. Journal of Geophysical Research-Biogeosciences, 115, G04025, doi:10.1029/2010JG001326. (PDF)

Litton CM, Giardina CP (2008) Belowground carbon flux and partitioning: Global patterns and response to temperature (Invited article). Functional Ecology 22: 941-954. (PDF)

Litton CM, Raich JW, Ryan MG (2007) Review: Carbon allocation in forest ecosystems. Global Change Biology, 13, 2089-2109. (PDF)

Invasive grasses, wildfire, and native forest restoration on Oahu

Landscape Fire

Figure 3a.  The spread of invasive species, particularly nonnative grasses, and repeated wildfires, both accidental and prescribed, have converted much of Hawaii's dry forest ecosystems to nonnative grasslands. 

Guinea grass

Figure 3b. Guinea grass (Urochloa maxima), a nonnative invasive grass in Hawaii, forms dense stands that outcompete native plants and has very high fine fuel loads that greatly increase fire potential, spread, and severity.


Figure 3c. A restoration trial with native species assemblages on a guinea grass dominated site, designed to simultaneously restore native biodiversity and decrease the probability and severity of future fire.

Wildland fires are a significant problem in Hawaiian landscapes where native woody communities have been replaced by nonnative invasive grasses.  Wildfires burning in areas dominated by invasive grasses, such as guinea grass (Megathyrsus maximus), typically degrade remnant native plant communites, and preclude the estabilshment and restoration of native species assemblages.  Many wildfires on military lands are ignited by training activities, with subsequent negative impacts on training opportunities and military preparedness.  In order to simultaneously train on military lands and protect remnant native species and communities, the invasive grass-wildfire cycle needs to be managed and ultimately eliminated. Our work is designed to provide a better understanding of the fuel, climatic, and fire behavior components of the invasive grass-wildfire cycle in Hawaiian dry ecosystems currently dominated by nonnative grasses.  Specifically, this work is designed to improve models to accurately predict the probability of ignition, rate of spread, and fire intensity in guinea grasslands.  In addition, we are exploring methods to restore native woody plant communities to these areas to reduce the likelihood of fire occurrence and spread, to eliminate further conversion of remnant native plant communities to nonnative grasslands, and to increase native biodiversity in these highly degraded ecosystems.  This work is funded by the Department of Defense (U.S. Army Garrison - Oahu), the USDA Forest Service (National Fire Plan), and the
the College of Tropical Agriculture and Human Resources - University of Hawaii at Manoa.

Publications to date
Pierce A, McDaniel S, Wasser M, Ainsworth A, Litton CM, Giardina CP, Cordell S (In press) Using a free-burning prescribed fire to test custom and standard fuel models for fire behavior prediction in a grass-invaded tropical dry shrubland.  Applied Vegetation Science: doi:10.1111/avsc.12111.

Ellsworth LM, Litton CM, Dale A, Miura T (In press) The grass-fire cycle at a landscape scale: Changes in land cover and fire behavior with nonnative grass invasion on a tropical island. Applied Vegetation Science: doi:10.1111/avsc.12110s.

Ammondt SA, Litton CM, Ellsworth LM, Leary JK (2013) Restoration of native plant communities in a Hawaiian dry lowland ecosystem dominated by the invasive grass Megathyrsus maximus. Applied Vegetation Science, 16, 29-39.

Ellsworth LM, Litton CM, Taylor AD, Kauffman JB (2013) Spatial and temporal variability of guinea grass (Megathyrsus maximus) fuel loads and moisture on Oahu, Hawaii. International Journal of Wildland Fire, 22, 1083-1092. (PDF)

Ammondt SA, Litton CM (2012) Competition between native Hawaiian plants and the invasive grass Megathyrsus maximus: Implications of functional diversity for ecological restoration. Restoration Ecology, 20, 638-646.

Impacts of nonnative ungulates on ecosystem structure and function in Hawaiian  forests

Fearl Pig

Figure 4a. Nonnative feral pigs degrade native wet forests in Hawai‘i via rooting and mixing of soil horizons, trampling and consumption of native plants, and transport of nonnative seeds (Photo Credit: Hawaii Volcanoes National Park).

Pig damage

Figure 4b. Feral pig damage in native wet forests on the Island of Hawai‘i. This fence-line photo,
taken only six months after the construction of a pig-proof fence, demonstrates pig disturbance to the soil surface. The left-side of the image (where pigs are still present) has almost no litter layer and limited plant establishment, while the right-side of the image (where pigs have been excluded) has an intact litter layer and abundant native forest regeneration.

Hawaiian  forest ecosystems are currently undergoing rapid degradation as a result of nonnative feral ungulates, with implications for forest composition, structure, and biogeochemistry. For example, feral pigs disturb soil via rooting and mixing of soil horizons, and plant communities via the trampling and consumption of native plants and transport of nonnative seeds. We are examining how dominant nonnative ungulates, and their subsequent removal, alters ecosystem structure and composition in native Hawaiian wet and dry forest ecosystems.
Our current work is focused on: (1) understanding native and nonnative plant community dynamics in the presence of nonnative ungulates, and following their removal;  (2) examining the biogeochemical impacts of nonnative ungulates in these forests, and the response to their removal; and (3) testing management strategies to improve native vegetation following nonnative ungulate removal. This work hass been funded by the USDA-CSREES-TSTAR Pacific Program, the DoD Strategic Environmental Research and Development Program (SERDP), and the  College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa.

Publications to date
Cole RJ, Litton CM (2014) Vegetation response to removal of non-native feral pigs from Hawaiian tropical montane wet forest. Biological Invasions, 16, 125-140. (PDF)

Murphy MJ, Inman-Narahari F, Ostertag R, Litton CM (2014) Invasive feral pigs impact native tree ferns and woody seedlings in Hawaiian forest. Biological Invasions, 16, 63-71. (PDF)

Chynoweth MW, Litton CM, Lepczyk CA, Hess SC, Cordell S (2013) Biology and impacts of Pacific Island invasive species. 9. Capra hircus, the feral goat (Mammalia: Bovidae). Pacific Science 67: 141-156. (PDF)

Cole RJ, Litton CM, Koontz MJ, Loh RK (2012) Vegetation recovery 16 years after feral pig removal from a wet Hawaiian forest. Biotropica, 44, 463-471.

Dunkell DO, Bruland GL, Evensen CI, Litton CM (2011) Runoff, sediment transport, and effects of feral pig (Sus scrofa) exclusion in a forested Hawaiian watershed. Pacific Science, 65, 175-194. (PDF)

Ecosystem-level impacts of nonnative grass invasion in Hawaiian Dry Forests

HI dry forest

 Figure 5.  We are using invasion of Hawaiian dry forests by a nonnative perennial bunchgrass to  understand the impacts of invasion on carbon cycling, water availability and use,  and nutrient  dynamics.  The image at the left shows one of our plots where the nonnative grass has been  removed from the understory.

Nonnative invasive plants are prevalent in terrestrial ecosystems worldwide and have long been recognized to adversely impact native species assemblages and biodiversity.  However, it is only in the past several decades that invasions have been implicated as driving changes in important ecosystem processes.  During this time progressively more attention has been focused on the consequences of invasions for ecosystem function, with particular emphasis on soil nutrient cycling.  We are using invasion of Hawaiian dry forest by an African perennial bunchgrass (Pennisetum setaceum) to examine how nonnative invasion into forest ecosystems impacts: (i) water availability and use; (ii) aboveground and belowground ecosystem carbon pools, fluxes and partitioning; and (iii) nutrient dynamics. The majority of this work is being conducted at the Kaupulehu Dry Forest Preserve, in a series of canopy-intact plots established in 2000, where the invasive grass understory was removed from half of the plots and left intact in the remaining half.

Publications to date
Thaxton JM, Cole TC, Cordell S, Cabin RJ, Sandquist DR, Litton CM (2010) Native species regeneration following ungulate exclusion and nonnative grass removal in a remnant Hawaiian dry forest. Pacific Science, 64, 533-544. (PDF)

Litton CM, Sandquist DR, Cordell S (2008) A nonnative invasive grass increases soil carbon flux in a Hawaiian tropical dry forest. Global Change Biology, 14 726-739. (PDF)

Litton CM, Sandquist DR, Cordell S (2006) Effects of non-native grass invasion on aboveground carbon pools and tree population structure in a tropical dry forest of Hawaii. Forest Ecology and Management, 231, 105-113. (PDF)

Impact of fire, invasive species, and their interactions on carbon cycling in tropical rainforests

Lava Ignited wildfire

 Figure 6.  We are using a natural elevation/precipitation gradient in Hawaii Volcanoes National Park  to examine how lava-ignited wildfires, nonnative invasive species, and their  interactions impact: (i)  aboveground carbon sequestration in vegetation and detritus, and (ii) fuel loads and fire behaviour.

Fire is increasingly recognized as an important natural disturbance in the tropics.  However, little is known about the evolutionary history of fire in shaping the structure and function of tropical rainforests. In addition, many tropical forests are now heavily impacted by nonnative species which can 
disrupt ecosystem processes and services, and alter successional trajectories and disturbance regimes.  We are examining the synergistic impacts of lava-ignited wildfire and nonnative species invasions on aboveground carbon pools in vegetation and detritus along a precipitation gradient in Hawaii Volcanoes National Park.  Potential changes in carbon sequestration in tropical forests as a result of wildfire and nonnative species interactions are particularly important in light of the ubiquitous presence of invasive species and the need for better understanding of the role they will play in disturbance regimes and global C cycling.  Future work will concentrate on understanding how invasive species impact fuel loading and fire behaviour in this system.

Publications to date
Litton CM, Kauffman JB. Impact of fire, invasive species, and their interactions on aboveground carbon cycling in tropical mesic to wet rainforests. Forest Ecology and Management, In prep.

Ainsworth A, Kauffman JB (2009) Response of native Hawaiian woody species to lava-ignited wildfires in tropical forests and shrublands. Plant Ecology, 201 197-209.

Litton CM, Kauffman JB (2008) Allometric models for predicting aboveground biomass in two widespread woody plants in Hawaii, U.S.A. Biotropica, 40 313-320. (PDF)

Impact of fire on plant community dynamics, soils, and ecosystem processes in native forests of south-central Chile

Pine invasion in Chile

 Figure 7.  We are working in endemic Nothofagus glauca forests in south-central Chile to examine  the impacts of wildfire, and subsequent invasion by the nonnative Pinus radiata,  on plant community  dynamics and ecosystem processes.

The temperate deciduous species Nothofagus glauca, endemic to Chile, exhibits characteristics commonly found in fire-adapted vegetation, yet the role of fire in the evolutionary history of the vegetation in this area is poorly understood.  We are examining the effects of wildfire on secondary postfire succession in a N. glauca forest in the Coastal Cordillera of south-central Chile.  
Our work has documented that the majority of the plants associated with this forest type exhibit adaptations to survive fire and/or colonize the postfire environment.  However, the presence and success of exotic invaders, particularly Pinus radiata, is altering the successional trajectory of this endemic community with unknown implications for important ecosystem processes.  Currently we are studying how invasion of these forests by P. radiata is impacting water availability and use.

Publications to date

Litton CM, Santelices R, Sandquist DR. Pinus radiata invasion following fire alters water availability in Nothofagus glauca forests of south-central Chile. Plant Ecology, In prep.

Litton CM, Santelices R (2003) Effect of wildfire on soil physical and chemical properties in a Nothofagus glauca forest, Chile. Revista Chilena de Historia Natural, 76, 529-542. (PDF)

Litton CM, Santelices R (2002) Early post-fire succession in a Nothofagus glauca forest in the Costal Cordillera of south-central Chile. International Journal of Wildland Fire, 11, 115-125. (PDF)

Impact of fire, as a natural disturance, on carbon cycling in lodgepole pine forests

Y NP Burned Landscape

 Figure 8.  Fire is a natural disturbance in most forest ecosystems that drives tremendous spatial  heterogeneity across landscapes.  We are examining how fire impacts carbon pools  and fluxes  across Rocky Mountain landscapes through postfire legacies in stand age and tree density.

Validating the different components of the carbon budget in forest ecosystems is essential for developing allocation rules that allow accurate predictions of global carbon pools and fluxes.  In addition, a better understanding of the effects of natural disturbances on carbon cycling is critical – particularly in light of changes in disturbance regimes that may occur with alterations in global climate.  This study investigated the indirect effects of fire on carbon cycling in lodgepole pine (Pinus contorta var. latifolia Engelm. ex Wats.) stands in Yellowstone National Park by examining aboveground and belowground carbon pools, fluxes and allocation patterns in post-fire stands that varied in tree density and stand age (four forest types: low (<1000 trees/ha), moderate (7,000–40,000 trees/ha), and high tree densities (>50,000 trees/ha) in 13-yr-old stands; and ~110-yr-old mature stands).

Publications to date

Litton CM, Ryan MG, Knight DH (2004) Effects of tree density and stand age on carbon allocation patterns in postfire lodgepole pine. Ecological Applications, 14, 460-475. (PDF)

Turner MG, Tinker DB, Romme WH, Kashian DM, Litton CM (2004) Landscape patterns of sapling density, leaf area, and aboveground net primary production in postfire lodgepole pine forests, Yellowstone National Park (USA). Ecosystems, 7, 751-775. (PDF)

Litton CM, Ryan MG, Knight DH, Stahl PD (2003) Soil-surface CO2 efflux and microbial biomass in relation to tree density thirteen years after a stand replacing fire in a lodgepole pine ecosystem. Global Change Biology, 9, 680-696.

Litton CM, Ryan MG, Tinker DB, Knight DH (2003) Belowground and aboveground biomass in young postfire lodgepole pine forests of contrasting tree density. Canadian Journal of Forest Research, 33, 351-363.