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Interactive impacts of rising temperature and land use change on terrestrial carbon flux and partitioning

Hawaii Experimental Tropical Forest

 



 Figure 1. The Hawaii Experimental Tropical Forest, Laupahoehoe Unit of the USDA Forest Service on the Island of Hawaii.








In collaboration with Dr. Christian Giardina of the Institute of Pacific Islands Forestry, USDA Forest Service we are conducting a study, funded by the National Science Foundation and the USDA Forest Service, to understand how rising temperatures and land-use change interact to impact the carbon sink strength of terrestrial ecosystems.  The initial phase of research will focus on carbon input, allocation, and loss across a land-use/temperature matrix in the newly created Hawaii Experimental Tropical Forest on the Island of Hawaii.

Publications to date
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 the partitioning of GPP to individual components.  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 resource availability, stand age, competition, and climate change.

Publications to date
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)
Ecosystem-level impacts of nonnative grass invasion in Hawaiian Dry Forests

HI dry forest




 Figure 3.  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
Litton CM, Sandquist DR, Cordell S. Nonnative grass invasion changes carbon flux and partitioning in Hawaiian tropical dry forest. Ecology, In prep.

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 4.  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.

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 5.  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 6.  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. (PDF)

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. (PDF)