Scientists & Staff
My current research at the Silas Little Experimental Forest in the New Jersey Pine Barrens focuses on quantifying and modeling factors driving fire danger and fire behavior. Severe wildfires in the Pine Barrens are strongly driven by weather, especially episodes of low relative humidity and high windspeeds associated with the passage of strong cold fronts, such as before and during the 18,000 acre Warren Grove fire of May 2007. Delivery of high quality weather data measured from our network of fire weather towers, and accurate, validated fire weather predictions by the EAMC for the region provide wildland fire managers with tools to detect and plan for these events. EAMC model predictions are evaluated using extensive field measurements in the Pine Barrens, including three eddy flux towers to measure turbulence and energy exchange, and a SODAR to measure windspeed and direction up to 700 meter height.
Fire weather interacts with complex fuel beds, and much of my collaborative research is focused on fuel mapping, quantification of complex fuel bed structure, and measuring the effects of prescribed fires on fuels and forest structure. The interactions of weather and fuel beds drive fuel moisture dynamics, and these are key elements of wildfire risk and fire behavior. Thus, fuel moisture dynamics and ecosystem scale characterization of energy and hydrologic fluxes are important parts of my research. I am also interested in tech-transfer, or how to best provide this information to wildland fire and other land managers.
My other research interests are the physical and biological processes that drive the carbon and nutrient dynamics of terrestrial ecosystems. This research addresses two major questions: 1) How do environmental factors, substrate quality and disturbances interact to control short-term carbon and nutrient dynamics, and 2) How do processes linked to global environmental change, such as forest and fire management, land use change, and climate change affect the long-term dynamics of these systems? Understanding the effects of forest management, fire, invasive insects, and land use change on carbon dynamics at landscape and regional scales is essential, because these human-induced changes are impacting the composition of the atmosphere, further driving climate change. My research approach involves the complementary use of measurements and models of land-atmosphere exchanges of energy, water, and CO2. For example, I use eddy covariance to quantify net CO2 exchange, and evaluate flux measurements against models and carbon budgets constructed from field measurements of biomass accumulation, litterfall and decomposition.
The integration of these disciplines, from operational fire danger rating and complex fuel bed characterization to landscape level measurements of forest productivity result in a synthetic framework to solve many of the complex questions assigned to the Silas Little Experimental Forest. My research also has included investigations of landscape-scale carbon dynamics in a mosaic of intensively-managed and naturally-regenerated forests in Florida, regional linkages in the nitrogen cycle between lowland and montane forests in Costa Rica, and the role of native herbivores in carbon and nitrogen dynamics of semiarid scrub in Argentina and Longleaf Pine forests in Florida.
- A validated fuel moisture model for complex fuel beds driven by MM5 fire weather predictions
- Development and delivery of a drought stress index based on eddy covariance measurements
- Impacts of disturbances on hydrologic and nutrient cycles in the Pine Barrens
Why This Research is Important
Wildfire risk is real in the Pine Barrens. This landscape is dominated by highly flammable forests consisting of Pitch Pine and dense understory shrubs and oaks, and it continues to be flammable despite repeated wildfires and/or fuel reduction treatments. These forests are adjacent to extensive wildland urban interface (WUI) and key transportation corridors, making suppression activities complicated. The need for accurate fire weather, fuel loading, and fuel moisture information is obvious.
My current research in the Pine Barrens also has important policy implications, because it focuses on the carbon dynamics of fire management, and how prescribed fire, wildfire, and other disturbances control rates of carbon sequestration by forests. By placing forest harvesting, prescribed fire treatments, and other disturbances in the context of forest productivity measurements and models, we have advanced an understanding of how these activities and processes affect long-term C dynamics. We are incorporating this information in a synthetic, predictive framework to assist State and Federal fire and forest managers optimize the reduction of wildfire risk and emissions while maintaining rates of C sequestration by forests.
- Ecological Society of America
- American Association for the Advancement of Science
- Association of Tropical Biology and Conservation
- Wilderness Society
- Pinelands Preservation Alliance
Featured Publications & Products
- Skowronski, Nicholas S.; Clark, Kenneth L.; Duveneck, Matthew; Hom, John. 2011. Three-dimensional canopy fuel loading predicted using upward and downward sensing LiDAR systems. Remote Sensing of Environment. 115: 703-714.
- Clark, Kenneth L.; Skowronski, Nicholas; Hom, John. 2010. Invasive insects impact forest carbon dynamics. Global Change Biology. 16: 88-101.
- Schafer, Karina V.; Clark, Kenneth L.; Skowronski, Nicholas; Hamerklynck, Erik P. 2010. Impact of insect defoliation on forest carbon balance as assessed with a canopy assimilation model. Global Change Biology. 16: 546-560.
- Hollinger, D.Y.; Ollinger, S.V.; Richardson, A.D.; Meyers, T.P.; Dails, D.B.; Martin, M.E.; Scott, N.A.; Arkebauer, T.J.; Baldocchi, D.D.; Clark, K.L.; Curtis, P.S.; Davis, K.J.; Desai, A.R.; Dragoni, D.; Goulden, M.L.; Gu, L.; Katul, G.G.; Pallardy, S.G.; Paw U, K.T.; Schmid, H.P.; Stoy, P.C.; Suyker, A.E.; Verma, S.B. 2010. Albedo estimates for land surface models and support for a new paradigm based on foliage nitrogen concentration. Global Change Biology. 16: 696-710.
- Clark, Kenneth L.; Skowronski, Nicholas; Hom, John; Duveneck, Matthew; Pan, Yude; Van Tuyl, Stephen; Cole, Jason; Patterson, Matthew; Maurer, Stephen. 2009. Decision support tools to improve the effectiveness of hazardous fuel reduction treatments in the New Jersey Pine Barrens. International Journal ofWildland Fire. 18: 268-277.
Publications & Products
- Kabrick, John M.; Clark, Kenneth L.; D'Amato, Anthony W.; Dey, Daniel C.; Kenefic, Laura S.; Kern, Christel C.; Knapp, Benjamin O.; MacLean, David A.; Raymond, Patricia; Waskiewicz, Justin D. 2017. Managing hardwood-softwood mixtures for future forests in eastern North America: assessing suitability to projected climate change. Journal of Forestry
- Mueller, Eric V.; Skowronski, Nicholas; Clark, Kenneth; Gallagher, Michael; Kremens, Robert; Thomas, Jan C.; El Houssami, Mohamad; Filkov, Alexander; Hadden, Rory M.; Mell, William; Simeoni, Albert. 2017. Utilization of remote sensing techniques for the quantification of fire behavior in two pine stands. Fire Safety Journal
- Simeoni, Albert; Owens, Zachary C.; Christiansen, Erik W.; Kemal, Abid; Gallagher, Michael; Clark, Kenneth L.; Skowronski, Nicholas; Mueller, Eric V.; Thomas, Jan C.; Santamaria, Simon; Hadden, Rory M. 2017. A preliminary study of wildland fire pattern indicator reliability following an experimental fire. Journal of Fire Sciences
- Thomas, Jan C.; Mueller, Eric V.; Santamaria, Simon; Gallagher, Michael; El Houssami, Mohamad; Filkov, Alexander; Clark, Kenneth; Skowronski, Nicholas; Hadden, Rory M.; Mell, William; Simeoni, Albert. 2017. Investigation of firebrand generation from an experimental fire: Development of a reliable data collection methodology. Fire Safety Journal
- Carlo, Nicholas J.; Renninger, Heidi J.; Clark, Kenneth L.; Schäfer, Karina V.R. 2016. Impacts of prescribed fire on Pinus rigida Mill. Tree physiology. 36(8): 967-982.
- Clark, Kenneth L.; Branch, Lyn C.; Hierro, Jose L.; Villarreal, Diego. 2016. Burrowing herbivores alter soil carbon and nitrogen dynamics in a semi-arid ecosystem, Argentina. Soil Biology & Biochemistry. 103: 253-261.
- El Houssami, Mohamad; Mueller, Eric; Filkov, Alexander; Thomas, Jan C; Skowronski, Nicholas; Gallagher, Michael R; Clark, Ken; Kremens, Robert; Simeoni, Albert. 2016. Experimental procedures characterizing firebrand generation in wildland fires. Fire Technology. 52(3): 731-751.
- Zscheischler, Jakob; Fatichi, Simone; Wolf, Sebastian; Blanken, Peter D.; Bohrer, Gil; Clark, Ken; Desai, Ankur R.; Hollinger, David; Keenan, Trevor; Novick, Kimberly A.; Seneviratne, Sonia I. 2016. Short-term favorable weather conditions are an important control of interannual variability in carbon and water fluxes. Journal of Geophysical Research: Biogeosciences
- Clark, Kenneth L.; Skowronski, Nicholas; Gallagher, Michael. 2015. Fire management and carbon sequestration in Pine Barren Forests. Journal of Sustainable Forestry. 34(1-2): 125-146.
- Heilman, Warren E.; Clements, Craig B.; Seto, Daisuke; Bian, Xindi; Clark, Kenneth L.; Skowronski, Nicholas S.; Hom, John L. 2015. Observations of fire-induced turbulence regimes during low-intensity wildland fires in forested environments: implications for smoke dispersion. Atmospheric Science Letters. doi: 10.1002/asl.581.
- Mueller, Eric; Skowronski, Nicholas; Clark, Kenneth; Kremens, Robert; Gallagher, Michael; Thomas, Jan; El Houssami, Mohamad; Filkod, Alexander; Butler, Bret; Hom, John; Mell, William; Simeoni, Albert. 2015. Initial results from a field experiment to support the assessment of fuel treatment effectiveness in reducing wildfire intensity and spread rate. In: Keane, Robert E.; Jolly, Matt; Parsons, Russell; Riley, Karin. Proceedings of the large wildland fires conference; May 19-23, 2014; Missoula, MT. Proc. RMRS-P-73. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 305-308.
- Renninger, Heidi J.; Carlo, Nicholas J.; Clark, Kenneth L.; Schäfer, Karina V.R. 2015. Resource use and efficiency, and stomatal responses to environmental drivers of oak and pine species in an Atlantic Coastal Plain forest. Frontiers in Plant Science. 6: 297.
- Skowronski, Nicholas S.; Haag, Scott; Trimble, Jim; Clark, Kenneth L.; Gallagher, Michael R.; Lathrop, Richard G. 2015. Structure-level fuel load assessment in the wildland-urban interface: a fusion of airborne laser scanning and spectral remote-sensing methodologies. International Journal of Wildland Fire. doi: 10.1071/WF14078 [11 p.].
- Clark, K.L.; Skowronski, N.S.; Gallagher, M.R.; Renninger, H.; Schäfer, K.V.R. 2014. Contrasting effects of invasive insects and fire on ecosystem water use efficiency. Biogeosciences. 11(23): 6509-6523.
- Clark, Kenneth L.; Skowronski, Nicholas; Gallagher, Michael. 2014. The fire research program at the Silas Little Experimental Forest, New Lisbon, New Jersey. In: Hayes, D.C.; Stout, S.L.; Crawford, R.H.; Hoover, A.P., eds. USDA Forest Service experimental forests and ranges research for the long term. New York, NY: Springer: 515-534. Chapter 22.
- Clark, Kenneth L.; Skowronski, Nicholas; Renninger, Heidi; Scheller, Robert. 2014. Climate change and fire management in the mid-Atlantic region. Forest Ecology and Management. 327: 306-315.
- Kiefer, Michael T.; Heilman, Warren E.; Zhong, Shiyuan; Charney, Joseph J.; Bian, Xindi; Skowronski, Nicholas S.; Hom, John L.; Clark, Kenneth L.; Patterson, Matthew; Gallagher, Michael R. 2014. Multiscale simulation of a prescribed fire event in the New Jersey Pine Barrens using ARPS-CANOPY. Journal of Applied Meteorology and Climatology. 53: 793-812.
- Kretchun, Alec M.; Scheller, Robert M.; Lucash, Melissa S.; Clark, Kenneth L.; Hom, John; Van Tuyl, Steve; Fine, Michael L. 2014. Predicted effects of gypsy moth defoliation and climate change on forest carbon dynamics in the New Jersey Pine Barrens. PLoS ONE. 9(8): e102531.
- Lucash, Melissa S.; Scheller, Robert M.; Kretchun, Alec M.; Clark, Kenneth L.; Hom, John. 2014. Impacts of fire and climate change on long-term nitrogen availability and forest productivity in the New Jersey Pine Barrens. Canadian Journal of Forest Research. 44(5): 404-412.
- Renninger, Heidi J.; Carlo, Nicholas; Clark, Kenneth L.; Schäfer, Karina V.R. 2014. Modeling respiration from snags and coarse woody debris before and after an invasive gypsy moth disturbance. Journal of Geophysical Research: Biogeosciences. 119(4): 630-644.
- Schäfer, K.V.R.; Renninger, H.J.; Clark, K.L.; Medvigy, D. 2014. Hydrological responses to defoliation and drought of an upland oak/pine forest. Hydrological Processes. 28(25): 6113-6123.
- Skowronski, Nicholas S.; Clark, Kenneth L.; Gallagher, Michael; Birdsey, Richard A.; Hom, John L. 2014. Airborne laser scanner-assisted estimation of aboveground biomass change in a temperate oak-pine forest. Remote Sensing of Environment. 151: 166-174.
- Song, Xin; Clark, Kenneth S.; Helliker, Brent R. 2014. Interpreting species-specific variation in tree-ring oxygen isotope ratios among three temperate forest trees. Plant, Cell & Environment. 37(9): 2169-2182.
- Cole, Jason A.; Johnson, Kristopher D.; Birdsey, Richard A.; Pan, Yude; Wayson, Craig A.; McCullough, Kevin; Hoover, Coeli M.; Hollinger, David Y.; Bradford, John B.; Ryan, Michael G.; Kolka, Randall K.; Wieshampel, Peter; Clark, Kenneth L.; Skowronski, Nicholas S.; Hom, John; Ollinger, Scott V.; McNulty, Steven G.; Gavazzi, Michael J. 2013. Database for landscape-scale carbon monitoring sites. Gen. Tech. Rep. NRS-119. Newtown square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 12 p.
- Medvigy, David; Jeong, Su-Jong; Clark, Kenneth L.; Skowronski, Nicholas S.; Schäfer, Karina V. R. 2013. Effects of seasonal variation of photosynthetic capacity on the carbon fluxes of a temperate deciduous forest. Journal of Geophysical Research Biogeosciences. 118(4): 1703-1714.
- Renninger, Heidi J.; Clark, Kenneth L.; Skowronski, Nicholas; Schäfer, Karina V.R. 2013. Effects of a prescribed fire on water use and photosynthetic capacity of pitch pines. Trees 27(4): 1115-1127.
- Schneider, Maximilian P. W.; Pyle, Lacey A.; Clark, Kenneth L.; Hockaday, William C.; Masiello, Caroline A.; Schmidt, Michael W.I. 2013. Toward a "molecular thermometer" to estimate the charring temperature of wildland charcoals derived from different biomass sources. Environmental Science & Technology. 47(20): 11490-11495.
- Clark, Kenneth L.; Skowronski, Nicholas; Gallagher, Michael; Renninger, Hedi; Schafer, Karina. 2012. Effects of invasive insects and fire on energy exchange and evapotranspiration in the New Jersey pine lands. Agricultural and Forest Meteorology. 166-167: 50-61.
- Medvigy, D.; Clark, K.L.; Skowronski, N.S.; Schäfer, K.V.R. 2012. Simulated impacts of insect defoliation on forest carbon dynamics. Environmental Research Letters. 7(4): 045703.
- Scheller, Robert M.; Kretchun, Alec M.; Van Tuyl, Steve; Clark, Kenneth L.; Lucash, Melissa S.; Hom, John. 2012. Divergent carbon dynamics under climate change in forests with diverse soils, tree species, and land use histories. Ecosphere. 3(11): art110.
- Hierro, Jose L.; Clark, Kenneth L.; Branch, Lyn C.; Villarreal, Diego. 2011. Native herbivore exerts contrasting effects on fire regime and vegetation structure. Oecologia. 166(4): 1121-1129.
- Kiefer, Michael T.; Heilman, Warren E.; Zhong, Shiyuan; Charney, Joseph J.; Bian, X.; Shadbolt, Ryan P.; Hom, John; Clark, Kenneth; Skowronski, Nicholas; Gallagher, Michael; Patterson, Matthew. 2011. Development of a fine scale smoke dispersion modeling system. Part II: Case study of a prescribed burn in the New Jersey Pine Barrens. In: Ninth symposium on fire and forest meteorology; 17-20 October 2011; Palm Springs, CA. Boston, MA: American Meteorological Society. 5 p.
- Miao, Zewei; Lathrop, Richard G.; Xu, Ming; La Puma, Inga P.; Clark, Kenneth L.; Hom, John; Skowronski, Nicholas; Van Tuyl, Steve. 2011. Simulation and sensitivity analysis of carbon storage and fluxes in the New Jersey Pinelands. Environmental Modelling & Software. 26(9): 1112-1122.
- Scheller, Robert M.; Van Tuyl, Steve; Clark, Kenneth L.; Hom, John; La Puma, Inga. 2011. Carbon sequestration in the New Jersey Pine Barrens under different scenarios of fire management. Ecosystems. 14: 987-1004.
- Clark, Ken; Skowronski, Nicholas; Michael, Gallagher; Heilman, Warren E.; Hom, John. 2010. Fuel consumption and particulate emissions during fires in the New Jersey Pinelands. In: Proceedings of the 3rd fire behavior and fuels conference; 2010 October 25-29; Spokane, WA. Birmingham AL: International Association of Wildland Fire. 19 p. [On CD-ROM].
- Scheller, Robert M.; Van Tuyl, Steve; Clark, Kenneth; Hayden, Nicholas G.; Hom, John; Mladenoff, David J. 2008. Simulation of forest change in the New Jersey Pine Barrens under current and pre-colonial conditions. Forest Ecology and Management. 255: 1489-1500.
- Skowronski, Nicholas; Clark, Kenneth; Nelson, Ross; Hom, John; Patterson, Matt. 2007. Remotely sensed measurements of forest structure and fuel loads in the Pinelands of New Jersey. Remote Sensing of Environment. 108: 123-129.
- Clark, Kenneth; Skowronski, Nick; Pan, Yude; Van Tuyl, Steve; Heilman, Warren. 2006. Fire research in the pine barrens of New Jersey. In: Dickinson, Matthew B., ed. 2006. Fire in eastern oak forests: delivering science to land managers, proceedings of a conference; 2005 November 15-17; Columbus, OH. Gen. Tech. Rep. NRS-P-1. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 271.
- Pan, Yude; Birdsey, Richard; Hom, John; McCullough, Kevin; Clark, Kenneth. 2006. Improved estimates of net primary productivity from MODIS satellite data at regional and local scales. Ecological Applications.
- Clark, Kenneth L.; Nadkarni, Nalini M.; Gholz, Henry L. 2005. Retention of inorganic nitrogen by epiphytic bryophytes in a tropical montane forest. BIOTROPICA. 37(3): 328-336.
- Powell, Thomas L.; Starr, Gregory; Clark, Kenneth L.; Martin, Timothy A.; Gholz, Henry L. 2005. Ecosystem and understory water and energy exchange for a mature, naturally regenerated pine flatwoods forest in north Florida. Canadian Journal of Forest Research 35:1568-1580
- Clark, Kenneth L.; Gholz, Henry L.; Castro, Mark S. 2004. Carbon dynamics along a chronosequence of slash pine plantation in north Florida. Ecological Applications. 14(4): 1154-1171.
National Research Highlights
Scientists Untangle Relationships Among Firing Technique, Fuel Consumption, and Turbulent Transfer in Forests
Forest Service research indicates that relatively low-intensity prescribed fires can be effective at reducing hazardous fuels in forests while minimizing impacts on local air quality.
Hardwood-Softwood Mixtures for Future Forests in Eastern North America: Assessing Suitability to Projected Climate Change
Despite growing interest in management strategies for climate change adaptation, there are few methods for assessing the ability of stands to endure or adapt to projected future climates. Forest Service scientists developed a means for assigning climate “compatibility” and “adaptability” scores to stands for assessing the suitability of tree species for projected climate scenarios. They used these scores to determine if mixed hardwood-softwood stands or “mixedwoods” were better suited to projected future climates than pure hardwood or pure softwood stands.
Forest Service scientists quantified consumption and accumulation of the forest floor and understory vegetation during and following prescribed fires in upland forest stands in the New Jersey Pinelands. Their findings suggest that prescribed burning in upland pine-dominated forests has little effect on long-term forest carbon dynamics at the landscape scale.
Forest Service scientists quantified rates of carbon sequestration and water use by forests before and after invasive insect defoliation and prescribed burns in the Pinelands of New Jersey. Ecosystem Water Use Efficiency (WUEe), a measure of the amount of water used to sequester carbon by forests, was reduced in oak-dominated and mixed stands during defoliation, whereas, prescribed fire had little effect on WUEe. Long-term data indicated that even when consumption losses from fires are considered, insect-defoliated stands were only half as productive compared to burned stands, while water use was less affected.
Forest Service scientists quantified rates of carbon sequestration by forests before and after prescribed burns were conducted by the New Jersey Forest Fire Service. Uptake of carbon dioxide during the summer following spring burns averaged 79 percent of pre-burn levels; and, it takes treated forests only 2 to 3 years to accumulate the amount of carbon released from the litter layer and understory during the fire.
Minor disturbances in forests that do not significantly alter biomass can reduce water use and increase ground water recharge to aquifers
Predicting the effects of smoke from low-intensity prescribed fires on local air-quality is being made easier by new tools developed by Forest Service scientists. These tools are now being validated through data collected from fuels, meteorological, and air quality monitoring networks set up near and within prescribed fires in the New Jersey Pine Barrens. The tools and observational data from this project help fire and forest managers in planning for prescribed burns to minimize adverse air-quality impacts in the vicinity of the burns.
The recovery of carbon and hydrologic cycling following two major disturbances in pine and oak-dominated stands in the New Jersey Pine Barrens---invasive insect defoliation and fire---are being measured by NRS scientists Kenneth Clark and Nicholas Skowronski.
Lasers, in what is termed Light Detection and Ranging (LiDAR) systems, are being used by NRS researchers Nicholas Skowronski and Kenneth Clark to measure forest structure and canopy fuel loading at the Silas Little Experimental Forest in the New Jersey Pine Barrens.