Steven McNulty | North Carolina State University (original) (raw)

Papers by Steven McNulty

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Forests, 2022

Sea-level rise and climate change stresses pose increasing threats to coastal wetlands that are v... more Sea-level rise and climate change stresses pose increasing threats to coastal wetlands that are vital to wildlife habitats, carbon sequestration, water supply, and other ecosystem services with global significance. However, existing studies are limited in individual sites, and large-scale mapping of coastal wetland degradation patterns over a long period is rare. Our study developed a new framework to detect spatial and temporal patterns of coastal wetland degradation by analyzing fine-scale, long-term remotely sensed Normalized Difference Vegetation Index (NDVI) data. Then, this framework was tested to track the degradation of coastal wetlands at the Alligator River National Wildlife Refuge (ARNWR) in North Carolina, United States, during the period from 1995 to 2019. We identified six types of coastal wetland degradation in the study area. Most of the detected degradation was located within 2 km from the shoreline and occurred in the past five years. Further, we used a state-of-th...

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70 Eddy covariance flux towers provide continuous measurements of net ecosystem 71 carbon exchang... more 70 Eddy covariance flux towers provide continuous measurements of net ecosystem 71 carbon exchange (NEE) for a wide range of climate and biome types. However, these 72 measurements only represent the carbon fluxes at the scale of the tower footprint. To quantify 73 the net exchange of carbon dioxide between the terrestrial biosphere and the atmosphere for 74 regions or continents, flux tower measurements need to be extrapolated to these large areas. 75 Here we used remotely-sensed data from the Moderate Resolution Imaging Spectrometer 76 (MODIS) instrument on board NASA's Terra satellite to scale up AmeriFlux NEE 77 measurements to the continental scale. We first combined MODIS and AmeriFlux data for 78 representative U.S. ecosystems to develop a predictive NEE model using a regression tree 79 approach. The predictive model was trained and validated using NEE data over the periods

Tree Physiology, 2021

Considering the temporal responses of carbon isotope discrimination (Δ13C) to local water availab... more Considering the temporal responses of carbon isotope discrimination (Δ13C) to local water availability in the spatial analysis of Δ13C is essential for evaluating the contribution of environmental and genetic facets of plant Δ13C. Using tree-ring Δ13C from years with contrasting water availability at 76 locations across the natural range of loblolly pine, we decomposed site-level Δ13C signals to maximum Δ13C in well-watered conditions (Δ13Cmax) and isotopic drought sensitivity (m) as a change in Δ13C per unit change of Palmer’s Drought Severity Index (PDSI). Site water status, especially the tree lifetime average PDSI, was the primary factor affecting Δ13Cmax. The strong spatial correlation exhibited by m was related to both genetic and environmental factors. The long-term average water availability during the period relevant to trees as indicated by lifetime average PDSI correlated with Δ13Cmax, suggesting acclimation in tree gas-exchange traits, independent of incident water avail...

Tree Physiology, 2019

Drought frequency and intensity are projected to increase throughout the southeastern USA, the na... more Drought frequency and intensity are projected to increase throughout the southeastern USA, the natural range of loblolly pine (Pinus taeda L.), and are expected to have major ecological and economic implications. We analyzed the carbon and oxygen isotopic compositions in tree ring cellulose of loblolly pine in a factorial drought (~30% throughfall reduction) and fertilization experiment, supplemented with trunk sap flow, allometry and microclimate data. We then simulated leaf temperature and applied a multi-dimensional sensitivity analysis to interpret the changes in the oxygen isotope data. This analysis found that the observed changes in tree ring cellulose could only be accounted for by inferring a change in the isotopic composition of the source water, indicating that the drought treatment increased the uptake of stored moisture from earlier precipitation events. The drought treatment also increased intrinsic water-use efficiency, but had no effect on growth, indicating that pho...

Forest Ecology and Management, 2015

Understanding and quantitatively evaluating the regional impacts of climate change and variabilit... more Understanding and quantitatively evaluating the regional impacts of climate change and variability (e.g., droughts) on forest ecosystem functions (i.e., water yield, evapotranspiration, and productivity) and services (e.g., fresh water supply and carbon sequestration) is of great importance for developing climate change adaptation strategies for National Forests and Grasslands (NFs) in the United States. However, few reliable continental-scale modeling tools are available to account for both water and carbon dynamics. The objective of this study was to test a monthly water and carbon balance model, the Water Supply Stress Index (WaSSI) model, for potential application in addressing the influences of drought on NFs ecosystem services across the conterminous United States (CONUS). The performance of the WaSSI model was comprehensively assessed with measured streamflow (Q) at 72 U.S. Geological Survey (USGS) gauging stations, and satellite-based estimates of watershed evapotranspiration (ET) and gross primary productivity (GPP) for 170 National Forest and Grassland (NFs). Across the 72 USGS watersheds, the WaSSI model generally captured the spatial variability of multi-year mean annual and monthly Q and annual ET as evaluated by Correlation Coefficient (R=0.71-1.0), Nash-Sutcliffe Efficiency (NS=0.31-1.00), and normalized Root Mean Squared Error (0.06-0.48). The modeled ET and GPP by WaSSI agreed well with the remote sensing-based estimates for multi-year annual and monthly means for all the NFs. However, there were systemic discrepancies in GPP between our simulations and the satellite-based estimates on a yearly and monthly scale, suggesting uncertainties in GPP estimates in all methods (i.e., remote sensing and modeling). Overall, our assessments suggested that the WaSSI model had the capability to reconstruct the long-term forest watershed water and carbon balances at a broad scale. This model evaluation study provides a foundation for model applications in understanding the impacts of climate change and variability (e.g., droughts) on NFs ecosystem service functions.

There is no scientific dispute regarding the existence of a greenhouse effect. There is no doubt ... more There is no scientific dispute regarding the existence of a greenhouse effect. There is no doubt that water vapor, carbon dioxide (CO 2), and methane concentrations are greenhouse gases. The data showing increases in CO 2 in the atmosphere are incontrovertible. Uncertainties arise when the Earth's biological responses to climate change are to be quantified. Such uncertainties can be compounded when the responses of ecosystems, especially forests, are to be delineated. Complex interactions among effects of climate change, disturbance, competition, invasive species, management intervention, land use change, and other actions must be clarified by modeling. Model development has improved greatly, but evaluation and validation remain difficult. Model outputs for the South show a fairly wide range of potential changes under scenarios developed from different climate models, suggesting that the assumption of steadystate conditions has little likelihood of occurrence. This implies that we should rethink management approaches, design research to include new ecosystem variables, and seek integrated ecosystem knowledge on scales heretofore rarely treated.

Although ecosystem service (ES) modeling has progressed rapidly in the last 10-15 years, comparat... more Although ecosystem service (ES) modeling has progressed rapidly in the last 10-15 years, comparative studies on data and model selection effects have become more common only recently. Such studies have drawn mixed conclusions about whether different data and model choices yield divergent results. In this study we apply inter- and intra-model comparisons to address these questions at national and provincial scales in Rwanda. We compare results of (1) carbon, annual, and seasonal water yield using InVEST and WASSI models, and the above plus the InVEST sediment regulation model using (2) 30- and 300 m resolution data and (3) three different input land cover datasets. For the inter-model comparison, we found the two models to give diverging results, with most metrics being complementary rather than directly comparable. WASSI and simpler InVEST models (carbon storage and annual water yield) were relatively insensitive to the choice of spatial resolution, but more complex InVEST models (s...

Tree Physiology

These details have been corrected only in this corrigendum to preserve the published version of r... more These details have been corrected only in this corrigendum to preserve the published version of record.

Disclaimer for External Links The appearance of external hyperlinks does not constitute endorseme... more Disclaimer for External Links The appearance of external hyperlinks does not constitute endorsement by the Department of Agriculture of the linked web sites, or the information, products or services contained therein. Unless otherwise specified, the Department does not exercise any editorial control over the information you may find at these locations. Please let us know about existing external links you believe are inappropriate and about specific additional external links you believe ought to be included. Disclaimer of Non-endorsement Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government, and shall not be used for advertising or product endorsement purposes. Cover Photographs: top: Crops fail to grow due to soil salinization along the lower elevation edge of farmland in eastern North Carolina. (Photo courtesy of Michael Gavazzi); bottom: Dead trees along a canal in eastern North Carolina.

Forests

Hurricanes are one of the most significant threats to coastal plain forest ecosystems and urban c... more Hurricanes are one of the most significant threats to coastal plain forest ecosystems and urban communities of the southeastern U.S., but their implications for watershed hydrology are unclear. Hurricanes have the potential to alter water balances, causing extensive flooding, biogeochemical cycle disruption, and water quality degradation, saltwater intrusion, and increased nutrient sedimentation export in coastal watersheds. This case study focused on Hurricane Michael, a recent catastrophic event that impacted the Gulf coast, the Florida panhandle, southwestern Georgia, and southeastern Alabama. Through empirical (Double Mass Curve) and process-based ecohydrological modeling (WaSSI model) on long-term streamflow data, we explored whether vegetation damage caused by this hurricane resulted in an increase in streamflow two years after the extreme event. We found that monthly streamflow from the Chipola River watershed with an area of 2023 km2 did not change (<6%) appreciably durin...

Context Forests cover nearly one-third of the US,providing wildlife habitat, clean air and water,... more Context Forests cover nearly one-third of the US,providing wildlife habitat, clean air and water, cultural and aesthetic values,carbon storage, recreational opportunities such as hiking,camping, fishing,and autumn leaf tours,and products that can be harvested such as timber, pulpwood,fuelwood,wild game, ferns, mushrooms,and berries. This wealth depends on forest biodiversity-the variety of plants,animals, and microbe species,and forest functioning-water flow, nutrient cycling,and productivity. These aspects of forests are strongly influenced by climate and human land use.

Journal of Forestry

Silvics of North America (SNA) is a widely used silvicultural manual. However, the last SNA was p... more Silvics of North America (SNA) is a widely used silvicultural manual. However, the last SNA was published in 1990. Therefore, 2,589 registered foresters were surveyed across four US states to answer two broad questions: (1) Should SNA be updated? And (2) would an updated SNA still be a useful tool for forest management? Most respondents indicated that the type and extent of content contained in the previous version of SNA was still desirable today. Aside from updating all sections with recent research findings, expansion was suggested for ecosystem services provided by species. An update to maps provided in SNA, through changes to natural ranges of tree species and other aesthetic improvement, was suggested by most survey respondents. These findings support the conclusion that the SNA would still be an essential source of information if 21st-century issues such as climate change impacts and adaptation measures were included in the update. Study Implications: There have been major ch...

lobal change involves the simultaneous and rapid alteration of several key environmental paramete... more lobal change involves the simultaneous and rapid alteration of several key environmental parameters that control the dynamics of forests. WC cannot predict with ccrtainty, through direct expcrimelitation, what the responses of forests to global change will be, because WC cannot carry out the multisite, multifactorial experiments required for doiilg so. The physical extent, complexity, and expcnsc of even single-factor experiments at the scale of the whole ecosystem challenge our abilities, although several such experiments have been succcssfiilly undertaken (e.g., lIeI,ucia et al. 1999, Wright and k1sm~issen 19%). To inform policy decisions, however, the scientific community can offer an interdisciplinary synthesis of existing information. When this synthesis takes the form of 3 computer model, qnantitativc predictions can be made that integrate what has been learned from single-factor cxpcriments. ‘I’hc success of such an ;lppro~lch depends on the quality and completeness of the in...

Key Findings  Since 1960, all but two southern capital cities (Montgomery, AL and Oklahoma City,... more Key Findings  Since 1960, all but two southern capital cities (Montgomery, AL and Oklahoma City, OK) have experienced a statistically significant increase in average annual temperature (approximately 0.016 C), but none has experienced significant trends in precipitation.  The South is forecasted to experience warmer temperatures for the duration of the 21 century; forecasts are mixed for precipitation changes during the same period.  Climate predictions range from wet and warm (1167 mm/19.06 C) to moderate and warm (1083 mm/19.45 C and 1106 mm/19.27 C) to dry and hot (912 mm/20.22 C).