John Hom

Effects of Urban Land-Use Change on Biogeochemical Cycles

Urban land-use change, the conversion of agricultural recand natural ecosystems to human settlements, has become an important component of global change. Virtually all of the projected increase in the worlds population is expected to occur in cities so that by the year 2007 more than half of the global population is expected to live in urban areas (United Nations 2004). Yet, urban settlements and surrounding areas are complex ecological systems that have only recently been studied from a rigorous ecological perspective (Pickett et al. 2001).

Decision support tools to improve the effectiveness of hazardous fuel reduction treatments in the New Jersey Pine Barrens

Our goal is to assist the New Jersey Forest Fire Service and federal wildland fire managers in the New Jersey Pine Barrens evaluate where and when to conduct hazardous fuel reduction treatments. We used remotely sensed LIDAR (Light Detection and Ranging System) data and field sampling to estimate fuel loads and consumption during prescribed fire treatments. This information was integrated with data on prescribed fire treatments conducted by the New Jersey Forest Fire Service over the last 15 years to produce and interpret maps of current fuel loads. Forest productivity measurements and models were then used to estimate rates of fuel accumulation through time. We could then calculate return intervals for desired fuel load conditions. Through formal workshops and frequent discussions with state and federal fire managers, our results enhance the ability of these agencies to make key decisions regarding the effectiveness and longevity of hazardous fuels treatments.

Divergent Carbon Dynamics under Climate Change in Forests with Diverse Soils, Tree Species, and Land Use Histories

Accounting for both climate change and natural disturbances—which typically result in greenhouse gas emissions—is necessary to begin managing forest carbon sequestration. Gaining a complete understanding of forest carbon dynamics is, however, challenging in systems characterized by historic over-utilization, diverse soils and tree species, and frequent disturbance. In order to elucidate the cascading effects of potential climate change on such systems, we projected forest carbon dynamics, including soil carbon changes, and shifts in tree species composition as a consequence of wildfires and climate change in the New Jersey pine barrens (NJPB) over the next 100 years. To do so, we used the LANDIS-II succession and disturbance model combined with the CENTURY soil model. The model was calibrated and validated using data from three eddy flux towers and the available empirical or literature data. Our results suggest that climate change will not appreciably increase fire sizes and intensity. The recovery of C stocks following substantial disturbances at the turn of the 20th century will play a limited but important role in this system. In areas characterized by high soil water holding capacity, reduced soil moisture may lead to lower total C and these forests may switch from being carbon sinks to becoming carbon neutral towards the latter part of the 21st century. In contrast, other areas characterized by lower soil water holding capacity and drought tolerant species are projected to experience relatively little change over the next 100 years. Across all soil types, however, the regeneration of many key tree species may decline leading to longer-term (beyond 2100) risks to forest C. These divergent responses were largely a function of the dominant tree species, and their respective temperature and soil moisture tolerances, and soil water holding capacity. In summary, the system is initially C conservative but by the end of the 21st century, there is increasing risk of de-stabilization due to declining growth and regeneration.

Responses of Northern U.S. Forests to Environmental Change

Section 1. An Introduction to Northern U.S. Forest Ecosystems.- 1. Forest Resources and Conditions.- 2. Geologic and Edaphic Factors Influencing Susceptibility of Forest Soils to Environmental Change.- 3. Climate and Atmospheric Deposition Patterns and Trends.- 4. Forest Declines in Response to Environmental Change.- Section 2. Global Change Impacts on Tree Physiology.- 5. Interacting Effects of Multiple Stresses on Growth and Physiological Processes in Northern Forest Trees.- 6. Physiological and Environmental Causes of Freezing Injury in Red Spruce.- 7. Tree Health and Physiology in a Changing Environment.- 8. Atmospheric Deposition Effects on Surface Waters, Soils, and Forest Productivity.- Section 3. Ecosystem-Scale Interactions with Global Change.- 9. Nitrogen Saturation in Experimental Forested Watersheds.- 10. Effects of Soil Warming on Carbon and Nitrogen Cycling.- 11. Regional Impacts of Climate Change and Elevated Carbon Dioxide on Forest Productivity.- 12. Regional Impacts of Ozone on Forest Productivity.- 13. Effects of Climate Change on Forest Insect and Disease Outbreaks.- 14. Forest Responses to Changing Climate: Lessons from the Past and Uncertainty for the Future.- Section 4. Summary.- 15. Summary of Prospective Global Change Impacts on Northern U.S. Forest Ecosystems.

The evolution of the New Jersey Pine Plains.

PREMISE OF THE STUDY Fire in the New Jersey Pine Plains has selectively maintained a dwarf growth form of pitch pine (Pinus rigida), which is distinct from the surrounding tall forest of the Pine Barrens and has several other inherited adaptations that enable it to survive in an environment dominated by fire. METHODS Pitch pine progeny from two Pine Plains sites, the West and East Pine Plains, were grown in common garden environments with progeny from two Pine Barrens stands, Batsto and Great Egg Harbor River. The tests were replicated in five locations: in New Jersey, Connecticut, two sites in Massachusetts, and Korea. One of the tests was monitored for up to 36 yr. KEY RESULTS Progeny of Pine Plains origin were, in general, shorter, more crooked, precocious, bore more cones, had a higher frequency of serotinous cones, and had a higher frequency of stem cones than did Pine Barrens progeny, wherever they were grown. CONCLUSIONS The Pine Plains is an ecotype that has evolved in response to disturbance. The several characters that distinguish it from the surrounding tall forest of the Pine Barrens are inherited. The dwarf stature and crooked form not only enable the ecotype to persist in an environment of frequent fires but also increase its flammability.

Database for landscape-scale carbon monitoring sites

This report describes the database used to compile, store, and manage intensive ground-based biometric data collected at research sites in Colorado, Minnesota, New Hampshire, New Jersey, North Carolina, and Wyoming, supporting research activities of the U.S. North American Carbon Program (NACP). This report also provides details of each site, the sampling design and collection standards for biometric measurements, the database design, data summary examples, and the uses of intensive ground-based biometric data. Additional information on location descriptions, data, databases, and documentation may be accessed at http://www.nrs.fs.fed.us/data/lcms.

Missing Rings, Synchronous Growth, and Ecological Disturbance in a 36-Year Pitch Pine (Pinus rigida) Provenance Study

Provenance studies are an increasingly important analog for understanding how trees adapted to particular climatic conditions might respond to climate change. Dendrochronological analysis can illuminate differences among trees from different seed sources in terms of absolute annual growth and sensitivity to external growth factors. We analyzed annual radial growth of 567 36-year-old pitch pine (Pinus rigida Mill.) trees from 27 seed sources to evaluate their performance in a New Jersey Pine Barrens provenance experiment. Unexpectedly, missing rings were prevalent in most trees, and some years—1992, 1999, and 2006—had a particularly high frequency of missing rings across the plantation. Trees from local seed sources (<55 km away from the plantation) had a significantly smaller percentage of missing rings from 1980–2009 (mean: 5.0%), relative to northernmost and southernmost sources (mean: 9.3% and 7.9%, respectively). Some years with a high frequency of missing rings coincide with outbreaks of defoliating insects or dry growing season conditions. The propensity for missing rings synchronized annual variations in growth across all trees and might have complicated the detection of potential differences in interannual variability among seed sources. Average ring width was significantly larger in seed sources from both the southernmost and warmest origins compared to the northernmost and coldest seed sources in most years. Local seed sources had the highest average radial growth. Adaptation to local environmental conditions and disturbances might have influenced the higher growth rate found in local seed sources. These findings underscore the need to understand the integrative impact of multiple environmental drivers, such as disturbance agents and climate change, on tree growth, forest dynamics, and the carbon cycle.

Responses of forests in the eastern US to air pollution and climate change

Abstract The interactions of elevated atmospheric carbon dioxide (CO 2 ) with physical (i.e., precipitation, light, and temperature) and chemical (i.e., ozone (O 3 ), nitrogen and sulfur deposition, and nutrients) environmental factors that affect plant growth have been demonstrated in experiments that simulate managed and natural forest ecosystems in the eastern United States. Elevated atmospheric CO 2 has been shown to substantially enhance photosynthesis and carbon gain. The response of a southern tree species, loblolly pine ( Pinus taeda L.), to a doubling of ambient CO 2 was a 50% increase (to 130%) in the rate of net photosynthesis and a 20% reduction in dark respiration, depending on the study and treatment conditions. Volume change showed similar trends with increases in stem wood volume growth of 52% to 152%. Carbon gain for northern tree species with similar experimental treatments showed a 37% increase in dry weight biomass for trembling aspen ( Populus tremuloides Michx.) and a 73% increase in dry weight biomass for yellow poplar ( Lirodendron tulipifera L.). The impact of a doubling of atmospheric CO 2 on forest net primary productivity at the regional scale indicates a potential increase of 49% in the southeastern United States and an increase of 30–37% in the northeastern United States.

Summary of Prospective Global Change Impacts on Northern U.S. Forest Ecosystems

In January 1989, the President’s Fiscal Year 1990 Budget to the Congress was accompanied by a report entitled, “Our Changing Planet: A U.S. Strategy for Global Change Research” (Committee on Earth Sciences, 1989). The report focused the attention of policy makers on the significant environmental issues arising from natural and human-induced changes in the global Earth system. The report announced the beginning of a research program, the U.S. Global Change Research Program, with a mission to improve our understanding of the causes, processes, and consequences of the changes affecting our planet. Interest in global change was heightened in 1990 with the publication of “Climate change: The IPCC Scientific Assessment” (Houghton et al., 1990) by the Intergovernmental Panel on Climate Change (IPCC), jointly sponsored by the World Meteorological Organization and the United Nations Environmental Programme. This assessment was updated and new technical issues were added in the second assessment volumes, “Climate Change 1995: The Science of Climate Change”(Houghton et al., 1996) and “Climate Change 1995: Impacts, Adaptations, and Mitigation of Climate Change” (Watson et al., 1996). The first IPCC assessment in 1990 and subsequent assessments have concluded that continued accumulation of anthropogenic greenhouse gases in the atmosphere will lead to climate change whose rate and magnitude are likely to have important impacts on natural and human systems.

Climate and Atmospheric Deposition Patterns and Trends

One of the most important factors impacting terrestrial and aquatic ecosystems is the atmospheric environment. Climatic and weather events play a significant role in governing the natural processes that occur in these ecosystems. The current characteristics of the vast number of ecosystems that cover the northeast and north central United States are, in part, the result of climate, weather, disturbance, and atmospheric pollution patterns that exist in the northeast and north central United States. For example, basic ecosystem processes (e.g., heat and moisture exchanges with the atmosphere, photosynthesis, and respiration) along with species diversity and ecosystem health throughout the region all depend, to some degree, on these patterns. Furthermore, future characteristics of ecosystems in the region will depend on future climate, weather, disturbance, and pollution patterns that may develop in response to natural or human-caused changes in our atmospheric environment.