A forest’s ability to sequester carbon dioxide depends on factors such as periodic disturbance regimes, land-use change, the composition and productivity of the vegetative community, and the location and age of forested stands. However, one of the driving forces that contributes to changes in forest carbon dynamics include climatic factors, such as changes in temperature and precipitation, as well as atmospheric CO₂ concentrations which can affect the physiology of plants in complex ways. Our theorized understanding of plant physiological response to changing environmental conditions have been based on latitudinal and altitudinal studies or greenhouse experiments that measure plant physiological traits on one or a handful of plant species – and as scientists work to reduce the large variability that exists behind climate projections and plant community predictions, the need to collect locational and species-specific data becomes increasingly evident. This dissertation aims to address this issue by examining the physiological responses to temperature for 23 different tree species that have historically different geographic range distributions categorized into three groups: northern, central, and southern. The ranges of all species overlap and coexist at Black Rock Forest (BRF), an eastern deciduous forest located in the Hudson Highlands of New York. Chapter 1 examines the physiology of 16 coniferous and broadleaved tree species to determine if geographic provenance has a significant effect on foliar respiration rates, response to elevated temperature, and the respiratory substrate used to fuel the respiratory process. Chapter 2 compares the photosynthetic capacities and temperature responses of 17 broadleaved tree species to determine which range group may be more tolerant of a warming climate. Appended to this dissertation is preliminary data of a growth chamber experiment, examining the plasticity of physiological traits expressed under elevated temperatures to assess whether northern red oak seedlings show potential to acclimate to projected climate conditions and regenerate with minimal physiological constraints. Collectively, the results of these studies find significant differences in photosynthetic capacities and photosynthetic and respiration responses to temperature among species and among range groups. Northern, central, and southern ranged trees show an acclimated response to carbon assimilation under current climate conditions. However, central ranged trees, which includes the northern red oak, a dominant tree species in this region of New York, may be at a physiological disadvantage, showing lower rates of photosynthetic capacities and a trending decline of carbon assimilation under elevated temperatures. Furthermore, preliminary data from a greenhouse experiment suggests that leaf morphology and physiology traits are not plastic for northern red oak seedlings, which further weakens its physiological competitiveness and regeneration potential under warming temperatures. The results presented in this study on the physiological traits and temperature responses not only allows for a more thorough understanding of the physiological tolerances of migrant and resident tree species in the New York region but provides new data that could be incorporated into carbon and species distribution models for better predictions on carbon sequestration of forests and geographic ranges of tree species.

Understanding the effects of land use on riparian systems is dependent upon the development of methodologies to recognize changes in sedimentation related to shifts in land use. Land use trends in southern New England consist of shifts from forested precolonial conditions, to colonial and agrarian land uses, and toward modern industrial-urban landscapes. The goals of this study were to develop a set of stratigraphic indices that reflect these land use periods and to illustrate their applications. Twenty-four riparian sites from first-and second-order watersheds were chosen for study. Soil morphological features, such as buried surface horizons (layers), were useful to identify periods of watershed instability. The presence of human artifacts and increases in heavy metal concentration above background levels, were also effective indicators of industrial-urban land use periods. Increases and peak abundance of non-arboreal weed pollen (Ambrosia) were identified as stratigraphic markers indicative of agricultural land uses. Twelve 14C dates from riparian soils indicated that the rise in non-arboreal pollen corresponds to the start of regional deforestation (AD 1749 ± 56 cal yr; mean ± 2 SD) and peak non-arboreal pollen concentration corresponds to maximum agricultural land use (AD 1820 ± 51 cal yr). These indices were applied to elucidate the impact of land use on riparian sedimentation and soil carbon (C) dynamics. This analysis indicated that the majority of sediment and soil organic carbon (SOC) stored in regional riparian soils is of postcolonial origins. Mean net sedimentation rates increased ∼100-fold during postcolonial time periods, and net SOC sequestration rates showed an approximate 200-fold increase since precolonial times. These results suggest that headwater riparian zones have acted as an effective sink for alluvial sediment and SOC associated with postcolonial land use.

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The Family Forest Research Center recently conducted a mail survey of about 1,400 Massachusetts landowners. Respondents were given questions about themselves and their land and were then asked to rate three carbon sequestration programs in terms of their likelihood to participate. An ordered logit model is used to estimate probabilities that landowners would participate in various improved forest management programs. There are several estimation issues to consider with the ordered logit model. The relative merits of alternative models, including the multinomial and binomial logit, rank-ordered logit, binary logit and mixed ordered logit are discussed. Results of the ordered logit indicate that older males with less education and who own less than 100 acres are less likely to participate in an improved forest management program. All landowners are less likely to participate in a program that requires a management plan and that has a lengthy time commitment, low revenue stream and early withdrawal penalty. Policy implications and direction for future research are discussed.

Farmers have been disrupting the carbon cycle ever since humans started converting forests to agricultural lands. But are there farming practices that can be applied to increase the carbon storage in the soil and subsequently counteract increasing carbon dioxide levels in the atmosphere? In this study I investigate if soil organic matter (SOM) and soil organic carbon (SOC) change with longer interruption between tillage events. The study was conducted by studying SOM concentrations and SOC pools in eight fields with different time since tillage (1 to 14 years). I found that SOM concentrations increased in the O horizon of the studied soil in response to increased time since tillage. Here, SOM concentrations were on average around 13 % one year after tillage, while fourteen-year-old farmland had a concentration around 15 %. In similar, SOC pool increased from around 0.1 kg C m-2 in the O horizon of 1 year old soil to 0.33 kg C m-2 14 years after tillage. While both SOM concentrations and SOC pools increased in the O horizon over time since tillage, the SOM concentration and SOC pools decreased in the subsoil. I found no net sequestering of SOC in response to less frequent tillage in comparison to more frequency tillage. My conclusion is that limiting tillage to 14-year cycles is not enough to increase carbon sequestration.

<p>Northern peatlands (>45°N) mostly initiated during the Holocene and have been a large C sink to the atmosphere. Northern peatland formation prefers wet and cold condition where the productivity persistently exceeds decomposition and thereby C accumulates. As the northern high latitude region is likely to be warmer in the future, whether northern peatlands will continue being C sinks or switch to C sources is uncertain. To address this issue, I revise and apply a process-based model designed for describing peatland biogeochemical processes, Peatland Terrestrial Ecosystem Model (PTEM), to simulate the C dynamics at both site and regional level, from 15 ka BP-2300. For the site-level simulation, PTEM 1.0 is substantially revised into PTEM 2.0 in terms of peat accumulation process, plant functional types, productivity and decomposition, and soil thermal properties. A simulation from peat initiation to 2300 is conducted for three northern peatland sites. I found PTEM 2.0 can effectively capture the historical C accumulation progress, when compared with the observation. The future simulation indicates northern peatlands have reduced C sink capacity or switch to a C source under N insufficiency and water table deepening. </p> <p>Afterwards, a historical pan-Arctic simulation during 15ka BP-1990 is conducted. PTEM 2.0 is revised into PTEM 2.1 by adding spatially-explicit run-on and run off processes. The spatially-explicit peat initiation dataset is derived from neural network approach and a spatially-explicit peat expansion trend is established on top of it. My estimated pan-Arctic peatland C storage is 396-421 Pg C with the long-term C accumulation rate (CAR) of 22.9 g C∙m-2 yr-1. The simulated spatial distribution of peat C and the temporal pattern of CAR both agree with literature values. I analyzed northern peatlands’ response to historical climate change since 0.5 ka BP and found decreased CAR in the warmer non-permafrost and permafrost-thaw region, while the opposite was found in the colder permafrost region. The results indicate warmer southern peatlands will first switch to a C source under warming while more northern peatlands will become larger sinks. </p> <p>Based on the result of historical simulation, a future simulation is conducted for 1990-2300 with peatland expansion/shrinkage considered. PTEM 2.1 is revised into PTEM 2.2 such that the water table depth, run-on and run-off are estimated from a TOPMODEL approach. In the 21st century, northern peatlands are projected to be a C source of 1.2-13.3 Pg C under five out of six climate scenarios. During 2100-2300, northern peatlands under all scenarios are a C source under all climate scenarios. Northern peatlands switch to C sources due to deepening water table depth, insufficient N availability, and plant functional type shift. I found that northern peatlands remain as a C sink until a mean pan-Arctic peatlands annual temperature reaches -2.09 - -2.89°C. This study predicts a northern peatland sink to a source shift around 2050, earlier than previous estimates of after 2100, and emphasizes the vulnerability of northern peatlands to climate change. </p>

In order to keep global average temperature below 2°C it is necessary to accelerate climate change mitigation actions and reduce global greenhouse gas emissions. This can be achieved by carbon capture and storage methods such as the production of biochar. Especially its production from municipal sewage sludge could decrease emissions and disposal costs as well as act as a valuable material for different fields of application afterwards. In this quantitative study, the potential for a biochar production system was investigated for the case of the Swedish island, Gotland. Documents and grey literature were reviewed to collect the necessary information and data and experts were asked to fill in information gaps to evaluate the following: Calculate the energy and mass balance of a biochar production system from municipal sewage sludge in 2018, to find possible applications for the produced biochar by investigating the heavy metal content as well as to assess the direct carbon sequestration potential of the produced biochar. The results indicate that in 2018, 540 t of biochar could have been produced with a net heat demand of around 543 MWhth and electricity consumption of 231 MWhel. Heavy metal contents were found to be very high especially for copper and zinc, which means that the produced biochar would only qualify for the EBC-BasicMaterial certification class of the European Biochar Certificate. The annual carbon sequestration potential resulted in 97.2 t of carbon stored in the material or 356.4 t of CO2 emissions saved. Further research needs to be conducted on economic factors of a biochar production system from municipal sewage sludge.

Carbon sequestration is paramount to reducing climate change. Grasslands, representing 40% of all terrestrial area, can serve as a primary sequestration location if optimal management strategies can be realized. This study used system dynamics modeling to examine the temporal dynamics of carbon stocks and flows in response to grass species composition, grazing intensity, and temperature and precipitation changes at the landscape level. While there are other biogeochemical models in existence, they are either meant to model large areas, including globally, or are meant to be at a farm level and have limited plot sizes, limiting the options for rangeland managers to test management strategies in larger areas. The aims included conducting a field study of the rangeland, create an initial model; evaluate how the model responded to grazing, temperature, and precipitation changes; and compare the model outcomes to prior work to test the behavior of the model as the start of validation. This thesis used four plant functional groups (C3 and C4 grasses, forbs, and legumes) as the base groups for the model. C4 grasses were not found in in the field study but served to test whether the model detected changes in sequestration when grassland composition is changed. The results demonstrated an approach of using functional groups in system dynamics modeling to optimize carbon sequestration while accounting for diverse management strategies, as has been seen in other biogeochemical models. The model was aligned with prior field research in terms of carbon sequestration levels. The model was able to note differences in grazing regimes, temperature, and precipitation changes in terms of carbon sequestration. Grazing scenarios showed that while increased grazing impacted aboveground litter, it had little impact on sequestration; there was only a 4% increase in carbon with no grazing, Changes in temperature, up to 3°C, were predicted to increase carbon sequestration by 16% from 0.442 to 0.514 kg*m-2*day-1 while decreases in precipitation, both alone and in combination with increasing temperatures, was predicted to decrease sequestration up to 44%. This has to do with the grassland composition, ii especially as this was a C3 dominated grassland which grows in the winter and early spring and required more water but lower temperatures for growth. Future research should continue model validation, test additional functional groups like shrubs, implement more soil carbon pools and flows and add a nitrogen component to the model.