The objective of this study was to examine some mechanisms of bottomland hardwood afforestation and their impacts on above- and belowground carbon sequestration. Six combinations of bottomland hardwood species and two levels each of fertilizer and herbicide were applied in a completely randomized design on two sites in the LMAV. Survival, ground line diameter and total height were monitored for two growing seasons. Soil carbon and nitrogen to a depth of one meter, herbaceous biomass, and tree biomass were sampled in the first and second years of establishment. Species mixes, fertilizer, and herbicide application significantly affected survival, growth, above- and belowground tree biomass carbon after two years of establishment. Survival was generally average, while growth for most species mixes was below expectation. Species mixes E (green ash/oak mix) and F (NRCS species mix) had the highest tree vegetation carbon both above- and belowground. Soil carbon and nitrogen were not significantly affected by any treatments.

In the continental United States, mean surface air temperature is expected to increase by up to 5°C within 100 years. With hotter temperatures, leaf budbreak is expected to occur earlier in forests, and leaf area is expected to increase in locations where temperature is limiting. The response of plant photosynthesis to hotter temperatures is less certain; plant productivity could increase or decrease. Past studies have found intraspecific variation in the responses of forest tree productivity, phenology, canopy leaf area, and leaf isoprene emission to warming, which all influence carbon uptake and yield for agricultural tree species; it is therefore important to understand not only how hot climates affect carbon uptake and biomass production between different tree species, but also in different genotypes of the same species. We conducted a common garden study at the Biosphere 2 research center near Oracle, AZ, USA. We created a hybrid poplar plantation of 168 trees, which were planted as cuttings in January 2013. The trees used in this study are comprised of 5 distinct genotypes of Populus deltoides × trichocarpa from a range of average annual air temperatures. We measured photosynthetic capacity, leaf phenological timing, canopy leaf area and aboveground woody biomass in 2014 growing season, and leaf isoprene emission in the 2015 growing season. We observed a strong effect of genotype on aboveground woody biomass increment, implying strong local adaptation to the home range and limited phenotypic plasticity in terms of physiological and biometric responses to high temperature environments. Our study suggests that genotypes from hotter home ranges are able to maintain photosynthetic capacity and canopy leaf area late into the growing season, despite high temperatures, and thus produce more aboveground woody biomass. This study may have implications for agricultural management—as temperatures warm where managers currently grow hybrid poplar for agricultural or other purposes, the genotypes from those home ranges would likely have reduced yield; managers could investigate the use of genotypes from home ranges with higher average temperatures to replace the vulnerable local varieties.

Nutrient availability and herbivory can regulate primary production in ecosystems, but little is known about how, or whether, they may interact with one another. Here I investigate how nitrogen availability and insect herbivory interact to alter above- and belowground plant community biomass in an old-field ecosystem. In 2004, 36 experimental plots were established in which soil nitrogen (N) availability (at three levels) was manipulated and insect abundance (at two levels) in a completely randomized plot design. In 2009, after six years of treatment, I measured aboveground biomass and assessed root production at peak growth. Overall, I found a significant effect of soil N availability on both above- and belowground plant biomass while insects affected only aboveground biomass of subdominant plant species and coarse root production; there were no statistical interactions between N availability and insect herbivory for any response variable. Specifically, responses of aboveground and belowground community biomass to nutrients were driven by reductions in soil N, but not additions, indicating that soil N may not be primarily limiting production in this ecosystem. Insect herbivory altered the aboveground biomass of the subdominant plant species and altered allocation patterns to coarse root production belowground. Overall, the results of six years of nutrient amendments and insect removals suggest strong bottom-up influences on total plant community productivity.

Crown architecture affects tree growth through the control of leaf area and its display. Yet the linkages between crown structure, leaf traits, and productivity of elite selections of forest trees and responses to intensive silviculture are not fully understood. It was hypothesized that trees with crown and leaf traits governing efficient light capture and photosynthesis at the canopy scale would be the most productive. To this end, families of loblolly (Pinus taeda) and slash pine (Pinus elliottii) were grown at three experimental sites in the West Gulf Coastal Plain of Texas and Louisiana under two silvicultural treatments, including repeated fertilization with control of competing vegetation (HI), and a control (C) consisting of fertilization at planting. Families and species differed in crown traits and aboveground productivity, and genotype differences increased throughout the first 5 years of stand development. Crown shape was important for light interception and growth initially, but at the onset of canopy closure, crown size, stand leaf area and its distribution within crowns affected canopy light interception and tree growth. Among all families and treatments, aboveground biomass productivity was positively related to absorbed photosynthetically active radiation (APAR) and canopy photosynthesis. Light-use efficiency (ε) varied from 0.41 to 0.56 g MJ-1 among families and was lowest in slash pine. Variability in aboveground biomass growth was related more to stand leaf area and APAR than to differences in light-use efficiency in these young stands. Leaf physiological, chemical and morphological attributes changed within crowns in accordance with developing light availability gradients. Physiological attributes, such as net photosynthesis, were better predictors of family performance when integrated at the canopy level than leaf level in the examined pine species. Crown size, light absorption, and aboveground growth generally ranked higher in the HI treatment than in the control, although the effects of the intensive silvicultural treatments did not differ statistically. Family performance was independent of treatment. Crown and canopy attributes, such as high leaf area index and large crowns with low leaf area density per crown volume, may be useful in the selection of highly productive genotypes of loblolly and slash pine under intensive silviculture.

Crown architecture affects tree growth through the control of leaf area and its display. Yet the linkages between crown structure, leaf traits, and productivity of elite selections of forest trees and responses to intensive silviculture are not fully understood. It was hypothesized that trees with crown and leaf traits governing efficient light capture and photosynthesis at the canopy scale would be the most productive. To this end, families of loblolly (Pinus taeda) and slash pine (Pinus elliottii) were grown at three experimental sites in the West Gulf Coastal Plain of Texas and Louisiana under two silvicultural treatments, including repeated fertilization with control of competing vegetation (HI), and a control (C) consisting of fertilization at planting. Families and species differed in crown traits and aboveground productivity, and genotype differences increased throughout the first 5 years of stand development. Crown shape was important for light interception and growth initially, but at the onset of canopy closure, crown size, stand leaf area and its distribution within crowns affected canopy light interception and tree growth. Among all families and treatments, aboveground biomass productivity was positively related to absorbed photosynthetically active radiation (APAR) and canopy photosynthesis. Light-use efficiency (ε) varied from 0.41 to 0.56 g MJ-1 among families and was lowest in slash pine. Variability in aboveground biomass growth was related more to stand leaf area and APAR than to differences in light-use efficiency in these young stands. Leaf physiological, chemical and morphological attributes changed within crowns in accordance with developing light availability gradients. Physiological attributes, such as net photosynthesis, were better predictors of family performance when integrated at the canopy level than leaf level in the examined pine species. Crown size, light absorption, and aboveground growth generally ranked higher in the HI treatment than in the control, although the effects of the intensive silvicultural treatments did not differ statistically. Family performance was independent of treatment. Crown and canopy attributes, such as high leaf area index and large crowns with low leaf area density per crown volume, may be useful in the selection of highly productive genotypes of loblolly and slash pine under intensive silviculture.

Nutrient availability and herbivory can regulate primary production in ecosystems, but little is known about how, or whether, they may interact with one another. Here I investigate how nitrogen availability and insect herbivory interact to alter above- and belowground plant community biomass in an old-field ecosystem. In 2004, 36 experimental plots were established in which soil nitrogen (N) availability (at three levels) was manipulated and insect abundance (at two levels) in a completely randomized plot design. In 2009, after six years of treatment, I measured aboveground biomass and assessed root production at peak growth. Overall, I found a significant effect of soil N availability on both above- and belowground plant biomass while insects affected only aboveground biomass of subdominant plant species and coarse root production; there were no statistical interactions between N availability and insect herbivory for any response variable. Specifically, responses of aboveground and belowground community biomass to nutrients were driven by reductions in soil N, but not additions, indicating that soil N may not be primarily limiting production in this ecosystem. Insect herbivory altered the aboveground biomass of the subdominant plant species and altered allocation patterns to coarse root production belowground. Overall, the results of six years of nutrient amendments and insect removals suggest strong bottom-up influences on total plant community productivity.

This work is part of a study of wet meadows within the project GA CR 526/09/1545. The objective of the project is to determine the importance of newly assimilated carbon for the plat-soil interactions of plants with in wet grassland ecosystems in changing environmental conditions. As part of this project, a wet grassland ecosystem near Hamr situated in the Nežárka river floodplain was assessed in terms of aboveground production. This work includes data from 2010 and 2011. Each year the biomass was sampled two times. At each sampling, 24 samples were collected from plots differing in the intensity of fertilization. The treatments included high intensity of fertilization, low intensity of fertilization and no fertilization. In 2010, the annual production of aboveground biomass was 863.88 gm-2 on plots with a high intensity of fertilization, 788.46 gm-2 on plots with low intensity of fertilization and areas 839.69 gm-2 on unfertilized plots. In 2011 the annual production of aboveground biomass was 1149.71 gm-2 on plots with high fertilization, 953.73 gm-2 in plots with low fertilization, and 930.25 gm-2 on plots without fertilization.

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<p dir="ltr">Forest ecosystems play a pivotal role in climate change mitigation. Sustainable forest management practices necessitate accurate quantification of forest aboveground carbon stocks (FACS). In the first part of this study, I compared the 13-year changes in FACS across three silvicultural systems, including even-aged management (EA), uneven-aged management (UEA), and non-harvested controls (NH), in Indiana's hardwood forests. Forest stands within each silvicultural system were assigned with one of the six treatment types, including clearcutting, shelterwood, or prescribed burning for EA, single-tree selection or patch cutting for UEA, or untreated controls. From 2008 to 2021, the FACS of the study area exhibited an increase from 91.5 ± 9.0 Mg/ha to 115.3 ± 2.1 Mg/ha. Single-tree selection, shelterwood, and prescribed burning were found to have minimal impacts on FACS. However, clearcutting and patch cutting resulted in a significant reduction in FACS, with subsequent recovery reaching only 30-37% of their pre-treatment levels after 13 years. Further investigations may use long-term inventory data to analyze the chronic recovery patterns on these sites.</p><p dir="ltr">In the second part of this study, I evaluated the feasibility of using 3DEP LiDAR in conjunction with the random forest algorithm for multiscale FACS prediction. It was found that the stand-scale model outperformed the plot-scale model, primarily due to a stand’s higher positioning accuracy and reduced boundary effects than the plot-scale model. This led to a reduction in RMSE from 25.43 Mg/ha (26%) to 16.74 Mg/ha (20%). Moreover, the stand-scale model exhibited robust landscape-level prediction performance even in scenarios where point density decreased from 7.7 points/m² to 2.0 points/m². However, the partitioned model including solely clearcut and patch sites produced a higher RMSE of 59% (17.82 Mg/ha) due to inaccurate LiDAR return classification and biased canopy height metrics extraction. Future research should delve into the mechanisms of point cloud classification to improve the FACS prediction accuracy for clearcut forest monitoring.</p><p dir="ltr">Overall, this thesis contributed to a deeper understanding of carbon dynamics in managed hardwood forests, highlighted the potential of using LiDAR technology for improved landscape-level carbon monitoring, and informed the decision-making processes in the context of climate change mitigation.</p><p><br></p>

Master of Science / Department of Biology / Jesse B. Nippert / Jesse B. Nippert / Anthropogenic climate change is likely to alter the function and composition of ecosystems worldwide through increased precipitation variability and temperatures. To predict ecosystem responses, a greater understanding of the physiological and growth responses of plants is required. Dominant species drive ecosystem responses, and it is essential to understand how they respond to understand potential ecosystem changes. Dominant species, such as switchgrass (Panicum virgatum L.), posses large genotypic and phenotypic variability, which will impact the degree of responses to projected climate changes. I studied the physiological and growth responses of switchgrass, a common perennial warm-season C4 grass that is native to the tallgrass prairie, to alterations in precipitation amount and temperature. The first experiment I conducted focused on the responses of three ecotypes of P. virgatum to three precipitation regimes (average, 25% below, 25% above). I concluded that the physiological responses of photosynthesis, stomatal conductance, transpiration, dark-adapted fluorescence, and mid-day water potential in P. virgatum were explained by ecotypic differences. Robust responses to altered precipitation were seen in the water use efficiency, mid-day water potential, and aboveground biomass. Ecotypic differences were also seen in several aboveground biomass variables, and most strikingly in flowering times and rates. There were few interactions between ecotype and precipitation, suggesting precipitation is a strong driver of biomass production, whereas adaption of ecotypes to their local environment affects physiological processes. A second experiment studied the response of local populations of P. virgatum to nocturnal warming. Results showed significant differences in daytime E, daytime gs, and flowering phenology between treatments. Differences in aboveground biomass were between topographic positions. I concluded that water availability, based on topographic position, is a strong driver of P. virgatum aboveground biomass production, but nocturnal warming has the potential to impact flowering phenology, physiological responses, and exacerbate plant water stress. I also reviewed the literature on the ecological effects of implementing switchgrass cultivation for biofuel. From the literature review, I concluded that large-scale switchgrass cultivation will have widespread ecological impacts. If landscape heterogeneity is maintained through harvest rotations, no till farming, and mixed species composition, ecosystem services can be maintained while providing economic value.