Three general questions are studied regarding plant carbon allocation strategies. (1) The R* Rule states that the superior competitor in a plant community should exclude all others by minimizing available limiting nutrient concentration below the level needed for survival of its competitors. I asked whether a plant carbon allocation strategy that minimizes the concentration of available limiting nutrient is consistent with Lotka's (1922) conjecture that ecosystems should evolve to maximize total energy flow (primary production). (2) In landscapes such as the Everglades, areas of landscape with higher energy flow (primary production) than the surrounding area also have higher available concentrations of limiting nutrient, rather than lower concentrations, which might be expected from the R* rule. I asked whether this pattern can be explained. (3) I asked how optimal allocation of carbon to plant defense allocation strategies might depend on different conditions of nutrient availability, shading, and herbivory. To address all three questions, I used a model revised from the G'DAY model (Comins and McMurtrie 1993) to study tree allocation of carbon resources between foliage, roots, and defense. With regard to the first question, I found that the allocation strategy that leads to minimum concentration of available nutrients is the same as the strategy for which energy flux to roots, rather than total energy flux, is maximized. Further, I found that the strategy that was competitively dominant was neither the strategy for which total energy flux was maximized, nor that for which available nutrient concentration was minimized. With regard to the second question, I found that, if a patch of vegetation on a landscape is able to capture nutrients from the surrounding landscape, for example, through relatively higher evapotranspiration, it could lead to the opposite of what is expected from the R* rule; that is, available limiting nutrient concentration is maximized when carbon flow to the roots is maximized. With regard to the last question, I found that under high herbivory, the optimal plant strategy for allocation of carbon to defense depends on the available nutrient concentration and amount of radiation to the plant, in agreement with some theoretical predictions.

Woody plant encroachment (WPE) into historic grasslands not only alters ecosystem structure but also yields a mosaic of vegetative growth-forms that differ in their inherent physiological capacities and physical attributes. C₃ plants tend to have a relatively broad range of temperature function but at the expensive of a lower optimum rate of photosynthesis. In contrast, C₄ grasses have a greater capacity for maximum uptake but across a relatively narrow range of temperatures. In considering which of these functional groups will outcompete the other within these regions undergoing WPE, one must account not only for these leaf physiological traits, but also the growth form induced differences in rooting depth, and therefore, potential access to deeper subsurface water. Laid upon these competitive interactions is an ever-changing environment, which for the semiarid southwestern US is predicted to become progressively warmer and characterized by highly variable precipitation with longer interstorm periods. In addition to aboveground changes in CO₂ assimilation, WPE influences soil nutrient, water, and carbon cycling. The objectives of this dissertation were to quantify: (1) the influence that temperature and available soil moisture have on regulating soil respiratory efflux within the microhabitats that results from WPE to estimate the influence this vegetative change will have on ecosystem CO₂ efflux; (2) the sensitivity of CO₂ uptake within grassland and woodland ecosystems to temperature and precipitation input in an effort to characterize how WPE might influence regional carbon and water balance; and (3) the role access to stable groundwater has in regulating the temperature sensitivity of ecosystems and their component fluxes. Major findings and contributions of this research include illustrating seasonal patterns of soil respiration within the microhabitats that result from WPE, such that an analysis of the relative contributions of these different components could be made. We found that soil respiration was not only consistently greater under mesquites, but that the relative contributions of these microhabitats varied significantly throughout the year, the duration of soil respiration after each rain was habitat-specific, and that the relationship between soil respiration and temperature followed a hysteretic pattern rather than a linear function (Appendix A). We found that a woodland ecosystem demonstrated a lower temperature sensitivity than a grassland across all seasonal periods of varying soil moisture availability, and that by maintaining physiological function across a wider range of temperatures throughout periods of limited precipitation, C₃ mesquites were acquiring large amounts of carbon while C₄ grasses were limited to functioning within a narrower range of temperatures (Appendix B). Finally, we found that having a connectivity to stable groundwater decoupled leaf and ecosystem scale temperature sensitivities relative to comparable sites lacking such access. Access to groundwater not only resulted in the temperature sensitivity of a riparian shrubland being nearly half that of the upland site throughout all seasonal periods, but also actual rates of net ecosystem productivity and leaf level rates of photosynthesis being dramatically enhanced (Appendix C).

Abstract Plant registration and selection work aimed at identifying the best genotypes for northern landscaping has been carried out in Finland since the 1980’s. In the University of Oulu Botanical Gardens, micropropagation methods have been developed for several woody plant taxa registered during the POHKAS (Northern Hardy Plants) project. Micropropagation is an effective method to conserve valuable genetic characteristics and to produce plantlets from woody species with limited mother stock material and in a limited time period. In this study the long-term field phenology and success of 19 micropropagated shrub and tree taxa was followed in plant selection experiments. Experiments were conducted at four northern field sites presenting different climatic conditions. Of the phenological monitoring parameters, the onset of foliation and flowering in the field revealed a strong relation to spring time temperature, being obviously latest to occur in northernmost site. The gradient between southern and northern sites for autumn phenology was not so obvious. However, between the different genotypes, the greatest differences were observed in the timing of autumn colouration and defoliation. Winter hardiness also showed clear differences between genotypes. Of the success parameters, it was most decisive as winter hardy genotypes had a higher occurrence of flowers and ornamental appearance, for example in Rosa majalis ‘Tornedal’. Some of these hardy genotypes with known characteristics were introduced to northern tourism areas to create examples of sustainable landscaping. Further, a list of potential plants for different northern sites was compiled. Special forms with both scientific and ornamental value are occasionally found in wild species. One example of this is the red-leaved form of a pubescent birch, Betula pubescens f. rubra, which was studied in the plant selection experiments, and was used as a model tree to evaluate the role of anthocyanins in northern plants in a case study of northern birches. In the case study, the red-leaved pubescent birch showed some differences in flavonoid responses and growth rate in comparison to Betula pubescens and Betula pubescens ssp. czerepanovii. Phenology of the B. p. f. rubra was corresponding to that of the B. pubescens. For cultivated woody plants the most important selection criteria for the northern areas are the suitability to local climate i.e. timing of phenological events and winter hardiness. Foliar anthocyanins seem to increase adaptation to northern growing conditions with high light intensity and low temperature.

Doctor of Philosophy / Department of Biology / John M. Blair / Juniperus virginiana, an important woody plant invader in the U.S. Central Plains, has increased considerably in density and cover in large areas previously dominated by tallgrass prairie. Change in the phenology and nitrogen use efficiency of the dominant plant communities as J. virginiana replaces native prairies may lead to increased plant productivity and biomass accumulation, but may also alter the microclimate and litter quality that affect soil microbial communities responsible for key soil processes. I have focused my investigations on changes in key soil processes that could lead to differences in soil N availability, as well as changes in ecosystem C and N pools and fluxes as J. virginiana expands into native grasslands. Juniperus virginiana forest soils exhibit greater cumulative annual net N mineralization (11.52 ± 0.38 µg N g¯1 soil y¯1) compared to prairie soils (7.90 ± 0.26 µg N g¯1 soil y¯1) (F = 60.67, P = 0.016), yet slightly reduced potential soil C flux. Examination of internal soil N cycling revealed that both J. virginiana and prairie soils minimize potential soil N losses, by rapid microbial immobilization of inorganic N, and constraining nitrification via substrate limitation or environmental constraints. Leaf-level photosynthetic nitrogen use efficiency (NUE) was over a magnitude higher in the dominant grass, Andropogon gerardii, but high annual ecosystem-level NUE and greater soil N availability may contribute to the higher productivity and rapid accrual of C in newly established J. virginiana forests. Increased plant productivity and elimination of fire in J. virginiana forests have allowed at least 80,000 kg ha-1 increase in ecosystem C storage in about half a century. Soil organic C, an important long-term sink, has also increased significantly in J. virginiana forests, with approximately 34% replacement of C4 grass-derived soil C with new C from trees in the A-horizon. The observed high productivity of J. virginiana and increased N availability necessary to support continued plant biomass accumulation are possible because of substantial (~ 44%) increase in ecosystem N in measured pools, which is a likely a result of reduced volatilization of N from biomass burning, possible increased exogenous N inputs, and/or N translocation from deeper soil horizons. Reduced fire return intervals in prairie provide an opportunity for J. virginiana to establish and facilitate N accrual, which may allow this species to accelerate is own establishment through creating conditions of increased N availability and efficient utilization of N.

The conversion of grasslands to woodlands is an ecosystem transformation that threatens grassland biodiversity, the provision of important ecosystem services, and the sustainability of rural livelihoods. A global phenomenon, woody plant encroachment (WPE) has been particularly problematic in the Southern Great Plains of the United States where the actions of private landowners are integral to sustaining grasslands. Increased diversity in landowners’ motivations for owning land have shifted the social landscape of rural areas necessitating a better understanding of landowners’ perspectives about WPE and their subsequent management actions. Towards this purpose, I employed a mail survey to private landowners in the Edwards Plateau of Texas, Central Great Plains of Oklahoma, and Flint Hills of Kansas to investigate landowner perceptions and management responses to WPE. First, I assessed landowners’ acceptance of WPE as a function of how they relate to their land (i.e., sense of place), their beliefs about the positive and negative consequences of woody plants, and their perceived threat of grassland conversion. Then, I examined the drivers of landowners’ goal intentions to manage woody plants and their current use of five adaptive management practices that prevent WPE. My results demonstrate that landowners vary in their sensitivity to WPE based on how they feel connected to their land. This was true even though most landowners had low acceptance thresholds for WPE, believed it led to numerous negative outcomes, and perceived it as increasingly threatening at greater levels of encroachment. Most landowners wanted to control or remove woody plants and were actively engaged in management practices to do so. These findings address uncertainties about landowners’ acceptance of WPE and grassland conservation actions and provide broad implications for how people perceive and respond to ecosystem transformation. / Master of Science / Around the world, grasslands are converting to tree and shrub woodlands at an unprecedented rate. This transformation profoundly reduces habitat available for grassland plants and animals and diminishes many ecosystem services that people and rural communities rely on. This loss of grasslands has been especially far-reaching throughout the Southern Great Plains of the United States. Because most of this region is privately owned, the management actions of landowners play a crucial role in preventing or allowing this conversion to continue. Recent shifts in land ownership motivations expanding beyond traditional agricultural production have created increased uncertainty about how private landowners view and react to this change. To investigate how landowners perceive and respond to this woody plant encroachment (WPE) phenomenon, I conducted a mail survey of landowners in the Edwards Plateau of Texas, the Central Great Plains of Oklahoma, and the Flint Hills of Kansas. Using sense of place, landowners’ beliefs about the potential positive and negative consequences of woody plants, and their perceptions of how threatening grassland conversion is, I assessed the thresholds at which landowners’ do or do not accept WPE. Then, I examined how acceptance of WPE relates to landowners’ management goals and current use of management practices to control or reduce woody plants. I found that most landowners believed that woody plants had many negative consequences and perceived increasing levels of threat at greater levels of encroachment. This related to low levels of acceptance for woody plants in grasslands. However, landowners’ threat perceptions and acceptance of WPE varied based on their sense of place. Finally, most landowners wanted to control or remove woody plants and were actively engaged in management practices to do so. My results provide critical information regarding how current landowners’ view and respond to grassland conversion and offer broad implications for how people perceive and respond to large-scale environmental change.

In the southern Great Plains, the encroachment of grassland ecosystems by mesquite (Prosopis glandulosa), is widespread, and prescribed fire is commonly used in its control. Despite this, substantial quantitative information concerning their influences on the community composition, functional dynamics, and soil organic carbon (SOC) storage potential of grassland ecosystems is lacking. The objectives of this study were to: a) quantify the effects of seasonal prescribed fire treatments and mesquite encroachment on aboveground net primary productivity (ANPP) and herbaceous community composition; b) characterize SOC pool sizes, turnover, and storage potential relative to vegetation type and fire treatment; c) evaluate the structure and diversity of soil microbial communities relative to vegetation type; and d) characterize the functional diversity of these same microbes using the GeoChip functional gene microarray. Repeated winter and summer fires led to increased ANPP rates (average, 434 and 313 g m-2 y-1, respectively), relative to unburned controls (average, 238 g m-2 y-1), altered herbaceous community composition, and increased the storage of resistant forms of SOC, but did not affect overall SOC storage. Herbaceous ANPP rates did not differ significantly as a result of mesquite encroachment, but herbaceous community composition and SOC storage did. Mesquite soils contained significantly more total, slow-turnover, and resistant forms of SOC than those that occurred beneath C3 or C4 grasses. Similarity among the soil bacterial and fungal communities associated with the major vegetation types in this system was low to moderate. Significant differences were detected among soil fungi, with the mesquite-associated fungi harboring significant differences in community structure relative to the fungal communities associated with each of the other vegetation types examined. Despite this result, few significant differences were detected with respect to the functional diversity of these communities, suggesting either a high degree of functional redundancy, or that the functional differences harbored by these communities are beyond the scope of the GeoChip. The results of this study demonstrate that both fire and mesquite encroachment have the potential to alter ecosystem components and processes significantly, providing new insight regarding the effects of these widespread land use and land cover changes on ecosystem structure and function.

abstract: Woody plant encroachment is a worldwide phenomenon linked to water availability in semiarid systems. Nevertheless, the implications of woody plant encroachment on the hydrologic cycle are poorly understood, especially at the catchment scale. This study takes place in a pair of small semiarid rangeland undergoing the encroachment of Prosopis velutina Woot., or velvet mesquite tree. The similarly-sized basins are in close proximity, leading to equivalent meteorological and soil conditions. One basin was treated for mesquite in 1974, while the other represents the encroachment process. A sensor network was installed to measure ecohydrological states and fluxes, including precipitation, runoff, soil moisture and evapotranspiration. Observations from June 1, 2011 through September 30, 2012 are presented to describe the seasonality and spatial variability of ecohydrological conditions during the North American Monsoon (NAM). Runoff observations are linked to historical changes in runoff production in each watershed. Observations indicate that the mesquite-treated basin generates more runoff pulses and greater runoff volume for small rainfall events, while the mesquite-encroached basin generates more runoff volume for large rainfall events. A distributed hydrologic model is applied to both basins to investigate the runoff threshold processes experienced during the NAM. Vegetation in the two basins is classified into grass, mesquite, or bare soil using high-resolution imagery. Model predictions are used to investigate the vegetation controls on soil moisture, evapotranspiration, and runoff generation. The distributed model shows that grass and mesquite sites retain the highest levels of soil moisture. The model also captures the runoff generation differences between the two watersheds that have been observed over the past decade. Generally, grass sites in the mesquite-treated basin have less plant interception and evapotranspiration, leading to higher soil moisture that supports greater runoff for small rainfall events. For large rainfall events, the mesquite-encroached basin produces greater runoff due to its higher fraction of bare soil. The results of this study show that a distributed hydrologic model can be used to explain runoff threshold processes linked to woody plant encroachment at the catchment-scale and provides useful interpretations for rangeland management in semiarid areas. / Dissertation/Thesis / M.S. Civil and Environmental Engineering 2013

Woody plant herbicide screening techniques were evaluated in an attempt to expedite the screening process and decrease amounts of herbicide active ingredient required. Rapid greenhouse screening of woody plant seedlings was performed in less than six months while rapid seed screening was performed in less than twenty days. A traditional field screen, requiring ten months, was performed for comparison purposes. Leaf area – biomass ratios were also examined for their influence on herbicide efficacy. Linear regressions were performed using traditional field screen data as the dependent variable and rapid screening technique data as the independent data. Rapid screens using triclopyr produced more statistically significant regressions compared to those involving imazapyr. Significant regressions were produced that could predict field response of several species using both herbicides and either rapid screening technique. This indicated that rapid screening techniques could determine herbicide efficacy and/or species spectrum of control in much less time with much less herbicide. Rapid seed screens could estimate species spectrum within five days after treatment. The rapid greenhouse screen and rapid seed screen techniques can provide woody plant herbicide developers initial efficacy and spectrum of control data in a cost- and time- effective manner. Testing showed that as woody plants mature from seedling to sapling, there is a decrease in the leaf area — total aboveground biomass ratio. The decrease in this ratio consistently decreased efficacy of both imazapyr and triclopyr at the lower active ingredient rates. Seedlings with the higher leaf area – biomass ratio had, on the average, higher efficacy response rates to herbicide treatments. / Master of Science

Neste estudo analisamos a diversidade e endemismos da flora lenhosa das florestas estacionais decíduas (FEDs) do norte e centro do Perú. Caracterizamos a diversidade das plantas lenhosas ao longo dos vales, para definir os valores de conservação da área a nível nacional. Os resultados indicam que as FEDs do vale do Marañón apresentam valores significativamente altos em endemias em relação às outras FEDs do Perú e FEDs vizinhas e o padrão de endemismos e estrutura populacional das espécies variam no gradiente geográfico e altitudinal. Em constraste, as FEDs do vale do rio Tambo, centro do Perú, são moderadamente ricas em espécies do que a média das FEDs neotropicais e apresentam escassos endemismos. Esta região necessita de mais esforços de pesquisas para conhecer mais profundamente os elementos da biodiversidade. Neste estudo, também realizamos a caracterização dendro-anatômica do lenho das árvores de 87 espécies, sendo o primeiro registro da anatomia da madeira das árvores dos dois vales. Das análises do lenho das 183 espécies registradas nas florestas do norte e centro do Perú, só 157 apresentam anéis de crescimento e precisam ser analisadas em detalhe com outras pesquisas de desenvolvimento cambial e técnicas tradicionais de análises dendrocronológicas. A derivação desta informação pode alcançar alto impacto em estudos de variabilidade climática e aplicações na conservação. Assim mesmo, a análise preliminar dendrocronológica das taxas de crescimento do tronco revelam que as árvores de Cedrela kuelapensis apresentam as taxas de crescimento mais altas e ressaltam como um excelente recurso para programas de reflorestamento nos vales interandinos, além, das populações endêmicas de Cordia iguaguana e Esenbeckia cornuta são principalmente de exemplares jovens. Esperamos que as informações dos cinco capítulos constituam-se uma eficiente e importante ferramenta para melhorar a gestão dos recursos florestais dos vales estudados. / In this study we analyzed the diversity and endemism of the woody flora of Seazonally dry tropical forests (SDTF) in northern and central Peru. We characterized the diversity of woody plants along the valleys to define the conservation values of the area at the national and international levels. The results indicate that the SDTF s of the Marañón Valley show surprisingly high values in endemics in relation to other SDTF s in Peru and neighboring SDTFs, and the pattern of endemism and population structure of the species varies in geographic and altitudinal grades. In contrast, the SDTFs of the Tambo River Valley, central Peru, are moderately rich in species that average the neotropical SDTFs and have scarce endemism. This region needs more efforts to get to know the elements of biodiversity more deeply. In this study, we also performed the dendroanatomic characterization of 87 species and is the first report of the anatomy of the wood for the two valleys. From the analysis of the wood of the 183 species recorded in the forests of northern and central Peru, only 157 have growth rings and need to be analyzed in detail with other studies of exchange rate development and traditional techniques of dendrochronological analysis. The derivation of this information can reach high impact in studies of climatic variability and conservation applications. Likewise, the preliminary dendrochronological analysis of growth rates reveals that Cedrela kuelapensis showed the highest growth rates and stands out as an excellent resource for reforestation programs in the inter-Andean valleys, in addition, Cordia iguaguana and Esenbeckia cornuta endemic populations are mainly from young individuals. We hope that the information in the five chapters constitutes in efficient and important tool to improve the management of forest resources in the valleys studied.

Neste estudo analisamos a diversidade e endemismos da flora lenhosa das florestas estacionais decíduas (FEDs) do norte e centro do Perú. Caracterizamos a diversidade das plantas lenhosas ao longo dos vales, para definir os valores de conservação da área a nível nacional. Os resultados indicam que as FEDs do vale do Marañón apresentam valores significativamente altos em endemias em relação às outras FEDs do Perú e FEDs vizinhas e o padrão de endemismos e estrutura populacional das espécies variam no gradiente geográfico e altitudinal. Em constraste, as FEDs do vale do rio Tambo, centro do Perú, são moderadamente ricas em espécies do que a média das FEDs neotropicais e apresentam escassos endemismos. Esta região necessita de mais esforços de pesquisas para conhecer mais profundamente os elementos da biodiversidade. Neste estudo, também realizamos a caracterização dendro-anatômica do lenho das árvores de 87 espécies, sendo o primeiro registro da anatomia da madeira das árvores dos dois vales. Das análises do lenho das 183 espécies registradas nas florestas do norte e centro do Perú, só 157 apresentam anéis de crescimento e precisam ser analisadas em detalhe com outras pesquisas de desenvolvimento cambial e técnicas tradicionais de análises dendrocronológicas. A derivação desta informação pode alcançar alto impacto em estudos de variabilidade climática e aplicações na conservação. Assim mesmo, a análise preliminar dendrocronológica das taxas de crescimento do tronco revelam que as árvores de Cedrela kuelapensis apresentam as taxas de crescimento mais altas e ressaltam como um excelente recurso para programas de reflorestamento nos vales interandinos, além, das populações endêmicas de Cordia iguaguana e Esenbeckia cornuta são principalmente de exemplares jovens. Esperamos que as informações dos cinco capítulos constituam-se uma eficiente e importante ferramenta para melhorar a gestão dos recursos florestais dos vales estudados. / In this study we analyzed the diversity and endemism of the woody flora of Seazonally dry tropical forests (SDTF) in northern and central Peru. We characterized the diversity of woody plants along the valleys to define the conservation values of the area at the national and international levels. The results indicate that the SDTF s of the Marañón Valley show surprisingly high values in endemics in relation to other SDTF s in Peru and neighboring SDTFs, and the pattern of endemism and population structure of the species varies in geographic and altitudinal grades. In contrast, the SDTFs of the Tambo River Valley, central Peru, are moderately rich in species that average the neotropical SDTFs and have scarce endemism. This region needs more efforts to get to know the elements of biodiversity more deeply. In this study, we also performed the dendroanatomic characterization of 87 species and is the first report of the anatomy of the wood for the two valleys. From the analysis of the wood of the 183 species recorded in the forests of northern and central Peru, only 157 have growth rings and need to be analyzed in detail with other studies of exchange rate development and traditional techniques of dendrochronological analysis. The derivation of this information can reach high impact in studies of climatic variability and conservation applications. Likewise, the preliminary dendrochronological analysis of growth rates reveals that Cedrela kuelapensis showed the highest growth rates and stands out as an excellent resource for reforestation programs in the inter-Andean valleys, in addition, Cordia iguaguana and Esenbeckia cornuta endemic populations are mainly from young individuals. We hope that the information in the five chapters constitutes in efficient and important tool to improve the management of forest resources in the valleys studied.