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Data from an airborne laser scanner, a dual-band interferometric synthetic aperture radar (DBInSAR), and Landsat were evaluated for estimating ages of even-aged loblolly pine stands in Appomattox-Buckingham State Forest, Virginia, U.S.A. The DBInSAR data were acquired using the GeoSAR sensor in summer, 2008 in both the P- and X-bands. The LiDAR data were acquired in the same summer using a small-footprint laser scanner. Loblolly pine stand ages were assigned using the establishment year of loblolly pine stands provided by the Virginia Department of Forestry. Random circular plots were established in stands which varied in age from 5 to 71 years and in site index from 21 to 29 meters (base age 25 years). LiDAR- and GeoSAR-derived independent variables were calculated. The final selected LiDAR model used common logarithm of age as the dependent variable and the 99.5th percentile of height above ground as the independent variable (R2adj = 90.2%, RMSE = 4.4 years, n=45). The final selected GeoSAR models used the reciprocal of age as the dependent variable and had three independent variables: the sum of the X-band magnitude, the 25th percentile of X/P-band magnitudes, and the 90th percentile of the X-band height above ground (R2adj = 84.1%, RMSE = 7.9 years, n=46). The Vegetation Change Tracker (VCT) algorithm was run using a digital elevation layer, a land cover map, and a series of Landsat (5 and 7) images. A comparison was made between the loblolly pine stand ages obtained using the three methods and the reference data. The results show that: (1) although most of the time VCT and reference data ages were different, the differences were normally small, (2) all three remote sensing methods produced reliable age estimates, and (3) the Landsat-VCT algorithm produced the best estimates for younger stands (5 to 22 years old, RMSEVCT=2.2 years, RMSEGeoSAR=2.6 years, RMSELiDAR=2.6 years, n=35) and the model that used LiDAR-derived variables was better for older stands. Remote sensing can be used to estimate loblolly pine stand age, though prior knowledge of site index is required for active sensors that rely primarily on the relationship between age and height. / Ph. D.

名古屋大学年代測定総合研究センターシンポジウム報告

This study develops understanding of vegetation change and water, sediment and carbon dynamics in semi-arid environments. Objectives were addressed using an integrated ecohydrological and biogeochemical approach. Fieldwork, over two contrasting grass-woody transitions at the Sevilleta National Wildlife Refuge, New Mexico, USA; quantified vegetation structure, soil structure and the spatial distribution of soil carbon resources. Over both transitions; woody sites showed a lower percentage vegetation cover and a greater heterogeneity in vegetation pattern, soil properties and soil carbon. Soil organic carbon differed in both quantity and source across the sites; with levels higher under vegetation, particularly at the woody sites. Biogeochemical analysis revealed soil organic carbon to be predominantly sourced from grass at the grassland sites. In contrast, at the woody sites soil organic carbon under vegetation patches was predominantly sourced from woody vegetation, whilst inter-patch areas exhibited a strong grass signature. Investigation of function focussed on the hydrological response to intense rainfall events. Rainfall-runoff monitoring showed woody sites to exhibit greater; runoff coefficients, event discharge, eroded sediment and event carbon yields. In contrast to grass sites, biogeochemical analysis showed the loss of organic carbon from woody sites to exhibit a mixed source signal, reflecting the loss of carbon originating from both patch and interpatch areas. To examine the linkages between vegetation structure and hydrological function, a flow length metric was developed to quantify hydrological connectivity; with woody sites shown to have longer mean flow pathways. Furthermore, in addition to rainfall event characteristics, flow pathway lengths were shown to be a significant variable for explaining the variance within fluxes of water, sediment and carbon. Results demonstrating increased event fluxes of sediment and carbon from woody sites have important implications for the quality of semi-arid landscapes and other degrading ecosystems globally. It is thus necessary to translate the understanding of carbon dynamics developed within this study to the landscape scale, so changing fluvial carbon fluxes can be incorporated into carbon budgets, research frameworks and land management strategies at policy-relevant scales.

Grass-dominated ecosystems in many regions around the world have experienced increased abundance of woody plants during the past 100 yrs. In the Rio Grande Plains of southern Texas, subtropical woodlands, dominated by C3 trees/shrubs capable of symbiotic N2-fixation, have become significant components of landscapes that were once dominated by C4 grasslands. Upland areas in this region now consist of small discrete clusters and large groves of woody vegetation embedded in a grassy matrix, while lower-lying portions of the landscape are dominated by closed-canopy woodlands. I used soil δ13C in conjunction with aerial photography and geostatistics to quantify landscape-scale vegetation dynamics in uplands of this savanna parkland. Spatial patterns of soil δ13C in grids and transects traversing woody patches indicated larger woody groves were formed from small discrete clusters of woody plants that spread laterally and eventually coalesced. Soil δ13C contour maps revealed some clusters are currently growing rapidly towards each other and might coalesce into groves in the near future, while some clusters remained relatively stable. Kriged maps of soil δ13C provided a strong spatial context for future studies aimed at understanding the functional consequences of this change in landscape structure. The dominant invading woody plant, honey mesquite (Prosopis glandulosa), was important in determining the spatial pattern of soil δ13C, supporting the hypothesis that they serve as recruitment foci and facilitate the establishment of subordinate woody species. Leaf δ15N values suggested that the N2-fixing mesquite influenced the N nutrition of nearby non-N2-fixing shrubs, thus, suggesting a mechanism by which mesquite could facilitate establishment of other woody species. In closed-canopy drainage woodlands, however, spatial patterns of soil δ13C were no longer controlled by the presence of mesquite, but by the amount of soil organic carbon and soil texture. The positive correlation between silt+clay and soil δ13C indicates that the formation of organomineral complexes and microaggregates may slow SOC turnover rates and favor the persistence of C4-derived SOC from the original grassland. This study enhances our understanding of potential patterns, causes and consequences of grassland to woodland conversions which are underway today in many grass-dominated ecosystems around the world.

Grass-dominated ecosystems in many regions around the world have experienced increased abundance of woody plants during the past 100 yrs. In the Rio Grande Plains of southern Texas, subtropical woodlands, dominated by C3 trees/shrubs capable of symbiotic N2-fixation, have become significant components of landscapes that were once dominated by C4 grasslands. Upland areas in this region now consist of small discrete clusters and large groves of woody vegetation embedded in a grassy matrix, while lower-lying portions of the landscape are dominated by closed-canopy woodlands. I used soil δ13C in conjunction with aerial photography and geostatistics to quantify landscape-scale vegetation dynamics in uplands of this savanna parkland. Spatial patterns of soil δ13C in grids and transects traversing woody patches indicated larger woody groves were formed from small discrete clusters of woody plants that spread laterally and eventually coalesced. Soil δ13C contour maps revealed some clusters are currently growing rapidly towards each other and might coalesce into groves in the near future, while some clusters remained relatively stable. Kriged maps of soil δ13C provided a strong spatial context for future studies aimed at understanding the functional consequences of this change in landscape structure. The dominant invading woody plant, honey mesquite (Prosopis glandulosa), was important in determining the spatial pattern of soil δ13C, supporting the hypothesis that they serve as recruitment foci and facilitate the establishment of subordinate woody species. Leaf δ15N values suggested that the N2-fixing mesquite influenced the N nutrition of nearby non-N2-fixing shrubs, thus, suggesting a mechanism by which mesquite could facilitate establishment of other woody species. In closed-canopy drainage woodlands, however, spatial patterns of soil δ13C were no longer controlled by the presence of mesquite, but by the amount of soil organic carbon and soil texture. The positive correlation between silt+clay and soil δ13C indicates that the formation of organomineral complexes and microaggregates may slow SOC turnover rates and favor the persistence of C4-derived SOC from the original grassland. This study enhances our understanding of potential patterns, causes and consequences of grassland to woodland conversions which are underway today in many grass-dominated ecosystems around the world.

This three part study attempted to enhance our understanding of vegetation change and its potential effects on ecohydrology in drylands. The first study developed a method to measure the velocity of shallow overland flow. Under rainfall simulation, dye tracers were applied to runoff and photographed to calculate mean surface velocity. Results showed this approach was a significant improvement explaining 13% more of the variation in mean velocity compared to traditional methods. Results from the first study were used to compare hydraulic parameters on shrub- and grass-dominated plots in the second study. Previous research has suggested microtopography in shrublands acts to concentrate flow, leading to increased runoff velocity compared to grasslands. However, present findings showed that flow velocities were similar on many grass and shrub plots; only plots with ground cover > 90% exhibited significantly lower flow velocities, and some shrub-dominated plots had lower flow velocities than grass-dominated plots implying that horizontal water flux is reduced under certain states of woody plant encroachment. In terms of ground cover characteristics, velocity increased rapidly with increases in the fraction of bare soil, up to a value of ~20% bare soil. Above ~20% bare soil, basal gap became a dominant factor suggesting a possible threshold where spatial metrics related to the distance between plants become important indicator of shallow flow velocity. The third study tested an approach to quantify woody plant canopy metrics over large areas. Radar has been used to map biomass in forests but few studies have examined open canopy ecosystems. Field measurements of shrublands were compared to satellite images to identify the relationship between radar signal and height and cover of woody vegetation. Results indicated that radar signal increased positively with shrub height or shrub volume explaining 74% and 90% of the variation, respectively. The effect of surface roughness and sub-canopy species on radar signal appears reduced when images are collected at large incidence angles.

There has been a noticeable shift in focus in biodiversity research in New Zealand over recent decades. Research has traditionally focused on biodiversity protection on the public estate, which was comprised primarily of ecosystems with lower productive potential (generally over 500m asl). Private lands generally have higher production potential and are often used for intensive cultivation and agricultural practices. They still however have significant potential for protecting biodiversity values. One of the key tools for protecting biodiversity values on privately owned lands in the Canterbury region are through legally binding QEII open space covenants and there is significant potential through industry certifications. QEII covenants are placed on the land in perpetuity and provide legally binding protection for biodiversity or landscape values within the covenant. This protection is voluntary and allows the land owner to continue to use the land for economic benefit providing it does not prove detrimental to biodiversity through monitoring outcomes. Case studies of QEII covenants that contain grazing clauses in the Canterbury region were used to determine what values are present and what monitoring is occurring in the field within these ecosystems. Photopoints and informal visual monitoring were the primary methods used by the QEII representatives to monitor vegetation in all of the covenants. Monitoring forms a critical feedback for all biodiversity protection. It is especially important to have an accurate feedback on vegetation condition and change from monitoring on properties that are grazed. Monitoring needs to be capable of providing sufficient information on vegetation change on these sites so that the most suitable grazing levels can be obtained by land managers. This thesis focuses on monitoring methods to ensure that this feedback is suitable and that the methods are cost effective. Current vegetation monitoring techniques were reviewed to determine which methods would be most suited to monitoring in these ecosystems where resources are tightly restricted and observers may not have existing skills and experience in monitoring these ecosystems. Methods reviewed were quadrats, transects, height-frequencies, photopoints, needle point, biomass, tagged plants, visual rank and remote sensing. Each method is described and then assessed on its suitability for monitoring tussock shrublands, with cost effectiveness being an important criterion. Of these methods quadrats, transects and height-frequencies were the most robust but also the most intensive and least cost effective methods. Visual rank, needle point and photopoints were the most cost effective, but are generally suited to monitoring single objectives. In most cases a combination of methods would be ideal to suit the objectives of the monitoring. QEII photopoint monitoring should follow guidelines more closely and include more complimentary information with their photographs. Clear monitoring objectives should be developed for every covenant that is grazed and these need to be determined before it is possible to accurately select appropriate monitoring methods. These objectives will also provide the monitoring program with more structure and direction. If possible a detailed management plan for each grazed covenant would be beneficial for values present. QEII are in a unique position, where they have the potential to develop a data base of biodiversity information for private land and contribute to other projects like the National Vegetation Survey (NVS).

There has been a noticeable shift in focus in biodiversity research in New Zealand over recent decades. Research has traditionally focused on biodiversity protection on the public estate, which was comprised primarily of ecosystems with lower productive potential (generally over 500m asl). Private lands generally have higher production potential and are often used for intensive cultivation and agricultural practices. They still however have significant potential for protecting biodiversity values. One of the key tools for protecting biodiversity values on privately owned lands in the Canterbury region are through legally binding QEII open space covenants and there is significant potential through industry certifications. QEII covenants are placed on the land in perpetuity and provide legally binding protection for biodiversity or landscape values within the covenant. This protection is voluntary and allows the land owner to continue to use the land for economic benefit providing it does not prove detrimental to biodiversity through monitoring outcomes. Case studies of QEII covenants that contain grazing clauses in the Canterbury region were used to determine what values are present and what monitoring is occurring in the field within these ecosystems. Photopoints and informal visual monitoring were the primary methods used by the QEII representatives to monitor vegetation in all of the covenants. Monitoring forms a critical feedback for all biodiversity protection. It is especially important to have an accurate feedback on vegetation condition and change from monitoring on properties that are grazed. Monitoring needs to be capable of providing sufficient information on vegetation change on these sites so that the most suitable grazing levels can be obtained by land managers. This thesis focuses on monitoring methods to ensure that this feedback is suitable and that the methods are cost effective. Current vegetation monitoring techniques were reviewed to determine which methods would be most suited to monitoring in these ecosystems where resources are tightly restricted and observers may not have existing skills and experience in monitoring these ecosystems. Methods reviewed were quadrats, transects, height-frequencies, photopoints, needle point, biomass, tagged plants, visual rank and remote sensing. Each method is described and then assessed on its suitability for monitoring tussock shrublands, with cost effectiveness being an important criterion. Of these methods quadrats, transects and height-frequencies were the most robust but also the most intensive and least cost effective methods. Visual rank, needle point and photopoints were the most cost effective, but are generally suited to monitoring single objectives. In most cases a combination of methods would be ideal to suit the objectives of the monitoring. QEII photopoint monitoring should follow guidelines more closely and include more complimentary information with their photographs. Clear monitoring objectives should be developed for every covenant that is grazed and these need to be determined before it is possible to accurately select appropriate monitoring methods. These objectives will also provide the monitoring program with more structure and direction. If possible a detailed management plan for each grazed covenant would be beneficial for values present. QEII are in a unique position, where they have the potential to develop a data base of biodiversity information for private land and contribute to other projects like the National Vegetation Survey (NVS).

Bush encroachment or the thickening of woody vegetation is a phenomenon occurring throughout savannas, which tends to be more pronounced in small protected areas. The consequences of bush encroachment are often negative for the conservation of biodiversity, for the promotion of tourism and the prevention of wildfires. Hence, effective monitoring of woody vegetation and the factors which influence its spread are essential. This is particularly the case for protected areas such as that of Bwabwata National Park (BNP) in north-east Namibia. With a complex land use history and different fire management approaches being adopted throughout the area, the effect of fire on woody vegetation in BNP is currently poorly understood. This study used a 20-year-old repeat photography monitoring project and satellite-based remote sensing products to explore woody cover dynamics in BNP. Results revealed that woody cover has increased by 13% since 1999 in BNP. Furthermore, the results show differences in the structure of woody vegetation. Repeated late dry season fires in the west of the park have driven an increasing dominance of 3m in eastern sections of the park. This influence of different fire regimes spatially across BNP, suggests that local fire management is a significant determinant of woody vegetation change. Woody vegetation change differs spatially across BNP due to frequent late dry season fires prevailing in the west and less frequent earlier season fires occurring in the east. Therefore, in order to reduce the mortality of woody species and conserve heterogenous height structure in the west, a reduction of frequent late dry season fires is required. Early dry season fires are shown to reduce the rate of increasing total woody cover change and, therefore, this fire management strategy arguably contributes towards the reduction of wildfire risk, conservation of biodiversity and promotion of tourism.