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Evan H. Delucia - One of the best experts on this subject based on the ideXlab platform.
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Physiological and morphological acclimation of shade-grown tree seedlings to late-season Canopy Gap formation
Plant Ecology, 1998Co-Authors: Shawna L Naidu, Evan H. DeluciaAbstract:Because acclimation to Canopy Gaps may involve coordination of new leaf production with morphological or physiological changes in existing, shade-developed leaves, we examined both new leaf production and photosynthesis of existing leaves on shade-grown seedlings after exposure to a late-season Canopy Gap. Midway through the summer, we transferred potted, shade-grown seedlings of four co-occurring temperate deciduous tree species representing a range of shade-tolerance categories and leaf production strategies to Gaps. Shade-tolerant Acer saccharum was the least responsive to Gap conditions. It produced few new, high-light acclimated leaves and increases in photosynthetic rates of shade-developed leaves appeared stomatally limited. Intermediately shade-tolerant Fraxinus americana and Quercus rubra responded most, by producing new leaves and increasing photosynthetic rates of existing shade-developed leaves to levels not significantly different from Gap-grown controls within four weeks of Gap exposure. Shade-intolerant Liriodendron tulipifera was intermediate in response. In these species, the degree of shoot-level morphological acclimation (new leaf production) and leaf-level physiological acclimation (photosynthetic increases in existing leaves) appear coupled. Mechanisms of acclimation also appear related to intrinsic patterns of nitrogen use and mobilization, the ability to adjust stomatal conductance, and shade tolerance.
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Hydraulic adjustment of maple saplings to Canopy Gap formation
Oecologia, 1997Co-Authors: Hafiz Maherali, Evan H. Delucia, Timothy W. SipeAbstract:The leaf-specific hydraulic conductivity (KL) of plant stems can control leaf water supply. This property is influenced by variation in leaf/sapwood area ratio (AL/AS) and the specific hydraulic conductivity of xylem tissue (KS). In environments with high atmospheric vapor pressure deficit (VPD), KL may increase to support higher transpiration rates. We predicted that saplings of Acerrubrum and A.pensylvanicum grown in forest Canopy Gaps, under high light and VPD, would have higher KL and lower AL/AS than similar sized saplings in the understory. Leaf-specific hydraulic conductivity and KS increased with sapling size for both species. In A. rubrum, KS did not differ between the two environments but lower AL/AS (P=0.05, ANCOVA) led to higher KL for Gap-grown saplings (P < 0.05, ANCOVA). In A.pensylvanicum, neither KS, AL/AS, nor KL differed between environments. In a second experiment, we examined the impact of sapling size on the water relations and carbon assimilation of A.pensylvanicum. Maximum stomatal conductance for A.pensylvanicum increased with KL (r2=0.75, P < 0.05). A hypothetical large A.pensylvanicum sapling (2 m tall) had 2.4 times higher KL and 22 times greater daily carbon assimilation than a small (1 m tall) sapling. Size-related hydraulic limitations in A.pensylvanicum caused a 68% reduction in daily carbon assimilation in small saplings. Mid-day water potential increased with A.pensylvanicum sapling size (r2=0.69, P < 0.05). Calculations indicated that small A.pensylvanicum saplings (low KL) could not transpire at the rate of large saplings (high KL) without reaching theoretical thresholds for xylem embolism induction. The coordination between KL and stomatal conductance in saplings may prevent xylem water potential from reaching levels that cause embolism but also limits transpiration. The KS of the xylem did not vary across environments, suggesting that altering biomass allocation is the primary mechanism of increasing KL. However, the ability to alter aboveground biomass allocation in response to Canopy Gaps is species-specific. As a result of the increase in KL and KS with sapling size for both species, hydraulic limitation of water flux may impose a greater restriction on daily carbon assimilation for small saplings in the Gap environment.
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growth allocation and water relations of shade grown quercus rubra l saplings exposed to a late season Canopy Gap
Annals of Botany, 1997Co-Authors: Shawna L Naidu, Evan H. DeluciaAbstract:For understory saplings to exploit Canopy Gaps successfully, carbon gain must increase in the Gap environment. We predicted that total biomass of shade-grown red oak saplings would increase after exposure to a late-season Canopy Gap, and that increased water and nutrient demand within the Canopy Gap would drive changes in the allocation of this carbon. Shade-grown red oak saplings acclimated to Gaps by increasing biomass during the season of Gap formation and increasing the potential for carbon gain in the following summer. Within-season carbon gain did not result from greater production of leaf area, so it most likely arose from higher photosynthetic rates of existing shade-developed foliage, which may be linked to accumulation of leaf nitrogen. During the season of Gap formation, shade-Gap plants increased allocation to storage of total non-structural carbohydrates (TNC), and to root growth. The increase in TNC storage suggests that shade-developed saplings exposed to Gaps were also primed for fast growth and carbon gain in the following summer. The increase in root growth suggests that higher nutrient and water demand drove allocation shifts to enhance the capacity for nutrient and water uptake in the Gap. Plant hydraulic conductivity (Ka) of shade-grown plants was limited upon exposure to the Gap, possibly because of embolism formation resulting from the abrupt increase in water demand. Greater water potential gradients compensated for limitations to Ka, allowing saplings to maintain high transpiration rates, suggesting that actual water uptake of shade-Gap plants was unaffected by Gap exposure.
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acclimation of shade developed leaves on saplings exposed to late season Canopy Gaps
Tree Physiology, 1997Co-Authors: Shawna L Naidu, Evan H. DeluciaAbstract:We hypothesized that photoinhibition of shade-developed leaves of deciduous hardwood saplings would limit their ability to acclimate photosynthetically to increased irradiance, and we predicted that shade-tolerant sugar maple (Acer saccharum Marsh.) would be more susceptible to photoinhibition than intermediately shade-tolerant red oak (Quercus rubra L.). After four weeks in a Canopy Gap, photosynthetic rates of shade-developed leaves of both species had increased in response to the increase in irradiance, although final acclimation was more complete in red oak. However, photoinhibition occurred in both species, as indicated by short-term reductions in maximum rates of net photosynthesis and the quantum yield of oxygen evolution, and longer-term reductions in the efficiency of excitation energy capture by open photosystem II (PSII) reaction centers (dark-adapted F(v)/F(m)) and the quantum yield of PSII in the light (phi(PSII)). The magnitude and duration of this decrease were greater in sugar maple than in red oak, suggesting greater susceptibility to photoinhibition in sugar maple. Photoinhibition may have resulted from photodamage, but it may also have involved sustained rates of photoprotective energy dissipation (especially in red oak). Photosynthetic acclimation also appeared to be linked to an ability to increase leaf nitrogen content. Limited photosynthetic acclimation in shade-developed sugar maple leaves may reflect a trade-off between shade-tolerance and rapid acclimation to a Canopy Gap.
F. Mark Danson - One of the best experts on this subject based on the ideXlab platform.
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testing the application of terrestrial laser scanning to measure forest Canopy Gap fraction
Remote Sensing, 2013Co-Authors: F A Ramirez, Richard P Armitage, F. Mark DansonAbstract:Terrestrial laser scanners (TLS) have the potential to revolutionise measurement of the three-dimensional structure of vegetation canopies for applications in ecology, hydrology and climate change. This potential has been the subject of recent research that has attempted to measure forest biophysical variables from TLS data, and make comparisons with two-dimensional data from hemispherical photography. This research presents a systematic comparison between forest Canopy Gap fraction estimates derived from TLS measurements and hemispherical photography. The TLS datasets used in the research were obtained between April 2008 and March 2009 at Delamere Forest, Cheshire, UK. The analysis of Canopy Gap fraction estimates derived from TLS data highlighted the repeatability and consistency of the measurements in comparison with those from coincident hemispherical photographs. The comparison also showed that estimates computed considering only the number of hits and misses registered in the TLS datasets were consistently lower than those estimated from hemispherical photographs. To examine this difference, the potential information available in the intensity values recorded by TLS was investigated and a new method developed to estimate Canopy Gap fraction proposed. The new approach produced Gap fractions closer to those estimated from hemispherical photography, but the research also highlighted the limitations of single return TLS data for this application.
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Terrestrial laser scanners to measure forest Canopy Gap fraction
2008Co-Authors: F. Mark Danson, F A Ramirez, Richard P Armitage, V. Bandugula, Nicholas J. Tate, K. J. Tansey, T. Tegzes, Ross A. Hill, Jacqueline Rosette, J. SuárezAbstract:The directional Gap fraction in forest and woodland canopies is the primary information that is used for the non-destructive estimation of Canopy leaf area index (LAI). In this study the directional Gap fraction of a mixed species forest stand was measured using three different terrestrial laser scanners providing measurements with two different beam divergences at two different wavelengths. Gap fractions estimated from the laser scanners were compared to the Gap fraction derived from hemispherical photographs recorded near simultaneously. The results showed that differences in wavelength gave rise to contrasting intensity images which contained complementary information on Canopy composition. Wider beam divergence gave rise to lower estimates of Gap fraction, and the terrestrial laser scanners underestimated Gap fraction when compared to data derived from the hemispherical photographs. Beam divergence, laser wavelength and range-related variation in intensity all affect Gap detection. These issues are discussed and future data processing techniques to provide consistent estimates of Canopy Gap fraction from terrestrial laser scanners are discussed.
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Forest Canopy Gap fraction from terrestrial laser scanning
IEEE Geoscience and Remote Sensing Letters, 2007Co-Authors: F. Mark Danson, David Hetherington, Felix Morsdorf, Benjamin Koetz, Britta AllgowerAbstract:A terrestrial laser scanner (TLS) was used to measure Canopy directional Gap fraction distribution in forest stands in the Swiss National Park, eastern Switzerland. A scanner model was derived to determine the expected number of laser shots in all directions, and these data were compared with the measured number of laser hits to determine directional Gap fraction at eight sampling points. Directional Gap fraction distributions were determined from digital hemispherical photographs recorded at the same sampling locations in the forest, and these data were compared with distributions computed from the laser scanner data. The results showed that the measured directional Gap fraction distributions were similar for both hemispherical photography and TLS data with a high degree of precision in the area of overlap of orthogonal laser scans. Analysis of hemispherical photography to determine Canopy Gap fraction normally requires some manual data processing; laser scanners offer semiautomatic measurement of directional Gap fraction distribution plus additional three-dimensional information about tree height, Gap size, and foliage distributions
Shawna L Naidu - One of the best experts on this subject based on the ideXlab platform.
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Physiological and morphological acclimation of shade-grown tree seedlings to late-season Canopy Gap formation
Plant Ecology, 1998Co-Authors: Shawna L Naidu, Evan H. DeluciaAbstract:Because acclimation to Canopy Gaps may involve coordination of new leaf production with morphological or physiological changes in existing, shade-developed leaves, we examined both new leaf production and photosynthesis of existing leaves on shade-grown seedlings after exposure to a late-season Canopy Gap. Midway through the summer, we transferred potted, shade-grown seedlings of four co-occurring temperate deciduous tree species representing a range of shade-tolerance categories and leaf production strategies to Gaps. Shade-tolerant Acer saccharum was the least responsive to Gap conditions. It produced few new, high-light acclimated leaves and increases in photosynthetic rates of shade-developed leaves appeared stomatally limited. Intermediately shade-tolerant Fraxinus americana and Quercus rubra responded most, by producing new leaves and increasing photosynthetic rates of existing shade-developed leaves to levels not significantly different from Gap-grown controls within four weeks of Gap exposure. Shade-intolerant Liriodendron tulipifera was intermediate in response. In these species, the degree of shoot-level morphological acclimation (new leaf production) and leaf-level physiological acclimation (photosynthetic increases in existing leaves) appear coupled. Mechanisms of acclimation also appear related to intrinsic patterns of nitrogen use and mobilization, the ability to adjust stomatal conductance, and shade tolerance.
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growth allocation and water relations of shade grown quercus rubra l saplings exposed to a late season Canopy Gap
Annals of Botany, 1997Co-Authors: Shawna L Naidu, Evan H. DeluciaAbstract:For understory saplings to exploit Canopy Gaps successfully, carbon gain must increase in the Gap environment. We predicted that total biomass of shade-grown red oak saplings would increase after exposure to a late-season Canopy Gap, and that increased water and nutrient demand within the Canopy Gap would drive changes in the allocation of this carbon. Shade-grown red oak saplings acclimated to Gaps by increasing biomass during the season of Gap formation and increasing the potential for carbon gain in the following summer. Within-season carbon gain did not result from greater production of leaf area, so it most likely arose from higher photosynthetic rates of existing shade-developed foliage, which may be linked to accumulation of leaf nitrogen. During the season of Gap formation, shade-Gap plants increased allocation to storage of total non-structural carbohydrates (TNC), and to root growth. The increase in TNC storage suggests that shade-developed saplings exposed to Gaps were also primed for fast growth and carbon gain in the following summer. The increase in root growth suggests that higher nutrient and water demand drove allocation shifts to enhance the capacity for nutrient and water uptake in the Gap. Plant hydraulic conductivity (Ka) of shade-grown plants was limited upon exposure to the Gap, possibly because of embolism formation resulting from the abrupt increase in water demand. Greater water potential gradients compensated for limitations to Ka, allowing saplings to maintain high transpiration rates, suggesting that actual water uptake of shade-Gap plants was unaffected by Gap exposure.
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acclimation of shade developed leaves on saplings exposed to late season Canopy Gaps
Tree Physiology, 1997Co-Authors: Shawna L Naidu, Evan H. DeluciaAbstract:We hypothesized that photoinhibition of shade-developed leaves of deciduous hardwood saplings would limit their ability to acclimate photosynthetically to increased irradiance, and we predicted that shade-tolerant sugar maple (Acer saccharum Marsh.) would be more susceptible to photoinhibition than intermediately shade-tolerant red oak (Quercus rubra L.). After four weeks in a Canopy Gap, photosynthetic rates of shade-developed leaves of both species had increased in response to the increase in irradiance, although final acclimation was more complete in red oak. However, photoinhibition occurred in both species, as indicated by short-term reductions in maximum rates of net photosynthesis and the quantum yield of oxygen evolution, and longer-term reductions in the efficiency of excitation energy capture by open photosystem II (PSII) reaction centers (dark-adapted F(v)/F(m)) and the quantum yield of PSII in the light (phi(PSII)). The magnitude and duration of this decrease were greater in sugar maple than in red oak, suggesting greater susceptibility to photoinhibition in sugar maple. Photoinhibition may have resulted from photodamage, but it may also have involved sustained rates of photoprotective energy dissipation (especially in red oak). Photosynthetic acclimation also appeared to be linked to an ability to increase leaf nitrogen content. Limited photosynthetic acclimation in shade-developed sugar maple leaves may reflect a trade-off between shade-tolerance and rapid acclimation to a Canopy Gap.
Britta Allgower - One of the best experts on this subject based on the ideXlab platform.
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Forest Canopy Gap fraction from terrestrial laser scanning
IEEE Geoscience and Remote Sensing Letters, 2007Co-Authors: F. Mark Danson, David Hetherington, Felix Morsdorf, Benjamin Koetz, Britta AllgowerAbstract:A terrestrial laser scanner (TLS) was used to measure Canopy directional Gap fraction distribution in forest stands in the Swiss National Park, eastern Switzerland. A scanner model was derived to determine the expected number of laser shots in all directions, and these data were compared with the measured number of laser hits to determine directional Gap fraction at eight sampling points. Directional Gap fraction distributions were determined from digital hemispherical photographs recorded at the same sampling locations in the forest, and these data were compared with distributions computed from the laser scanner data. The results showed that the measured directional Gap fraction distributions were similar for both hemispherical photography and TLS data with a high degree of precision in the area of overlap of orthogonal laser scans. Analysis of hemispherical photography to determine Canopy Gap fraction normally requires some manual data processing; laser scanners offer semiautomatic measurement of directional Gap fraction distribution plus additional three-dimensional information about tree height, Gap size, and foliage distributions
John Armston - One of the best experts on this subject based on the ideXlab platform.
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sensitivity of direct Canopy Gap fraction retrieval from airborne waveform lidar to topography and survey characteristics
Remote Sensing of Environment, 2014Co-Authors: X T Chen, John Armston, Mathias Disney, Philip Lewis, J T HanAbstract:Recently, Armston et al. (2013) have demonstrated that a new, physically-based method for direct retrieval of Canopy Gap probability PGap from waveform lidar can improve the estimation of PGap over discrete return lidar data. The success of the approach was demonstrated in a savanna woodland environment in Australia. The huge advantage of this method is that it uses the data themselves to solve for the Canopy contrast term i.e. the ratio of the reflectance from crown and ground, ρv/ρg. In this way the method avoids local calibration that is typically required to overcome differences in either ρv or ρg. To be more generally useful the method must be demonstrated on different sites and in the presence of slope and different sensor and survey configurations. If it is robust to these things, slope in particular, then we would suggest it is likely to be widely useful. Here, we test the robustness of the retrieval of PGap from waveform lidar using the Watershed Allied Telemetry Experimental Research dataset, over the Heihe River Basin region of China. The data contain significant Canopy, terrain and survey variations, presenting a rather different set of conditions to those previously used. Results show that ρv/ρg is seen to be stable across all flights and for all levels of spatial aggregation. This strongly supports the robustness of the new PGap retrieval method, which assumes that this relationship is stable. A comparison between PGap estimated from hemiphotos and from the waveform lidar showed agreement with Pearson correlation coefficient R = 0.91. The waveform lidar-derived estimates of PGap agreed to within 8% of values derived from hemiphotos, with a bias of 0.17%. The new waveform model was shown to be stable across different off-nadir scan angles and in the presence of slopes up to 26° with R ≥ 0.85 in all cases. We also show that the waveform model can be used to calculate PGap using just the mean value of Canopy returns, assuming that their distribution is unimodal. Lastly, we show that the method can also be applied to discrete return lidar data, albeit with slightly lower accuracy and higher bias, allowing PGap comparisons with previously-collected lidar datasets. Our results show the new method should be applicable for estimating PGap robustly across large areas, and from lidar data collected at different times and using different systems; an increasingly important requirement.
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Direct retrieval of Canopy Gap probability using airborne waveform lidar
Remote Sensing of Environment, 2013Co-Authors: John Armston, Mathias Disney, Philip Lewis, Peter Scarth, Stuart R. Phinn, Richard Lucas, Peter Bunting, Nicholas R. GoodwinAbstract:Armston, J., Disney, M., Lewis, P., Scarth, P., Phinn, S., Lucas, R., Bunting, P., Goodwin, N. (2013). Direct retrieval of Canopy Gap probability using airborne waveform lidar. Remote Sensing of Environment, 134, 24-38.