Biology subjects

Asner, G. P.

Publications and source records attributed to Asner, G. P..

4 recordsLinked to original sources

bioRxiv2025

Remote sensing reveals inter- and intraspecific variation in riparian cottonwood (Populus spp) response to drought

O_LIUnderstanding how vegetation responds to drought is fundamental for understanding the broader implications of climate change on foundation tree species that support high biodiversity. Leveraging remote sensing technology provides a unique vantage point to explore these responses across and within species. C_LIO_LIWe investigated interspecific drought responses of two Populus species (P. fremontii, P. angustifolia) and their naturally occurring hybrids using leaf-level visible through shortwave infrared (VSWIR; 400-2500 nm) reflectance. As F1 hybrids backcross with either species, resulting in a range of backcross genotypes, we heretofore refer to the two species and their hybrids collectively as "cross types." We additionally explored intraspecific variation in P. fremontii drought response at the leaf and canopy levels using reflectance data and thermal unmanned aerial vehicle (UAV) imagery. We employed several analyses to assess genotype-by-environment (GxE) interactions concerning drought, including principal component analysis, support vector machine, and spectral similarity index. C_LIO_LIFive key findings emerged: (1) Spectra of all three cross types shifted significantly in response to drought. The magnitude of these reaction norms can be ranked from hybrids>P. fremontii>P. angustifolia, suggesting differential variation in response to drought; (2) Spectral space among cross types constricted under drought, indicating spectral--and phenotypic--convergence; (3) Experimentally, populations of P. fremontii from cool regions had different responses to drought than populations from warm regions, with source population mean annual temperature driving the magnitude and direction of change in VSWIR reflectance. (4) UAV thermal imagery revealed that watered, warm-adapted populations maintained lower leaf temperatures and retained more leaves than cool-adapted populations, but differences in leaf retention decreased when droughted. (5) These findings are consistent with patterns of local adaptation to drought and temperature stress, demonstrating the ability of leaf spectra to detect ecological and evolutionary responses to drought as a function of adaptation to different environments. C_LIO_LISynthesis. Leaf-level spectroscopy and canopy-level UAV thermal data captured inter- and intraspecific responses to water stress in cottonwoods, which are widely distributed in arid environments. This study demonstrates the potential of remote sensing to monitor and predict the impacts of drought on scales varying from leaves to landscapes. C_LI

plant biology↗

bioRxiv2024

Disentangling the effect of heritability and plasticity on Populus fremontii leaf reflectance across a temperature gradient

Globally, vegetation biodiversity is expected to decline as the rate of plant adaptation struggles to keep pace with rising temperatures. To support conservation efforts through remote sensing, we disentangled the nested effects of genetic and environmental influences on reflectance spectra, leveraging spectroscopy to assess plant adaptations to temperature. Specifically, we quantified the relative effect of plasticity and heritability on Populus fremontii (Fremont cottonwood) leaf reflectance using clonal replicates propagated from 16 populations and grown across three common gardens spanning a mean annual temperature gradient representing the thermal range of P. fremontii. We used variance partitioning to decompose phenotypic variation expressed in the leaf spectra into genotypic and environmental components to estimate broad-sense heritability. Heritability was strongly expressed in the spectral red edge ([~]680-750nm) and shortwave infrared ([~]1400-3000nm), though the heritability peak in the red edge was sensitive to extreme temperatures. By comparing distances of group centroids in principal component space, we determined that P. fremontii intraspecific spectral variation was shaped by the interaction between common garden site conditions and source population. Support vector machine models indicated pronounced environmental influence on spectral variation, as P. fremontii source population and garden location were classified at 71.8% and 92.6% accuracy, respectively. These findings emphasize the utility of reflectance data in separating genetic and environmental influences on plant phenotypes, offering a pathway to scale these insights across broader landscapes and aid in the conservation and management of vulnerable ecosystems in a warming climate.

ecology↗

bioRxiv2022

Does forest heterogeneity affect mean throughfall for regenerating secondary forests on Borneo?

Tropical landscape regeneration affects hydrological ecosystem functioning by regulating the amount of water that reaches the soil surface and changing soil infiltration rates. This affects the recharge and storage of water in the soil and streamflow responses. Therefore, it is important to assess how the fraction of rainfall that reaches the forest floor changes as secondary forests mature, and how forest structure affects throughfall via changes in storage capacity and evapotranspiration. Therefore, we monitored throughfall for twelve regenerating, logged-over forest plots in Sabah, Malaysian Borneo over a 7-month period and tested if inclusion of measures of forest heterogeneity improved the prediction of throughfall as a fraction of precipitation. On average across all plots, throughfall was 84% of precipitation, but was lower (as low as 74%) in plots with a longer recovery time since logging. There was a significant relationship between throughfall and tree density and basal area, as well as the Shannon Diversity Index and the coefficient of variation of the diameter at breast height, although species and structural diversity measures (Shannon Index and the coefficient of variation) did not improve model performance substantially. The overall best performing model was a linear regression with tree density. There was no relation between LiDAR-derived Top of Canopy (TCH) and mean throughfall, suggesting that this remotely sensed proxy of canopy height is not needed to estimate throughfall and more in-depth analysis of other LiDAR-products such as point clouds may be required. Our results imply that estimating throughfall in this forest type can be reliably achieved using tree density, and that this is not substantially affected by species diversity or structural heterogeneity variables, at least in the context of logged and regenerating forests in Sabah. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=137 SRC="FIGDIR/small/500051v1_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@e7b11borg.highwire.dtl.DTLVardef@11c923dorg.highwire.dtl.DTLVardef@c4f3c6org.highwire.dtl.DTLVardef@607ab8_HPS_FORMAT_FIGEXP M_FIG Forest of a similar size or height can have a different structure. In this study we investigate if diversity also affects the amount of throughfall for plots across a disturbance gradient. C_FIG

ecology↗

bioRxiv2019

THE INFLUENCE OF ECOSYSTEM AND PHYLOGENY ON TROPICAL TREE CROWN SIZE AND SHAPE

1The sizes and shapes of tree crowns are of fundamental importance in ecology, yet understanding the forces that determine them remains elusive. A cardinal question facing ecologists is the degree to which general and non-specific versus ecological and context-dependent processes are responsible for shaping tree crowns. Here, we test this question for the first time across diverse tropical ecosystems. Using trees from 20 plots varying in elevation, precipitation, and ecosystem type (savanna-forest transitions) across the paleo- and neo-tropics, we test the relationship between crown dimensions and tree size. By analyzing these scaling relationships across environmental gradients, biogeographic regions, and phylogenetic distance, we extend Metabolic Scaling Theory (MST) predictions to include how local selective pressures shape variation in crown dimensions. Across all sites, we find strong agreement between mean trends and MST predictions for the scaling of crown size and shape, but large variation around the mean. While MST explained approximately half of the observed variation in tree crown dimensions, we find that local, ecosystem, and phylogenetic predictors account for the half of the residual variation. Crown scaling does not change significantly across regions, but does change across ecosystem types, where savanna tree crowns grow more quickly with tree size than forest tree crowns. Crowns of legumes were wider and larger than those of other taxa. Thus, while MST can accurately describe the central tendency of tree crown size, local ecological conditions and evolutionary history appear to modify the scaling of crown shape. Importantly, our extension of MST incorporating these differences accounts for the mechanisms driving variation in the scaling of crown dimensions across the tropics. These results are critical when scaling the function of individual trees to larger spatial scales or incorporating the size and shape of tree crowns in global biogeochemical models.

ecology↗