Browsing by Author "Peterson, John A."

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    Needleless shoots and loss of apical dominance in greenhouse-grown loblolly pine (Pinus taeda L.)
    Peterson, John A. (Virginia Tech, 1994)
    Loblolly pine that is winter-sown in the greenhouse and spring-outplanted has been observed to exhibit growth abnormalities in the form of multiple apical and needleless shoots. Seedlings that exhibit growth abnormalities are of questionable value in the evaluation of progeny tests. The use growth data from this seedling material could result in biased and erroneous or invalid conclusions about individual tree or family performance. To determine the causes of growth abnormality development, and to suggest possible remedies, two experiments were initiated. The first experiment examined the effects of raising five Virginia controlled-cross families in two different greenhouses and subsequently outplanting the seedlings on two contrasting sites. The second examined the effects of pre-planting exposure to 0, 4, or 6 weeks of shortened days followed by 0, 400 or 600 hours of chilling and post-planting supplemental water. Experiment one results indicated that abnormalities were more apparent at the better growing site. Further, pre-planting hardening-off likely increased the dormancy status of the seedlings and somewhat alleviated growth abnormalities. It was determined that families varied in the expression of abnormalities. Abnormalities were only observed during the first summer after outplanting; symptoms were alleviated after overwintering. Experiment two results indicated that treatments that influenced the dormancy status of the seedlings influenced the development of growth abnormalities. Pre-planting shortened days resulted in increased needles per total stem units for the second flush. Pre-planting chilling and post-planting supplemental water increased apical dominance.
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    Soil Respiration and Related Abiotic and Remotely Sensed Variables in Different Overstories and Understories in a High-Elevation Southern Appalachian Forest
    Hammer, Rachel L.; Seiler, John R.; Peterson, John A.; Thomas, Valerie A. (MDPI, 2023-08-15)
    Accurately predicting soil respiration (Rs) has received considerable attention recently due to its importance as a significant carbon flux back to the atmosphere. Even small changes in Rs can have a significant impact on the net ecosystem productivity of forests. Variations in Rs have been related to both spatial and temporal variation due to changes in both abiotic and biotic factors. This study focused on soil temperature and moisture and changes in the species composition of the overstory and understory and how these variables impact Rs. Sample plots consisted of four vegetation types: eastern hemlock (Tsuga canadensis L. Carriere)-dominated overstory, mountain laurel (Kalmia latifolia L.)-dominated understory, hardwood-dominated overstory, and cinnamon fern (Osmundastrum cinnamomeum (L.) C. Presl)-dominated understory, with four replications of each. Remotely sensed data collected for each plot, light detection and ranging, and hyperspectral data, were compiled from the National Ecological Observatory Network (NEON) to determine if they could improve predictions of Rs. Soil temperature and soil moisture explained 82% of the variation in Rs. There were no statistically significant differences between the average annual Rs rates among the vegetation types. However, when looking at monthly Rs, cinnamon fern plots had statistically higher rates in the summer when it was abundant and hemlock had significantly higher rates in the dormant months. At the same soil temperature, the vegetation types’ Rs rates were not statistically different. However, the cinnamon fern plots showed the most sensitivity to soil moisture changes and were the wettest sites. Normalized Difference Lignin Index (NDLI) was the only vegetation index (VI) to vary between the vegetation types. It also correlated with Rs for the months of August and September. Photochemical reflectance index (PRI), normalized difference vegetation index (NDVI), and normalized difference nitrogen index (NDNI) also correlated with September’s Rs. In the future, further research into the accuracy and the spatial scale of VIs could provide us with more information on the capability of VIs to estimate Rs at these fine scales. The differences we found in monthly Rs rates among the vegetation types might have been driven by varying litter quality and quantity, litter decomposition rates, and root respiration rates. Future efforts to understand carbon dynamics on a broader scale should consider the temporal and finer-scale differences we observed.