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Browsing by Author "Maier, Christopher A."

Now showing 1 - 11 of 11
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    Biomass and nutrient mass of Acacia dealbata and Eucalyptus globulus bioenergy plantations
    Albaugh, Timothy J.; Rubilar, Rafael A.; Maier, Christopher A.; Acuna, Eduardo A.; Cook, Rachel L. (2017-02)
    We quantified biomass and nutrient accumulation of Acacia dealbata Link and Eucalyptus globulus Labill. planted at stem densities of 5000 and 15000 ha(-1) in a bioenergy plantation in Chile. We tested the hypotheses that species and stocking will not affect biomass or nutrient accumulation. Species and stocking did not affect biomass accumulation after five years; however, species and stocking did influence nutrient mass. A. dealbata had higher nitrogen mass than E. globulus for total (397 kg ha(-1) more, i.e., 126% higher), foliage (188 kg ha(-1), 218%), branch (55 kg ha(-1), 95%), stem (120 kg ha(-1), 86%), and root (34 kg ha (-1), 109%) components, likely because A. dealbata fixes nitrogen. A. dealbata had lower calcium mass than E. globulus for branch (111 kg ha(-1), 60%) and stem (69 kg ha(-1), 39%) components. Root nitrogen and phosphorus masses and foliage, branch and root boron masses were significantly lower with a stocking density of 5000 ha(-1). Low stocking produced the same amount of total biomass as high stocking for both species and would be less expensive to plant. A. dealbata had higher nitrogen mass and likely increased soil nitrogen. E. globulus had high calcium mass in the stem and branches; off-site losses could be mitigated with stem-only harvests and debarking of stems in the field. Given the rainfall patterns and water availability constraints in Chile, additional criteria including water use efficiency would be required to determine the best species for bioenergy plantations in Chile. (C) 2017 Elsevier Ltd. All rights reserved.
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    The combined effects of fertilization and relative water limitation on tissue water relations, hydraulic parameters and shallow root distribution in loblolly pine (Pinus taeda L.)
    Russell, Edward Morgan (Virginia Tech, 2019-08-27)
    One goal of this research was to characterize shoot tissue-level responses in loblolly pine to soil moisture limitation in combination with fertilization as well as to more severe soil moisture limitation. We found that neither fertilization alone, nor fertilization in combination with soil moisture limitation resulted in changes to shoot tissue water relations parameters classically characterized in drought response studies. More severe water limitation was necessary to elicit responses, and those responses had not been fully described previously. The more severe water limitation resulted in increased capacitance beyond turgor loss, increased relative water content at turgor loss, a more negative turgor loss point, an increased bulk modulus of elasticity, more negative osmotic potential at 100% relative water content, and an increased apoplastic water fraction. As there were indications of reduced water use and moisture stress in the absence of shoot level responses under less severe drought, such parameters are insufficient alone to characterize moisture stress in fertilized and in less severely water limited loblolly trees. Additionally, we sought a morphological or physiological explanation for the reduced transpiration and increased water use efficiency reported for fertilized trees in the Virginia Piedmont. Our characterizations of the responses of root distribution and hydraulics to limited soil moisture here complement existing research, which demonstrated changes to root distribution and hydraulics in response to fertilization. The responses we discovered in fertilized trees that accompanied reduced transpiration and increased water use efficiency that differed from responses to reduced soil moisture alone were primarily large decreases to shallow root presence. We found this to be readily quantified using measures of root length density. Decreases to whole-tree hydraulic conductivity were also shown to occur with fertilization and were shown not to occur in shoot tissue, suggesting limitation via rhizosphere or root xylem conductance. Our results support the supposition that fertilization narrows hydraulic safety margins and potentially predisposes loblolly trees to moisture stress, particularly prolonged, severe water limitation following fertilization. Finally, we tested the validity of throughfall exclusion for simulating reduced rainfall using a greenhouse 'split-pot' study, which applied spatially fixed heterogeneous soil moisture to young, well-watered loblolly pines. The 'split-pot' experiments demonstrated that spatially fixed soil moisture heterogeneity does not confound drought effects; needle area specific transpiration was not decreased, nor was water use efficiency increased. This supports the validity of inferences taken from drought simulation experiments with loblolly pine where throughfall exclusion troughs reduce soil moisture content in a consistent, spatially heterogeneous manner.
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    A common garden experiment examining light use efficiency and heat sum to explain growth differences in native and exotic Pinus taeda
    Albaugh, Timothy J.; Fox, Thomas R.; Maier, Christopher A.; Campoe, Otavio C.; Rubilar, Rafael A.; Cook, Rachel L.; Raymond, Jay E.; Alvares, Clayton A.; Stape, Jose L. (2018-10-01)
    Previous work indicates that Pinus taeda L. grows faster and has a higher carrying capacity when grown outside its native range. We were interested in examining the hypotheses that growth, light use efficiency (volume growth and absorbed photosynthetically active radiation relationship, LUE) and volume growth per unit heat sum is the same for native and exotic plantations. To test these hypotheses, we installed a common garden experiment where the same six genetic entries of P. taeda (four clonal varieties, one open pollinated family and one control mass pollinated family) were planted at three densities (618, 1235, and 1853 stems ha(-1)) with three or four replications at three sites (Virginia (VA), and North Carolina (NC) in the United States and Parana State in Brazil (BR)). The VA and BR sites were outside the native range of P. taeda. After five years of growth, the BR site had larger trees and stand scale basal area and volume were increasing faster than the other sites. Site did not affect LUE but density and genetic entry did. The sites were at different latitudes but the average photosynthetically active radiation at the top of the canopy was similar for the years when all sites were operational, likely because the BR site receives more rain annually and the cloudiness associated with the rain may have reduced available light. We estimated an hourly heat sum where the daytime temperature was between 5 and 38 degrees C, hours where vapor pressure deficit exceeded 1.5 kPa and days following nights where nighttime temperatures were less than 0 degrees C were excluded. Site was significant for the cumulative volume and heat sum relationship, for a given level of cumulative degree hours the sites ranked BR > VA > NC in cumulative volume. The different growth per unit of degree hours for each site indicated that something other than the heat sum was causing the observed difference in growth. Other factors including respiration and extreme climatic conditions may contribute to growth differences per unit degree hour and including these differences in the analysis would require a more detailed modeling effort to examine. The sites used in this study are ideally suited to continue testing additional hypotheses to explain the different growth between native and exotic P. taeda plantations because they have the same genotypes at all sites and consequently eliminate differences in genetics as a potential explanation for observed growth differences.
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    Comparative water use in short-rotation Eucalyptus benthamii and Pinus taeda trees in the Southern United States
    Maier, Christopher A.; Albaugh, Timothy J.; Cook, Rachel I.; Hall, Kevin; McInnis, Daniel; Johnsen, Kurt H.; Johnson, John; Rubilar, Rafael A.; Vose, James M. (2017-08-01)
    Short rotation Eucalyptus plantations offer great potential for increasing wood-fiber production in the southern United States. Eucalyptus plantations can be highly productive (>35 m(3) ha(-1) year but they may use more water than intensively managed pine (primarily Pinus taeda L) plantations. This has raised concern about how expansion of Eucalyptus plantations will affect water resources. We compared tree water use, stem growth, and WUE (kg wood per m(3) water transpired) in adjacent nine-year-old Eucalyptus benthamii and P. taeda plantations with similar stand density and leaf area. Sap flux (F-d, g cm(-2) s(-1)) was measured continuously over one year using thermal dissipation probes. Stem biomass, stem growth, tree water use (E-t, L day(-1)), canopy transpiration per unit leaf area (E-1, mmol m(-2) s(-1)), and canopy stomatal conductance (G(s), mmol m(2) s(-1)) were quantified. Eucalyptus had higher daily Fd (196.6 g cm(-2) day(-1)) and mean daily E-t (24.6 L day(-1)) than pine (105.8 g cm(-2) day(-1), 15.2 L day(-1)). Eucalyptus exhibited a seasonally bimodal pattern in daily E-t that did not occur in pine. Monthly E-t was23-51% higher in Eucalyptus and differences between species were greatest in the spring and fall. Annual E-t was 32% higher in Eucalyptus (9.13 m(3) H2O year(-1)) than pine (5.79 m(3) H2O year(-1)). Annual stem biomass increment was greater in Eucalyptus (Eucalyptus: 22.9; pine: 11.8 kg tree(-1) year(-1)), and Eucalyptus had greater WUE (Eucalyptus: 2.86; pine 1.72 kg biomass m(-3) H2O year(-1)). Pine exhibited a lower seasonal minimum and higher seasonal maximum leaf area index (LAI). At low LAI, there was no significant difference between species in E-l or G(s); however, at maximum LAI, pine E-l and G(s) were 46 and 43%, respectively of rates observed in Eucalyptus. The species differed in G(5) response to vapor pressure deficit (D). At a similar reference G(s) (G(s),(ref) at D =1 kPa), pine exhibited greater stomatal sensitivity to D. These results suggest that (1) Eucalyptus trees had higher sap flux and total water use than pine, (2) Eucalyptus had greater stem growth and WUE, and (3) species differences in water use were driven primarily by differences in E-l and G(s). Published by Elsevier B.V.
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    Complementarity increases production in genetic mixture of loblolly pine (Pinus taeda L.) throughout planted range
    Carter, David R.; Albaugh, Timothy J.; Camo, Otávio C.; Grossman, Jake J.; Rubilar, Rafael A.; Sumnall, Matthew; Maier, Christopher A.; Cook, Rachel L.; Fox, Thomas R. (ESA, 2020-09-01)
    Increased genotypic diversity has been associated with increased biomass production in shortrotation tree species. Increasing the genotypic diversity of loblolly pine (Pinus taeda L.) in an attempt to increase productivity has not been extensively studied nor tested operationally or over long durations (i.e., >7 yr). We used genetically mixed and pure rows of loblolly pine growing throughout its planted range— Virginia, North Carolina, and Brazil—to test the effects of genetic mixing on volume production. There were no significant effects of mixing rows compared to pure rows on uniformity or mortality. Under intensive silviculture, individual trees planted in mixed rows had approximately 7% greater volume than those in the pure rows (estimate = 0.015 m³/tree ± 0.006) in the final year of measurement—year 8 for Brazil and year 10 for North Carolina and Virginia. Scaling the increase in individual stem volume under mixed rows and intensive silviculture to 1235 stems ha⁻¹ would equate to an additional 1.85 m³∙ha⁻¹∙yr⁻¹ in mean annual increment. Measuring the net biodiversity effect, our data suggest the positive growth response is driven by complementarity and not selection, meaning both genetic entries tend to grow larger when grown together. Additional trials are necessary to test the effects of mixing rows across large plots and to assess whether this increase is sustained throughout the rotation. If this increasing trend were to hold for intensively managed plantations, strategically mixing rows to increase productivity could be a valuable addition to an intensively managed plantation requiring relatively little added operational consideration to implement.
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    Crown architecture, crown leaf area distribution, and individual tree growth efficiency vary across site, genetic entry, and planting density
    Albaugh, Timothy J.; Maier, Christopher A.; Campoe, Otavio C.; Yanez, Marco A.; Carbaugh, Eric D.; Carter, David R.; Cook, Rachel L.; Rubilar, Rafael A.; Fox, Thomas R. (2020-02)
    We examined crown architecture and within crown leaf area distribution effects on Pinus taeda L. growth in North Carolina (NC), Virginia (VA), and Brazil (BR) to better understand why P. taeda can grow much better in Brazil than in the southeastern United States. The NC, VA, and BR sites were planted in 2009, 2009, and 2011, respectively. At all sites, we planted the same two genetic entries at 618, 1236, and 1854 trees ha(-1). In 2013, when trees were still open grown, the VA and NC sites had greater branch diameter (24%), branch number (14%), live crown length (44%), foliage mass (82%), and branch mass (91%), than the BR site. However, in 2017, after crown closure and when there was no significant difference in tree size, site did not significantly affect these crown variables. In 2013, site significantly affected absolute leaf area distribution, likely due to differences in live crown length and leaf area, such that there was more foliage at a given level in the crown at the VA and NC sites than at the BR site. In 2017, site was still a significant factor explaining leaf area distribution, although at this point, with crown closure and similar sized trees, there was more foliage at the BR site at a given level in the crown compared to the VA and NC sites. In 2013 and 2017, when including site, genetic entry, stand density, and leaf area distribution parameters as independent variables, site significantly affected individual tree growth efficiency, indicating that something other than leaf area distribution was influencing the site effect. Better BR P. taeda growth is likely due to a combination of factors, including leaf area distribution, crown architecture, and other factors that have been identified as influencing the site effect (heat sum), indicating that future work should include a modeling analysis to examine all known contributing factors.
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    Genetics by Nutrient Availability Interactions on Short-term Carbon Pools and Fluxes in Young Pinus taeda Plantations
    Tyree, Michael Christopher (Virginia Tech, 2008-09-11)
    The objective of this research was to determine how genetics and nutrient availability influence C cycling in intensively managed southern pine forests. This work consisted of a two year field and a complimentary one year greenhouse study each split into above- and below-ground pools and fluxes. Both the greenhouse and field experiment showed differences between contrasting genotypes in gas exchange parameters and C partitioning patterns, but genetic by nutrient availability interactions were only observed in the field. In the field study, some genotypes were better able to tolerate nutrient limitations due to more favorable canopy architecture and lower N demand. Our results clearly show that contrasting ideotypes have the potential to respond differently to differences in nutrient availability in terms of biomass partitioning, leaf physiology, and leaf biochemistry (Chapter 3). Both experiments showed short-term improvements to soil physical and chemical properties, which have been shown to correlate with higher site quality. In both the greenhouse and field experiment, we concluded that increased C loss by way of total soil CO₂ efflux (FS) made up only a small percent total C incorporated as LR. Short-term results led us to conclude that combining LR treatments and planting of genotypes with low nutrient demand or high nutrient use efficiency may increase soil organic matter (SOM) while avoiding loss of stem volume from nutrient immobilization. Data from our field study showed a strong genotype by soil amendment interaction for FS over all sampling dates with the relative importance of contributing factors (heterotrophic or root respiration) also changing (Chapter 5). Overall, logging residue incorporation increased total system C gain per ha more than did fertilization alone, but there were differences between genotypes planted (Chapter 6). Data from the field experiment show that although LR incorporation did not decrease overall net primary productivity, it did decrease biomass partitioning to merchantable products (main stem) depending on genotype. These data underline the importance of matching appropriate genotypes to specific site conditions and silvicultural prescriptions.
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    Growth and Physiological Responses to Fertilizer Application in Clonal Loblolly Pine
    Stovall, Jeremy Patrick (Virginia Tech, 2010-06-16)
    More than 20 million clonal loblolly pines have been planted throughout the southeastern United States. Fertilizer has been applied to more than 6.5 million hectares of plantations to alleviate deficiencies of nitrogen and phosphorus that limit growth. Because cloning loblolly pine in large numbers has only become possible in the last decade, it is unknown how clones may respond differently to fertilizer application. Growth, growth efficiency, and biomass partitioning responses to fertilizer application were investigated among 25 clones planted in the Virginia Piedmont. Closely related clones varied in their fertilizer stem volume responses, but not enough to be statistically significant (p = 0.11). Clones varied in growth efficiency and partitioning to individual tissues, but clone-by-fertilizer interactions were not observed. Clonal variability was observed in root morphology, and maximum rooting depth showed a significant clone-by-fertilizer interaction. Clones with rapid growth rates can be selected with a range of other desirable traits. Short-term (i.e. weeks) responses to fertilization are often inconsistent with long-term (i.e. years) responses, but are critical to understanding growth responses. We investigated carbon allocation in two full-sibling clones of loblolly pine under two levels of fertilizer application over four months in a greenhouse. Using monthly harvests of some trees and ecophysiological measurements throughout, we determined carbon allocation on a monthly scale. In response to fertilizer application, both clones reduced allocation belowground and increased allocation to foliage to some extent, increasing whole-canopy photosynthetic capacity. However, these changes in allocation were ephemeral. By the end of the experiment, root-shoot ratios were no longer significantly affected by fertilizer application. Clones had allocation patterns distinct from one another, with one allocating more belowground and the other allocating more to stem mass. While their overall growth responses to fertilizer application were similar, the physiological mechanisms that resulted in these responses were different between clones. Results of the two studies indicate that while fertilizer responses may not need to be included when testing clones for deployment, knowledge of the fertilizer responses of widely-deployed clones would offer forest managers opportunities to apply clone-specific precision-silvicultural systems to optimize growth rates and manage for a range of products.
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    Management intensity effects on growth and physiological responses of loblolly pine varieties and families growing in the Virginia Piedmont and North Carolina Coastal Plain of the United States
    Yanez Arce, Marco Aliro (Virginia Tech, 2014-08-18)
    Varietal forestry may increase the productivity of loblolly pine (Pinus taeda L.) in the Southern United Sates. However, the effects of these genetic x environment interactions are still poorly understood. In this study we examined the responses in growth, stand uniformity and leaf level physiology of loblolly pine clonal varieties and families to silvicultural intensity and site effects. We also looked for patterns in observed traits that were consistent between crown ideotypes. Two varieties of each crown ideotype (narrow vs broad crowns) and two families (controlled mass pollinated (CMP) and open pollinated (OP) family) were tested on the Virginia Piedmont (VA) and the North Carolina Coastal Plain (NC) under different silvicultural intensities (operational vs intensive), and planting density (617, 1235 and 1852 trees per hectare). Data were collected during the first four growing season after establishment. At NC, intensive silviculture increased crown-width, height and dbh by 33%, 14%, and 23%, respectively. At VA, intensive silviculture increased crown-width, height and dbh by 41%, 10%, and 23%, respectively. Intensive silviculture also increased slightly but significantly the stand uniformity of stem growth. However, the differences in productivity between silvicultural treatments were not explained by differences in leaf-level physiology. Across all treatments and sites the varieties generally grew faster than the OP family, but the differences were higher at VA. Varieties did not differ in stem growth, but the broadest crown variety had greater stand uniformity, photosynthetic rate (Asat), carbon isotope discrimination (∆¹³) and lower fascicle size than the OP family. None of the traits assessed inthis study was consistent within the ideotypes. Varieties classified in the same crown-ideotypes may respond differently to the environmental effects of site and silviculture, which reinforces the need of matching varietal forestry with precision silviculture to achieve gains in productivity.
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    Quantification and Physiology of Carbon Dynamics in Intensively Managed Loblolly Pine (Pinus taeda L.)
    Gough, Christopher Michael (Virginia Tech, 2003-07-28)
    Loblolly pine (Pinus taeda L.) occupies 13 million hectares in the United States and represents a critical component of the global carbon (C) cycle. Forest management alters C dynamics, affecting the C sequestration capacity of a site. Identifying drivers that influence C cycling, quantifying C fluxes, and determining how management alters processes involved in C cycling will allow for an understanding of C sequestration capacity in managed forests. Objectives of the first study included (1) investigating environmental, soil C, root, and stand influences on soil CO2 efflux on the South Carolina coastal plain and (2) quantifying soil CO2 efflux over a rotation in loblolly pine stands located on the South Carolina coastal plain and the Virginia piedmont. In relation to the first objective, temporal variation in soil CO2 efflux was most highly related to soil temperature. Spatial and temporal variability in soil CO2 efflux was weakly related to soil C and root biomass, and not related to coarse woody debris, stand age, stand volume, or site index [Chapter 2]. Soil CO2 efflux was not related to stand age on the South Carolina sites while efflux was positively related to age on the Virginia sites. Cumulative soil C efflux on the South Carolina sites over 20 years is an estimated 278.6 Mg C/ha compared with an estimated 210.9 Mg C/ha on the Virginia sites [Chapter 3]. Objectives of the second study were (1) to investigate short-term effects of fertilization on processes permitting enhanced growth in loblolly pine and (2) to determine the short-term effects of fertilization on autotrophic, heterotrophic, and soil respiration. Major results from the study include the finding that fertilization caused a transient rise in photosynthetic capacity, which paralleled changes in foliar nitrogen. Leaf area accumulation and enhanced growth following fertilization was partly due to enhanced C fixation capacity [Chapter 4]. Fertilization altered the contribution of autotrophic and heterotrophic respiration to total soil CO2 efflux. Enhanced specific root respiration was short-lived while suppressed microbial respiration following fertilization was maintained over the course of the nearly 200-day study. Respiring root biomass growth increased total soil respiration over time [Chapter 5].
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    Soil Respiration and Decomposition Dynamics of Loblolly Pine (Pinus taeda L.) Plantations in the Virginia Piedmont
    McElligott, Kristin Mae (Virginia Tech, 2017-02-24)
    Forests of the southeastern U.S. play an important role in meeting the increasing demand for forest products, and represent an important carbon (C) sink that can be managed as a potential tool for mitigating atmospheric CO2 concentrations and global climate change. However, realizing this potential depends on full accounting of the ecosystem carbon (C) budget. The separate evaluation of root-derived, autotrophic (RA) and microbially-derived heterotrophic (RH) soil respiration in response to management and climate change is important, as environmental and ecological factors often differentially affect these components, and RH can be weighed against net primary productivity (NPP) to estimate the C sink or source status of forest ecosystems. The objective of this research was to improve the quantitative and mechanistic understanding of soil respiratory fluxes in managed loblolly pine (Pinus taeda L.) plantations of the southeastern U.S. To achieve this overall objective, three studies were implemented to: 1) estimate the proportion and seasonality of RH:RS in four stand age classes, and identify relationships between RH:RS and stand characteristics 2) evaluate the effects of forest nutrient management and throughfall reduction on factors that influence RH and decomposition dynamics, including litter quality, microbial biomass, and enzyme activity and 3) evaluate the sensitivity of sources of RH (mineral soil-derived heterotrophic respiration; RHM, and leaf litter-derived heterotrophic respiration; RHL) to varying soil and litter water content over the course of a dry down event, and assess whether fertilization influences RH. Stand age and measurement season each had a significant effect on RH:RS (P < 0.001), but there were no interactive effects (P = 0.202). Mean RH:RS during the 12-month study declined with stand age, and were 0.82, 0.73, 0.59, and 0.50 for 3-year-old, 9-year-old, 18- year-old, and 25-year-old stands, respectively. Across all age classes, the winter season had the highest mean RH:RS of 0.85 while summer had the lowest of 0.55. Additionally, there were highly significant (P < 0.001) and strong (r > 0.5) correlations between RH:RS and peak LAI, stem volume, and understory biomass. Fertilization improved litter quality by significantly decreasing lignin:N and lignin:P ratios, caused a shift in extracellular enzyme activity from mineral soil N- and P-acquiring enzyme activity to litter C-acquiring enzyme activity, and increased microbial biomass pools. Throughfall reduction decreased litter quality by increasing lignin:N and lignin:P, but also increased C-acquiring enzyme activity. RHL was more sensitive to water content than RHM, and increased linearly with increasing litter water content (R2 = 0.89). The contribution of RHL to RH was greatest immediately following the wetting event, and decreased rapidly to near-zero between three – 10 days. RHM also had a strong relationship with soil water content (R2 = 0.62), but took between 200 – 233 days to attain near-zero RHM rates. Fertilization had no effect on RHM (P = 0.657), but significantly suppressed RHL rates after the wetting event (P < 0.009). This research provides estimates of RH:RS in managed loblolly pine systems that can be used to improve regional ecosystem C modeling efforts, and demonstrates the need to consider the impact of stand age and seasonal patterns to identify the point at which plantations switch from functioning as C sources to C sinks. Additionally, it demonstrates that the controls over RH are dynamic and influenced in the short-term by fertilization and changed precipitation regimes, with the greatest impact on properties affecting litter RH compared to mineral soil. Future research should work to improve the mechanistic understanding of the seasonal and spatial variability of RH and related controlling biotic and abiotic parameters to remedy the variability in existing RS and ecosystem C models. Understanding how management and climate change may impact factors that control RH will ultimately improve our understanding of what drives changes in forest C fluxes.