Chamaecyparis Thyoides Research Articles

Unexpectedly strong heat stress induction of monoterpene, methylbutenol, and other volatile emissions for conifers in the cypress family (Cupressaceae)

We investigated the biogenic volatile organic compound (BVOC) emission rates and composition of Cupressaceae species and how the emissions change in response to moderate warming and more severe heat stress. A total of 8 species from 7 distinct Cupressaceae genera were targeted in this study and exposed to laboratory-simulated heatwaves. Each plant was enclosed in a temperature-controlled glass chamber and allowed to equilibrate at 30 °C for 24 h. The temperature was then increased stepwise from 33 °C to 43 °C in 2 °C increments, with each step lasting 2 h, and was finally kept at 45 °C for 12 h. The BVOC emissions were measured periodically using an automated air sampler coupled to a gas chromatograph.Most of the sampled Cupressaceae species (6 out of 8) were low BVOC emitters (<0.3 μgC g−1 h−1) at 30 °C. However, the BVOC emissions of all 8 species increased strongly with temperature, and in most species (5 out of 8), the emissions continued to increase with longer exposure times to heat stress. The largest increase was observed in Thuja occidentalis and Chamaecyparis thyoides, which reached maximum emissions of 350 and 190 μgC g−1 h−1, respectively. Of the different BVOCs, monoterpenes responded most strongly to heat stress, with Q10 temperature coefficients typically ranging between 7.6 and 22, which were significantly greater than the model-predicted value of 2.7. Other BVOCs including sesquiterpenes, C9 aromatics (only detected in Calocedrus decurrens), methylbutenols, and other C5 oxygenates were also induced by heat stress, but generally at a lower magnitude than monoterpenes.Our results indicate that Cupressaceae are a large but typically dormant source of reactive volatile hydrocarbons (mostly monoterpenes) whose emissions can be activated by heat stress. This phenomenon could have important implications for ozone and aerosol formation, air quality, and human health, particularly in urban areas that are prone to heatwaves.

Mapping an Indicator Species of Sea-Level Rise along the Forest–Marsh Ecotone

Atlantic White Cedar (Chamaecyparis thyoides) (AWC) anchors a globally threatened ecosystem that is being impacted by climate change, as these trees are vulnerable to hurricane events, sea-level rises, and increasing salinity at the forest–marsh ecotone. In this study, we determined the current amount and distribution of AWC in an area that is experiencing sea-level rises that are higher than the global average rate. We used a combination of a field investigation and aerial photo interpretation to identify known locations of AWC, then integrated Sentinel-1 and 2A satellite data with abiotic variables into a species distribution model. We developed a spectral signature of AWC to aid in our understanding of phenology differences from nearby species groups. The selected model had an out-of-bag error of 7.2%, and 8 of the 11 variables retained in the final model were derived from remotely sensed data, highlighting the importance of including temporal data to exploit divergent phenology. Model predictions were strong in live AWC stands and, accurately, did not predict live AWC in stands that experienced high levels of mortality after Hurricane Sandy. The model presented in this study provides high utility for AWC management and tracking mortality dynamics within stands after disturbances such as hurricanes.

The effects of forest composition and management on evapotranspiration in the New Jersey Pinelands

Forests deliver contrasting ecosystem services in relation to water, both provisioning it through filtration and recharge, and consuming it through evapotranspiration. Understanding forest evapotranspiration is critical for landscapes managed in part for the social benefits of their water provisioning ecosystem services. We used the flux disaggregation algorithm for the Atmosphere-Land Exchange Inverse model (DisALEXI) with remotely sensed data to characterize landscape-scale evapotranspiration at 30-m spatial resolution over the forested coastal plain Pinelands of southern New Jersey, USA. We examined changes in evapotranspiration due to forest compositional and cover differences, then evaluated the effects of three common management actions (thinning, seed tree regeneration, and prescribed burning) on stand evapotranspiration. Among various forest compositions, upland oak forests had the lowest annual evapotranspiration, while Atlantic white cedar had the highest. In uplands, increasing proportions of conifers increased evapotranspiration, as did increased canopy cover in conifer stands. Seed tree harvests reduced evapotranspiration for about 13 years, while thinning reduced forest water use for approximately six years. Prescribed fires had variable effects, but their typical application did not reduce evapotranspiration for a complete growing season. Our research can help to inform models and decision-making around forests and landscape water yield.

Roles of climatic and anthropogenic factors in shaping Holocene vegetation and fire regimes in Great Dismal Swamp, eastern USA

The Great Dismal Swamp wetland, spanning >400 km2 along the Virginia and North Carolina border, was shaped by a complex combination of geomorphic, climatic, and anthropogenic forcings during the last 14,000 years. Pollen, macrofossils, charcoal, and physical properties from sediment cores at seven sites provide a detailed record of the spatial heterogeneity of the wetland and the roles played by natural hydrologic variability, wildfire, and human modification of drainage in shaping vegetation and habitats. Cold-temperate forests occupied regional uplands from at least 13.5–10.3 cal ka BP. Marshes dominated by grasses and other herbaceous taxa began developing along low-elevation streams as early as 10.3 cal ka BP, resulting in accumulation of organic silts. Long-hydroperiod, peat accumulating marshes, with abundant floating aquatic plants, developed as early as 9.6 cal ka BP, as rapid rates of sea-level rise elevated the water table and facilitated wetland development and peat accumulation along stream courses. By the mid-Holocene (c. 7–6.5 cal ka BP), when local sea-level rise began slowing and reached about 12–15 m below present, shorter hydroperiod, peat-accumulating marshes dominated the landscape, with increased wildfire activity. Great Dismal Swamp vegetation shifted from marshes to peat-accumulating forested wetlands by c. 3.7 cal ka BP; these were dominated by varying combinations of Nyssa (tupelo), Taxodium (cypress), and Chamaecyparis thyoides (Atlantic white cedar). Wildfires were infrequent during this time, and the forested wetlands persisted, with minor compositional changes related to climate-driven fluctuations in stream flow, until colonial ditching and logging began in the swamp during the late 18th century. These activities decreased cypress and cedar populations, and, by the mid-20th century, expanded ditching resulted in even drier conditions and expansion of maple-gum (dominated by Acer and Liquidambar), and pine-pocosin (dominated by Pinus) forests. The distribution of these forests differs from that of the late Holocene and represents a fundamental shift in hydrology, peat structure, vegetation, and fire regime due to landscape alterations of the last few centuries.

Geographic Variation in Survival and Growth of Atlantic White-Cedar (Chamaecyparis Thyoides [L.] B.S.P.): Implications for Artificial Regeneration of a Declining Species

Abstract Atlantic white-cedar (Chamaecyparis thyoides [L.] B.S.P.; AWC), a wetland tree species native to the eastern United States, is declining rangewide. This decline has stimulated interest in restoring AWC in parts of its range. However, restoration could benefit from more research on this species, especially that focus on where to source seedlings for artificial reforestation. This study presents results out to years 18–20 from a southern New Jersey common garden established in the early 2000s as part of the first rangewide provenance planting of AWC. The goal of this research was to expand our understanding of intraspecific variation in AWC linked to the geographic origin of genetic sources. Results indicated that genotype performance was linked to their geographic origin and that local sources were among the top performers when taking all metrics into consideration (e.g., survival, height, basal area). Top-performing provenances were sourced within plus or minus two decimal degrees latitude of the planting site. Although local sources remain suitable for artificial regeneration of this species in southern New Jersey, nearby southern sources could be deployed to achieve out-planting success and conservation of this imperiled species in a warming climate. We hope this work will inform AWC restoration efforts and bring visibility to this declining wetland species.

Atlantic White-Cedar (Chamaecyparis thyoides[L.] B.S.P.) Response Post-Hurricane Disturbance

AbstractAtlantic white-cedar (Chamaecyparis thyoides [L.] B.S.P.) is considered critically imperiled across much of its range. This species occurs in freshwater swamps, rarely further inland than 160 km from the Atlantic or Gulf Coasts and is susceptible to several natural and anthropogenic disturbances (i.e., tropical cyclones, fire, saltwater inundation, overharvesting). As the frequency and intensity of tropical storms increase, understanding the regeneration of Atlantic white-cedar will be critical to its conservation. This study evaluated the regeneration of Atlantic white-cedar 14 years after Hurricane Katrina. All Atlantic white-cedar ≥2.5 cm at breast height were inventoried within an ~9 ha study area located within Grand Bay National Wildlife Refuge in Jackson County, Mississippi, USA. Additionally, the competing woody vegetation was surveyed. After Hurricane Katrina, the number of Atlantic white-cedar stems increased by 191%. This long-term study provides the first analysis of Atlantic white-cedar regeneration post–tropical cyclone disturbance within the Gulf Coast and allows conservationists a better understanding of the effects of tropical cyclone disturbance on this species.

An Analysis of Atlantic White Cedar (Chamaecyparis thyoides (L.) B.S.P.) Tree Rings as Indicators of Ghost Forest Development in a Globally Threatened Ecosystem

Atlantic White Cedar (AWC) swamps are a globally threatened type of wetland ecosystem and are a new form of ghost forest in the mid-Atlantic region of the US. Hydrogeomorphic regimes foster peat formation, resulting in unique biodiversity and carbon sequestration services. Our sites include regimes that are exposed to sea-level rise and storm-driven seawater intrusion, yet other sites are protected by higher elevations. In this study, we evaluated climatic variables to discern differences in tree ring formation as an indicator of growth among nine stands including micro-tidal, oligohaline sites as well as other protected areas which served as a control. Standard dendrochronological techniques were used, and series were divided into two sub-chronologies, 1895 to 1971 (early) and 1972 to 2018 (recent). AWC growth in response to precipitation parameters, e.g., Palmer Drought Severity Index (PDSI), were largely non-significant but were somewhat reversed among sub-chronologies. Early correlations were primarily negatively correlated with PDSI, while recent correlations were mostly positive, which suggests that even though inundation may reduce photosynthate availability for growth, precipitation has begun to increase growth by alleviating osmotic and toxic stresses associated with seawater. Analysis of climatic variables and tree growth at the reference site found that other anthropogenic stressors associated with ditching exert a greater influence. Hurricane impacts on tree growth exhibited no lasting negative effects; however, an AWC ghost forest report from New Jersey connected mortality to a hurricane. Hydrogeomorphic regimes may delay rather than eliminate risks associated with sea-level rise and storm-driven seawater.

Ensemble Species Distribution Model Identifies Survey Opportunities for At-Risk Bearded Beaksedge (Rhynchospora crinipes) in the Southeastern United States

Locating additional occurrences of at-risk species can inform assessments of their status and conservation needs (including potential legal protections). The perennial bearded beaksedge (Rhynchospora crinipes) ranges from Mississippi to North Carolina, but known occurrences are limited. Because of the species' apparent rarity, a model to identify areas with suitable habitat conditions for the species will allow conservationists to effectively prioritize and allocate scarce surveying resources. We used known occurrence records, a suite of environmental datasets, and four species distribution modeling techniques (generalized additive, GAM; maximum entropy, MaxEnt; generalized boosted, GBM; and weighted ensemble) to generate maps to inform surveys for R. crinipes. The ensemble approach improved predictive performance (AUC-PR = 0.95) compared to other techniques (individual model AUC-PR ranged from 0.7 to 0.8). We also obtained quantitative insights on the species' habitat relationships, including the likelihood of R. crinipes's presence near Atlantic white cedar (Chamaecyparis thyoides) habitat and floodplains, which is consistent with prior field observations. The ensemble model indicated that 3.6% of the study area could be suitable habitat, but only 0.38% had high suitability. Small stream riparian habitats and Atlantic swamp forests in Alabama, Florida, and Georgia had the highest proportion of suitable areas. Prioritizing surveys in areas with model-indicated high habitat suitability is expected to reveal additional R. crinipes occurrences. We suggest surveying efforts for other at-risk species may benefit from using an ensemble modeling approach to identify and prioritize survey areas and improve ecological knowledge of these species.

Impact of Channel Dredging and Straightening in an Atlantic White Cedar (Chamaecyparis thyoides L. (B.S.P.)) Freshwater Tidal Wetland

Stotts, S.; Callahan, J., and Gulledge, O., 2021. Impact of channel dredging and straightening in an Atlantic white cedar (Chamaecyparis thyoides L. (B.S.P.)) freshwater tidal wetland. Journal of Coastal Research, 37(5), 973–986. Coconut Creek (Florida), ISSN 0749-0208. Once prominent up the eastern coast of the United States, freshwater wetlands with Atlantic white cedar (AWC; Chamaecyparis thyoides L. (B.S.P.)) are now vanishing due to saltwater intrusion and anthropogenic landscape alterations. This study utilizes a historic, anthropogenic disturbance to provide insight into the AWC response to salinization. A major straightening and dredging project in the 1920s, including 16 oxbow cuts, allowed brackish water to move upstream in the St. Jones River in Dover, Delaware, leading to the die-off of an AWC swamp. The sampled AWC experienced climate change, storms, hydrologic alterations, and sea-level rise. Annual ring width and suppression event chronologies were developed from dead AWC and were compared to groupings of climate variables in the predisturbance (1895–1920) and postdisturbance (1928–1958) periods. Results of the dendrochronological analysis indicate that the AWC in this study died at an average age of 49.3 years, earlier than typically expected for such species. After the straightening and dredging, the AWC experienced changes in growth response to temperature while suppression events became positively correlated with elevated temperature (p = 0.024) and high precipitation (p = 0.019). The system also showed signs of becoming more sensitive to storm events in the postdisturbance period.

Impact of control structures on hydrologic restoration within the Great Dismal Swamp

The Great Dismal Swamp (GDS) is a 45,000-ha state and federally protected Coastal Plain peatland located on the border of North Carolina and Virginia that contains stands of Bald cypress and the globally threatened Atlantic white cedar. Centuries of drainage and logging have substantially altered the hydrology of the GDS, negatively affecting its ecosystem structure and function. To restore a seasonally flooded, saturated hydrologic regime to portions of the swamp, adjustable water control structures (WCS) were installed at strategic locations within existing drainage ditches. The objective of this study was to determine if the installation of the WCSs significantly altered the hydropatterns of two target restoration areas, resulting in hydrologic conditions comparable to nearby reference sites with desired forest communities. The water table (WT) was monitored for three years prior to WCS installation (pre-WCS) and three years after WCS installation (post-WCS). Comparison of WT data from the pre and post-WCS periods, using jurisdictional wetland criteria and empirical cumulative distribution functions (ECDFs), indicated increased saturated conditions within the target restoration areas following installation of the WCS. Paired Before-After Control-Impact (BACIP) statistical analysis revealed the WCS installation had a significant positive impact on WT levels in the target restoration areas relative to the reference sites. Hydrologic restoration will aid the effort to restore target forest communities within the swamp, reduce fire susceptibility, prevent peat oxidation, maintain carbon storage, and reduce non-target vegetation competition.

Monitoring soil carbon flux with in-situ measurements and satellite observations in a forested region

Carbon dioxide (CO2) flux plays a key role in the energy balance of ecosystems and effective monitor CO2 flux from soil at both large scale and high temporal resolution remains a critical scientific problem of soil science. To address this scientific problem, this study tested a novel model to estimate CO2 flux from soil with highly dense vegetation cover. In contrast to previous approaches, the developed model monitored daily CO2 flux at both high spatial and temporal resolutions. This model is applicable for different forest types by fusing the daily TERRA Moderate Resolution Imaging Spectroradiometer (MODIS), Land Remote Sensing Satellite (Landsat) measurements, and monthly in-situ CO2 flux measurements collected by non-permanent chambers in the Great Dismal Swamp (GDS), the U.S. Then, daily vegetation index and surface soil temperature were estimated at high spatial resolution, and the CO2 flux was retrieved through a semi-empirical model. Two-year ground observations in the GDS were used to train and validate the model. Over the GDS area, the validation results of the retrieved CO2 flux had a coefficient of determination (R2) of 0.47, and a root mean square error (RMSE) of 1.25e + 05 μg CO2/m2/h. Further analysis showed that the performance of the proposed method varied slightly with forest types. The difference between R2 was less than 0.07 and the difference between RMSE was less than 0.08e + 05 μg CO2/m2/h. The GDS has three main forest types: maple gum (Acer rubrum and Nyssa sylvatica), Atlantic white cedar (Chamaecyparis thyoides), and pine pocosin (Pinus serotina). For the maple-gum, the R2 was 0.51, and the RMSE was 1.14e + 05 μg CO2/m2/h. For Atlantic white cedar, the R2 was 0.62, and the RMSE was 1.15e + 05 μg CO2/m2/h. For pine pocosin, the R2 was 0.44, and the RMSE was 1.07e + 05 μg CO2/m2/h. The proposed method enables estimation of CO2 flux within forested areas, and forest type affects the monitoring results.

Surface soil temperature seasonal variation estimation in a forested area using combined satellite observations and in-situ measurements

Surface soil temperature is the soil temperature from the surface to 10 cm in depth. Surface soil temperature plays a significant role in agricultural drought monitoring, ecosystem energy transfer modeling, and global carbon cycle evaluation. Studies have been proposed to estimate surface soil temperature, but surface soil temperature monitoring within forested areas still poses a significant challenge. In this study, we proposed a surface soil temperature retrieval method using combined satellite observations and in-situ measurements for the Great Dismal Swamp (GDS). The GDS is a U.S. protected area managed and protected by the U.S. Fish and Wildlife Service. It is located along the boundary of Virginia and North Carolina, with maple gum, Atlantic white cedar, and pine pocosin as the main forest cover types. Ground-based surface soil temperature measurements were collected for these forest types from May 2015 to April 2017. Both the Land Remote Sensing Satellite (Landsat) Thermal Infrared Sensor (TIRS) and the Moderate Resolution Imaging Spectroradiometer (MODIS) carry two thermal infrared (TIR) channels. The TIR channels with similar corresponding wavelengths were first fused using an improved fusing model to generate high resolution TIR measurements. Then the enterprise algorithm was applied to calculate land surface temperature (LST) from the fused TIR bands. An improved soil temperature retrieval method was applied to generate surface soil temperature based on LST and vegetation index (VI) within the study area for the three forest types. In-situ measurements were used to build the surface soil temperature retrieval method, and results were then validated. The normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI) were integrated separately as VIs in the model to monitor surface soil temperature. The R2 for retrieved surface soil temperature through satellite observations was 0.76, and the RMSE was 1.96 ℃ when NDVI was integrated in the model; the R2 was 0.78, and the RMSE was 1.85 ℃ when EVI was used.

A Framework for Determining Population-Level Vulnerability to Climate: Evidence for Growth Hysteresis in Chamaecyparis thyoides Along Its Contiguous Latitudinal Distribution

The impact of ecological and climatological factors on individual organisms over time and space is inherently complex and creates substantial uncertainty about how climate change will influence the global biosphere. To understand some of this complexity, we investigated the factors influencing individual growth of Chamaecyparis thyoides over 61 years within 18 populations across the ca 1500 km and 11 degrees of latitude. We then applied a vulnerability framework to understand how the variability of tree growth response to climate varies between populations and regions across our network. Surprisingly, we found the growth of trees in the central portion of our network responded more synchronously to warming and drought than trees in the southern end of our network, suggesting greater vulnerability in the central populations with continued warming. Our analyses and framework approach revealed substantial complexity in growth responses to climate within and between populations. We found potential resiliency within all populations, but higher inter-population than intra-population variability in response to climate. We found that latitude was an important proxy for the growth response to temperatures during the non-growing season and spring, but that ecosystem structure can modify the growth response and vulnerability to drought during the summer. The range of growth responses to warming is greater in the southern populations than in more northernly populations. This asymmetrical distribution of growth response across our study network provides evidence for a kind of ecological hysteresis, more southerly populations could be more resilient with warming. Despite the fact that this species primarily lives in wetlands, we found drought stress to be an important constraint on growth. Our study and analyses help to explain the disparities between forecasts of how climatic change might impact tree species and ecosystems over space.

Multivariate Climate Field Reconstructions Using Tree Rings for the Northeastern United States

AbstractHigh‐resolution paleoclimate records are essential for improving our understanding of internal variability and the detection and attribution of forced climate system responses. The densely populated northeastern United States is at risk from increasing temperatures, severe droughts, and extreme precipitation, but the region has limited annual and seasonal‐resolution paleoclimate records beyond the instrumental record. Chamaecyparis thyoides, L. (B.S.P.), Atlantic white cedar, a wetland conifer found within 200 km of the Atlantic coastline of the United States, is a promising tree‐ring proxy that can fill in these data gaps. Here, we develop and analyze a new network of Atlantic white cedar tree‐ring chronologies across the northeastern United States and demonstrate that site selection is important for regional paleoclimate reconstructions. Ring width variability reflects winter through summer temperatures at inland and hydrologically stable sites in the northernmost section of the species' range. Ombrotrophic sites along the coast record hydrological signals and correlate with growing season precipitation. We demonstrate skillful regional climate field reconstructions for the last several centuries and show the increased skill from incorporating our moisture sensitive sites into broad‐scale products like the North American Drought Atlas. This comprehensive understanding of the species' climate responses leads to a tree‐ring network that provides the long‐term multivariate climate context at multidecadal and centennial time scales for the large‐scale ocean‐atmospheric processes that influence the climate of the region. We use this network to examine the covariance of temperature and drought across the New England area over the past two centuries.

A late Holocene subfossil Atlantic white cedar tree-ring chronology from the northeastern United States

Tree-rings provide precise annually dated climate information, but their application can be limited by the relatively short lifespan of many trees. To overcome this limitation, tree-ring records can be extended over longer time periods by connecting living trees with older “sub-fossil” trees, which can provide information on longer timescales throughout the Holocene. These long chronologies are proxy records of past climate, provide precise chronological information for extreme events, and give insight into the range of natural climate variability prior to the instrumental period. In the densely populated northeastern United States, few tree-ring records are longer than 500 years, and there are no millennial-length tree-ring chronologies for the region. Here, we use a combination of standard dendrochronological and radiocarbon techniques, including use of the 774 CE radiocarbon excursion, to generate an absolutely dated 2500 year-long tree ring record from living, archaeological, and subfossil Atlantic white cedar (Chamaecyparis thyoides) found in the coastal northeastern United States. Our chronology demonstrates the potential to develop multi-millennial Chamaecyparis thyoides tree-ring records to address previously unanswered questions regarding late Holocene hydroclimate, extreme events, and temperature variability in New England.

Carbon Chemistry of Intact Versus Chronically Drained Peatlands in the Southeastern USA

AbstractThe Great Dismal Swamp National Wildlife Refuge (GDS) is a large temperate swamp in Virginia/North Carolina, USA with peat soils historically resistant to microbial decomposition. However, this peatland has been subject to ~200 years of disturbance during which extensive drainage, fire suppression, and widespread logging have increased decomposition and dramatically decreased the distribution of Atlantic white cedar (AWC). The purpose of this study was to determine the impact of long‐term drainage and AWC loss on the carbon chemistry of GDS peats. Peat cores were collected from three drained GDS vegetation communities (pocosin, AWC, and red maple‐black gum) and compared to cores collected from an intact, undrained AWC peatland at the Alligator River National Wildlife Refuge (AR) in North Carolina. The AR peats had higher lignin content in the deeper peat intervals, and lignin content and percent organic carbon were largely invariant with depth compared to the GDS peats. The concentrations of syringyl group phenols were greater in the surface layers of GDS peats, likely reflecting the selective removal of AWC and transition from gymnosperms to angiosperms. Acid to aldehyde ratios for vanillyl and syringyl group phenols indicated that the GDS peats were more decomposed, particularly at depth, and that this occurred under aerobic conditions. Moreover, solid‐state 13C NMR confirmed a coincident loss of carbohydrates and increase in recalcitrant by‐products of carbohydrate degradation with depth. These data indicate that long‐term drainage has accelerated the decomposition of peat at the GDS, reducing the capacity and stability of the carbon sink.

Growth Rates of Atlantic White Cedar Depend on Hydrologic Regimes at Two Time Scales

Atlantic white cedar (AWC) stands form peat substrates in association with a seasonally flooded, saturated hydrologic regime. Less than 2% of the AWC swamp land area present during the pre-colonial era remains, and most of the current area now exhibits a temporarily flooded hydrologic regime. The purpose of this study was to quantify radial AWC growth at time scales that were cumulative (throughout ~60-year lifespans) and annual to clarify the relationship with hydrologic regime and climate in drained and undrained stands. Two 60-year-old stands having either drained or undrained conditions were selected in national wildlife refuges in Virginia and North Carolina, USA. Shallow groundwater wells fitted with continuous recorders measured depth-to-water-table during the 1999 calendar year to verify hydrologic regimes, and tree ring widths were evaluated from 54 trees per site. Cumulative time scale growth of individual tree stems was strongly suppressed by high water tables in the undrained stand. Annual growth rates among climate variables also diverged such that wetter months were positively correlated with tree ring width in the drained stand. Results suggest that AWC tree ring growth patterns can provide natural resource managers with insights into historic hydrologic conditions that influence ecosystem services and biodiversity.

Carbon Dioxide Emissions and Methane Flux from Forested Wetland Soils of the Great Dismal Swamp, USA

The Great Dismal Swamp, a freshwater forested peatland, has accumulated massive amounts of soil carbon since the postglacial period. Logging and draining have severely altered the hydrology and forest composition, leading to drier soils, accelerated oxidation, and vulnerability to disturbance. The once dominant Atlantic white cedar, cypress, and pocosin forest types are now fragmented, resulting in maple-gum forest communities replacing over half the remaining area. In order to determine the effect of environmental variabes on carbon emissions, this study observes 2 years of CO2 and CH4 soil flux, which will also help inform future management decisions. Soil emissions were measured using opaque, non-permanent chambers set into the soil. As soil moisture increased by 1 unit of soil moisture content, CH4 flux increased by 457 μg CH4–C/m2/h. As soil temperature increased by 1 °C, CO2 emissions increased by 5109 μg CO2–C/m2/h. The area of Atlantic white cedar in the study boundary has an average yearly flux of 8.6 metric tons (t) of carbon from CH4 and 3270 t of carbon from CO2; maple-gum has an average yearly flux of 923 t of carbon from CH4 and 59,843 t of carbon from CO2; pocosin has an average yearly flux of 431 t of carbon from CH4 and 15,899 t of carbon from CO2. Total Cha−1year−1 ranged from 1845 kg of Cha−1year−1 in maple-gum to 2024 kg Cha−1year−1 for Atlantic white cedar. These results show that soil carbon gas flux depends on soil moisture, temperature and forest type, which are affected by anthropogenic activities.

The potential to strengthen temperature reconstructions in ecoregions with limited tree line using a multispecies approach

AbstractTree-ring reconstructions of temperature often target trees at altitudinal or latitudinal tree line where annual growth is broadly expected to be limited by and respond to temperature variability. Based on this principal, regions with sparse tree line would seem to be restricted in their potential to reconstruct past temperatures. In the northeastern United States, there are only two published temperature reconstructions. Previous work in the region reconstructing moisture availability, however, has shown that using a greater diversity of species can improve reconstruction model skill. Here, we use a network of 228 tree-ring records composed of 29 species to test the hypothesis that an increase in species diversity among the pool of predictors improves reconstructions of past temperatures. Chamaecyparis thyoides alone explained 31% of the variability in observed cool-season minimum temperatures, but a multispecies model increased the explained variance to 44%. Liriodendron tulipifera, a species not previously used for temperature reconstructions, explained a similar amount of variance as Chamaecyparis thyoides (12.9% and 20.8%, respectively). Increasing the species diversity of tree proxies has the potential for improving reconstruction of paleotemperatures in regions lacking latitudinal or elevational tree lines provided that long-lived hardwood records can be located.

Late growing season carbon subsidy in native gymnosperms in a northern temperate forest.

Evergreen tree species that maintain positive carbon balance during the late growing season may subsidize extra carbon in a mixed forest. To test this concept of 'carbon subsidy', leaf gas exchange characteristics and related leaf traits were measured for three gymnosperm evergreen species (Chamaecyparis thyoides, Tsuga canadensis and Pinus strobus) native to the oak-hickory deciduous forest in northeast USA from March (early Spring) to October (late Autumn) in a single year. All three species were photosynthetically active in Autumn. During the Summer-Autumn transition, photosynthetic capacity (Amax) of T. canadensis and P. strobus increased (T-test, P < 0.001) and was maintained in C. thyoides (T-test, P = 0.49), while dark respiration at 20 °C (Rn) and its thermal sensitivity were generally unchanged for all species (one-way ANOVA, P > 0.05). In Autumn, reductions in mitochondrial respiration rate in the daylight (RL) and the ratio of RL to Rn (RL/Rn) were observed in P. strobus (46.3% and 44.0% compared to Summer, respectively). Collectively, these physiological adjustments resulted in higher ratios of photosynthesis to respiration (A/Rnand A/RL) in Autumn for all species. Across season, photosynthetic biochemistry and respiratory variables were not correlated with prevailing growth temperature. Physiological adjustments allowed all three gymnosperm species to maintain positive carbon balance into late Autumn, suggesting that gymnosperm evergreens may benefit from Autumn warming trends relative to deciduous trees that have already lost their leaves.