Research Items (80)
Many currently forested areas in the southern Appalachians were harvested in the early 1900s and cleared for agriculture or pasture, but have since been abandoned and reverted to forest (old-field succession). Land-use and land-cover changes such as these may have altered the timing and quantity of water yield (Q). We examined 80 years of streamflow and vegetation data in an experimental watershed that underwent forest–grass–forest conversion (i.e., old-field succession treatment). We hypothesized that changes in forest species composition and water use would largely explain long-term changes in Q. Aboveground biomass was comparable among watersheds before the treatment (208.3 Mg ha−1), and again after 45 years of forest regeneration (217.9 Mg ha−1). However, management practices in the treatment watershed altered resulting species composition compared to the reference watershed. Evapotranspiration (ET) and Q in the treatment watershed recovered to pretreatment levels after 9 years of abandonment, then Q became less (averaging 5.4 % less) and ET more (averaging 4.5 % more) than expected after the 10th year up to the present day. We demonstrate that the decline in Q and corresponding increase in ET could be explained by the shift in major forest species from predominantly Quercus and Carya before treatment to predominantly Liriodendron and Acer through old-field succession. The annual change in Q can be attributed to changes in seasonal Q. The greatest management effect on monthly Q occurred during the wettest (i.e., above median Q) growing-season months, when Q was significantly lower than expected. In the dormant season, monthly Q was higher than expected during the wettest months.
Many currently forested areas in the southern Appalachians were harvested in the early 1900s and cleared for agriculture or pasture, but have since been abandoned and reverted to forest (old-field succession). Land use and land cover changes such as these may have altered the timing and quantity of water yield (Q). We examined 80 years of streamflow and vegetation data in an experimental watershed that underwent forest-grass-forest conversion (i.e., old-field succession treatment). We hypothesized that changes in forest species composition and water use would largely explain long-term changes in Q. Aboveground biomass was comparable among watersheds before the treatment (208.3 Mg ha−1), and again after 45 years of forest regeneration (217.9 Mg ha−1). However, management practices in the treatment watershed altered resulting species composition compared to the reference watershed. Evapotranspiration (ET) and Q in the treatment watershed recovered to pretreatment levels after nine years of abandonment, then Q became less (averaging 5.4 % less) and ET more (averaging 3.4 % more) than expected after the 10th year up through present day. We demonstrate that the decline in Q and corresponding increase in ET could be explained by the shift in major forest species from predominantly Quercus and Carya before treatment to predominantly Liriodendron and Acer through old-field succession. The annual change in Q can be attributed to changes in seasonal Q. The greatest management effect on monthly Q occurred during the wettest (i.e., above median Q) growing season months when Q was significantly lower than expected. In the dormant season, monthly Q was higher than expected during the wettest months.
In mountainous areas such as the southern Appalachians USA, riparian zones are difficult to define. Vegetation is a commonly used riparian indicator and plays a key role in protecting water resources, but adequate knowledge of floristic responses to riparian disturbances is lacking. Our objective was to quantify changes in stand-level floristic diversity of riparian plant communities before (2004) and two, three, and seven years after shelterwood harvest using highlead cable-yarding and with differing no-cut buffer widths of 0 m, 10 m, and 30 m distance from the stream edge. An unharvested reference stand was also studied for comparison. We examined: (1) differences among treatment sites using a mixed linear model with repeated measures; (2) multivariate relationships between ground-layer species composition and environmental variables (soil water content, light transmittance, tree basal area, shrub density, and distance from stream) using nonmetric multidimensional scaling; and (3) changes in species composition over time using a multi-response permutation procedure. We hypothesized that vegetation responses (i.e., changes in density, species composition, and diversity across the hillslope) will be greatest on harvest sites with an intermediate buffer width (10-m buffer) compared to more extreme (0-m buffer) and less extreme (30-m buffer and no-harvest reference) disturbance intensities. Harvesting initially reduced overstory density and basal area by 83% and 65%, respectively, in the 0-m buffer site; reduced by 50% and 74% in the 10-m buffer site; and reduced by 45% and 29% in the 30-m buffer site. Both the 0-m and 10-m buffer sites showed increased incident light variability across the hillslope after harvesting; whereas, there was no change in the 30-m and reference sites over time. We found significant changes in midstory and ground-layer vegetation in response to harvesting with the greatest responses on the 10-m buffer site, supporting our hypotheses that responses will be greatest on sites with intermediate disturbance. Ground-layer species composition differed significantly over time in the 0-m buffer and 10-m buffer sites (both P < 0.0001), but did not change in the 30-m buffer and reference sites (both P > 0.100). Average compositional dissimilarity increased after seven years, indicating greater within-stand heterogeneity (species diversity) after harvesting. These vegetation recovery patterns provide useful information for evaluating management options in riparian zones in the southern Appalachians.
The pace of environmental and socioeconomic change over the past 100 years has been rapid. Changes in fire regimes, climate, and land use have shaped the structure and function of most forest ecosystems, including oak (Quercus spp. L.) forests in the eastern United States. New stressors such as air pollution and invasive species have contributed to and interacted with climate and fire to alter current forest conditions. While changing fire regimes have altered species composition of the current forest, oak regeneration is constrained by many factors that may affect future forests. Over the remainder of the twenty-first century, an accelerating pace of climate and socioeconomic changes will influence the future range of variation in Eastern oak forests. Some of these impacts will be direct, such as changes in tree growth rates, while other impacts will be indirect, such as new disturbance regimes. While it is likely that fire will be important in shaping oak forests in the twenty-first century, it is less clear exactly what that role will be. For example, it is uncertain whether our current scientific knowledge on the use of prescribed fire in oak forests will be applicable under novel climate and changing socioeconomic conditions. We propose that the combination of climate change, wildfire, and other disturbances will create stand conditions that favor oaks with or without management. However, management intervention (e.g., prescribed fire, thinning, or a combination) could reduce wildfire hazard, particularly in the wildland-urban interface, and create more desirable stand conditions that are resilient to future stressors such as changing precipitation patterns and warmer temperatures.
Climate change and forest disturbances are threatening the ability of forested mountain watersheds to provide the clean, reliable, and abundant fresh water necessary to support aquatic ecosystems and a growing human population. Here we used 76 years of water yield, climate, and field plot vegetation measurements in six unmanaged, reference watersheds in the southern Appalachian Mountains of North Carolina, USA to determine whether water yield has changed over time, and to examine and attribute the causal mechanisms of change. We found that annual water yield increased in some watersheds from 1938 to the mid-1970s by as much as 55%, but this was followed by decreases up to 22% by 2013. Changes in forest evapotranspiration were consistent with, but opposite in direction to the changes in water yield, with decreases in evapotranspiration up to 31% by the mid-1970s followed by increases up to 29% until 2013. Vegetation survey data showed commensurate reductions in forest basal area until the mid-1970s and increases since that time accompanied by a shift in dominance from xerophytic oak and hickory species to several mesophytic species (i.e., mesophication) that use relatively more water. These changes in forest structure and species composition may have decreased water yield by as much as 18% in a given year since the mid-1970s after accounting for climate. Our results suggest that changes in climate and forest structure and species composition in unmanaged forests brought about by disturbance and natural community dynamics over time can result in large changes in water supply. This article is protected by copyright. All rights reserved.
Exurban development (e.g., second homes) in woodlands spreads urban land use impacts beyond suburbs, but because exurban developments often retain many components of original ecosystem structure-such as a forest canopy rather than open lawn-their ecological impacts may be underestimated. Changes in seed-dispersing ant behavior prompted by exurban land use, such as edge avoidance, may pose deleterious impacts on the woodland plants (myrmecochores) they disperse, and hence the floristic diversity of exurban forests. We examined the effects of exurbanization on seed-dispersing ant nesting and foraging, seed retrieval, dispersal direction and subsequent impact on myrmecochores. We used a matrix of forested and exurbanized habitats to test whether (1) exurban edges decrease ant nest colonization and seed foraging, (2) ants disperse seeds away from exurban edges, and (3) consequently, there is lower ant-dispersed plant abundance nearer exurban edges. We found that exurban development poses little impact on keystone seed-dispersing ants because they foraged, colonized and thrived in fragmented woodland habitats as well as they did in intact forests. Exurban edges changed ant behavior, however, so that they generally moved seeds toward forest interiors, and, hence, away from edges. Corresponding to this behavioral change, we found that ant-dispersed plants declined with proximity to edges, whereas other woodland herbs with dispersal modes other than ants were unaffected. Exurbanization poses little threat to seed-dispersing ant viability, but, by changing foraging patterns (specifically, limiting the directionality of dispersal), it indirectly threatens the plants they disperse. Edge effects on biota commonly are associated with cascades through abiotic resources, but we show a deleterious biotic cascade between exurban edge, keystone ants and herbaceous plants. Species-mediated services, such as seed dispersal and pollination, are key resources, and assessing the full consequences of land use change therefore necessitates evaluation of impacts on biotic interactions.
- Jul 2015
Climate change will affect tree species growth and distribution; however, under the same climatic conditions species may differ in their response according to site conditions. We evaluated the climate-driven patterns of growth for six dominant deciduous tree species in the southern Appalachians. We categorized species into two functional groups based on their stomatal regulation and xylem architecture: isohydric, diffuse-porous and anisohydric, ring-porous. We hypothesized that within the same climatic regime: (1) species-specific differences in growth will be conditional on topographically-mediated soil moisture availability; (2) in extreme drought years, functional groups will have markedly different growth responses; and (3) multiple hydroclimate variables will have direct and indirect effects on growth for each functional group.
The importance of the herbaceous layer in regulating ecosystem processes in deciduous forests is generally unknown. We use a manipulative study in a rich, mesophytic cove forest in the southern Appalachians to test the following hypotheses: (i) the herbaceous functional group (HFG) in meso-phytic coves accelerates carbon and nutrient cycling , (ii) high litter quality input and rapid nutrient turnover associated with HFG will have a positive effect on overstory tree growth, and (iii) the HFG regulates tree regeneration with negative effects on seedling establishment due to competition for resources. We established treatment plots in a mesic, cove-hardwoods forest and removed the herbaceous flora (HR, removed twice per year) or added herbaceous organic material (OMA, once per year) for comparison to a no removal (NR) reference for a total of 14 years. The OMA treatment stimulated soil N-mineralization and increased lit-terfall mass and N content. OMA N-mineralization rates were more than two times greater than both the NR and HR treatments; however, we did not detect significant differences in soil CO 2 efflux among treatments. Higher overstory litterfall mass and N in the OMA treatment plots indicated that overstory trees were benefiting from the enhanced soil N-mineralization. Higher overstory leaf mass and N suggests an important linkage between HR and aboveground net primary production even though this did not translate into greater tree basal area increment. We found an increase in regener-ation of all tree species with HFG removal, and the response was particularly evident for Acer rubrum seedlings.
- Jan 2015
This chapter provides a synthesis of the more than 30 years of research on Watershed 7 (WS 7) at Coweeta Hydrologic Laboratory. It argues that findings from WS 7 provide important information on the management of southern Appalachians mixed-hardwood forests. The WS 7 study provides an opportunity to conduct detailed research on the effectiveness of previously established best management practices for forest road construction activities, and to evaluate some new road standards meant to reduce erosion and sediment movement. Water yield responses measured following harvest on WS 7 also support the regional use of a previously derived empirical model for predicting short-term annual flow responses for forest management planning in similar hardwood forests. The chapter concludes with a summary of perceptions of long-term changes in economic values and ecological services in a management context.
Few studies have examined how insect outbreaks affect landscape-level hydrologic processes. We report the hydrologic effects of the invasive, exotic hemlock woolly adelgid (HWA) in a headwater catchment in the southern Appalachian Mountains. The study watershed experienced complete mortality of an evergreen tree species, Tsuga canadensis (L.) Carr. (eastern hemlock), after infestation was first detected in 2003. Hemlock mortality resulted in a ~6% reduction in basal area in the watershed, and this loss was primarily concentrated in riparian zones. We used a paired watershed approach to quantify changes in water yield and peak stormflow using streamflow data from the infested watershed and a nearby watershed with significantly lower hemlock basal area. We hypothesized that yield would increase shortly after hemlock infestation, but decrease over the longer-term. We found that annual yield did not increase significantly in any year after infestation, but decreased significantly by 12.0 cm (~8%) in 2010. Monthly yield also decreased after infestation, but changes were limited to the dormant season. The decline in yield is likely to persist as hemlock is replaced by species with higher transpiration rates. Peakflow increased significantly after infestation during the two largest flow events in the post-infestation period. Changes in stormflow during extreme events may have been temporary as another evergreen, Rhododendron maximum, may have mitigated some of the changes after hemlock loss. Thus, streams draining watersheds where eastern hemlock has been lost due to HWA infestation demonstrate permanent reductions in yield and transient increases in peakflow during large flow events. This article is protected by copyright. All rights reserved.
Understanding the patterns of past disturbance allows further insight into the complex composition, structure, and function of current and future forests, which is increasingly important in a world where disturbance characteristics are changing. Our objectives were to define disturbance causes, rates (percent disturbance per decade), magnitudes and frequency (time since last disturbance) for both secondary and old-growth mixed-oak stands, and to determine if all mixed oak stands experience similar disturbance history. The study was located in two southern Appalachian forests in western North Carolina, USA: Coweeta Hydrologic Laboratory, a 2,185 ha experimental forest with some history of harvesting, and the Joyce Kilmer Wilderness, a 6,805 ha old-growth forest with no known harvesting. We used dendroecological techniques to evaluate the disturbance histories and create chronologies of these mixed-oak forests. Average decadal disturbance rates ranged from 4.3% to 13.8%, similar to rates common in eastern temperate forests (5% to 20%). The decades of peak recruitment common to several stands were the 1840s, which coincides with the historical accounts of a hurricane; the 1900s through the 1940s, which coincide with logging and elimination of Castanea dentata (Marshall) Borkh. by chestnut blight; and the 1960s, which coincides with drought and an elm spanworm infestation. The large peaks of disturbance were often synchronous and widespread, affecting stands across both Coweeta and Joyce Kilmer. However, there were also scattered pulses of disturbance unique to single stands, suggesting that localized events also played a role in the disturbance dynamics. Periods of constant low rates of disturbance present in all stands also indicate the importance of small canopy gaps in these forests. We found that stands similar in disturbance regimes were also similar in species composition. Results from our study provide information on how past disturbances, both regional and local events, have shaped the current forest. This understanding could help inform models to better predict how forests might respond to future climate (e.g., rising temperatures and increasing precipitation variability) and disturbance patterns (e.g., more frequent and severe events).
We synthesized the current information on mesophytic cove forests in the southern Appalachians, assessed the range of variation in herb species composition and diversity in stands with different disturbance histories and environmental conditions, identified key knowledge gaps, and suggested approaches to fill these knowledge gaps. The purpose of this synthesis was to provide information to forest managers to help make decisions about conservation assessments and strategies for rich cove forests in the southern Appalachians. An important finding is that no single study or data set can provide conclusive evidence or clear management strategies. However, an overriding conclusion is that the magnitude of impact and the management actions necessary to restore herbaceous communities are directly proportional to the severity of disturbance, current condition (e. g., presence of Rhododendron), site heterogeneity, and historical land use (e.g., agricultural activity). These factors plus a host of other stressors (e.g., climate variability, air pollution, invasives) are likely to have a strong influence on the highly variable patterns observed when comparing herbaceous diversity of 'old-growth' or uncut forests to human disturbed forests (e. g., cutting, air pollution, conversion, invasive plants or insects). Results from this review reinforce our premise that factors controlling herbaceous species presence and abundance are highly complex, thus broad generalizations about the impacts of a single factor such as logging should be interpreted with caution. Of the stressors known to affect forest trees (e.g., pests and pathogens, acidic deposition, air pollution, drought, and wind), little to no information exists on how these same stressors will affect herbaceous plants. A limited number of studies have examined the demography or physiology of forest herbs, particularly across all life stages. While the demography of a few genera have been studied (e.g., Hexastylis, Asarum, Trillium, Arisaema, Goodyera, Hepatica), little to no information exists for the majority of woodland herbs. Species identity is important when considering management of rich cove forests. Diversity may increase following canopy disturbances that favor recruitment of early-seral herbaceous species; therefore, simple indices of diversity (H', S, and E) are not the best measure of recovery in mesophytic rich coves, particularly where shade-adapted 'rich-cove indicator' species have been replaced by these species. Species-specific life histories and the influence of prevailing site conditions are important lines of research for understanding recovery and sustainability of mesophytic rich cove forests.
Background/Question/Methods Climate change poses challenges for forest management and conservation to determine how to maintain forests under novel climates. Temperature increases and precipitation changes, in particular, are likely to become a major factor limiting tree species growth and distribution. Trees growing under the same climatic conditions may differ according to local site-related variations in soil nutrients and moisture. We evaluated the climate driven patterns of growth for dominant hardwood species in the southern Appalachians. We hypothesized that there would be species-specific differences in growth responses to climate variability, and that these responses would depend on whether the species were growing in mesic or dry topographic positions within the same climatic regime. We extracted increment growth cores from Acer, Betula, Liriodendron, and Quercus trees across the elevation gradient in the Coweeta Basin, in western North Carolina. We used standard dendrochronological methods to cross-date and measure tree-ring widths, and to calculate annual basal area increment (BAI). We examined the relationships between on-site, long-term climatic data and standardized tree-ring chronologies from 1935 to 2003. Climate variables included precipitation, minimum and maximum daily air temperature, solar radiation, Palmer Drought Severity Index (PDSI), streamflow, dry spell length, and number of storms. Results/Conclusions Species differed in BAI growth over time depending on their physiology and how they responded to topographic moisture conditions. Quercus species growing on dry, upslope sites had higher BAI than corresponding species growing on mesic sites; whereas, Acer, Liriodendron and Betula had lower BAI on dry sites than mesic sites. All species, except Betula, were positively related (p<0.05) to winter minimum temperature. Cool, wet springs were negatively correlated (p<0.05) with Quercus growth, due in part to the decreased available energy during cool, wet springs. The single best predictor of growth across all species was the number of storms in the growing season (p<0.05), not PDSI or annual precipitation. In our long-term record, the number of growing season storms has been significantly decreasing over time. Precipitation distribution, rather than the total amount, will likely regulate future southern Appalachian forest productivity.
Background/Question/Methods Few studies have examined how insect outbreaks affect landscape-level hydrologic and biogeochemical processes. Here, we report the hydrologic and biogeochemical effects of the invasive, exotic Hemlock Woolly Adelgid (Adelges tsugae Annand; HWA) in a headwater catchment in the southern Appalachian mountains. The study area has experienced high mortality of the evergreen eastern hemlock (Tsuga canadensis (L.) Carr.) due to HWA infestation first detected in 2004. We used a paired watershed approach to quantify changes in nitrate nitrogen (NO3-N) fluxes and watershed yield using stream flow and chemistry data from two nearby watersheds with similar elevation, slope and soil properties but differing in pre-infestation hemlock abundance with the infested watershed having ~6% hemlock basal area and the reference watershed having almost no hemlock. We used the same paired approach to reconstruct storm hydrographs and compare expected and observed storm flow parameters, including peakflow and event duration, based on 5-minute streamflow records. Results/Conclusions Annual watershed NO3-N fluxes increased significantly after HWA infestation, with the greatest increases during late spring. The response peaked with a 232% annual increase in NO3-N fluxes during the second year and then recovered to near pre-HWA levels in the fifth year following infestation indicating that water quality effects are transient. Annual watershed yield did not increase, although some months showed significant increases in yield immediately after infestation. We did find significant changes in the storm hydrograph following infestation. Mean flow event duration, peakflow and total stormflow increased 2, 20 and 21%, respectively, for storms exceeding 2.0 cm precipitation during the dormant season. Changes in stormflow parameters were more consistent across years during the dormant season (Nov-Apr) than during the growing season indicating that dormant season changes will persist while changes during the growing season are likely to be transient because hemlock is being rapidly replaced by deciduous species. While water quantity effects were not observable over longer time scales, the observed increases in stormflow suggest that there may be important effects on water quantity during extreme events. Streams draining watersheds where a significant proportion of hemlock has been lost may experience significantly higher stream flows during large storms, particularly in the dormant season.
In the southern Appalachians, Rhododendron maximum L. (Ericaceae) is a key evergreen understory species, often forming a subcanopy in forest stands. Little is known about the significance of R. maximum cover in relation to other forest structural variables. Only recently have studies used Global Positioning System (GPS) technology as a field-based method to map the perimeter of shrub patches as a means of estimating canopy cover. We assessed the viability of using GPS technology to accurately measure R. maximum canopy cover in mountainous terrain; and we compared canopy cover to other R. maximum abundance variables, forest structural attributes, and environmental factors. We selected forty 20 × 40 m permanent plots at Coweeta Hydrologie Laboratory in western North Carolina to employ a variety of methods (visual estimates, GPS, and x-y coordinate measurements) to estimate canopy cover of R. maximum within each plot. We found a positive relationship between the GPS method and the more accurate x-y coordinate measurements (r = 0.967, p < 0.001). We compared the GPS-derived estimates to other measures of R. maximum abundance and found positive relationships between cover and density (r² = 0.800, p < 0.001), basal area (r² = 0.747, p < 0.001), total biomass (r² = 0.761, p < 0.001), and leaf area index (r² = 0.761, p < 0.001). The GPS method is a reliable field-based technology to estimate evergreen canopy cover and it could be used to estimate more difficult to measure parameters of R. maximum, given the significant relationships found in this study.
The impacts of exotic insects and pathogens on forest ecosystems are increasingly recognized, yet the factors influencing the magnitude of effects remain poorly understood. Eastern hemlock (Tsuga canadensis) exerts strong control on nitrogen (N) dynamics, and its loss due to infestation by the hemlock woolly adelgid (Adelges tsugae) is expected to decrease N retention in impacted stands. We evaluated the potential for site variation in N availability to influence the magnitude of effects of hemlock decline on N dynamics in mixed hardwood stands. We measured N pools and fluxes at three elevations (low, mid, high) subjected to increasing atmospheric N deposition where hemlock was declining or absent (as reference), in western North Carolina. Nitrogen pools and fluxes varied substantially with elevation and increasing N availability. Total forest floor and mineral soil N increased (P < 0.0001, P = 0.0017, resp.) and forest floor and soil carbon (C) to N ratio decreased with elevation (P < 0.0001, P = 0.0123, resp.), suggesting that these high elevation pools are accumulating available N. Contrary to expectations, subsurface leaching of inorganic N was minimal overall (<1 kg ha−1 9 months−1), and was not higher in stands with hemlock mortality. Mean subsurface flux was 0.16 ± 0.04 (SE) (kg N ha−1 100 days−1) in reference and 0.17 ± 0.05 (kg N ha−1 100 days−1) in declining hemlock stands. Moreover, although subsurface N flux increased with N availability in reference stands, there was no relationship between N availability and flux in stands experiencing hemlock decline. Higher foliar N and observed increases in the growth of hardwood species in high elevation stands suggest that hemlock decline has stimulated N uptake and growth by healthy vegetation within this mixed forest, and may contribute to decoupling the relationship between N deposition and ecosystem N flux.
Background/Question/Methods Numerous paired watershed studies have addressed the role of forests in regulating water yield and have demonstrated the tight interaction between vegetation and streamflow production. New challenges, such as the effects of non-random species loss on water yield, are emerging, and are already influencing forested ecosystems in the eastern US. In particular, eastern hemlock (Tsuga canadensis (L.) Carr.) is one of the principal riparian and cove canopy species in the southern Appalachian Mountains. Throughout its range, eastern hemlock is facing potential widespread mortality from hemlock woolly adelgid (HWA; Adelges tsugaeAnnand). We used a paired watershed approach to estimate the impact that the loss of hemlock will have on streamflow. Monthly streamflow records from two closely–located watersheds similar in size, aspect, elevation, but differing substantially in pre-management cover conditions were used to estimate the impact of hemlock before (2000–2004) and after (2005–2010) HWA infestation on the hydrologic budget. We hypothesized that hemlock loss would result in increased annual streamflow (ca. 10%), and that the timing of the streamflow increase would not be evenly distributed, with winter and spring experiencing greater increases compared to summer and fall. Results/Conclusions Prior to HWA infestation, monthly streamflow relationships between reference and HWA infested watersheds were highly significant (R2 > 0.93, P < 0.05), except for Sep and Oct, in which either the replication was low due to weir repairs during 2003 (R2 = 0.96, P < 0.12), or the spread of the data was insufficient (R2 = 0.86, P = 0.07), respectively. After infestation, relationships between reference and infested watersheds appeared to be better described by a different linear model. For all months except Jun and Nov, as streamflow increased in the reference watershed, a greater increase in the HWA infested watershed resulted. After HWA infestation, we predicted what monthly streamflow for the disturbed watershed would have been under the given climate conditions had HWA infestation not occurred. We observe both higher and lower streamflow than expected after HWA infestation. In general these departures were all within the bounds of prediction error; however, some months and years had significant departures. After summing all the significant departures in streamflow from expected, we found higher streamflow than expected by approximately 3–5% of total annual streamflow and 3–7% of annual evapotranspiration during years 2005, 2009 and 2010.
Background/Question/Methods We chose a rich, mesophytic cove forest in the Coweeta Basin, western North Carolina to evaluate the role of a diverse herbaceous layer in ecosystem function. We hypothesized that the experimental removal of a functional group of species would alter ecosystem processes. In summer 1998, we established 6 replicates of herbaceous removal (HR), 6 organic matter addition (OMA), and 6 controls. For fourteen years (1998-2011), we manually removed all herbs and deciduous shrubs from the HR plots and added organic matter (105 g m-2 fresh weight) to the OMA plots. All tree species were allowed to regenerate and grow. Tree seedlings <5.0 cm height were counted and tree seedlings ≥5.0 cm height were tagged and measured. We measured in situ soil CO2 efflux, in situ soil nitrogen availability, forest floor nutrient release using ion exchange resin sheets, and forest floor mass, carbon and nitrogen. Results/Conclusions Acer rubrum seedling recruitment was higher on the HR treatment than the control. Other tree species were less abundant and there were no differences among treatments. Even though soil moisture and temperature were comparable among treatments over time, soil N mineralization was higher on the OMA treatment than on HR and control in 2006 and 2011. As expected, soil CO2 efflux was higher in the summer than spring and winter. Average summer CO2 efflux was 3.51 mmol m-2 s-1 across all treatments in 2011, and it was lowest on the HR treatment after fourteen years of herbaceous removal. No significant differences were found for forest floor mass; however, forest floor Oe + Oa nitrogen was greater in the control than the HR or OMA treatments in some years.
The death of eastern hemlock (Tsuga canadensis) trees in response to infestation by the introduced hemlock woolly adelgid (Adelges tsugae) may affect ecosystem processes and structure of streams. Prior to hemlock mortality, we documented the conditions of eight small streams and their associated riparian forests within the Appalachian Mountains of North Carolina, U.S.A. Hemlock was the dominant tree species on all riparian sites and was always associated with rhododendron (Rhododendron maximum). Significant trends of increasing canopy openness, increasing light to the streams and increasing annual temperature range were observed. Contributions of hemlock to litterfall, in-stream wood, and benthic organic matter were important at the beginning of the study, suggesting that the loss of hemlock may significantly modify the trophic dynamics and physical structure of southern Appalachian streams. Increased growth of rhododendron in response to hemlock mortality may compensate for the trophic influences of hemlock loss. However, because of rhododendron's negative effect on growth of seedlings of other tree species, the greatest ecosystem impact of hemlock wooly adelgid may be more extensive rhododendron thickets within the riparian corridors of southern Appalachian streams.
- Jun 2012
In the Southern Appalachian Mountains of eastern USA, pine-hardwood ecosystems have been severely impacted by the interactions of past land use, fire exclusion, drought, and southern pine beetle (SPB, Dendroctonus frontalis). We examined the effects of restoration treatments: burn only (BURN); cut + burn on dry sites (DC + B); cut + burn on sub-mesic sites (MC + B); and reference sites (REF; no cutting or burning) on shortleaf pine-hardwood forests. We also evaluated the effectiveness of seeding native bluestem grasses. Structural (down wood, live and dead standing trees, shrubs, herbaceous layer) and functional (forest floor mass, C, and N; soil C, N, P, and cations; and soil solution N and P) attributes were measured before and the first and second growing seasons after treatment. We used path analysis to test our conceptual model that restoration treatments will have direct and indirect effects on these ecosystems. Total aboveground mass loss ranged from 24.33 Mg ha−1 on the BURN to 74.44 Mg ha−1 on the DC + B treatment; whereas, REF gained 13.68 Mg ha−1 between pre-burn and post-burn. Only DC + B sites had increased soil NO3–N, NH4–N Ca, Mg, and PO4–P and soil solution NO3–N, NH4–N, O–PO4 for several months.
Aims Wilderness and other natural areas are threatened by large-scale disturbances (e.g., wildfire), air pollution, climate change, exotic diseases or pests, and a combination of these stress factors (i.e., stress complexes). Linville Gorge Wilderness (LGW) is one example of a high elevation wilderness in the southern Appalachian region that has been subject to stress complexes including chronic acidic deposition and several wildfires, varying in intensity and extent. Soils in LGW are inherently acidic with low base cation concentrations and decades of acidic deposition have contributed to low pH, based saturation, and Ca:Al ratio. We hypothesized that wildfires that occurred in LGW followed by liming burned areas would accelerate the restoration of acidic, nutrient depleted soils. Because soils at LGW had extremely low concentrations of exchangeable Ca2+ and Mg2+ dolomitic lime was applied to further boost these cations. We evaluated the effectiveness of dolomitic lime application in restoring exchangeable Ca2+ and Mg2+ and subsequently increasing pH and Ca:Al ratio of soils and making Ca and Mg available to recovering vegetation. Methods Five treatment areas were established: severely burned twice (2000 & 2007) with dolomitic lime application (2xSBL); moderately burned twice with lime application (2xMBL); severely burned twice, unlimed (2xSB); moderately burned once (2000), unlimed (1xMB); and a reference area (REF; unburned, unlimed). In 2008 and 2009, we measured overstory, understory, and ground-layer vegetation; forest floor mass and nutrients; and soil and soil solution chemistry within each treatment area. Results All wildfire burned sites experienced substantial overstory mortality. However, understory biomass doubled between sample years on the most recently burned sites due to the rapid regrowth of ericaceous shrubs and prolific sprouting of deciduous trees. Burning followed by lime application (2xSBL and 2xMBL) significantly increased shallow soil solution NO3-N, but we found no soil solution NO3-N response to burning alone (2xSB and 1xMB). Surface soil base saturation and exchangeable Ca2+ were significantly affected by liming; Ca2+ concentrations were greater on 2xMBL and 2xSBL than 2xSB, 1xMB and REF. There was a smaller difference due to moderate burning along with greater soil Ca2+ on 1xMB compared to REF, but no difference between 2xSB and REF. Surface and subsurface soil exchangeable Al3+ were lower on 2xSBL than 2xSB, 2xMBL, 1xMB, and REF. Liming decreased soil acidity somewhat as surface soil pH was higher on the two burned sites with lime (pH = 3.8) compared to 2xSB without lime (pH = 3.6). Conclusions Liming resulted in decreased soil Al3+ on 2xSBL coupled with increased soil Ca2+ on both 2xSBL and 2xMBL, which improved soil Ca/Al ratios. However, the soil Ca/Al ratio response was transitory, as exchangeable Al3+ increased and Ca/Al ratio decreased over time. Higher lime application rates may be necessary to obtain a substantial and longer-term improvement of cation-depleted soils at LGW.
Rhododendron maximum L. is an evergreen, clonal shrub that forms a dominant sub-canopy layer and is a key species in southern Appalachian forests. We investigated the age and distribution of R. maximum across the Coweeta Basin, a 1626 ha watershed in western North Carolina. We selected 16 perennial, second-order streams and used a Global Positioning System to establish site boundaries and map the coverage of R. maximum across the hillslopes from stream to ridge. In each site, three transects from stream edge to the ridge were used to measure diameters of overstory trees (> 2.5 cm dbh), tree saplings (< 2.5 cm dbh) and shrubs including R. maximum stems. Along each transect, we cut cross-sections of R. maximum ramets and extracted increment cores from nearest neighbor trees to determine ages. The 16 sites ranged in size from 0.3 to 1.9 ha depending on the distance from stream to ridge. Rhododendron maximum cover ranged from 25 to 100% and ages ranged from 6 to 120 years. Rhododendron maximum establishment year showed a skewed unimodal distribution with the peak establishment occurring between 1928 and 1940. Although the R. maximum age and distance-from-stream relationship was statistically significant, the relationship was not meaningful as distance-from-stream only explained 2.6% of the variation in R. maximum age (r 2 = 0.026, P = 0.0003, n = 487). Distance from stream only explained 4.2% of the variation in overstory tree age (r²= = 0.042, P = 0.0015, n=237). It appears that R. maximum has not expanded upslope over the last 100 years; rather the ranges in sizes and ages suggest that ramets are recruiting under established R. maximum canopies particularly in the wetter, near stream locations.
- Oct 2011
Understanding changes in community composition caused by invasive species is critical for predicting effects on ecosystem function, particularly when the invasive threatens a foundation species. Here we focus on dynamics of forest structure, composition and microclimate, and how these interact in southern Appalachian riparian forests following invasion by hemlock woolly adelgid, HWA, Adelges tsugae. We measured and quantified changes in microclimate; canopy mortality; canopy and shrub growth; understory species composition; and the cover and diversity in riparian forests dominated by eastern hemlock Tsuga canadensis over a period of seven years. Treatments manipulated hemlock mortality either through invasion (HWA infested stands) or girdling (GDL) hemlock trees.
The herbaceous layer varies with topographic heterogeneity and harbors the great majority of plant diversity in eastern deciduous forests. We described the interplay between disturbances, both natural and human-caused, and composition, dynamics, and diversity of herbaceous vegetation, especially those in early successional habitats. Management actions that create low to moderate disturbance intensity can promote early successional species and increase diversity and abundance in the herb layer, although sustaining communities such as open areas, savannahs, and woodlands may require intensive management to control invasive species or implement key disturbance types. A mixture of silvicultural practices along a gradient of disturbance intensity will maintain a range of stand structures and herbaceous diversity throughout the central hardwood forest.
- Mar 2011
Long-term records from USDA Forest Service Experimental Forests and Ranges (EF&Rs) are exceptionally valuable scientific resources and common ground for research in natural resource management. Coweeta Hydrologic Laboratory, Southern Appalachian Mountains in western North Carolina, is one of 82 EF&Rs located throughout the United States and Puerto Rico. Since its establishment in 1934, the wealth and breadth of scientific knowledge gained from Coweeta Hydrologic Laboratory research has provided both public and private land managers information on forest land management and has added to the knowledge base of natural resource science.
- Aug 2010
- 95th ESA Annual Convention 2010
Background/Question/Methods Despite the implementation of various biological and chemical controls, eastern hemlock trees (Tsuga canadensis (L.) Carr.) are declining throughout much of the eastern US due to hemlock woolly adelgid (HWA). The decline is especially rapid in the southern Appalachian region of the US. We used a combination of intensive measurements and monitoring at the Coweeta Hydrologic Laboratory in western N.C. to (1) determine the spatial distribution of hemlock in southern Appalachian ecosystems, (2) monitor the rate of spread and decline of HWA infested tress, and (3) quantify the impacts of HWA induced hemlock mortality on water, carbon, and nutrient cycling pools and processes. Our primary objective was to use our understanding of the impacts of hemlock decline on ecosystem structure and function to guide restoration strategies. Results/Conclusions Eastern hemlock is present in mixed stands within riparian zones in the southern Appalachians; highest hemlock densities occur within 50 m of streams and hemlock can occupy as much as 50% of the basal area. HWA was first detected in a few scattered trees in the Coweeta basin in 2003. However, by 2005, HWA was detected in 100% of hemlock trees across a network of vegetation plots. By 2008, average crown loss of infested trees exceeded 80%. Sapflow measurements and modeling approaches showed that annual stand level transpiration has been reduced by 10%, with greater reductions (up to 30%) in the spring and fall. Carbon cycle components were impacted within three years of infestation. We observed a rapid decrease in stem growth in hemlocks, increased growth of co-occurring hardwoods, and decreased fine root biomass and soil respiration. Changes in nutrient cycling were not detected, suggesting that some of the impacts of hemlock mortality on ecosystem processes make take several years to manifest. While we anticipate a substantial pulse of coarse woody debris (CWD) as hemlock trees fall, likely replacement species (Betula and Acer) decompose quickly. Restoring hydrologic processes, forest structure, and CWD are the highest priorities for ecological restoration. In particular, establishing evergreen tree cover will be necessary to restore soil moisture dynamics and establishing species with recalcitrant CWD will be necessary to maintain temporal CWD dynamics in the forest floor and streams.
We examined the relationships between hemlock distribution and abundance and terrain attributes for the Coweeta Basin in the southern Appalachian Mountains. Field measurements were combined with GIS mapping methods to develop predictive models of abundance and distribution of Tsuga canadensis (L.) Carrière (eastern hemlock) and evaluate the co-occurrence of Rhododendron maximum L. (rosebay) and Kalmia latifolia L. (mountain laurel). Terrain variables were derived from USGS DEM 30-meter digital maps. Elevation, slope, aspect, terrain shape index, landform, and distance from stream were calculated from field measurements and the digital data. Terrain attributes such as elevation (r 2 5 0.97, p , 0.0001), distance to stream (r 2 5 0.94, p , 0.0001), and terrain shape index (r 2 5 0.61, p 5 0.0015) were good predictors of T. canadensis abundance. Terrain shape index explained 56% of the variation in R. maximum percent aerial cover (r 2 5 0.56, p 5 0.005). In the Coweeta Basin, T. canadensis was distributed as few, large trees mostly concentrated in near-stream locations, and it was closely associated with R. maximum. Tsuga canadensis mortality due to Adelges tsugae Annand (hemlock wooly adelgid) will result in a minor decrease in basin-wide basal area, but will substantially reduce near-stream basal area, and will also remove the largest trees in near-stream environments. In similar landscapes across the southern Appalachians, where T. canadensis co-occurs with R. maximum, riparian shading will likely remain unchanged.
We characterized structural and functional attributes along hillslope gradients in headwater catchments. We endeavored to identify parameters that described significant transitions along the hillslope. On each of four catchments, we installed eight 50 m transects perpendicular to the stream. Structural attributes included woody and herbaceous vegetation; woody debris and forest floor mass, nitrogen (N) and carbon (C); total soil C and N; litterfall amount and quality by species; and microclimatic conditions. Functional attributes included litter decomposition, soil microarthropods, soil CO2 evolution, soil solution chemistry, and soil extractable N. Forest floor mass, N and C, and soil depth increased with distance from the stream and transitioned between 10 and 20 m. In contrast, litterfall N rate (kilograms of nitrogen per hectare per day), downed woody debris, soil A-horizon C and N, and soil solution NO3 concentration all decreased with distance, and exhibited significant transitions. Certain overstory species were more abundant in the uplands than near the stream. Herbaceous diversity and richness were similar across the hillslope, but species distributions varied in response to hillslope moisture content. Taken together, these results suggest that at 10–20 m from the stream, transitions occur that separate riparian from upland conditions and may provide valuable insight into riparian zone definition.
We examined vegetation responses to prescribed fire on three mixed-oak sites located in the Blue Ridge Physiographic province of the southern Appalachian Mountains: Alarka Laurel Branch (AL), Robin Branch (RB), and Roach Mill Branch (RM). Each of the study sites was within a sub-watershed that drained a first order stream. Our objectives were to: 1) evaluate overstory mortality following prescribed fire treatments; and 2) assess changes in composition, abundance, and diversity of overstory (stems > 5.0 cm dbh), understory (stems < 5.0 cm dbh, ≥ 0.5 m height), and herbaceous layer (woody stems <0.5 m height and all herbaceous plants) vegetation in mixed-oak ecosystems. Each site included a burned and unburned area (control). Before the prescribed fire treatments were applied, we established permanent plots (10 X 20 m) in the prescribed burn areas (12 plots in AL, 12 plots in RB, and 10 plots in RM) and adjacent unburned areas (5 plots in AL, 6 plots in RB, and 4 plots in RM), for a total of 49 plots. Within the plots, we sampled vegetation before and after the prescribed burns. All of the prescribed fires were low to moderate intensity; i. e., they had moderate flame temperatures and low flame heights. After the prescribed fires, overstory mortality was low for all sites, and there were no significant differences between mortality in burned areas and that in unburned areas. Understory density was lower on the burned than the unburned plots the first (t = -5.26, P < 0.0001) and second (t = -3.85, P = 0.0020) growing seasons after burning. There was either an increase (AL, RB) or no change (RM) in herbaceous layer cover depending on the site and no significant change in species diversity after burning for any site. Thus, we found no negative effects of prescribed fire on herbaceous flora.
We examined the long-term effects of a prescribed fire in a southern Appalachian watershed in Nantahala National Forest, western North Carolina, USA. Fire was prescribed in 1995 on this site by forest managers to restore a degraded pine (Pinus spp.)-hardwood community, specifically to stimulate forage production, promote pine and oak (Quercus spp.) regeneration, and increase plant diversity. Before and after the prescribed fire, permanent plots were sampled across a south-facing hillslope, which corresponded to three community types: mesic, near-stream cove (riparian); dry, mixed-oak (mid-slope); and xeric, pine-hardwood (ridge). In an earlier paper, we reported the first two years of post-burn vegetation response from this prescribed burn. In our current study, we compared the pre-burn (1994) forest condition with 10 years post-burn (2005) vegetation measurements to determine the effects of fire on the mortality and regeneration of overstory trees, understory shrubs, and herbaceous-layer species. Overstory mortality was high immediately after the burn at the ridge location and ten years after the fire. Mortality of pitch pine (Pinus rigida Miller) (91.8 %) and hickory (Carya spp.) (77.5 %) reduced overstory basal area from 26.97 m2 ha-1 pre-burn to 18.86 m2 ha-1 post-burn in 1995 and to 9.13 m2 ha-1 in 2005. At the mid-slope and riparian locations, no significant overstory mortality occurred over time. Understory density was significantly higher 10 years after the burn (2005) than pre-burn, and basal area had returned to pre-burn levels. Density of mountain laurel (Kalmia latifolia L.), black huckleberry (Gaylussacia baccata [Wang.] K. Koch), and blueberry (Vaccinium spp.) had increased due to prolific sprouting. The prescribed fire had varying effects on diversity across the hillslope gradient over time. On the ridge, overstory diversity declined following the fire (H’basal area = 1.14 in 1994, H’basal area = 0.75 in 1995, and H’basal area = 0.80 in 2005). Diversity significantly increased in the herbaceous layer and remained higher than pre-burn conditions through 2005 (H’cover = 1.02 in 1994, H’cover = 1.97 in 1995, and H’cover = 2.25 in 2005). For the mid-slope and riparian positions, no change in diversity was observed in the overstory, understory or herbaceous layer.
We examined nutrient cycling responses to prescribed fire on three sub-mesic, mixed-oak sites located in the Blue Ridge Physiographic province of the southern Appalachian Mountains: Alarka Laurel Branch (AL), Robin Branch (RB), and Roach Mill Branch (RM). Each study site was located within a sub-watershed that drained a first order stream. Our objective was to quantify the effects of prescribed burning on forest floor mass, nitrogen and carbon pools; and soil and soil water available nitrogen. Each site included a burned and unburned control area; both burned and control areas were sampled before and after burning. Within each plot, we sampled forest floor mass, carbon and nitrogen, soil and soil solution nitrate (NO 3-N) and ammonium (NH 4-N) concentrations before and after the prescribed burns. All prescribed fires were conducted in the dormant season and were low to moderate intensity. All sites lost a significant amount of forest floor mass due to burning; 82 to 91% of the Oi layer and 26 to 46% of the Oe + Oa layer. Soil NH 4-N concentrations increased in surface soils (0-5 cm) only, immediately after burning, but return to pre-burn levels by mid-summer. Burning had no measurable effect on soil solution inorganic nitrogen concentrations. Low levels of solution NO 3-N and NH 4-N after burning and no change in stream NO 3-N concentrations indicated that no inorganic nitrogen was lost from these sites.
Elliott, K. J. and J. M. Vose (Coweeta Hydrologic Laboratory, Southern Research Station, USDA Forest Service, Otto, NC 28763). Effects of prescribed burning on shortleaf pine (Pinus echinata Mill.)/mixed-hardwood forests. J. Torrey Bot. Soc. 132: 236-251. 2005.-We examined the effects of a single dormant season fire on overstory and understory species diversity and composition and tree seedling regeneration patterns the first and second years following a prescribed burn in the Conasauga River Watershed of southeastern Tennessee and northern Georgia. We asked: Can a single dormant season fire initiate a trajectory of overstory and understory species change consistent with restoring Pinus echinata/mixed-oak/bluestem (Andropogon gyrans and Schizachyrium scoparium)-grass community types? Six sub-watersheds (similar in vegetation, soil type, stream size, and disturbance history) were located within the Conasauga River Watershed; four of the sites were burned in March 2001, and two sites were designated as controls. Within each site, vegetation was measured in layers: the overstory layer (trees > or = 5.0-cm DBH), the midstory layer (woody stems < 5.0-cm DBH and > or = 0.5 m height), and the ground flora layer (woody stems < 0.5-m height and all herbaceous species). All plots were sampled before the prescribed burn (Sept. 2000) and after the burn in July of 2001 and 2002. Consistent with the goals of the land managers, all the prescribed fires resulted in low-to-moderate intensity and low severity fires. However, we found no significant change in overstory, midstory, or ground flora species diversity after burning. We found no regeneration of P. echinata seedlings after the prescribed fire. Although fire reduced basal area of woody species in the midstory, prolific sprouting from hardwoods resulted in higher density of fire-sensitive hardwoods such as Acer rubrum, Oxydendrum arboretum, and Nyssa sylvatica. Density of Pinus strobus, an undesirable species, was reduced by 20% and its basal area was reduced by 50% after the burn. Overstory mortality occurred in small size class hardwoods as a result of the fire, but most of the mortality occurred in P. echinata and P. virginiana Miller due to infestation with pine bark beetles. The prescribed fires were not of sufficient intensity to: reduce overstory basal area, prepare a seedbed for successful pine germination, affect diversity of any of the vegetation layers, or promote A. gyrans and S. scoparium recruitment. Thus, additional fire treatments or a combination of fire and thinning treatments will be necessary to restore these ecosystems to P. echinata/mixed-oak/bluestem grass community types.
We predicted the eff ects of sulfate (SO 4) deposition on wilderness areas designated as Class I air quality areas in western North Carolina using a nutrient cycling model (NuCM). We used three S deposition simulations: current, 50% decrease, and 100% increase. We measured vegetation, forest fl oor, and root biomass and collected soil, soil solution, and stream water samples for chemical analyses. We used the closest climate stations and atmospheric deposition stations to parameterize NuCM. Th e areas were: Joyce Kilmer (JK), Shining Rock (SR), and Linville Gorge (LG). Th ey diff er in soil acidity and nutrients, and soil solution and stream chemistry. Shining Rock and LG have lower soil solution base cation and higher acidic ion concentrations than JK. For SR and LG, the soil solution Ca/Al molar ratios are currently 0.3 in the rooting zone (A horizon), indicating Al toxicity. At SR, the simulated Ca/Al ratio increased to slightly above 1.5 after the 30-yr simulation regardless of S deposition reduction. At LG, Ca/Al ratios ranged from 1.6 to 2.4 toward the end of the simulation period, the 100% increase scenario had the lower value. Low Ca/Al ratios suggest that forests at SR and LG are signifi cantly stressed under current conditions. Our results also suggest that SO 4 retention is low, perhaps contributing to their high degree of acidifi cation. Th eir soils are acidic, low in weatherable minerals, and even with large reductions in SO 4 and associated acid deposition, it may take decades before these systems recover from depletion of exchangeable Ca, Mg, and K.
Chestnut blight fungus (Endothia parasitica [Murr.] P.J. And. & H.W. And.)) is a classic example of an invasive species, which severely damaged populations of its host, Castanea dentata, and had widespread and long-term impacts on eastern North American forests. Concurrently, forests were further disturbed by lumbering, which was common across the region from the mid 1800s to the early 1900s. In 1926, local infestations of chestnut blight were reported in the Coweeta Basin, Southern Appalachian Mountains of North Carolina. We used permanent plot inventories of the Basin (first sampled in 1934 and twice afterward in 1969–72 and 1988–93) to describe the distribution of species along a complex environmental gradient. Specifically, we asked: How does vegetation change over approximately 60years following logging and the demise of C. dentata? Does the association between vegetation and environment determine the pattern of species distributions through time? Which species replaced C. dentata across this complex environmental gradient? We used nonmetric multidimensional scaling ordination and multiresponse permutation procedure for the analyses of the inventory periods. In 1934, C. dentata was the most important species in the Coweeta Basin. It was present in 98% of the plots and contributed 22% of the total density and 36% of the total basal area. Diversity increased significantly over time and was attributed to an increase in evenness of species distribution. The canopy dominant, C. dentata, was replaced by more than one species across the environmental gradient. Importance values of Quercus prinus, Acer rubrum, Cornus florida, Tsuga canadensis, and Oxydendrum arboreum increased by 2–5% across the basin following the decline of C. dentata. Tsuga canadensis increased in abundance and distribution, especially near streams across elevations. Liriodendron tulipifera replaced C. dentata in moist coves, which have low terrain shape and high organic matter content. In contrast, Q. prinus and A. rubrum were ubiquitous, much like C. dentata before the chestnut blight becoming dominant or co-dominant species across all environmental conditions.
Cover board arrays were used to measure the relative abundance of macroinvertebrates and terrestrial salamanders on prescribed burn and control sites in xeric southern Appalachians of northern Georgia and southeastern Tennessee pine-oak forests. Three microsite variables were measured at each cover board: cover board moisture level, temperature under the cover board, and soil moisture. Soil moisture was significantly higher on the burn sites than the controls after the prescribed fire. Two groups of macroinvertebrates, Homoptera and Hymenoptera, were more abundant on the burn sites than the control sites. Coleoptera and Stylommatophora were significantly more abundant in riparian and low slope positions than upland positions; whereas, the other macroinvertebrate groups were not significantly related to slope position. Thirteen salamanders were found during the four sampling periods. Overall, there was little evidence of negative post-fire impacts on macroinvertebrates or salamanders.
In many forested ecosystems, the architecture and functional ecology of certain tree species define forest structure and their species-specific traits control ecosystem dynamics. Such foundation tree species are declining throughout the world due to introductions and outbreaks of pests and pathogens, selective removal of individual taxa, and over-harvesting. Through a series of case studies, we show that the loss of foundation tree species changes the local environment on which a variety of other species depend; how this disrupts fundamental ecosystem processes, including rates of decomposition, nutrient fluxes, carbon sequestration, and energy flow; and dramatically alters the dynamics of associated aquatic ecosystems. Forests in which dynamics are controlled by one or a few foundation species appear to be dominated by a small number of strong interactions and may be highly susceptible to alternating between stable states following even small perturbations. The ongoing decline of many foundation species provides a set of important, albeit unfortunate, opportunities to develop the research tools, models, and metrics needed to identify foundation species, anticipate the cascade of immediate, short- and long-term changes in ecosystem structure and function that will follow from their loss, and provide options for remedial conservation and management.
- Jul 2005
- Water Encyclopedia
Transpiration is a key process in the application of phytoremediation to soil or groundwater pollutants. To be successful, vegetation must transpire enough water from the soil or groundwater to control or take up the contaminant. Transpiration is driven by a combination of abiotic (climate, soil water availability, and groundwater depth) and biotic (leaf area, stomatal functions, root amount and distribution, and hydraulic characteristics) that need to be evaluated when considering appropriate site and species combinations. The protocols are not trivial, but transpiration can be measured at a variety of scales using techniques such as direct measurements of sap flow on individual trees, eddy flux gradient analyses, or gauged watersheds. Alternatively, models can be used to estimate transpiration, but these usually require on-site calibration or parameterization to produce accurate predictions. Case study analyses across a range of site conditions and species indicate a maximum transpiration capacity of approximately 7.5 × 10⁶ liters of water per hectare per year (8 × 10⁵ gallons of water per acre per year), with a range of 1.5 × 10⁶ to 7.5 × 10⁶ liters per hectare per year (1.6 × 10⁵ to 8 × 10⁵ gallons per acre per year). Variation among sites is related to species, tree size, and stocking (i.e., vegetation density) differences. Application of a physiologically based and site-specific parameterized model suggests reasonable agreement between measured and predicted transpiration estimates for the Air Force Plant 4 site in central Texas.
- Jun 2005
We evaluated the effects of three regeneration harvest methods on plant diversity and soil resource availability in mixed-hardwood ecosystems. The study area is in the Wine Spring Creek watershed on the Nantahala National Forest of the Southern Appalachian Mountains in western North Carolina. The regeneration treatments were: an irregular, two-aged shelterwood cut (2A), with 5.0 m(2)/ha residual basal area; a shelterwood cut (SW), with 9.0 m(2)/ha residual basal area; a group selection cut (GS), with 0.10-0.20 ha openings and 25% overstory removal on area basis at first entry; fourth, the control, consisted of two uncut sites (UC). Each harvest treatment was replicated three times across the landscape in similar plant community types. Within each treatment area, permanent plots were marked and inventoried for overstory, midstory, and herbaceous layer plants. In each permanent plot, we collected soil samples in winter (December-March) to reduce temporal variation due to vegetation phenological stage and rainfall events. We analyzed soil samples for extractable calcium (Ca), magnesium (Mg), potassium (K), cation exchange capacity (CEC), pH, bulk density, A-horizon depth, total carbon
Prescribed burning is being used in the Conasauga River Watershed in southeastern Tennessee and northern Georgia by National Forest managers to restore degraded pine/oak communities. The purpose of these burns is to restore shortleaf pine (Pinus echinata Miller)/mixed-oak forests with more diverse understories, which include native bluestem grasses (Andropogon gyrans Ashe and Schizachyrium scoparium (Michx.) Nash). Although burning might be an effective tool for restoring these stands to a shortleaf pine/mixed-oak/bluestem grass community type, it is not known whether these restoration burns will have a negative impact on water quality. Six subwatersheds (similar in vegetation, soil type, stream size and location, and disturbance history) were located within the Conasauga River Watershed. Four of the sites were burned in Mar. 2001, and two sites were designated as controls. To evaluate initial effects of prescribed burning on water quality, we measured soil solution and streamwater nutrient concentrations and streamwater sediment concentration (TSS; total suspended solids) weekly over a 10-month period. Consistent with goals of the land managers, all the prescribed fires resulted in low- to moderate-intensity and low-severity fires. Soil solution and streamwater NO3 - - N and NH4+-N did not increase after burning on any of the sites. We found no differences in TSS between burn and control streams in any of the sample periods. In addition, we found no detectable differences between control and burned sites for concentrations of PO43-, SO42-, Ca2+, Mg2+, K+, or pH in soil solution or streamwater. Thus, these prescribed restoration fires did not have a significant effect on soil solution and stream chemistry or stream sediment (TSS) concentrations. Our results suggest that low-intensity, low-severity fires, such as those in this study, could be used as a tool to restore vegetation structure and composition in these mixed pine-hardwood ecosystems without negatively impacting water quality.
As a result of this most recent SPB epidemic (1999-2003), thousands of hectares of dead pine trees have created wildfire-hazard conditions in the southern Appalachians. One of the challenges for land managers is how to return fire to these ecosystems after (1) nearly a decade of exclusion, and (2) the more recent SPB mortality enhanced fuel loads. Higher fuel loads have the potential to increase fire intensity and severity. At the extremes, fires of high intensity and severity can have a large effect on ecosystem structure and function. The objectives of our research were: (1) to quantify fuel load reduction methods (pine overstory felling, material left on site followed by prescribed fire; prescribed fire only; and no treatment) in pine/hardwood forests heavily impacted by southern pine beetle induced tree mortality, and (2) to evaluate the effects of further restoration treatments including planting shortleaf (Pinus echinata) pine and seeding native bluestem grasses on ecosystem structure and function in these pine-hardwood forests. Eight sites on the Cherokee National Forest, eastern Tennessee were chosen to evaluate restoration of shortleaf pine ecosystems. Four sites were cut+burn (2 dry, 2 sub-mesic), two sites were burn only, and two sites were used as references. All eight sites had substantial pine mortality before the initiation of fuel treatments (Figure 1). Sites were cut in summer 2005 and burned in March 2006. All site measurements for vegetation composition and diversity, carbon and nitrogen pools, soil and soil water chemistry, and success of planted pine and bluestem grasses for the pre-treatment (2005) and two years post-treatment (2006, 2007) have been completed. We have provided demonstrations and tours to user groups, oral and poster presentations at scientific meetings, and three published manuscripts (2 proceedings and 1 peer reviewed). In addition, three peer-reviewed manuscripts, one MS thesis, and one proceedings paper are in progress (see Deliverables table below).
- Mar 2004
Understory prescribed burning is being suggested as a viable management tool for restoring degraded oak–pine forest communities in the southern Appalachians yet information is lacking on how this will affect ecosystem processes. Our objectives in this study were to evaluate the watershed scale effects of understory burning on total aboveground biomass, and the carbon and nitrogen pools in coarse woody debris (CWD), forest floor and soils. We also evaluated the effects of burning on three key biogeochemical fluxes; litterfall, soil CO2 flux and soil net nitrogen mineralization. We found burning significantly reduced understory biomass as well as the carbon and nitrogen pools in CWD, small wood and litter. There was no significant loss of carbon and nitrogen from the fermentation, humus and soil layer probably as the result of low fire intensity. Burning resulted in a total net loss of 55 kg ha−1 nitrogen from the wood and litter layers, which should be easily replaced by future atmospheric deposition. We found a small reduction in soil CO2 flux immediately following the burn but litterfall and net nitrogen mineralization were not significantly different from controls throughout the growing season following the burn. Overall, the effects of burning on the ecosystem processes we measured were small, suggesting that prescribed burning may be an effective management tool for restoring oak–pine ecosystems in the southern Appalachians.
- Feb 2004
Transpiration is a key process in the application of phytoremediat ion 'to soil or groundwater pollutants. To be successful, vegetation must transpire . enough water from the soil or groundwater to control or take up the,cdntam- in&. Transpiration is driven by a combination of abiotic (climate, soil water availability, and groundwater depth) and biotic (leaf area, stomatal functions, root amount and distribution, and hydraulic characteristies) that need to be evaluated when considering appropriate site and species combinations. The protocols are not trivial, but transpiration can be measured at a variety of scales using techniques such as direct measurements of sap flow on individual trees, eddy flux gradient analyses, or gauged watersheds. Alternatively, models can be used to estimate transpiration, but these usually require on-site calibration or parameterization to produce accurate predictions. Case study analyses across a range of site conditions and species indicate a maximum transpiration capacity of approximately 7.5 x lo6 liters of water per hectare per year (8 x IO5 gallons of water per acre per year), with a range of 1.5x lo6 to 7.5x lo6 liters per hectare per year (1.6 x 105 to 8x lti gallons per acre per year). Variation among sites is related to species, tree size, and .stocking (i.e., vegetation density) differences. Application of a physiologically based and site-specific parameterized model suggests reasonable agreement between . measured and predicted transpiration estimates for the Air Force Plant 4 site in central Texas.
Information is lacking on ecosystem effects of understory burning in mesic mixed-oak (Quercus spp.) forests of the southern Appalachians. Native Americans used periodic fires in these forests for driving game and opening the forest. In April 1998, we conducted a low- to moderate-intensity fire in a cove-hardwood forest in the Nantahala National Forest, western North Carolina. In March 1998, before burning, permanent plots were established along three parallel transects to measure forest floor mass, carbon (C), and nitrogen (N); soil nutrient (NO3-, NH4+, PO4-, Ca, Mg, and K) availability; and vegetation mor- tality and regeneration. Forest floor material was sampled by components: small wood, litter (Oi), and a combined fermenta- tion and humus component (Oe + Oa). Soil nutrient availability was estimated using cation and anion exchange membrane sheets. Vegetation measurements included the overstory and understory layers. All parameters were resampled during sum- mer 1998 and 1999 in the same manner as the pre-burn inventories. Burning reduced the total mass, carbon, and nitrogen of the Oi layer by 92%, 93%, and 91%, respectively. Reductions in mass, carbon, and nitrogen of the Oe + Oa layer were 48%, 46%, and 56%, respectively. Burning resulted in increased exchangeable K, Ca, Mg, NH4, PO4, and NO3 availability in soil on the burned area compared with the control. One year after burning, there were no significant differences in exchangeable nutrients between the burned and the control area. Overstory mortality was substantial, with 55% of the trees killed by the fire. However, most of the mortality occurred in trees 20 cm DBH were killed. In the understory, all the aboveground stems were killed; although 50% of these individuals sprouted during the grow- ing season (July 1998), some of these sprouts did not survive through the following year (July 1999). Moderate-intensity understory burning may be a useful tool to restore mesic mixed-oak communities in the southern Appalachians. Reintroduc- tion of fire into these ecosystems may be beneficial by increasing soil nutrient availability, promoting regeneration and sur- vival of Quercus spp., increasing diversity of understory species, and reducing abundance of shade-tolerant and fire-intoler- ant species such as Acer rubrum.
Southern Appalachian forests are undergoing considerable change due to altered disturbance regimes. For example, fire exclusion has had a major impact on the structure and function of pine-hardwood ecosystems. Recently, fire has been prescribed for a variety of applications: 1) stand-replacement in the form of a mimicked wildfire, 2) site-preparation as part of a fell-and-burn prescription, and 3) understory burning for fuels reduction and wildlife habitat improvement. Assessing watershed-scale responses to burning requires identification of key parameters indicative of changes in structure and function. In the southern Appalachians, nitrogen in the form of NO, is a key indicator of ecosystem change or response to disturbance. We compared stream NO,-N responses among stand-replacement fires (Winespring Creek and Hickory Branch), a fell-and-burn prescription (Jacobs Branch), and a wildfire in an old-growth deciduous forest (Joyce Kilmer). Nitrate-nitrogen concentration increased following two of the four fires. Concentrations following the fell-and- burn prescription fire increased from CO.01 to a maximum of 0.075 mg L-r and remained elevated for 8 months. Similarly, stream NO, concentration increased approximately 2 weeks following the old-growth deciduous wildfire from 0.04 to a maximum of 0.50 mg L ' and remained elevated for 6 weeks. There were no significant differences in NO, following one of the stand-replacement fires or between treatment and control or pn- and post-burn following the other stand-replacement fire due to maintenance of an unburned riparian area. Although the old-growth deciduous wildfire was essentially an understory burn, the magnitude of stream N response suggests that unavailable recalcitrant forms of N may have been released during the wildfire, as well as a reflection of the potential inefficiency of old-growth forests at sequestering mobilized nutrients. In all cases, hydrologic losses of NO,-N were insignificant with respect to effects on water quality and site depletion of N.
In 1975, we initiated a long-term interdisciplinary study of forest watershed ecosystem response to clear-cutting and cable logging in watershed 7 at the Coweeta Hydrologic Laboratory in the southern Appalachian Mountains of North Carolina. This paper describes 20 years of change in species composition, aboveground biomass, leaf area index (LAI), and nutrient pools in the 59-ha mixed hardwood forest of watershed 7 following commercial clear-cutting in winter 1977. We measured woody species in 24 permanently marked plots before cutting in 1974 and during subsequent years (19771997). By 1997 (20 years after cutting), aboveground biomass was 81.7, 96.9, and 85.4 Mg·ha1 in the cove hardwood; mesic, mixed-oak; and dry, mixed-oak communities, respectively. Leaf biomass and LAI accumulated relatively faster than total aboveground biomass in all three communities. By 1984, only 78 years after cutting, leaf biomass and LAI were nearly equal to the amount estimated for the precut forest. In 1997, nitrogen accumulation was 36, 44, and 61% and phosphorus accumulation was 48, 66, and 59% in the cove-hardwoods; mesic, mixed-oak; and dry, mixed-oak communities of the corresponding precut communities, respectively. Potassium, calcium, and magnesium accumulations were less than either nitrogen or phosphorus accumulation.
Chainsaw felling, burning, and planting of eastern white pine (Pinus strobus L.) have been prescribed on degraded pine/hardwood stands in the Southern Appalachians to improve overstory composition and productivity. The desired future condition of the overstory is a productive pine/hardwood mixture, with white pine, which is resistant to southern pine beetle (Dendroctonus frontalis), as the dominant pine. We evaluated the growth of white pine planted after fell-and-burn treatments through eight growing seasons after planting on three sites that differed in their fire characteristics and carbon and nitrogen losses. The three sites (JE, JW, and DD) differed in heat penetration and forest floor consumption. Although very little consumption of the Oe+Oa humus layer occurred during burning, consumption of the Oi litter layer was 94%, 94%, and 63% at JE, JW, and DD, respectively. Corresponding to the forest floor layer consumption (Oi and Oe+Oa combined), 46% of forest floor N was lost at JE, 45% of forest floor N was lost at JW, and less than 0.1% of the forest floor N was lost at DD. Biomass and density of woody competitor species were not significantly related to white pine size or growth. By the eighth growing season, no differences in white pine size or growth were detected between JE and JW, but DD had significantly smaller white pine trees. The size difference between DD and the other two sites was attributed to the replanting of seedlings at DD in 1992. However, relative growth rate (RGR) was significantly higher on DD in 1998 than the other two sites. Eight growing seasons after planting, white pine growth was negatively related to percent Oi layer consumed on the JE and JW sites. We also found significant relationships between white pine RGR and percent Oi consumed using data from all three sites. Although fire severity had a long-term effect on pine growth, fire severity was considered low overall on these sites because there were limited losses from the forest floor Oe+Oa layer. However, white pine increment and RGR were significantly related to percent forest floor Oi mass and N loss. This loss of site N capital could have a significant negative effect on growth of planted white pine over the long term. South. J. Appl. For.
Disturbance such as catastrophic windthrow can play a major role in the structure and composition of southern Appalachian forests. We report effects of Hurricane Opal followed by salvage logging on vegetation dynamics (regeneration, composition, and diversity) the first three years after disturbance at the Coweeta Hydrologic Laboratory in western North Carolina. The objective of this study was to compare species composition and diversity of understory and groundlayer species in a hurricane + salvage logged (H+S) forest to an adjacent undisturbed forest. Abundance of groundlayer species was much higher in the H+S forest than in the undisturbed forest, and abundance increased over time. Percent cover, density, and species richness were significantly higher in the H+S forest than in the undisturbed forest. In addition, percent cover increased by approximately 85% between 1997 and 1999 in the H+S plots. Shannon's index of diversity (H′) based on percent cover was significantly higher in the H+S forest than the undisturbed forest by the third year after disturbance. However, there was no significant difference in H′ based on density between H+S forest and the undisturbed forest in either year. In the undisturbed forest, 59 species and 50 genera represented 30 families. By 1999 (the third year after disturbance), the H+S forest retained 93 species, 72 genera and 42 families. The Asteraceae and Liliaceae had the highest number of species in both sampled forests, with more species of Liliaceae in the H+S plots. Micro-relief created from pit and mound topography from uprooting of windthrown trees, shade from the slash-debris left on site from the salvage logging, and shade from the remaining overstory trees created a mosaic of environmental conditions. This environmental heterogeneity could be responsible for the mix of early (shade intolerant) and late (shade tolerant) successional herbaceous species, and a higher species richness and diversity than the undisturbed forest.
- Apr 2001
Long-term changes (∼20 years) in water yield, the storm hydrograph, stream inorganic chemistry, and sediment yield were analyzed for a 59 ha mixed hardwood covered catchment (Watershed 7) in the southern Appalachian mountains (USA) following clearcutting and cable logging. The first year after cutting, streamflow increased 26 cm or 28% above the flow expected if the forest had not been cut. In subsequent years, discharge increases declined at a rate of 5–7 cm per year until the fifth year when changes in flow returned to baseline values. Later in forest succession, between ages 15 and 18 years, both significant increases and decreases in annual water yield were observed; these discharge dynamics are discussed in relation to vegetation regrowth dynamics. Flow responses predicted from an empirical regional scale model were within 17% of experimental values during the first 4 years of regrowth. Intra-annual analysis showed that proportionally larger increases (48%) in flow occurred in the low flow months of August–October. Storm hydrograph analysis showed that, on an average, initial flow rate and peakflow rates increased 14–15% and stormflow volume increased 10%.
ELLIO~, K. J., J. M. VOSE, W. T SWANK, AND P V. BOLSTAD. Long-term patterns in vegetation-site relationships in a southern Appalachian forest. J. Torrey Bot. Soc. 126320-334. 1999.-W- used permanent plot inventories from 1969-1973 and 1988-1993 to describe forest species distribution patterns of the Coweeta Hydrologic Laboratory, a 2,185 ha basin in western North Carolina, USA. We used canonical correspondence analysis to explore the vegetation-site patterns for the 1970s and 1990s inventories combined. Site variables were determined by direct measurements or calculated by digital geographical information system mapping methods. Site variables were percent slope, elevation, terrain shape, precipitation, modified azimuth, soil organic matter content, soil depth, soil clay content, depth of A-horizon, potential solar radiation, and mean temperature during the growing season. Fifty percent of the variation in the vegetation distribution was explained by the site variables used in the canonical correspondence analysis. Soil organic matter, terrain shape, and elevation were the variables most strongly related to vegetation distribution. Species associated with convex terrain (upper slopes and ridges), such as Pinus rigida, Quercus coccinea, and Quercus velutina, decreased in abundance from the 1970s to the 1990s; species associated with soils having high organic matter content and deep A-horizons, such as Liriodendron tulipifera, Rhododendron maximum, and Tsuga canadensis increased in abundance. Individual species responded differently to site gradients. For example, Acer rubrum, Quercus prinus, Oxydendrum arboreum, and Nyssa sylvatica were located in the center of the ordination space (i.e., their occurrence was not related to any of the site variables), which suggests that these species are habitat generalists.
- Feb 1999
In April 1995, the USDA Forest Service conducted a prescribed burn along with a south-facing slope of southern Appalachian watershed, Nantahala National Forest, western NC. Fire had been excluded for over 70 years and the purpose of the burn was to create a mosaic of fire intensities to restore a degraded pine/hardwood community and to stimulate forage production and promote oak regeneration along a hillslope gradient. Permanent plots were sampled at three locations along a gradient from 1500 to 1700 m. Plot locations corresponded to three community types: mesic, near-riparian cove (low slope); dry, mixed-oak (mid slope); and xeric, pine/hardwood (ridge). Before burning (1994–1995) and post-burn (summer, 1995 and summer, 1996) vegetation measurements were used to determine the effects of fire on the mortality and regeneration of overstory trees, understory shrubs, and herbaceous species. After the burn, mortality was highest (31%) at the ridge location, substantially reducing overstory (from 26.84 pre-burn to 19.05 m2 ha−1 post-burn) and understory shrub (from 6.52 pre-burn to 0.37 m2 ha−1 post-burn) basal area. At the mid-slope position, mortality was only 3%, and no mortality occurred at the low slope. Not surprisingly, percent mortality corresponded to the level of fire intensity. Basal area of Kalmia latifolia, Gaylussacia baccata, and Vaccinium spp. were substantially reduced after the fire, but density increased due to prolific sprouting. The prescribed fire had varying effects on species richness and diversity across the hillslope gradient. On the ridge, diversity was significantly increased in the understory and herb-layer, but decreased in the overstory. On the mid slope, no change was observed in the overstory, but diversity significantly decreased in the understory. On the low slope, no change was observed in the overstory or understory.
TO document how species richness and diversity (H') recover from severe large-scale disturbance, we report temporal patterns of species composition and diversity following grass-to-forest succession from a long-term experiment in the Coweeta Basin, west-ern North Carolina. The original experiment-clear-cutting, 5 yr of grass cover followed by a herbicide treatment, and abandonment in a Southern Appalachian mixed deciduous for-est-represents the most severe human disturbance in the Coweeta Basin. For several years after cessation of management, Robinia pseudoacacia quickly sprouted from roots and ex-ceeded the growth rates of other species. Lzriodendron tulif@ra increased in density and basal area because of its prolific seedling establishment and rapid growth rate. Regeneration of large seeded species was mixed-sparse for Quercus rubra and Q coccinea and nonexistent for Q prinus and Q. uelutina. In the overstory, density-based H' increased from 1958, before
- May 1997
Watershed 7, a southwest-facing watershed in the Coweeta Basin, western North Carolina, USA, was clearcut in 1977. Twenty-four permanent plots were inventoried in 1974 before cutting and in 1977, 1979, 1984, and 1993 after clearcutting. This study evaluates changes in species diversity during early succession after clearcutting and differences in overstory tree and ground flora response to disturbance by clearcutting and their interaction with previous disturbances and subsequent stand development. To quantify species diversity, we computed Shannon-Weaver's index of diversity (H′) and Pielou's evenness index (J′). Woody species diversity remained relatively stable; however, woody species richness increased in the cove-hardwoods and hardwood-pines, but remained relatively constant in the mixed-oak hardwoods. Although revegetation was rapid, forest composition has changed through succession. Opportunistic species, such as Liriodendron tulipifera, Robinia pseudoacacia, and Acer rubrum, increased in abundance, whereas Quercus velutina, Carya spp., and Q. rubra decreased. Ground flora diversity declined in the cove-hardwoods and mixed-oak hardwoods communities, but the decrease in the hardwood-pines was not significant. The abundance (g biomass m−2) of ground flora was much lower in 1993 than in 1984; 79% less in the cove-hardwoods, 90% less in the mixed-oak hardwoods, and 79% less in the hardwood-pines. Watershed 7 is apparently in a transition state between early and late successional species abundance. Early successional, shade-intolerant species, such as Erechtites, Solidago, Eupatorium, Panicum, and Aster, have declined, whereas late successional, shade-tolerant species, such as Viola, Galium, Sanguinaria, Uvularia, and Veratrum are not yet well established.
We measured growing season soil CO2 evolution under elevated atmospheric [CO2] and soil nitrogen (N) additions. Our objectives were to determine treatment effects, quantify seasonal variation, and compare two measurement techniques. Elevated [CO2] treatments were applied in open-top chambers containing ponderosa pine (Pinus ponderosa L.) seedlings. N applications were made annually in early spring. The experimental design was a replicated factorial combination of CO2 (ambient, + 175, and +350 L L–1 CO2) and N (0, 10, and 20 g m–2 N as ammonium sulphate). Soils were irrigated to maintain soil moisture at > 25 percent. Soil CO2 evolution was measured over diurnal periods (20–22 hours) in October 1992, and April, June, and October 1993 and 1994 using a flow-through, infrared gas analyzer measurement system and corresponding pCO2 measurements were made with gas wells. Significantly higher soil CO2 evolution was observed in the elevated CO2 treatments; N effects were not significant. Averaged across all measurement periods, fluxes, were 4.8, 8.0, and 6.5 for ambient + 175 CO2, and +350 CO2 respectively).Treatment variation was linearly related to fungal occurrence as observed in minirhizotron tubes. Seasonal variation in soil CO2 evolution was non-linearly related to soil temperature; i.e., fluxes increased up to approximately soil temperature (10cm soil depth) and decreased dramatically at temperatures > 18C. These patterns indicate exceeding optimal temperatures for biological activity. The dynamic, flow-through measurement system was weakly correlated (r = 0.57; p < 0.0001;="" n="56)" with="" the="">2 measurement method.
Conversion of low-quality, natural mixed pine/hardwood ecosystems, containing a mountain laurel (Kalmia latifolia L.) dominated understory, to more productive eastern white pine (Pinus strobus L.)/mixed-hardwood systems is a common prescription on relatively xeric southern Appalachian forest sites. We examined the effects of mechanical release, interspecific competition, and annual precipitation on growth of planted white pine in four 14-yr-old stands in the southern Appalachians. Two stands were mechanically released at age 6. No significant differences in biomass, basal area, or diameter were found between treatments for all species combined. Radial increment was significantly less during a drought year for both treatments. Height increment was less sensitive to severe moisture limitation than radial increment. Height and radial increment were compared to distance-dependent and distance-independent measures of competition for the nonreleased stands. Indices based on height and height/distance explained the greatest amount of variation in both radial and height increment. The influence of post-release severe drought may have delayed or diminished the response to release. The competitive influence of understory dominant mountain laurel at stand age 14 appears to be slight compared to the influence of other competing hardwood vegetation. South. J. Appl. For. 21(1):19-23.
Overstory, shrub-layer, and herbllayer flora composition and abundance patterns in eleven forest sites were studied to evaluate species diversity and richness before implementing three types of harvest treat- ments. The sites were within the Wine Spring Creek Watershed and were classified as high elevation, dry, Quercus rubra-Rhododendron calendulaceum based on McNab and Browning's Landscape Ecosystem Classification system. Evaluation of species diversity was determined by Shannon-Weine r's index of diver- sity (H') and Pielou's species evenness index (J'). Overstory H' based on tree density ranged from 1.62 to 2.50 and H' based on tree basal area ranged from 0.94 to 2.22. The importance values for woody species, showed four species that occurred on all sites (Acer rubrum, Quercus rubra, Amelanchier arborea, and Castanea dentata) accounted for 32 to 84% of overstory abundance. Shrub-layer H',,,,,,, ranged from 0.64 to 2.33 and H',, ranged from 0.40 to 2.26. Rhododendron calendulaceum and Castanea dentata were the only species present on all sites and accounted for 28.5 to 92.3% of the shrub-layer abundance. Herb-layer H' oenslfy ranged from 1.72 to 3.02 and J',,,,,, was low, between 0.5 and 0.6 on most sites. Herb-layer diversity was determined by a few dominant species. Although species richness ranged from 51 to 73, seven genera of understory herbs (Prenanthes trifoliata, Thelypteris noveboracensis, Viola hastata, Medeola virginiana, Solidago (curtisii and arguta), and Curer spp., and Aster spp.) occurred on all sites and accounted for 50 to 91% of the total density and 27 to 75% of the total cover. Early successional species were well represented at all sites. Seedling survivorship, germination, and overstory contribution of seeds, caused varied site representation of species. This study provides base line data for observing variation in species richness and diversity that will result from experimental harvest methods.
We measured growing season soil CO, evolution under elevated atmospheric CO, and soil nitrogen (N) additions. Our objectives were to determine treatment effects, quantify seasonal variation, and determine regulating mechanisms. Elevated CO, treatments were applied in open- top chambers containing 3-year-old ponderosa pine ponderosa Dougl. ex Laws.) seedlings. Nitrogen applications were made annually in early spring. The experimental design was a replicated factorial combination of CO, (ambient, f175, and +350 pL.L-' CO,) and N (0, 10, and 20 g. m-* N as ammonium sulfate). Soils were irrigated to maintain soil moisture at >25%. Soil CO, evolution was measured over diurnal periods (20-22 h) in April, June, and October 1993 using a flow-through, infrared gas analyzer measurement system. To examine regulating mechanisms, we linked our results with other studies measuring root biomass with destructive sampling and root studies using minirhizotron techniques. Significantly higher soil CO, evolution was observed in the elevated CO, treatments in April and October; N effects were not significant. In October, integrated daily values for CO, evolution ranged from 3.73 to 15.68 g C0,.m-2.day-' for the ambient CO, + 0 N and 525 pL.L-' CO, + 20 g.rn-' N, respectively. Soil CO, flux among treatments was correlated with coarse root biomass (r2 = 0.40; p >F = 0.0380), indicating that at least some of the variation observed among treatments was related to variation in root respiration. Across all sample periods and treatments, there was a significant correlation (r2 = 0.63; p >F = 0.0001) between soil CO, evolution and percent fungal hyphae observed in minirhizotron tubes. Hence, some of the seasonal and treatment variation was also related to differences in heterotrophic activity.
, ABSTRACT. We evaluated the competitive environment around planted white pine (Pinus strobus L.) seedlings and monitored the response of seedling growth to competition from naturally regenerating herbaceous and woody species for 2 yr after prescribed burning. We eval- uated the ability of distance-inde pendent and distance-dependent competition indices to predict resource availability, determined if white pine seedlings responded to resource reduction by competitors, and identified species-specific contributions to the competitive environment through canonical correspondence analysis (CCA). Distance-independent measures of competition were not as well correlated with pine seedling growth as were distance-dependent measures. In 1991, competition was less important in 1991 than in 1992, and ordinating the
A 16 ha watershed in the Coweeta Basin was clearcut in 1939 and 1962. Vegetation was inventoried in 1934 and at about 7-year intervals to 1991. After the first clearcut, tree diversity remained high until after the second cut. Diversity based on density and basal area decreased significantly 14 years after the second clearcut and remained low through 1991. Diversity was highest in the early establishment stage of stand development, then declined at the intermediate stage with canopy closure. Evenness based on basal area declined more than evenness based on density because basal area of Liriodendron tulipifera increased substantially from 1977 to 1991. Trends in diversity were due to changes in evenness rather than changes in species richness.
We measured net photosynthesis, leaf conductance, xylem water potential, and growth of Pinus strobus L. seedlings two years after planting on two clear-cut and burned sites in the southern Appalachians. Multiple regression analysis was used to relate seedling net photosynthesis to vapor pressure deficit, seedling crown temperature, photosynthetically active radiation (PAR), needle N, xylem water potential, and soil water, and to relate seedling size and growth to physiological measurements (average net photosynthesis, leaf conductance, and cumulative xylem water potential), soil water, needle N, seedling temperature, and PAR. Seedling net photosynthesis was significantly related to vapor pressure deficit, midday water potential, crown temperature, and PAR (r2 = 0.70) early in the growing season (May 1992) with vapor pressure deficit alone explaining 42% of the variation. As neighboring vegetation developed, light became more limiting and significantly reduced seedling net photosynthesis later in the growing season (July, August, and September). Final seedling diameter was significantly related to competitor biomass, average photosynthetic rate, and needle N (r2 = 0.68).
- Apr 1994
The tree and shrub species on a 16-ha watershed in the Coweeta Basin were sampled in 1984 and again in 1991 to determine the effects of drought on tree species composition and basal area growth. Mortality and radial growth were determined for tree species within three community types that represent a moisture gradient from moist to dry: cove-hardwoods > mixed-oak > oak-pine. Tree mortality from 1984 to 1991 was 20% and 23% in the cove-hardwoods and mixed-oak communities, respectively, compared to only 12% in the oak-pine type. With the exception of Oxydendrum arboreum and Robinia pseudoacacia, the oaks had higher percentage mortality than any other genus; Quercus velutina had 29%, 37%, and 20% mortality in the cove-hardwoods, mixed-oak, and oak-pine types, respectively; Quercus prinus had 23% mortality in the mixed-oak type; Quercus coccinea had 36% mortality in the mixed-oak type; and Quercus marilandica had 27% mortality in the oak-pine type. Mortality occurred mostly in the small-size class individuals (< 10 cm in diameter) for all species, suggesting that thinning was still an important process contributing to mortality 29 yr after clearcutting. Although growth of Liriodendron tulipifera was much higher than growth of either Quercus prinus or Quercus coccinea, growth in Liriodendron was significantly reduced by the 1985–88 drought and no growth reduction was observed for these two dominant Quercus species during the same time period.
Growth and nutrient use efficiency were determined for red pine (Pinus resinosa Ait.) seedlings grown at various levels of light, nitrogen, and phosphorus. Nutrient use effi- ciency was estimated for nitrogen (NUE) and phosphorus (PUE) and was calculated as biomass production divided by total nutrient content. Seedlings grown in high light had four to five times more biomass than those in the low light treatment. Nitrogen supply had a significant effect on total biomass as well as other biomass components. Phosphorus supply did not have a significant effect on any of the biomass components. NUE and PUE decreased with increased supply of N and P, respectively. The results of this study suggest that red pine seedlings can adjust their nutrient use efficiency, particularly for N, when light and nutrient availability are varied. NUE was highest with high light and low N-high P supply in nutrient solutions. FOR. Sci. 40(l):47-58.
We examined the physiological performance and.growth of Pinus strobus L. seedlings the first growing season after planting on two clear-cut and burned sites in the southern Appalachians. Growth of the seedlings was related to physiological measurements (net photosynthesis (P(N)), transpiration, leaf conductance, and xylem water potential), soil water, foliar N, seedling temperature, and light environment using regression analysis. Diameter growth increased with increasing foliar N concentration and decreased as competitor biomass increased. Competition reduced growth by lowering foliar N, shading seedlings, and possibly reducing photosynthetic capacity. Increased temperature and lower available soil water may obscure these relationships on a harsh site.
Three southern Appalachian stands with sparse and unproductive pine-hardwood overstories and dense Kalmia latifolia L. understories were treated to restore productivity and diversity on steep slopes. An adaptation of the fell and burn practice was applied in summer and fall 1990. About one-half of the woody fuels were consumed at each site. A range of fire intensities was observed. Flame temperatures approached 800-degrees-C, but the heat pulse into the forest floor only reached 60-degrees-C at 5 cm. Humus and chaffed leaf litter remained on most of the surface after burning. Evidence of soil erosion was spotty and related to points of local soil disturbance. No soil left the sites. At the end of the first growing season, 23% of the burned surfaces were covered by growing plants and 62% by residual forest floor and woody debris. Felling and burning reduced evapotranspiration so that soil in the treated areas remained moister than under adjacent uncut stands. Opening the sites increased soil temperatures 2 to 5-degrees-C at 10 cm during the first 16 months after treatment.
- Mar 1993
The effects of competition from three northern hardwood tree species on red pine (Pinus resinosa Ait.) seedlings were examined on two clear-cut sites in western Maine. We examined how planted red pine seedlings altered their nutrient use efficiency and shoot morphology under changing environmental conditions and how these changes related to their ability to tolerate competition. A three-factor experimental design was used to determined the effects of species of competitors and their abundance as well as fertilization on red pine seedling growth, nutrient use efficiency, and leaf morphology. The competitors were striped maple (Acer pensylvanicum L.), red maple (Acer rubrum L.), and pin cherry (Prunus pensylvanica L.) established at two densities (high and zero) with two levels of fertilization (0 and 224 g m⁻² of 10-10-10 NPK commercial fertilizer). Nitrogen and phosphorus use efficiencies were calculated as total aboveground biomass divided by total nutrient content. Specific leaf area (cm² g⁻¹), leaf area ratio (cm² g⁻¹), and total leaf area (cm²) were measured for all red pine seedlings. Plots were harvested at two time periods, when pine seedlings were 2 years old (1989) and 3 years old (1990). Total biomass, annual production, and leaf area index (m² leaf area m⁻² ground surface area) were calculated for competitors on each plot.
Pin cherry (Prunuspensylvanica L.f.) and striped maple (Acerpensylvanicum L.) are potentially important competitors of red pine (Pinusresinosa Ait.) planted on recently clear-cut hardwood sites. By experimentally manipulating initial competitor densities on 2.0-m2 plots, we were able to quantify and compare the effects of competitor species on red pine seedlings 2 years after planting on two sites in western Maine. Various measures of competitor biomass and leaf area index (LAI) were highly correlated; thus, we used LAI to quantify competitor abundance. On the site with poorer growth for both competitors and red pine, the only red pine variable significantly correlated with competitor LAI was specific leaf area (SLA) of current needles. On the site with better growth for all species, various measures of red pine biomass as well as diameter at ground level and SLA were significantly correlated with competitor LAI. Seedling height was not significantly correlated with competitor LAI at either site. Although there were no significant differences between competitor species in terms of their effect per unit of LAI, pin cherry tended to achieve much higher LAI (and biomass) than did striped maple and thus had a greater negative impact on red pine seedling growth. We conclude that general predictions of the early effects of competition under field conditions are possible, but that the strength of the relationships may be influenced by the extent to which microsite factors and site characteristics are incorporated.
- Jul 1992
Above-ground biomass distribution, leaf area, above-ground net primary productivity and foliage characteristics were determined for 90- and 350-year-oldPinus edulis-Juniperus monosperma ecosystems on the Colorado Plateau of northern Arizona. These ecosystems have low biomass, leaf area and primary productivity compared with forests in wetter environments. Biomass of the 350-year-old pinyon-juniper stand examined in this study was 54.1 mg ha−1; that of the 90-year-old stand was 23.7 mg ha−1. Above-ground net primary production averaged 2.12 mg ha−1 year−1 for the young and 2.88 mg ha−1 year−1 for the mature stand; tree production was about 80% of these values for both stands. Projected ecosystem leaf area (LAI) of the stands was 1.72 m2 m−2 and 1.85 m2 m−2, respectively. Production efficiency (dry matter production per unit leaf area) was 0.129 kg m−2 year−1 for the young, and 0.160 kg m−2 year−1 for the mature stand. Production efficiency of the study sites was below the 0.188 kg m−2 year−1 reported for xeric, pure juniper stands in the northern Great Basin. Biomass of pinyon-juniper ecosystems of northern Arizona is generally below the 60–121 mg ha−1 reported for pinyon-juniper stands of the western Great Basin in Nevada. A climatic gradient with summer precipitation decreasing between southeast Arizona and northwest Nevada occurs in the pinyon-juniper region. Great Basin pinyon-juniper ecosystems lie at the dry-summer end of this gradient while pinyon-juniper ecosystems of the Colorado Plateau lie at about the middle of this gradient. In spite of wetter summers, pinyon-juniper ecosystems of northern Arizona are less productive than those of the Great Basin.
Competition between ponderosa pine seedlings and various grasses and forbs was studied on a site in northern Arizona burned in 1982 by a wildfire. Two-year-old pine seedlings were planted in 3.05 x 3.05 m plots in April 1983, followed by the sowing of grass and forb seeds on the same plots in July 1983 after summer rains had begun. Predawn xylem water potential of the pine seedlings was measured biweekly throughout the 1983 and 1984 growing seasons. Extractable soil nitrogen was measured at the beginning and end of both growing seasons. After the wildfire, nitrate and ammonium levels were significantly higher in the burned area than in an adjacent unburned area. Nitrate and ammonium concentrations in various grass treatment plots were significantly (P < 0.05) different at both the beginning and end of the growing season. Pine seedling xylem water potential differed among treatments, with potentials being lowest on plots sown with Agropyron desertorum. The differences in seedling xylem water potential and available soil nitrogen were reflected in differences in pine seedling growth. The most effective competitors were Agropyron desertorum and Dactylis glomerata. Results indicated that competition occurred for both moisture and available nitrogen. For. Sci. 33(2):356-366.
We used permanent plot inventories of the Coweeta Basin (USDA FS Experimental Forest), Southern Appalachian Mountains of North Carolina (first sampled in 1934 and again in 1969-72 and 1988-93) to describe the distribution of species along an environmental gradient. We also explored the influence of large-scale disturbance on this deciduous forest. Chestnut blight fungus (Endothia parasitica) is an invasive species, which severely damaged populations of Castanea dentata and had widespread and long-term impacts on eastern North American forests. In 1926, local infestations of chestnut blight were reported in the Coweeta Basin; by 1930 most C. dentata trees were dead or dying from the blight. Concurrently, forests were further disturbed by lumbering, which was common across the region from the mid 1800s to the early 1900s. We used nonmetric multidimensional scaling for the analyses of the inventory periods. In 1934, C. dentata was the most abundant tree species. It was present in 98% of the plots and contributed 22% of the total density and 36% of the total basal area. By the 1970s, only sprouting stems of C. dentata remained in the forest due to chestnut blight induced mortality. The canopy dominant, C. dentata, was replaced by more than one species across the environmental gradient. Subsequently, diversity increased significantly over time and was attributed to an increase in evenness of species distribution. Quercus prinus, Acer rubrum, Cornus florida, Tsuga canadensis, and Oxydendrum arboreum increased by 2-5% across the basin following the decline of C. dentata. Tsuga canadensis increased in abundance and distribution, especially near streams across elevations. Liriodendron tulipifera replaced C. dentata in moist coves, which have low terrain shape and high organic matter content. In contrast, Q. prinus and A. rubrum were ubiquitous, much like C. dentata before the chestnut blight, becoming dominant or co-dominant species across all environmental conditions.
Pine regeneration following wildland fire continues to be a serious prob- lem across the western and southeastern U.S. Frequency of large wildfires has increased over the last several decades and restoration of these burned areas is a major problem confronting land managers. Prescribed fires are used primarily to re- duce heavy fuel loads and secondarily to reduce competition or prepare sites for natural or planted pine regeneration. In 1983, an experiment was initiated near the Fort Valley Experimental Forest to evaluate the growth of ponderosa pine (Pinus ponderosa1) seedlings planted after a severe wildfire. This study evaluated different herbaceous species effects on survival and growth of ponderosa pine seedlings. The study reported that competition from nonnative grass species (Dactylis glomerata and Agropyron desertorum) significantly reduced water and nitrogen availability and pine seedling growth; whereas, native grasses (Bouteloua gracilis and Sitanion hystrix) had no effect on soil resources or pines. In southern Appalachia, pine re- generation success after wildland fire varies depending on fire severity and growing season precipitation. After a high intensity, moderate severity fire on dry southern Appalachian ridges, pitch pine (Pinus rigida) seedling germination was high (3,000 seedlings/ha); however, most pine seedlings did not survive beyond the first year due to unusually low precipitation late in the growing season. Even in these mountains that normally receive high precipitation, drought can reduce pine seedling growth and induce mortality. More often, light and nitrogen are the limiting resources to pine seedling growth, and sprouting hardwoods are more competitive than herbaceous species with the regenerating pines. Further studies in southern Appalachia suggest that successful regeneration of pine (e.g., Pinus strobus, P. echinata, or P. rigida) after prescribed fire will not be achieved without planting pine seedlings and reducing fast growing hardwood competitors.
Allometric equations were developed to predict aboveground dry weight of herbaceous and woody species on prescribe-burned sites in the Southern Appalachians. Best-fit least-square regression models were developed using diameter, height, or both, as the independent variables and dry weight as the dependent variable. Coefficients of determination for the selected total biomass models ranged from 0.620 to 0.992 for herbaceous species and from 0.698 to 0.999 for the wood species. Equations for foliage biomass generally had lower coefficients of determination than did equations for either stem or total biomass of woody species.
The key components of watershed processes are inputs in precipitation, interactions of vegetation, soil and water including evapotranspiration (water yield), overland flow (erosion), and storage and filtering (nutrients), and outputs in streamflow. Fire effects occur at the vegetation-soil interface and can result in altering overland flow and infiltration rate of water. Fire can affect infiltration rates by collapsing soil structure and reducing soil porosity, contributing ash and charcoal residues which can clog soil pores, and raindrop splash can compact soil and firther contribute to loss of soil porosity. An extreme example is the development of hydrophobic soils as observed in the western U.S. following severe wildfire. Watershed responses to fire depend on intensity and severity. Many factors influence fire severity including the quality and quantity of fuels, soil properties, topography, climate, and weather. The most important factors influencing the response to fire are vegetation mortality and the loss of the forest floor which are directly proportional to fire severity. Vegetation mortality reduces nutrient and water uptake, soil stability with root death, and the litter source for forest floor replenishment. The forest floor litter and humus (duQ layers provide soil cover, act as a sponge, and enhance infiltration. Large storm events immediately after a fie can accelerate surface runoff and compact soil.