Lindsay R. Boring

Early Regeneration of a Clear-Cut Southern Appalachian Forest

The components of hardwood forest regeneration on a southern Appalachian watershed were assessed during the 1st yr following clear—cutting. First—year net primary production (NPP) on the clear—cut was 1955 kg/ha, representing 22% of the NPP of a nearby undisturbed hardwood forest. First—year nutrient pools in NPP for N, P, K, Mg, and Ca were estimated at 29—44% of those in the NPP of the control. The greatest NPP and nutrient pools were represented in descending order by hardwood sprouts, herbs, vines, and seedlings. Woody successional species (Robinia pseudo—acacia, Liriodendron tulipifera, and Vitis aestivalis var. argentifolia) and herbs (Aster spp., Solidago spp., and Erechtites hieracifolia) were important in revegetation due to competitive advantages in growth rates, growth forms, and propagative capacities. The woody successional species had higher tissue concentrations of N and P than most other woody species. Herbs as a group had significantly higher foliar concentrations of K than woody species. Woody successional and herbaceous species collectively had higher biomass and elemental pools than other woody species. Following forest disturbance, these fast—growing species conserve substantial pools of nutrients in their biomass and initiate a rapid recovery of forest elemental cycling processes.

Sources, fates, and impacts of nitrogen inputs to terrestrial ecosystems: review and synthesis

The relative importance of nitrogen inputs from atmospheric deposition and biological fixation is reviewed in a number of diverse, non-agricultural terrestrial ecosystems. Bulk precipitation inputs of N (l–l2 kg N ha−1 yr−1) are the same order of magnitude as, or frequently larger than, the usual range of inputs from nonsymbiotic fixation (< 1 – 5 kg N ha−1 yr−1), especially in areas influenced by industrial activity. Bulk precipitation measurements may underestimate total atmospheric deposition by 30–40% because they generally do not include all forms of wet and dry deposition. Symbiotic fixation generally ranges from ≅ 10–160 kg N ha−1 yr−1) in ecosystems where N-fixing species are present during early successional stages, and may exceed the range under unusual conditions.Rates of both symbiotic and nonsymbiotic fixation appear to be greater during early successional stages of forest development, where they have major impacts on nitrogen dynamics and ecosystem productivity. Fates and impacts of these nitrogen inputs are important considerations that are inadequately understood. These input processes are highly variable in space and time, and few sites have adequate comparative information on both nitrogen deposition and fixation.- more intensive studies of total atmospheric deposition, especially of dry deposition, are needed over a wide range of ecosystems;- additional studies of symbiotic fixation are needed that carefully quantify variation over space and time, examine more factors regulating fixation, and focus upon the availability of N and its effects upon productivity and other nutrient cycling processes;- process-level studies of associative N-fixation should be conducted over a range of ecosystems to determine the universal importance of rhizosphere fixation;- further examination of the role of free-living fixation in wood decomposition and soil organic matter genesis is needed, with attention upon spatial and temporal variation; and- investigations of long-term biogeochemical impacts of these inputs must be integrated with process-level studies using modern modelling techniques.

Successional changes in plant species diversity and composition after clearcutting a Southern Appalachian watershed

Abstract 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-Weavers index of diversity (H′) and Pielous 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.

Regeneration Patterns in Canopy Gaps of Mixed-Oak Forests of the Southern Appalachians: Influences of Topographic Position and Evergreen Understory

-Canopy gaps in southern Appalachian mixed-oak forests were assessed for the effects of topographic, gap and stand variables on density of wood seedlings. Seedling density was significantly correlated with percent slope and positively with gap age (1-5 yr). Density varied substantially among topographic positions and increased with gap size. Species richness decreased over time and increased with gap size. Regeneration was dominated by Acer rubrum L. Other important species included Quercus coccinea Muench., Q. rubra L., Q. velutina Lamarck, Liriodendron tulipifera L. and Cornus florida L. Some known gap species increased in density with increasing gap size. Competitive inhibition effects of the evergreen understory (Rhododendron maximum L. and Kalmia latifolia L.) were also examined. Gaps containing over 50% cover of R. maximum had significantly lower densities than all other gaps, including gaps with >50% K latifolia cover. Height distributions of major regenerating species were skewed away from small (<15 cm) height classes. Species establishment was a function of gap area, gap age, topographic position and cover of R. maximum. In addition, species of varying degrees of tolerance of understory conditions are capable of establishment in small to medium size canopy openings in the absence of an evergreen shrub understory.

Nitrification potentials in early successional black locust and in mixed hardwood forest stands in the southern Appalachians, USA

Soil nitrogen mineralisation and nitrification potentials, and soil solution chemistry were measured in black locust (Robinia pseudo-acacia L.), in pine-mixed hardwood stands on an early successional watershed (WS6), and in an older growth oak-hickory forest located on an adjacent, mixed hardwood watershed (WS14) at Coweeta Hydrologic laboratory, in the southern Appalachian mountains, U.S.A. Nitrification potentials were higher in black locust and pine-mixed hardwood early successional stands than in the oak-hickory forest of the older growth watershed. Ammonification rates were the main factor controlling nitrification in the early successional stands. There was no evidence of inhibition of nitrification in soils from the older growth oak-hickory forest site.Within the early successional watershed, black locust sites had net mineralisation and nitrification rates at least twice as high as those in the pine mixed-hardwood stands. Concentrations of exchangeable nitrate in the soil of black locust stands were higher than in pine-mixed hardwoods at 0–15 cm in March and they were also higher at 0–15, 16–30 and 31–45 cm depth in the black locust dominated sites in July. Soil solution nitrate concentrations were higher under black locust than under pine-mixed hardwoods. Areas dominated by the nitrogen fixing black locust had greater nitrogen mineralisation and nitrification rates, resulting in higher potential for leaching losses of nitrate from the soil column in the early successional watershed.

Distribution of native legumes (Leguminoseae) in frequently burned longleaf pine (Pinaceae)–wiregrass (Poaceae) ecosystems

Legume species distribution and abundance and selected environmental variables were quantified across a complex gradient (varying in both water-holding capacity and fertility) for frequently burned longleaf pine (Pinus palustris)-wiregrass (Aristida stricta) ecosystems. Legumes were present in all months; however, abundance peaked in June and was minimal after killing frosts in October. Legume species were prominent in the flora (43 species encountered) ubiquitous (94% of 2-m(2) subplots had at least one legume species), and abundant (nearly 120 000 stems/ha). Although most species were widely distributed throughout the gradient, Lespedeza angustifolia was distinctly associated with the more hydric end of the gradient, while both Petalostemon pinnatum and Galactia microphylla were located in the more xeric extreme. The percentage variation in species that could be accounted for by environmental variation was low (27%). Of the variation that could be accounted for, a number of environmental variables were important, including soil moisture, pine basal area (i.e., light), and bivalent base cations (e.g., Ca(2+)). Although gradients in resource availability among sites did not affect the distribution of species or abundance of legumes strongly, variation in resources are likely to regulate N(2)-fixation rates of the various native legume species, and thereby affect ecological functions such as maintenance of N capital and productivity.

Changes in vegetation structure and diversity after grass-to-forest succession in a Southern Appalachian watershed

Abstract 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, western 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 forest—represents the most severe human disturbance in the Coweeta Basin. For several years after cessation of management, Robinia pseudoacacia quickly sprouted from roots and exceeded the growth rates of other species. Liriodendron tulipifera 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. velutina. In the overstory, density-based H′ increased from 1958, before grass conversion, to 15 yr and 28 yr following disturbance. In contrast, basal area-based H′ had significantly declined at 15 yr, then increased at 28 yr. The initial decline in basal area-based H′ was attributed to a decline in evennness of species distribution (J′) rather than to a change in species richness. The severe disturbance increased the abundance of early successional woody species and of herbaceous genera that tolerate open habitats, such as Erichtites, Phytolacca, and Erigeron. Shade-tolerant understory ferns and herbs such as Polystichum acrostichoides, Dennstaedtia punctilobula, Galium latifolium and Viola cucullata gradually became more abundant. The 28-yr-old forest of WS6 had much lower species richness than the adjacent reference watersheds, but more than threefold higher density.

Federal legislation and wetlands protection in Georgia: Legal foundations, classification schemes, and industry implications

Abstract This paper integrates the legal, biological, and industrial implications of wetlands protection. The development and current status of United States law governing operations in forested wetlands are reviewed, including the regulations promulgated by the U.S. Army Corps of Engineers that determine whether permits are needed. The definitions and delineation schemes used in the Southeast for determining wetlands are summarized. Emphasis is placed on evaluation of ecological parameters presently used in determining wetlands. Since certain new criteria used in wetlands delineations have not been widely tested, the questions that need to be explored for further interpretations of jurisdiction over wetlands will be addressed. Implications for forest management practices are discussed.

Interactions Among Abiotic Drivers, Disturbance and Gross Ecosystem Carbon Exchange on Soil Respiration from Subtropical Pine Savannas

Globally, soil CO2 efflux rates (Fs) have been linked to changes in soil water content (SWC), rainfall and temperature and/or productivity. However, within an ecosystem, Fs can vary based on site structure and function, which can be affected by a combination of abiotic and biotic factors. This becomes particularly important when an ecosystem is faced with disturbances, such as drought or fire. Site-specific compensatory responses to disturbances may therefore alter C mineralization, as well as root respiration. Hence, single location Fs estimates may not be a representative for ecosystems across their distributional ranges. We conducted a 6-year study along an edaphic moisture gradient of longleaf pine ecosystems that were maintained with prescribed fire, using eddy covariance and soil respiration measurements to address how Fs varies with changes in ecosystem structure and function, as well as disturbances. Lower air temperatures (Tair) decreased Fs at all sites, but that response was also affected by productivity and SWC. Productivity significantly altered Fs rates at all sites, especially when we accounted for changes in temperature and SWC. Plant regrowth post-fire temporarily increased Fs (10–40%), whereas drought reduced Fs at all sites. Our results show that site productivity, Fs and the degree to which ecosystems adapt to climate variations and disturbance can be site specific. Hence, model forecasting of carbon dynamics would strongly benefit from multi-location measurements of Fs across the distributional range of an ecosystem.

Quantifying energy use efficiency via maximum entropy production: A case study from longleaf pine ecosystems

Reviewer’s comment: The framework presented in this study is built on Stoy et al., 2014, which in turn used a formulation by Holdway et al., 2010. These essentially simplify the concept of entropy to temperature normalization of fluxes of energy, carbon and water exchange. While a temperature normalized index for these quantities is likely to be highly useful in itself, does it warrant invoking entropy? Moreover, there are several inconsistencies, and not adequate explanation for how entropy for different fluxes is estimated. For instance, eq 4.6. which the authors define as the entropy efficiency of metabolism, is essentially a ratio of NEE:GPP. This has been previously identified as carbon use efficiency and extensively studied (for. e.g. see DeLucia et al., 2007 and references therein). In many instances, it is unclear how energy and entropy are related. It would be useful to present side-by-side comparisons.