Forest Development over a Twenty-Year Chronosequence of Reforested Urban Sites

Urbanization causes a variety of negative ecological impacts, impairing forests, streams, and other ecosystems. While urban forests are the subject of increasing research attention, planted urban forests are less well-understood than remnant forests; however, these systems may be distinct in terms of ecosystem structure and function. The current study investigates a chronosequence of reforested urban sites in Lexington, KY, USA, with a focus on overstory and understory woody plant community characteristics. Monitoring plots were established in each of the 20 sites; tree height, dbh, and species were surveyed for the overstory, and species and height were surveyed for the understory. Canopy height increased non-linearly with time since planting, rapidly increasing in years 6–10, but remaining relatively steady after year 15. While the overstory was dominated by planted native species, the understory was predominately non-native species, some of which are considered invasive. Overall, the nonlinear logistic relationship of canopy height to time since planting may be driven by species-specific effects—with trees such as ash (Fraxinus spp. L.) and black locust (Robinia pseudoacacia L.) important during the early years after planting, but declining over time due to pests and other pressures. Alternatively, this complex relationship of canopy height with time may be driven by uncontrolled factors such as site quality, landscape position, planted species, etc. The significance of invasive species in the understory suggests that the long-term health of these sites will be compromised without intentional ongoing maintenance to ensure continued forest development toward desired native community characteristics

Quantifying the Effects of Biomass Market Conditions and Policy Incentives on Economically Feasible Sites to Establish Dedicated Energy Crops

This study used a spatially-explicit model to identify the amount and spatial distribution of economically feasible sites for establishing dedicated energy crops under various market and policy scenarios. A sensitivity analysis was performed for a biomass market with different discount rates and biomass prices as well as policy scenarios including propriety tax exemption, carbon offset payments, and the inclusion of farmland for biomass production. The model was applied to a four-county study area in Kentucky representing conditions commonly found in the Ohio River Valley. Results showed that both biomass price and discount rate have a can strongly influence the amount of economically efficient sites. Rising the biomass price by 5 $·t−1 and lowering discount rate by 1$·t−1 and 5%) resulted in an over fourteen fold increment. Property tax exemption resulted in a fourfold increase, a carbon payment on only 1 $·t−1 caused a twelve fold increase and extending the landbase from marginal land to farmland only slightly increase the economically efficient sites. These results provide an objective evaluation of market and policy scenarios in terms of their potential to increase land availability for establishing dedicated energy crops and to promote the bioenergy industry

Improving Woody Biomass Estimation Efficiency Using Double Sampling

Although double sampling has been shown to be an effective method to estimate timber volume in forest inventories, only a limited body of research has tested the effectiveness of double sampling on forest biomass estimation. From forest biomass inventories collected over 9,683 ha using systematic point sampling, we examined how a double sampling scheme would have affected precision and efficiency in these biomass inventories. Our results indicated that double sample methods would have yielded biomass estimations with similar precision as systematic point sampling when the small sample was ≥ 20% of the large sample. When the small to large sample time ratio was 3:1, relative efficiency (a combined measure of time and precision) was highest when the small sample was a 30% subsample of the large sample. At a 30% double sample intensity, there was a \u3c 3% deviation from the original percent margin of error and almost half the required time. Results suggest that double sampling can be an efficient tool for natural resource managers to estimate forest biomass

First-Year Vitality of Reforestation Plantings in Response to Herbivore Exclusion on Reclaimed Appalachian Surface-Mined Land

Conventional Appalachian surface-mine reclamation techniques repress natural forest regeneration, and tree plantings are often necessary for reforestation. Reclaimed Appalachian surface mines harbor a suite of mammal herbivores that forage on recently planted seedlings. Anecdotal reports across Appalachia have implicated herbivory in the hindrance and failure of reforestation efforts, yet empirical evaluation of herbivory impacts on planted seedling vitality in this region remains relatively uninitiated. First growing-season survival, height growth, and mammal herbivory damage of black locust (Robinia pseudoacacia L.), shortleaf pine (Pinus echinata Mill.), and white oak (Quercus alba L.) are presented in response to varying intensities of herbivore exclusion. Seedling survival was generally high, and height growth was positive for all species. The highest herbivory incidence of all tree species was observed in treatments offering no herbivore exclusion. While seedling protectors lowered herbivory incidence compared with no exclusion, full exclusion treatments resulted in the greatest reduction of herbivore damage. Although herbivory from rabbits, small mammals, and domestic animals was observed, cervids (deer and elk) were responsible for 95.8% of all damaged seedlings. This study indicates that cervids forage heavily on planted seedlings during the first growing-season, but exclusion is effective at reducing herbivory

Development of Mine Soils in a Chronosequence of Forestry-Reclaimed Sites in Eastern Kentucky

Surface mining for coal has contributed to widespread deforestation and soil loss in coal mining regions around the world, and particularly in Appalachia, USA. Mined land reforestation is of interest in this and other regions where forests are the dominant pre-mining land use. This study evaluated mine soil development on surface-mined sites reforested according to the Forestry Reclamation Approach, representing a chronosequence of time ranging from 0 to 19 years after reclamation. Soils were sampled in depth increments to 50 cm and analyzed for a suite of soil physical and chemical characteristics. Overall, soil fines (silt + clay) tended to increase over time since reclamation (17% silt at year 0 increasing to 35% at year 11; 3.2% clay at year 0 increasing to 5.7% at year 14) while concentrations of metals (e.g., Al, Mg, Mn, Na) demonstrated varied relationships with time since reclamation. Concentrations of organic carbon (OC) tended to increase with time (0.9% OC at year 0 increasing to 2.3% at year 14), and were most enriched in near-surface soils. Some soil characteristics (e.g., Na, OC, Ca) demonstrated patterns of increasing similarity to the forest control, while others were distinct from the forest control throughout the chronosequence (e.g., Al, clay, Mn, gravel). Future surveys of these soils over time will elucidate longer-term patterns in soil development, and better characterize the time scales over which these soils might be expected to approximate forest soil conditions

\u3ci\u3eAnnals of Forest Science\u3c/i\u3e Promotes Multidisciplinary Research on Forests and Wood in a Changing World and Is Now a Full Open Access Journal

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Comparing individual-tree approaches for predicting height growth of underplanted seedlings

International audienceAbstractKey messageIndividual-tree seeding height growth models developed using tree inventory data were comparable to those requiring the unique observation of point-based canopy structure data at each seedling.ContextQuantitative approaches describing the relationship between canopy structure and seedling growth can inform silvicultural decision making regarding the development of tree reproduction beneath a dominant forest canopy.AimsIndividual-tree seedling growth models with canopy structure predictors derived from tree inventory data have not been well-explored. This study compared a model framework fit using point-based measures of canopy structure observed at the seedling level to one fit using area-wide canopy structure variables derived from standard inventory plot data.MethodsSpecies-specific models predicting 5-year height growth were fit for cherrybark oak (Quercus pagoda Raf.), water oak (Quercus nigra L.), and yellow-poplar (Liriodendron tulipifera L.) underplanted within a canopy structure gradient created by silvicultural manipulation of a closed-canopy forest in Georgia, USA.ResultsThough the species varied in shade tolerance and growth rates, the general relationship between the predictor variables and height growth was similar among species and model type. Models highlight the importance of including predictor variables that describe seedling size along with openness and vertical structure of the forest canopy.ConclusionWhile the two model frameworks had comparable fit statistics, the one with predictors derived from tree inventory data may have enhanced utility as it can be directly integrated into existing individual-tree forest growth simulators

Twenty Years of Urban Reforestation: Overstory Development Structures Understory Plant Communities in Lexington, KY, USA

Urban forests provide critical ecosystem services in an increasingly urbanized global landscape. The reforestation of undeveloped parcels and serially mowed grasslands can increase urban forest cover, but plant community development in planted urban forests is poorly understood. We conducted a study to elucidate the roles of time since tree planting, invasive species abundance, and other abiotic and biotic site-level factors in structuring understory plant communities within a 20-year chronosequence of planted urban forests in Lexington, KY, USA. We assessed the percent of groundcover of all understory species in fixed-radius plots on the site. Understory herbaceous plant communities demonstrated shifts from graminoid dominance to forb dominance over time, and plant communities in successively younger sites were increasingly dissimilar from that of the 20-year-old site. Invasive plant species were abundant, representing 21% of total groundcover across all surveyed plots, and became increasingly prevalent over time. Understory plant diversity was negatively associated with invasive species abundance. Overall, site factors, including time since planting, forest canopy closure, density of tree and shrub reproduction, and soil pH, accounted for much of the variability among understory communities. Understory plant communities across the chronosequence of planted sites demonstrated apparent structural shifts with overstory canopy development, but the increasing prevalence of invasive species and their negative impacts to plant diversity warrant future management to ensure the continuation of the desired successional trajectories

Quantifying the Effects of Biomass Market Conditions and Policy Incentives on Economically Feasible Sites to Establish Dedicated Energy Crops

This study used a spatially-explicit model to identify the amount and spatial distribution of economically feasible sites for establishing dedicated energy crops under various market and policy scenarios. A sensitivity analysis was performed for a biomass market with different discount rates and biomass prices as well as policy scenarios including propriety tax exemption, carbon offset payments, and the inclusion of farmland for biomass production. The model was applied to a four-county study area in Kentucky representing conditions commonly found in the Ohio River Valley. Results showed that both biomass price and discount rate have a can strongly influence the amount of economically efficient sites. Rising the biomass price by 5 $·t−1 and lowering discount rate by 1$·t−1 and 5%) resulted in an over fourteen fold increment. Property tax exemption resulted in a fourfold increase, a carbon payment on only 1 $·t−1 caused a twelve fold increase and extending the landbase from marginal land to farmland only slightly increase the economically efficient sites. These results provide an objective evaluation of market and policy scenarios in terms of their potential to increase land availability for establishing dedicated energy crops and to promote the bioenergy industry