Hardwood Forest Sites Research Articles

Conversion of low-value stands by corridor method in Left-Bank Forest-Steppe, Ukraine

Abstract The aim of the study was to identify the influence of different widths and cardinal directions of felled corridors on the condition and mensuration characteristics of the English oak trees planted there during the conversion of low-value young stands using the corridor method. The study was carried out in oak forests in the forest-steppe zone at a permanent sample plot. The experiment included the conversion of a low-value 8-year-old stand to improve its species composition. The sample plots were laid out in a fertile hardwood forest site. The conversion was realised by felling corridors of various widths (6, 9 and 12 m) and directions and planting English oak trees (Quercus robur L.) within them in rows. For the planted oaks, tending felling was carried out three times: weeding (8 years), cleaning (13 years) and thinning (32 years). A comparative analysis of mensuration characteristics (average height, diameter, growing stock, radial increment, health condition, etc.) was carried out for 32-year-old oak trees grown in the corridors and a part of a low-value stand in the unfelled strips after the tending felling. It was found that the average height and diameter at breast height of oaks in the 6, 9 and 12 m wide corridors of different cardinal directions did not differ significantly. The difference in oak stocks within 6 and 9 m wide corridors of different cardinal directions was also insignificant. The stock differences were statistically significant for 6 and 12 m wide corridors as well as for 9 and 12 m wide ones. The article made recommendations on the width of felled corridors and unfelled strips to effectively convert low-value young stands by the corridor method.

Stasis in forest regeneration following deer exclusion and understory gap creation: A 10-year experiment.

Chronically elevated ungulate browse pressure in temperate forests worldwide often generates ecological legacies characterized by low plant diversity and contributes to the formation of dense, nearly monodominant, and highly recalcitrant layers of understory vegetation. Once established, these recalcitrant layers combined with continued browsing may jointly constrain tree establishment and diversity so completely that understory recovery may be unattainable without mitigating browse pressure, the recalcitrant layer, or both. Here, we investigate the independent and synergistic effects of both white-tailed deer (Odocoileus virginianus) browsing and hay-scented fern (Dennstaedtia punctilobula) competition on tree regeneration in a 10-year experiment. Specifically, we examine how tree seedling establishment, growth, and composition are filtered by fern cover versus fern removal (gaps), browser presence versus absence (exclosures), and their combined effects during 10 years at three hardwood forest sites in Pennsylvania, USA. Fern gaps enhanced establishment for multiple tree species, increasing seedling density and diversity, particularly in the first 3 years post-treatment, and enhancing richness (≤1 species) over the course of the experiment. Excluding deer for a decade increased the height growth of other regeneration and altered species composition, but had no effect on diversity, richness, and density. Notably, we observed higher Prunus serotina seedling densities outside exclosures, possibly due to greater secondary dispersal. We argue that browsing legacies in second growth forests established at the turn of the last century created two conditions inimical to diverse forest regeneration: an overstory dominated by two species, P. serotina and Acer rubrum (86% of basal area), and a dense recalcitrant understory layer dominated by a native fern. The first condition limits propagule supply, the second strongly filters seedling establishment, and both create impoverished forest understories composed of few individuals and species. In undisturbed forest understories, the inertia toward impoverishment was sustained across the decade even where browsing was eliminated. Consequently, stand replacing disturbances (whether natural or anthropogenic) that disrupt the understory layer and reinitiate succession may be necessary to propel forests out of their current stasis and down a pathway leading to greater diversity.

Interactive Effects of White-Tailed Deer, an Invasive Shrub, and Exotic Earthworms on Leaf Litter Decomposition

Herbivore overabundance and species invasions could alter decomposition rates in temperate forests, with consequent effects on carbon sequestration, nutrient retention, and other ecosystem processes. At local scales, herbivores, invasive plants, and soil macroinvertebrates can be important drivers of decomposition, but interactive effects among these different groups are unknown. We tested for the effects of white-tailed deer, Amur honeysuckle, and earthworm activity (manipulated via mesh exclusion) on litter decomposition rates and loss of litter nitrogen (N) in five hardwood forest sites in southwestern Ohio. Each site consisted of a 20 × 20-m deer exclosure paired with a deer access plot; honeysuckle was removed from half of each plot. Effects of earthworm activity were tested using paired litter boxes of fine mesh (0.25 mm; earthworms excluded) or coarse mesh (10 mm; earthworm access). Restriction of earthworm activity in fine mesh treatments slowed litter decomposition and increased retention of N in the litter layer compared to coarse mesh. Deer access interacted with mesh treatments, with faster decomposition occurring in deer access, coarse mesh treatments relative to others. Greater earthworm biomass in deer access plots relative to deer exclosure plots corresponded with more rapid litter decomposition. Honeysuckle presence did not affect litter decomposition, but did increase litter N retention. The interactions between deer and earthworm activity indicate that reductions in deer populations may slow litter decomposition rates, increasing complexity of habitat structure at the soil surface, which relates to habitat for plants and animals.

Physiological responses of eastern hemlock (Tsuga canadensis) to light, adelgid infestation, and biological control: Implications for hemlock restoration

The rapid loss of eastern hemlock (Tsuga canadensis) in the southern Appalachian Mountains due to hemlock woolly adelgid (Adelges tsugae, HWA) infestation has resulted in substantial changes to ecosystem structure and function. Several restoration strategies have been proposed, including silvicultural treatments that increase incident light in forest understories. We conducted a four-year manipulative field experiment on surviving mid-story hemlock trees to investigate the effects of release from light limitation on HWA infestation and physiological parameters, expecting that higher light levels would improve tree carbon balance. Mixed hardwood forest sites were either previously uninfested with HWA (UN), infested with HWA (I), or infested with HWA and had a history of predatory beetle releases for biological control (I+P). At each site, we identified ten eastern hemlock trees in the mid-story and cut ~15 m radius canopy gaps around half of them while leaving the canopy intact over the other half. We compared short- and long-term indices of carbon gain and stress: leaf net photosynthesis (Anet); leaf fluorescence (Fv/Fm); leaf total non-structural carbohydrate concentration ([TNC]); new shoot growth; HWA density; and basal area growth. We found that trees experienced greater leaf-level stress in gaps and when HWA was actively feeding. Despite being more stressed, trees in gaps fixed 2x more carbon than those in reference conditions. High Anet in the spring translated into high leaf [TNC] in the spring, coinciding with when HWA was actively feeding. Although infested and uninfested trees had similar leaf [TNC] maxima, infestation prevented trees from allocating this carbon to shoot and basal area growth; this was particularly true for reference trees. Greater shoot growth in gap trees translated to greater annual basal area growth—by the end of the study, trees in gaps were growing 9x more than trees in reference conditions, and this was generally regardless of infestation status. In terms of growth and carbon balance, eastern hemlock consistently benefited from the increased light and soil moisture found in gaps; there was inconsistent and rather weak evidence that predator beetles conferred an additional advantage. Our results indicate that silvicultural treatments may improve long-term health and survival of infested trees and that integration of such treatments with existing strategies is worthy of continued exploration.

A record of flooding on the White River, Arkansas derived from tree-ring anatomical variability and vessel width

ABSTRACTTree rings preserve important records of past flooding. We present the results of an examination of inter-annual tree-ring anatomical variability and vessel width in overcup oak (Quercus lyrata) and river flooding at a bottomland hardwood forest site near the confluence of the White and Mississippi Rivers. We developed two flood chronologies based on (1) visual identification of “flood-ring” anatomical anomalies and (2) a simple method for quantitative measurements of earlywood vessel width (VW). Using visual flood rings, we have developed a response index (RI) chronology of floods from 1780–2013 and, using the VW measurements, we have developed a quantitative reconstruction of spring river levels from 1800–2013. Both the RI and VW chronologies are strongly related to spring river flooding and indicate that major floods such as those in 1805, 1826, 1844, 1852, 1858, occurred in the period prior to the systematic collection of stage data, and that the frequency of extreme events has greatly varied over the past two centuries. These chronologies provide important new information about Lower Mississippi River flooding in past centuries, and our simple method of measuring VW is a potentially useful new approach to the development of tree-ring records of flooding.

Assessing the Effects of Climate Change and Air Pollution on Soil Properties and Plant Diversity in Northeastern U.S. Hardwood Forests: Model Setup and Evaluation

The integrated forest ecosystem model ForSAFE-Veg was used to simulate soil processes and understory vegetation composition at three—sugar maple, beech, yellow birch—hardwood forest sites in the Northeastern United States (one at Hubbard Brook, NH, and two at Bear Brook, ME). Input data were pooled from a variety of sources and proved coherent and consistent. While the biogeochemical component ForSAFE was used with limited calibration, the ground vegetation composition module Veg was calibrated to field relevés. Evaluating different simulated ecosystem indicators (soil solution chemistry, tree biomass, ground vegetation composition) showed that the model performed comparably well regardless of the site’s soil condition, climate, and amounts of nitrogen (N) and sulfur (S) deposition, with the exception of failing to capture tree biomass decline at Hubbard Brook. The model performed better when compared with annual observation than monthly data. The results support the assumption that the biogeochemical model ForSAFE can be used with limited calibration and provide reasonable confidence, while the vegetation community composition module Veg requires calibration if the individual plant species are of interest. The study welcomes recent advances in empirically explaining the responses of hardwood forests to nutrient imbalances and points to the need for more research.

Vegetation dynamics associated with changes in atmospheric nitrogen deposition and climate in hardwood forests of Shenandoah and Great Smoky Mountains National Parks, USA

Ecological effects of atmospheric nitrogen (N) and sulfur (S) deposition on two hardwood forest sites in the eastern United States were simulated in the context of a changing climate using the dynamic coupled biogeochemical/ecological model chain ForSAFE-Veg. The sites are a mixed oak forest in Shenandoah National Park, Virginia (Piney River) and a mixed oak-sugar maple forest in Great Smoky Mountains National Park, Tennessee (Cosby Creek). The sites have received relatively high levels of both S and N deposition and the climate has warmed over the past half century or longer. The model was used to evaluate the composition of the understory plant communities, the alignment between plant species niche preferences and ambient conditions, and estimate changes in relative species abundances as reflected by plant cover under various scenarios of future atmospheric N and S deposition and climate change. The main driver of ecological effects was soil solution N concentration. Results of this research suggested that future climate change might compromise the capacity for the forests to sustain habitat suitability. However, vegetation results should be considered preliminary until further model validation can be performed. With expected future climate change, preliminary estimates suggest that sustained future N deposition above 7.4 and 5.0 kg N/ha/yr is expected to decrease contemporary habitat suitability for indicator plant species located at Piney River and Cosby Creek, respectively.

Estimation of plant area index and phenological transition dates from digital repeat photography and radiometric approaches in a hardwood forest in the Northeastern United States

Long-term, continuous digital camera imagery and tower-based radiometric monitoring were conducted at a representative hardwood forest site in the Northeastern United States, part of the AmeriFlux network. In this study, the phenological metrics of the leaf area index (LAI), plant area index (PAI) and associated transition dates (e.g., timing of the onset of leaf expansion and the cessation of leaf fall) were compared using 4-year of data from Bartlett Experimental Forest. We used digital repeat photography (DRP) imagery collected using two different methods (“canopy cover” and “phenocam” approaches), together with above- and below-canopy measurements of photosynthetically active radiation (PAR). The growth-period LAI estimated from canopy cover images (LAICANOPY) and the above and below canopy PAR measurements (LAIfPARt) were within approximately the same range, in term of magnitude, as previous results for multiple comparative methods, although growing-season LAICANOPY was slightly lower (3.11m2m−2 to 3.35m2m−2) than LAIfPARt (3.19m2m−2 to 3.67m2m−2). In addition, we derived phenological transition dates from PAICANOPY, PAIfPARt, and color-based metrics calculated from the phenocam imagery (green (GCC) and red (RCC) chromatic coordinates). The transition dates in both spring and autumn differed somewhat according to method, presumably due to the vegetation status detection abilities of each vegetation metric. We found that LAI estimation from canopy cover images may be influenced by automatic exposure settings, which limits the ability to detect subtle changes in phenology during the transition phases in both spring and autumn. Particularly in autumn, the color-based metrics calculated from the phenocam imagery are decoupled from leaf area dynamics and thus PAI. While above and below canopy PAR measurements could yield the better indicators for estimating LAI, its seasonal dynamics, and associated phenological transition dates in long-term monitoring, we argue that there are obvious benefits to the multi-sensor approach used here.

Spatio-temporal variation in foodscapes modifies deer browsing impact on vegetation

Ungulate browsers often alter plant composition and reduce diversity in forests worldwide, yet our ability to predict browse impact on vegetation remains equivocal. Theory suggests, however, that ungulate distribution and foraging impacts are shaped by scale-dependent decisions based on variation in habitat composition and structure encountered within their home range. Examine how variation in habitat composition at landscape (259 ha) scales modulates browse impact on vegetation at local scales. We measured vegetation richness and abundance in plots with and without white-tailed deer (Odocoileus virginianus) at 23 northern hardwood forest sites distributed across a 6500 km2 area in Pennsylvania, USA. Experimental sites were embedded within landscapes with varying levels of habitat composition and deer densities. Browsing reduced vegetation richness and cover by as much as 53 and 70%, respectively; however, we found browse impact was modulated by variation in the relative abundance of managed habitats that alter forage availability. Specifically, relative to fenced areas, browse impact weakened and ultimately disappeared as the proportion of forage-rich habitats (e.g., recent harvests) increased to ≥20%. Conversely, vegetation grew increasingly depauperate as landscapes contained greater proportions of forage-poor habitats (i.e., older harvests), particularly when browsed. Our results underscore how management actions that alter forage availability to ungulates throughout the landscape (i.e. the foodscape) can shape forest-ungulate interactions and suggest a new paradigm whereby managers evaluate and undertake actions at the appropriate spatio-temporal scales to proactively limit the deleterious impact of browsing on plant biodiversity.

CO2 time series patterns in contrasting headwater streams of North America

We explored the underlying patterns of temporal stream CO2 partial pressure (pCO2) variability using high-frequency sensors in seven disparate headwater streams distributed across the northern hemisphere. We also compared this dataset of >40,000 pCO2 records with other published records from lotic systems. Individual stream sites exhibited relatively distinct pCO2 patterns over time with few consistent traits across sites. Some sites showed strong diel variability, some exhibited increasing pCO2 with increasing discharge, whereas other streams had reduced pCO2 with increasing discharge or no clear response to changes in flow. The only “universal” signature observed in headwater streams was a late summer pCO2 maxima that was likely driven by greatest rates of organic matter respiration due to highest annual temperatures. However, we did not observe this seasonal pattern in a southern hardwood forest site, likely because the region was transitioning from a severe drought. This work clearly illustrates the heterogeneous nature of headwater streams, and highlights the idiosyncratic nature of a non-conservative solute that is jointly influenced by physics, hydrology, and biology. We suggest that future researchers carefully select sensor locations (within and among streams) and provide additional contextual information when attempting to explain pCO2 patterns.

Influence of Intensity and Duration of Invasion by Amur Honeysuckle (Lonicera maackii) on Mixed Hardwood Forests of Indiana

AbstractThe expansion of populations of invasive species continues to compromise the ecological and economic integrity of our natural resources. The negative effects of invasive species on native biota are widely reported. However, less is known about how the duration (i.e., age of oldest invaders) and intensity (i.e., density and percent cover) of an invasion influences native plant diversity and abundance at the microsite scale. We examined the influence of density, percent cover, and age of Amur honeysuckle (a nonnative invasive shrub), and several environmental factors on native plant taxa at 12 mixed hardwood forests in Indiana, USA. Overall, study sites with the greatest taxonomic diversity (Shannon's Diversity; H′), richness (S), percent cover, and density of native vegetation also had the lowest percent cover of Amur honeysuckle in the upper vertical stratum (1.01 to 5 m). Based on linear mixed model analyses, percent cover of Amur honeysuckle in the upper vertical stratum was consistently and negatively correlated with H′, S, total percent cover, and woody seedling density of native taxa at the microsite scale (P < 0.05). Duration of Amur honeysuckle at the microsite scale was not significant when percent cover of Amur honeysuckle in the upper vertical stratum was included in models. However, duration of Amur honeysuckle invasion was significantly correlated with dependent variables and with upper-stratum honeysuckle cover, suggesting that older Amur honeysuckle in a microsite resulted in greater light competition from above for native understory plant species. Beyond increased cover and shading, our results do not provide evidence of duration-related effects from long-term dominance of honeysuckle in our sampled mixed hardwood forest sites.

Snowpack-atmosphere gas exchanges of carbon dioxide, ozone, and nitrogen oxides at a hardwood forest site in northern Michigan

Abstract Snowpack-atmosphere gas exchanges of CO2, O3, and NOx (NO + NO2) were investigated at the University of Michigan Biological Station (UMBS), a mid-latitude, low elevation hardwood forest site, during the 2007–2008 winter season. An automated trace gas sampling system was used to determine trace gas concentrations in the snowpack at multiple depths continuously throughout the snow-covered period from two adjacent plots. One natural plot and one with the soil covered by a Tedlar sheet were setup for investigating whether the primary source of measured trace gases was biogenic (i.e., from the soil) or non-biogenic (i.e., from the snowpack). The results were compared with the “White on Green” study conducted at the Niwot Ridge (NWT) Long Term Ecological Research site in Colorado. The average winter CO2 flux ± s.e. from the soil at UMBS was 0.54 ± 0.037 µmol m-2 s-1 using the gradient diffusion method and 0.71 ± 0.012 µmol m-2 s-1 using the eddy covariance method, and in a similar range as found for NWT. Observed snowpack-O3 exchange was also similar to NWT. However, nitrogen oxides (NOx) fluxes from snow at UMBS were 10 times smaller than those at NWT, and fluxes were bi-directional with the direction of the flux dependent on NOx concentrations in ambient air. The compensation point for the change in the direction of NOx flux was estimated to be 0.92 nmol mol-1. NOx in snow also showed diurnal dependency on incident radiation. These NOx dynamics in the snow at UMBS were notably different compared to NWT, and primarily determined by snow-atmosphere interactions rather than by soil NOx emissions.

Earthworms Reduce Biotic 15-Nitrogen Retention in Northern Hardwood Forests

Invasive exotic earthworms are significantly influencing understory community composition, soil, and ecosystem processes in northern hardwood forests in North America, but their effect on the retention of nitrogen (N) has been inconclusive. We examined this in two northern hardwood forest sites in New York state, USA through a tracer study. In both spring and fall, we added tracer amounts of 15N as nitrate—to simulate atmospheric deposition—with the biologically less active tracer bromide (Br−) to areas both with and without large populations of invasive earthworms. Total recovery of 15N was lower in earthworm-invaded plots, largely due to less retention in litter and upper soil horizons. Although the strong relationship between retention in the upper soil horizons and total 15N recovery suggests that earthworm destruction of the forest floor may be one mechanism reducing the capacity for N retention, in some cases the mineral soil in earthworm-invaded plots retained substantial N. Biotic pools, particularly litter and microbial biomass, retained significantly less 15N in earthworm-invaded plots than in their uninvaded counterparts. In plots invaded by earthworms, negative effects of earthworms on trees were revealed through root-uptake assays suggesting somewhat greater plant demand for ammonium in the spring and in lower 15N recovery in maple seedlings the year following tracer addition. Although similar patterns of Br− movement across treatments suggested that earthworms had smaller effects on hydrologic tracer movement than expected, they appear to have significant effects on the biological processes that underlie N retention.

Land snail diversity and composition in relation to ecological variations in Central European floodplain forests and their history

We explored patterns of land snail assemblages using 93 alluvial forest sites in six river floodplains of the Elbe drainage basin (northwestern Bohemia, Czech Republic). Differences in species richness and composition across the four floodplain forest types (i.e., alder carrs, ash-alder forests, willow-poplar softwood forests, and hardwood forests) were analysed using generalized linear models, multidimensional scaling and redundancy analysis with the Monte Carlo permutation test. The studied floodplain forest types did not differ in species richness, except for the alder carrs which were significantly poorer. The number of species expressed a significant unimodal response along with elevation and Ellenberg nutrients, and further significantly decreased towards the most humid sites. Contrary to species richness, the main forest types clearly differed based on land snail species composition, with the exception of the ash-alder and willow-poplar forest sites which became completely overlapped in the ordination space. The main changes in species composition were mostly associated with elevation and Ellenberg moisture on the first MDS axis: Ellenberg nutrients and light were fitted on the second and the third axes, respectively. These variables, along with calcium content estimated using Ellenberg indicator values for soil reaction, had significant effects on the variation and snail species composition in the final RDA model. No response of either species richness or compositional changes was found for the measured content of topsoil calcium, most likely due to the higher importance of other variables. On the basis of some recently published data we can conclude that historical development and long-term human activities on the succession of floodplain assemblages have resulted in a sharp impoverishment of strictly land snail species of several hardwood forest sites in the majority of lower river stretches. Whilst in most areas there are no exact palaeoecological data available, these historical influences were closely correlated with the site elevation in our dataset as the main difference in species composition was hard to explain solely using environmental predictors.

Effects of Management on the Amount and Characteristics of Woody Debris in Mixed Stands of Caspian Forests

Woody debris (WD), including coarse woody debris (CWD) and fine woody debris (FWD), is an essential structural and functional component of forest ecosystems. This study was carried out in Caspian hardwood forest sites. In this study, the volume and composition of WD were inventoried by line intersect sampling and fixed area plot sampling in unmanaged and managed forests on 6 compartments (3 managed and 3 unmanaged). Estimates of the total volume of WD in managed and unmanaged forests ranged from 11.9 m3.ha-1 to 25.82 m3.ha-1, respectively. The results of independent t tests indicated that the amount of CWD in the unmanaged forests was significantly higher than CWD in the managed ones (t22, 0.05 = 2.64, P = 0.015). Also, the results of independent t tests indicated that the amount of FWD in the managed forests was significantly higher than FWD in unmanaged forests (t4, 0.05 = 5.07, P = 0.007). In the unmanaged forests, WD in decay classes 3, 4, and 5 accounted for 77% of the total WD volume, but in the managed forests, WD in decay classes 1 and 2 accounted for 87% of the total WD volume. The results suggest preserving the current unmanaged forests (protected forests) and maintaining the structural and functional integrity of woody debris.

Current and projected abundance of potential nest sites for cavity‐nesting ducks in hardwoods of the north central United States

AbstractClearing of hardwood forests was widespread in the north central region of the United States at the turn of the 20th century, but largely subsided by the 1920s. Hardwood trees in the region have since regenerated and matured into sizes capable of producing nest cavities suitable for cavity‐nesting ducks. We estimated regional nest‐site abundance for cavity‐nesting ducks during 2008, 2018, and 2028 from cavity density and tree‐abundance estimates obtained at 4 hardwood forest sites in conjunction with Forest Inventory and Analysis data and tree‐growth modeling software from the United States Forest Service (Forest Vegetation Simulator). Land cover data were used to determine area of hardwood forests ≤0.5 km, 0.5–1 km, 1–1.5 km, 1.5–2 km, and >2 km from wetlands and open water available to cavity‐nesting ducks. We estimated 13.2 million, 17.0 million, 19.0 million, and 20.1 million potential duck nest cavities available ≤0.5 km, ≤1 km, ≤1.5 km, and ≤2 km of water, respectively, in the region and predicted nest cavity abundance will increase 41% from 2008 to 2028. Hardwood forests in Indiana, Michigan, Ohio, and Wisconsin currently have the highest abundances of potential nest sites, but cavity‐bearing forests in Minnesota, Michigan, and Wisconsin were more commonly proximate to wetlands and open water. Because current and future estimates indicate sufficient nest sites to support growing cavity‐nesting duck populations in the north central United States, we recommend regional management efforts focus on protecting, restoring, and maintaining quality wetlands in proximity to hardwood forests. © 2011 The Wildlife Society.

Observations and modeling of formaldehyde at the PROPHET mixed hardwood forest site in 2008

Abstract We report the first field measurements of gas-phase formaldehyde (HCHO) via laser-induced fluorescence (LIF) obtained August 1–8, 2008 at the PROPHET mixed hardwood forest site at the University of Michigan Biological Station. HCHO mixing ratios above the canopy ranged from a nighttime minimum of ∼0.5 ppb v to afternoon maxima of ∼4.2 ppb v . Daytime HCHO mixing ratios were compared to two zero-dimensional box models: one based on the Master Chemical Mechanism v3.2 (MCM), the other using a simplified treatment of HCHO production. Both models over-predicted HCHO relative to observations. Sensitivity analyses demonstrated that increasing vertical dilution and/or decreasing OH concentrations would result in a significant reduction in this over-prediction for both models, as did reducing NO concentrations in the MCM based model. On average, the two models agreed to within 9%, though sensitivity analyses of changing NO and HO 2 concentrations result in significant deviation. This displays that modeled HCHO production is heavily-dependent on the yields and rates of RO 2 destruction pathways under low NO conditions, which may have implications for simplified mechanisms and global predictions of isoprene emission based on satellite HCHO measurements.

Heating up the forest: open‐top chamber warming manipulation of arthropod communities at Harvard and Duke Forests

Summary1. Recent observations indicate that climatic change is altering biodiversity, and models suggest that the consequences of climate change will differ across latitude. However, long‐term experimental field manipulations that directly test the predictions about organisms’ responses to climate change across latitude are lacking. Such experiments could provide a more mechanistic understanding of the consequences of climate change on ecological communities and subsequent changes in ecosystem processes, facilitating better predictions of the effects of future climate change.2. This field experiment uses octagonal, 5‐m‐diameter (c. 22 m3) open‐top chambers to simulate warming at northern (Harvard Forest, Massachusetts) and southern (Duke Forest, North Carolina) hardwood forest sites to determine the effects of warming on ant and other arthropod populations and communities near the edges of their ranges. Each site has 12 plots containing open‐top chambers that manipulate air temperature incrementally from ambient to 6 °C above ambient. Because the focus of this study is on mobile, litter‐ and soil‐dwelling arthropods, standard methods for warming chambers (e.g. soil‐warming cables or infrared heaters applied to relatively small areas) were inappropriate and new technological approaches using hydronic heating and forced air movement were developed.3. We monitor population dynamics, species composition, phenology and behaviour of ants and other arthropods occupying these experimental chambers. Microclimatic measurements in each chamber include the following: air temperature (three), soil temperatures (two each in organic and mineral soil), photosynthetically active radiation (PAR), relative humidity and soil moisture (one each). In two chambers, we are also measuring soil heat flux, associated soil temperatures at 2 and 6 cm and volumetric water content. To assess the composition, phenology and abundance of arthropod communities within the experiment, we use monthly pitfall trapping and annual Winkler sampling. We also census artificial and natural ant nests to monitor changes in ant colony size and productivity across the temperature treatments.4. This experiment is a long‐term ecological study that provides opportunities for collaborations across a broad spectrum of ecologists, including those studying biogeochemical, microbial and plant responses to warming. Future studies also may include implementation of multifactorial climate manipulations, examination of interactions across trophic levels and quantification of changes in ecosystem processes.

Maximum entropy modeling of mature hardwood forest distribution in four U.S. states

In the eastern United States, mature hardwood forest provides habitat for many species of native flora and fauna, but is much less common now than historically. This study examined the utility of maximum entropy modeling and spatial application to identify ecosystem types like mature hardwood forest. I performed pilot modeling in Charles County, Maryland, where I compared fine-scale geographic data available locally to coarse-scale data available nationally. As expected, a model constructed with the best locally available data, including LiDAR-derived canopy height and fine-scale soil maps, outperformed a model constructed with nationally consistent data. However, the model using national data nevertheless accurately identified most mature hardwood forest sites and excluded most young forest. I then applied the coarse-scale approach to four states: Pennsylvania, Ohio, Kentucky, and Tennessee. Average test AUC (area under the receiver operating curve) based on 10 replicates varied from 0.76 to 0.80 when comparing mature hardwood forest locations to general forest locations. The maximum training or test sensitivity plus specificity threshold, depending on the state, captured 78–79% of positive locations while rejecting 74–81% of negative locations. The maximum entropy approach is versatile, and can be applied to other ecosystems and species.

Habitat and Host Tree Selection by Wintering Yellow-bellied Sapsuckers in East Texas

Yellow-bellied Sapsucker (Sphyrapicus varius) foraging ecology has long been a focus of study, primarily due to their sap-foraging behavior throughout the year and speculation on how sapsuckers subsist by foraging on dormant host trees during winter. Wintering sapsucker habitat use as related to host tree selection is not clearly defined, particularly in the southwestern portion of its range. We studied Yellow-bellied Sapsucker habitat use and host tree selection in two bottomland hardwood forest sites in eastern Texas during winters, 2005–2006 and 2006–2007. Habitat surrounding overcup oak (Quercus lyrata) host trees was generally characterized by fewer trees/ha, lower species diversity and richness, and taller trees than random plots. Overcup oak host trees tended to be healthier than overcup oak non-host trees, but host trees had thinner, less complex bark than non-host trees, irrespective of tree size and health. Also, digestible cell and protein content was similar between host and non-host trees, irrespective of tree size and health. Selection of host trees with thinner, less complex bark suggest sapsuckers use visual cues to focus host selection upon bark morphology and evidence of previous use. Combined, wintering sapsuckers may increase foraging efficiency and maximize caloric intake by increasing energy gained/unit time foraging on already established, and presumably productive host trees. Despite similarities in habitat, health and cell and protein content between host and non-host trees, Yellow-bellied Sapsuckers selected healthy host trees with thin, less complex bark where stable levels of digestible cell content and protein over time provide a reliable, consistent food source throughout winter.