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Wintergreen ferns keep their leaves for an entire year before replacing them with new leaves in the spring. The overwintering leaves of Dryopteris intermedia provide carbon to the new leaves, and if these old leaves cannot become prostrate before winter via the hinge that develops at the base of the petiole, they are frost damaged and broken, which may affect the development of the new leaves in the subsequent year. I compared the vernal development of new leaves in D. intermedia between plants whose old leaves were intact and those whose petioles had been experimentally broken in the fall to determine the importance of the softening of the petiole-base in old leaves to the development of new leaves. Compared to the control, plants whose old leaves had broken petioles had a one-week delay in the development of their new leaves. This delay demonstrates that the evolutionary development of the petiole hinge may have been critical to the functional benefit associated with new leaf development in the wintergreen leaf habit in ferns. [ABSTRACT FROM AUTHOR]

Abstract: Deciduous forests are regenerating following industrial disturbance in large areas of eastern North America and western Europe. To understand the long-term process of forest regeneration, the microenvironment and flora of post-industrial plots were compared with non-industrial controls at two 19th century iron furnace sites in southeastern Ohio, USA. Post-industrial plots had a shrub and canopy structure similar to controls, and showed comparable litter cover, soil organic content, and bulk density. Post-industrial and control plots remained clearly distinguishable in soil moisture, pH, and cation concentrations, however, consistent with leaching from industrial waste. Post-industrial areas were dominated by shade-tolerant plant species typical of long-established second-growth forest in the region, suggesting functional suitability of the industrial soils and an abundance of potential colonists. Open-habitat species persisted in post-industrial plots, showing a significantly higher richness and abundance than control plots. Annual growth increments showed later establishment of canopy tree species in the post-industrial plots, suggesting that the presence of open-habitat species reflected delayed canopy closure in the post-industrial area. Slag, clinker, iron–ore, and terrace microsites consistently differed in species composition within the post-industrial areas despite their relatively small size and close proximity. Thus, industrial effects appear to be perpetuated by long-term persistence of species distributions and hitherto unsuspected sensitivity to physical and chemical gradients. Forest composition and spatial structure retain a distinctive industrial character even 120years after abandonment. [Copyright &y& Elsevier]

Disruptions to historic disturbance and herbivory regimes have altered plant assemblages in forests worldwide. An emerging consensus suggests that these disruptions often result in impoverished forest biotas. This is particularly true for eastern U.S. deciduous forests where large gaps and understory fires were once relatively common and browsers were far less abundant. Although much research has focused on how disturbance and browsers affect tree diversity, far less attention has been devoted to forest understories where the vast majority (>75%) of the vascular species reside. Here we test the hypothesis that the reintroduction of disturbances resembling historic disturbance regimes and moderate levels of ungulate browsing enhance plant diversity. We explore whether once-common disturbances and their interaction with the top-down influence of browsers can create conditions favorable for the maintenance of a rich herbaceous layer in a region recognized as a temperate biodiversity hotspot in West Virginia, USA. We tested this hypothesis via a factorial experiment whereby we manipulated canopy gaps (presence/absence) of a size typically found in old-growth stands, low-intensity understory fire (burned/unburned), and deer browsing (fenced/unfenced). We tracked the abundance and diversity of more than 140 herb species for six years. Interactions among our treatments were pervasive. The combination of canopy gaps and understory fire increased herbaceous layer richness, cover, and diversity well beyond either disturbance alone. Furthermore, we documented evidence that deer at moderate levels of abundance promote herbaceous richness and abundance by preferentially browsing fast- growing pioneer species that thrive following co-occurring disturbances (i.e., fire and gaps). This finding sharply contrasts with the negative impact browsers have when their populations reach levels well beyond those that occurred for centuries. Although speculative, our results suggest that interactions among fire, canopy gaps, and browsing provided a variable set of habitats and conditions across the landscape that was potentially capable of maintaining much of the plant diversity found in temperate forests. [ABSTRACT FROM AUTHOR]

Aim The assembly of a forest flora on sites abandoned from agriculture is potentially limited by the physical and chemical suitability of soils. This paper describes the post-agricultural development of soil in deciduous forest sites to gauge its importance in limiting a second-growth forest flora. Location Northern Delaware and south-eastern Pennsylvania, USA. Methods A chronosequence of 99 second-growth forest sites was assembled in the Piedmont region. Stand age ranged from 0–20 to > 100 years since canopy closure, as determined from historical aerial photographs. Seventy-four sites are likely to have experienced cultivation before regeneration of forest. The presence of large rocks or pit-and-mound microtopography suggests that the remaining 25 sites were not cultivated, although they were probably used as pasture and/or woodlot. Soil organic content, moisture, pH, and concentrations of extractable potassium, phosphorous, calcium, magnesium and sulphur were measured in samples from each site. Coarse woody debris, size of the largest tree, canopy openness and several microtopographic features were also recorded. Results Most soil variables fell into two separate but internally correlated groups: the first group including organic matter, moisture and sulphur; the second including pH, calcium, potassium and magnesium. In formerly cultivated sites, organic matter, moisture and sulphur increased gradually through the chronosequence, approaching values recorded in uncultivated sites at 81–100 years. Calcium, potassium, magnesium and pH declined sharply between the 21–40- and 41–60-year classes – probably an indirect effect related to geographic location and selective abandonment. Phosphorous also declined with time, but the decline was not as clearly defined. Main conclusions The progress of soil recovery observed here is faster than rates implied in other studies, possibly because these sites experienced a period as pasture before reversion to forest. Sites appear to have returned to undisturbed-forest levels as fast as or faster than the predicted accumulation of a forest flora, suggesting that assembly of second-growth forest communities is not limited by the rate of soil development in this region. [ABSTRACT FROM AUTHOR]

The article presents a study which investigates the flight periods, sex ratios and habitat frequencies of mecopteran species in the U.S. Mid-Atlantic floodplain forest, freshwater tidal marsh, and their ecotone. Six Malaise traps was operated in Dyke Marsh Wildlife Preserve (DMWP) in Fairfax County, Virginia from April 1998 until December 1999 and has acquired 104 mecopterans in five species. Two traps were place in each of the three main Preserve habitats which include the low forest, freshwater tidal marsh and the ecotone between them. The results showed that mecopterans were more abundant in the forest rather than in the ecotone and marsh, and they have a female-biased sex ratio.

Abstract: We investigated the assumption, necessary for comparison between bottom-up scaling of plot level fluxes to top-down scaling of regional models, that small plots of sap flux are representative of the transpiration component of regional land-surface atmosphere water vapor interactions. We conducted sap flux measurements in three stands dominated by sugar maple (Acer saccharum Marsh.) representing old-growth (Sylvania, SV), second-growth (Willow Creek, WC), and thinned second-growth stands (Hay Creek, HC). Using the sap flux-scaled estimates of transpiration we tested whether (1) differences in A. saccharum transpiration between the three stands could be explained by leaf area index and/or stand inventory measures, and (2) the Terrestrial Regional Ecosystem Exchange Simulator (TREES) model could capture differences in the response of transpiration to environmental variables. We found large differences between the three stands over two growing seasons in A. saccharum canopy transpiration per unit ground area (1.61, 3.66, and 0.85mmday−1 for SV, WC, and HC respectively) and canopy transpiration per unit leaf area (0.31, 1.00, and 0.21mmday−1 for SV, WC, and HC respectively). While none of these differences could be explained with stand or environmental variables, the TREES model was able to effectively capture the half-hourly temporal variability in the sap flux data. TREES incorporates an adaptive parameterization scheme which improves upon traditional sensitivity tests of models. By incorporating both simple plant hydraulic theory and adaptive parameterization we were able to minimize the necessary parameters to those that are sensible and easily applied regionally. Our results indicate that while the assumption of uniform water loss from A. saccharum forests regionally is incorrect, models that incorporate simple plant hydraulics effectively capture the dynamics of transpiration across disparate stands. [Copyright &y& Elsevier]

Scatter-hoarding rodents should space food caches to maximize cache recovery rate (to minimize loss to pilferers) relative to the energetic cost of carrying food items greater distances. Optimization models of cache spacing make two predictions. First, spacing of caches should be greater for food items with greater energy content. Second, the mean distance between caches should increase with food abundance. However, the latter prediction fails to account for the effect of food abundance on the behavior of potential pilferers or on the ability of caching individuals to acquire food by means other than recovering their own caches. When considering these factors, shorter cache distances may be predicted in conditions of higher food abundance. We predicted that seed caching distances would be greater for food items of higher energy content and during lower ambient food abundance and that the effect of seed type on cache distance variation would be lower during higher food abundance. We recorded distances moved for 8636 seeds of five seed types at 15 locations in three forested sites in Pennsylvania, USA, and 29 forest fragments in Indiana, USA, across five different years. Seed production was poor in three years and high in two years. Consistent with previous studies, seeds with greater energy content were moved farther than less profitable food items. Seeds were dispersed less far in seed-rich years than in seed-poor years, contrary to predictions of conventional models. Interactions were important, with seed type effects more evident in seed- poor years. These results suggest that, when food is superabundant, optimal cache distances are more strongly determined by minimizing energy cost of caching than by minimizing pilfering rates and that cache loss rates may be more strongly density-dependent in times of low seed abundance. [ABSTRACT FROM AUTHOR]

Ozone (O 3 ) damage to leaves can reduce plant photosynthesis, which suggests that declines in ambient O 3 concentrations ([O 3 ]) in the United States may have helped increase gross primary production (GPP) in recent decades. Here, we assess the effect of long-term changes in ambient [O 3 ] using 20 years of observations at Harvard forest. Using artificial neural networks, we found that the effect of the inclusion of [O 3 ] as a predictor was slight, and independent of O 3 concentrations, which suggests limited high-frequency O 3 inhibition of GPP at this site. Simulations with a terrestrial biosphere model, however, suggest an average long-term O 3 inhibition of 10.4% for 1992-2011. A decline of [O 3 ] over the measurement period resulted in moderate predicted GPP trends of 0.02-0.04 μmol C m -2  s -1  yr -1 , which is negligible relative to the total observed GPP trend of 0.41 μmol C m -2  s -1  yr -1 . A similar conclusion is achieved with the widely used AOT40 metric. Combined, our results suggest that ozone reductions at Harvard forest are unlikely to have had a large impact on the photosynthesis trend over the past 20 years. Such limited effects are mainly related to the slow responses of photosynthesis to changes in [O 3 ]. Furthermore, we estimate that 40% of photosynthesis happens in the shade, where stomatal conductance and thus [O 3 ] deposition is lower than for sunlit leaves. This portion of GPP remains unaffected by [O 3 ], thus helping to buffer the changes of total photosynthesis due to varied [O 3 ]. Our analyses suggest that current ozone reductions, although significant, cannot substantially alleviate the damages to forest ecosystems., (© 2016 John Wiley & Sons Ltd.)

Abstract The role of mid-latitude forests in the sequestration of carbon (C) is of interest to an increasing number of scientists and policy-makers alike. Net CO2 exchange can be estimated on an annual basis, using eddy-covariance techniques or from ecological inventories of C fluxes to and from a forest. Here we present an intercomparison of annual estimates of C exchange in a mixed hardwood forest in the Morgan-Monroe State Forest, Indiana, USA for two years, 1998 and 1999. Based on eddy-covariance measurements made at 1.8 times canopy height from a tower, C uptake by the forest was 237 and 287 g C m-2 y-1 for 1998 and 1999, respectively. For the same time period, biometric and ecophysiological measures and modelled estimates of all significant carbon fluxes within deciduous forests were made, including: change in living biomass, aboveground and belowground detritus production, foliage consumption, and forest floor and soil respiration. Using this ecological inventory method for these same two time periods, C uptake was estimated to be 271 and 377 g C m-2 y-1 , which are 14.3% and 31.4% larger, respectively, than the tower-based values. The relative change between this method's annual estimates is consistent with that of the eddy-covariance based values. Our results indicate that the difference in annual C exchange rates was due to reduced heterotrophic soil respiration in 1999. [ABSTRACT FROM AUTHOR]

Given that forests represent the primary terrestrial sink for atmospheric CO2 , projections of future carbon (C) storage hinge on forest responses to climate variation. Models of gross primary production (GPP) responses to water stress are commonly based on remotely sensed changes in canopy 'greenness' (e.g., normalized difference vegetation index; NDVI). However, many forests have low spectral sensitivity to water stress (SSWS) - defined here as drought-induced decline in GPP without a change in greenness. Current satellite-derived estimates of GPP use a vapor pressure deficit (VPD) scalar to account for the low SWSS of forests, but fail to capture their responses to water stress. Our objectives were to characterize differences in SSWS among forested and nonforested ecosystems, and to develop an improved framework for predicting the impacts of water stress on GPP in forests with low SSWS. First, we paired two independent drought indices with NDVI data for the conterminous US from 2000 to 2011, and examined the relationship between water stress and NDVI. We found that forests had lower SSWS than nonforests regardless of drought index or duration. We then compared satellite-derived estimates of GPP with eddy-covariance observations of GPP in two deciduous broadleaf forests with low SSWS: the Missouri Ozark (MO) and Morgan Monroe State Forest (MMSF) AmeriFlux sites. Model estimates of GPP that used VPD scalars were poorly correlated with observations of GPP at MO (r(2) = 0.09) and MMSF (r(2) = 0.38). When we included the NDVI responses to water stress of adjacent ecosystems with high SSWS into a model based solely on temperature and greenness, we substantially improved predictions of GPP at MO (r(2) = 0.83) and for a severe drought year at the MMSF (r(2) = 0.82). Collectively, our results suggest that large-scale estimates of GPP that capture variation in SSWS among ecosystems could improve predictions of C uptake by forests under drought., (© 2014 John Wiley & Sons Ltd.)