Forest In Maryland Research Articles

Transpiration rates of red maple (Acer rubrum L.) differ between management contexts in urban forests of Maryland, USA

The hydrological functioning of urban trees can reduce stormwater runoff, mitigate the risk of flood, and improve water quality in developed areas. Tree canopies intercept rainfall and return water to the atmosphere through transpiration, while roots increase infiltration and storage in the soil. Despite this, the amount of stormwater that trees remove through these functions in urban settings is not well characterized, limiting the use of urban forests as practical stormwater management strategies. To address this gap, we use ecohydrological approaches to assess the transpiration rates of urban trees in different management settings. Our research questions are: Do transpiration rates of trees of the same species vary among different management contexts? Do relationships between environmental drivers and transpiration change among management contexts? These management settings included single trees over turfgrass and a cluster of trees over turfgrass in Montgomery County, MD, and closed canopy forest with a leaf litter layer in Baltimore, MD. We used sap flux sensors installed in 18 mature red maple (Acer rubrum L.) trees to characterize transpiration rates during the growing season. We also measured soil volumetric water content, air temperature, relative humidity, and precipitation at each site. In agreement with our initial hypothesis, we found that single trees had nearly three times the daily sum of sap flux density (JS) of closed canopy trees. When averaged over the entire measurement period, JS was approximately 260, 195, and 91 g H2O cm−2 day−1 for single trees, cluster trees and closed canopy trees, respectively. Additionally, single trees were more responsive to VPD than closed canopy and cluster trees. These results provide a better understanding of the influence of management context on urban tree transpiration and can help to identify targets to better manage urban forest settings to reduce urban stormwater runoff.

Seed Rain and Disturbance Impact Recruitment of Invasive Plants in Upland Forest

AbstractA critical question in invasion biology involves the relative importance of propagule rain and community invasibility. For plant invasions, invasibility is often related to disturbance, but few studies of forest invaders have simultaneously investigated both canopy and ground-level disturbance. We investigated the relative importance of seed rain, canopy disturbance, and soil disturbance in a mature forest in Maryland on the recruitment of four invasive species: wine raspberry (Rubus phoenicolasiusMaxim.), Japanese barberry (Berberis thunbergiiDC), multiflora rose (Rosa multifloraThunb.), and Japanese stiltgrass [Microstegium vimineum(Trin.) A. Camus]. Using complete censuses of a 9-ha plot at two points in time (2011–12 and 2014), we mapped new recruits, and related their locations to canopy and soil disturbance, as well as to a seed rain index based on locations of reproducing plants and seed-dispersal kernels.We found that propagule rain, as measured by the seed rain index, was a significant predictor of recruitment forB. thunbergii,R. phoenicolasius, andM. vimineum. ForR. multiflora, seed sources were not located, precluding assessment of propagule rain, but recruitment was linked to canopy disturbance, as was recruitment ofM. vimineum. However, because reproduction ofR. phoenicolasiusand, in some years, ofB. thunbergiiis higher in treefall gaps, these gaps experience higher propagule rain, with the result that recruitment is indirectly associated with these gaps. Ground-layer disturbance was an important predictor of recruitment only forB. thunbergii. Our findings reveal that the importance of propagule rain is the most consistent driver of recruitment, but canopy or ground-layer disturbance promotes recruitment of some invasive plant species.

Leaf Litter and Arboreal Ants (Hymenoptera: Formicidae) in a Mid-Atlantic Forest

The majority of ant diversity studies have been conducted in the tropics, but the number of studies conducted in temperate regions, like the US, is on the rise. Our research measured the richness and diversity of ants (Hymenoptera: Formicidae) in a coastal, temperate forest of Maryland. We collected leaf litter along twenty-four 100-m transects during May, July, and September of 2015 and measured litter depth and mass to determine if there was a relationship with ant abundance (density). We used Berlese funnels to collect 14 ant species (4208 individuals; n = 144 samples). Neither leaf-litter depth nor mass had an impact on ant abundance or species richness. We used aspirators and hand-collection methods to examine arboreal-ant foraging preference on deciduous and coniferous trees. Total species richness for both tree types was 21; we collected 19 species from deciduous trees and 17 from coniferous trees. Four species detected on deciduous trees were not present on conifers, and 2 species from conifers were not observed on deciduous trees. We observed higher abundances on deciduous trees (P = 0.016) and detected a preference for larger trees. We provide suggestions for conservation efforts for the coastal forests of Maryland, and our study contributes to the growing species inventory of ants on Maryland's eastern shore.

Monitoring of Dung Beetle (Scarabaeidae and Geotrupidae) Activity Along Maryland's Coastal Plain

Our understanding of how human activities impact insect communities is limited. Dung beetles, well known for the ecosystem services they provide, are faced with many conservation threats, particularly from deforestation and agriculture. Here we used 200-m transects and human-dung—baited pitfall traps to examine dung beetle populations in 7 forests of Maryland's Coastal Plain. We set traps once a month, from May 2014 to April 2015, to determine species presence, abundance, range, and seasonality. We collected 6463 individuals representing 22 species; Janes Island State Park (JISP) had the highest abundance (2705 individuals) and Martinak State Park (MSP) had the highest species richness (19 species). During summer 2015, we examined the succession of dung beetles attracted to bait in JISP and MSP. We set 10 traps once a month (May–August) in each site and collected beetles on days 1, 3, 5, 7, 14, and 21 without dung replacement. In JISP, Onthophagus hecate (Scooped Scarab) was abundant throughout each 21-d period, and accounted for 68% of all beetles collected. In MSP, most specimens were collected by day 5. Here we provide information for conservation of locally rare or uncommon species.

An Experimental Test of Epi- and Endozoochory of Arbuscular Mycorrhizal Fungi Spores by Small Mammals in a Maryland Forest

Small mammals have been proposed as important dispersers of the spores of arbuscular mycorrhizal fungi (AMF), yet few data exist to support this hypothesis. We experimentally tested 2 models of small-mammal dispersal of AMF spores by quantifying their impact on the mycorrhizal inoculum potential of sterile soil flats in a northeast mesophytic forest in Maryland. Epizoochory did not provide a mechanism for spore dispersal in our study. However, our data demonstrated that endozoochory by several small-mammal species can be an effective dispersal mode for AMF. In the field experiment, inoculum potential of soil from plots that were accessible to Peromyscus leucopus (White-footed Mouse) was significantly higher than in control plots, which excluded small mammals. This study provides experimental evidence that White-footed Mice disperse AMF spores.

Toward more robust projections of forest landscape dynamics under novel environmental conditions: Embedding PnET within LANDIS-II

Ecological models built on phenomenological relationships and behavior of the past may not be robust under novel conditions of the future because global changes are producing environmental conditions that forests have not experienced historically. We developed a new succession extension for the LANDIS-II forest landscape model, PnET-Succession, to simulate forest growth and succession using physiological first principles. PnET-Succession integrates the tree physiology model PnET-II with the existing LANDIS-II Biomass Succession extension. PnET-Succession simulates the competition of tree species cohorts for water and light as a function of photosynthetic processes driven by foliar nitrogen. Competition for water is simulated on each grid cell through a dynamic soil-water balance that receives precipitation and loses water through runoff, consumption in photosynthesis, and evapotranspiration. Competition for light is modeled by tracking solar radiation through canopy layers according to a standard Beer-Lambert formula. PnET-Succession requires average monthly photosynthetically active radiation, atmospheric CO2 concentration, temperature and precipitation as inputs. The new extension also dynamically calculates species establishment probabilities in each time step as a function of water and radiation stress. We calibrated PnET-Succession to biomass and LAI measurements from the Duke Experimental Forest in North Carolina (USA) and tested the calibrated model against data from the Green Ridge State Forest in Maryland. The new extension shows considerable promise for studying forest response to climate change, including changes in carbon stocks.

Valuing ecosystem services from Maryland forests using environmental accounting

Forests provide a multitude of benefits vital to the ecosystems, economies and people of Maryland. While markets exist to set the price for an economic good like timber, ecosystem services are viewed as free externalities. This research enumerates the biophysical value of forest ecosystem services in Maryland and provides a connection between biophysical and economic methods for valuing the environment. The hydrology, soil, carbon, air pollution, pollination and biodiversity of a forest are measured from a biophysical standpoint with emergy and converted to dollars using new emergy-to-dollar ratios, termed eco-prices. The functioning of the forest is compared to the most likely alternative land-use in Maryland (suburbia) and biophysical value is assigned based on this difference. The research seeks to value ecosystem services provided by forests in Maryland and proposes that society should invest commensurate value in the production and perpetuation of ecosystem services. To help ensure that Maryland forests continue to produce ecosystem services at the current rate, investment should total between $273 and $744 million per year in the State of Maryland, $270–$736 per year for a typical hectare of forest.

Why do leaf-tying caterpillars abandon their leaf ties?

Leaf-tying caterpillars act as ecosystem engineers by building shelters between overlapping leaves, which are inhabited by other arthropods. Leaf-tiers have been observed to leave their ties and create new shelters (and thus additional microhabitats), but the ecological factors affecting shelter fidelity are poorly known. For this study, we explored the effects of resource limitation and occupant density on shelter fidelity and assessed the consequences of shelter abandonment. We first quantified the area of leaf material required for a caterpillar to fully develop for two of the most common leaf-tiers that feed on white oak, Quercus alba. On average, Psilocorsis spp. caterpillars consumed 21.65 ± 0.67 cm2 leaf material to complete development. We also measured the area of natural leaf ties found in a Maryland forest, to determine the distribution of resources available to caterpillars in situ. Of 158 natural leaf ties examined, 47% were too small to sustain an average Psilocorsis spp. caterpillar for the entirety of its development. We also manipulated caterpillar densities within experimental ties on potted trees to determine the effects of cohabitants on the likelihood of a caterpillar to leave its tie. We placed 1, 2, or 4 caterpillars in ties of a standard size and monitored the caterpillars twice daily to track their movement. In ties with more than one occupant, caterpillars showed a significantly greater propensity to leave their tie, and left sooner and at a faster rate than those in ties as single occupants. To understand the consequences of leaf tie abandonment, we observed caterpillars searching a tree for a site to build a shelter in the field. This is a risky behavior, as 17% of the caterpillars observed died while searching for a shelter site. Caterpillars that successfully built a shelter traveled 110 ± 20 cm and took 28 ± 7 min to find a suitable site to build a shelter. In conclusion, leaf-tying caterpillars must frequently abandon their leaf tie due to food limitation and interactions with other caterpillars, but this is a costly behavior.

Impact of Conifer Forest Litter on Microwave Emission at L-Band

This study reports on the utilization of microwave modeling, together with ground truth, and L-band (1.4-GHz) brightness temperatures to investigate the passive microwave characteristics of a conifer forest floor. The microwave data were acquired over a natural Virginia Pine forest in Maryland by a ground-based microwave active/passive instrument system in 2008/2009. Ground measurements of the tree biophysical parameters and forest floor characteristics were obtained during the field campaign. The test site consisted of medium-sized evergreen conifers with an average height of 12 m and average diameters at breast height of 12.6 cm. The site is a typical pine forest site in that there is a surface layer of loose debris/needles and an organic transition layer above the mineral soil. In an effort to characterize and model the impact of the surface litter layer, an experiment was conducted on a day with wet soil conditions, which involved removal of the surface litter layer from one half of the test site while keeping the other half undisturbed. The observations showed detectable decrease in emissivity for both polarizations after the surface litter layer was removed. A first-order radiative transfer model of the forest stands including the multilayer nature of the forest floor in conjunction with the ground truth data are used to compute forest emission. The model calculations reproduced the major features of the experimental data over the entire duration, which included the effects of surface litter and ground moisture content on overall emission. Both theory and experimental results confirm that the litter layer increases the observed canopy brightness temperature and obscure the soil emission.

Overlap of food and microhabitat preferences among some native and nonnative slugs in mid-Atlantic forests of eastern North America

Introduced competitors do not share an evolutionary history that would promote coexistence mechanisms, i.e. niche partitioning. Thus, nonnative species can harm a trophically similar native species by competing with them more intensely than other native species. However, nonnative species may only be able initially to invade habitats in which resource overlap with native species is small. The nonnative slug Arion subfuscus exists in close sympatry with the native philomycid slugs Philomycus carolinianus and Megapallifera mutabilis in central Maryland forests. Resource use by most terrestrial gastropods is poorly known, but seems to suggest high dietary and macrohabitat overlap, potentially placing native gastropod species at high risk of competitive pressure from invading species. However, A. subfuscus was introduced to North America 150 years ago, supporting the possibility that A. subfuscus initially entered an empty niche. We tested the hypothesis that P. carolinianus and M. mutabilis would exhibit greater overlap in food and microhabitat use with A. subfuscus than they would with each other. We established food preferences by examining the faecal material of wild-caught slugs, distinguishing food types and quantifying them by volume on a microgrid. We determined microhabitat preferences by surveying the substrates of slugs in the field. The overlap in substrate and food resources was greater between A. subfuscus and P. carolinianus than between the two native species. However, substrate choice was correlated with local substrate availability for P. carolinianus, suggesting flexibility in habitat use, and the slight overlap in food use between A. subfuscus and P. carolinianus may be low enough to minimize competition.

Treefall gaps required for establishment, but not survival, of invasive Rubus phoenicolasius in deciduous forest, Maryland, USA

AbstractAlthough plant invasions are often associated with disturbance, localized disturbances can promote invasion either by: (i) creating sites where individuals establish; or (ii) enabling an invader to colonize the entire stand. The former is expected when both establishment and survival to reproductive age require disturbed conditions, whereas the latter should occur in systems when either establishment or survival are limited to disturbed sites. We investigated the role of localized disturbance, specifically treefalls, in the invasion of the Asian Rubus phoenicolasius in a deciduous forest in Maryland, USA. We investigated the density and demography of R. phoenicolasius in treefall gaps of various sizes, but identical age to non‐gap areas, using Classification and Regression Tree (CART) analyses to identify the most important predictors. To explore how the demography of established individuals responds to disturbed versus undisturbed conditions, we carried out a garden experiment with three different levels of shade (5, 12 and 22% full sun). We found vegetative and sexual reproduction, and seedling establishment, to be limited to large gaps in an old stand, but not in a stand in an earlier age of succession. However, in the garden experiment, established plants were able to survive and grow under all shade treatments. These findings indicate that R. phoenicolasius requires disturbances such as treefalls to establish in forests, but established plants will survive canopy closure, leading to stand‐wide invasion. Managers should be able to prevent invasion, however, by inspecting large gaps for new recruits every 3 years.

Demographic genetics of American beech (Fagus grandifolia Ehrh.) IV. Development of genetic variability and gene flow during succession in a coastal plain forest in Maryland

AbstractGenetic recovery of an American beech (Fagus grandifolia) population in deciduous forests that were once pastures was studied using 16 allozyme loci from 410 individuals in a 600 m × 600 m study plot in Maryland, USA. We also examined the spatio‐temporal genetic structure of the American beech population at a regional scale. Overall genetic diversity of mature trees was measured by estimating average heterozygosity (H = 0.156). Rare alleles were observed in five loci, Lap, 6Pdgh3, Pgi, Adh1 and Got3. Mature individuals were divided into three size classes based on d.b.h. The genetic component of each size class was compared and it was revealed that several alleles (Pgm‐a, 6Pgdh3‐a and Lap‐b) were shared only in specific size classes. The spatial distribution of the genotypes demonstrated a conspicuous localization in three loci (Aco, Adh1 and Idh). Spatial autocorrelation analyses were carried out among the mature trees for a 20 m interval, and were positive for 0–120 m and negative for >180 m. Distrograms indicated that a unique genetic localization occurs among mature individuals. Seven hundred and seventy‐five seedlings in the 10 m × 120 m transect were analyzed to measure gene flow via seed and/or pollen. We obtained a genetic neighborhood area of 1.17 ha and an effective population size of 32.4. The temporal and spatial modes of genetic recovery of the population are discussed in the context of conservation biology.

Laser remote sensing of canopy habitat heterogeneity as a predictor of bird species richness in an eastern temperate forest, USA

Habitat heterogeneity has long been recognized as a fundamental variable indicative of species diversity, in terms of both richness and abundance. Satellite remote sensing data sets can be useful for quantifying habitat heterogeneity across a range of spatial scales. Past remote sensing analyses of species diversity have largely been limited to correlative studies based on the use of vegetation indices or derived land cover maps. A relatively new form of laser remote sensing (lidar) provides another means to acquire information on habitat heterogeneity. Here we examine the efficacy of lidar metrics of canopy structural diversity as predictors of bird species richness in the temperate forests of Maryland, USA. Canopy height, topography and the vertical distribution of canopy elements were derived from lidar imagery of the Patuxent National Wildlife Refuge and compared to bird survey data collected at referenced grid locations. The canopy vertical distribution information was consistently found to be the strongest predictor of species richness, and this was predicted best when stratified into guilds dominated by forest, scrub, suburban and wetland species. Similar lidar variables were selected as primary predictors across guilds. Generalized linear and additive models, as well as binary hierarchical regression trees produced similar results. The lidar metrics were also consistently better predictors than traditional remotely sensed variables such as canopy cover, indicating that lidar provides a valuable resource for biodiversity research applications.

Would Forest Landowners Use Poultry Manure as Fertilizer?

Abstract When manure nutrients exceed local cropland's assimilative capacity, the potential for water quality problems exists. Concerns about water quality in Maryland have led to the passage of the Water Quality Improvement Act, which will affect the disposal of poultry litter on cropland. Because Maryland's forest soils test low for phosphorus, forest fertilization may be an alternative use for the litter. A representative sample of 402 Maryland landowners owning 40 or more acres was asked whether they would consider using poultry litter as a forest fertilizer under various incentives. When offered $20 per acre, landowners owning more acres, located in certain counties, and who were younger than the other survey respondents were most likely to consider using poultry litter. Landowners who had a forest management plan were less likely to be willing.

Application of imaging spectroscopy to mapping canopy nitrogen in the forests of the central appalachian mountains using hyperion and aviris

Earth Observing 1 (EO-1) Hyperion and Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) imagery were used to predict canopy nitrogen (N) concentration for mixed oak forests of Green Ridge State Forest in Maryland. Nitrogen concentration was estimated for 27 ground plots using leaf samples of the dominant tree species from each plot that were dried, ground and analyzed in the laboratory for foliar N concentration. Foliar N data were composited based on relative species composition to determine overall canopy N concentration for the plot. Hyperion and AVIRIS images were converted to surface reflectance and related to canopy N using partial least squares (PLS) regression of first-derivative reflectance for wavelengths reported in the literature to be associated with N absorption features. The PLS model for Hyperion employed four factors and accounted for 97.8% of the variation in N concentrations and 40.4% of the variation in the spectral data whereas the AVIRIS model used three factors accounting for 84.9% of the variation in N and 72.4% of the variation in the spectral information. In the area of overlap between the AVIRIS and Hyperion images, >70% of the estimates from the two sensors were within 0.25%N of each other, indicating a very close fit between the models generated using data from Hyperion and AVIRIS. This research indicates the applicability of hyperspectral data in general and Hyperion data in particular for mapping canopy nitrogen concentration.

POPULATION-LEVEL CHARACTERISTICS OF DASYMUTILLA NIGRIPES, D. VESTA, AND TIMULLA VAGANS (HYMENOPTERA: MUTILLIDAE)

Abstract A total of 308 females and 182 males of Dasymutilla nigripes (Fab.), D. vesta (Cresson), and Timulla vagans (Fab.) (Hymenoptera: Mutillidae) were collected during 1996 and 1997 in a cleared vacant lot in a deciduous forest in Maryland. Mandibles of females abraded at rates that varied with time of year but were very similar for all members of any given cohort at any specific time. The number of generations varied from 1 to 3 per year depending on the species and year. Some adult females of each species overwintered, and during one 15-day period in 1996 overwintered females of D. vesta were estimated to constitute more than 60% of the total female population. Exceptional females were estimated to live as long as 10 to 12 months although 2 to 2 1/2 months was more typical. In early and mid-season, males generally emerged synchronously with females, but relatively few males were collected during late-season emergences of females. In some cases, discrete size ranges of adults indicated that as many a...

Phylogenetic diversity of rhizobial strains nodulating Robinia pseudoacacia L.

Lack of knowledge exists regarding the diversity of rhizobial strains nodulating black locust (Robinia pseudoacacia L.), which is a neophytic tree species widely distributed in Europe. Seventeen rhizobial strains isolated from nodules of black locust at a German location were examined by phenotypic characterization and 16S rDNA analysis. The isolates were classified in nine 16S rDNA genotypes using a set of seven endonucleases. Based on RFLP analysis and sequencing, the strains were shown to belong to the genera Mesorhizobium (76%) and Rhizobium (24%). Five genotypes were identical to the species Mesorhizobium amorphae, Mesorhizobium loti, Mesorhizobium huakuii, Rhizobium leguminosarum and Rhizobium tropici. A strong similarity between the 16S rDNA sequence of another two genotypes and M. amorphae (99.9%) as well as the Mesorhizobium strain R88b (99.8%) was found. The two remaining genotypes were classified in the genus Rhizobium, without a significant relationship at the species level. Comparing isolates nodulating Rob. pseudoacacia and Amorpha fruticosa, a parallel picture of phylogenetic diversity was detected with a range of phylogenetically different rhizobia and M. amorphae dominating. For this study, 18 rhizobial strains which had originally been isolated from a forest in Maryland where black locust is native were additionally analysed. Results revealed seven genotypes all belonging to the genus Mesorhizobium, with four genotypes identical to the isolates from the German sampling location. Whereas the genotype identical to M. amorphae dominated within the strains obtained from the German location, the dominance of a genotype identical to M. huakuii was found among the strains from the native location. Summarizing data from both locations, Rob. pseudoacacia was nodulated with various genomic species, most of which belonged to the genus Mesorhizobium. Concerning phenotypic features such as growth rate, pH tolerance or use of certain carbohydrates, most isolates corresponded to described species and genera. However, there were differences in salt tolerance between these isolates and the corresponding reference strains. Overall, the results demonstrated a high phenotypic and phylogenetic diversity of rhizobial strains nodulating Rob. pseudoacacia. This may be a characteristic of neophytic and other widely spread legumes and may contribute to the success of black locust as a pioneer tree species for the temperate zone.

Maryland's Forest Conservation Act: A Process for Urban Greenspace Protection During the Development Process

The Maryland Forest Conservation Act (FCA) was passed in 1991 to protect the state's forest resources during development. Compliance is required for any project for which grading is required on a unit of land 40,000 ft2 (0.42 ha) or greater. Applicants must generate and submit two documents. The first, a forest stand delineation (FSD), must identify forest stands, specimen trees, and sensitive areas such as steep slopes, hydric or erodible soils, critical habitat areas, streams, and floodplains. This map is used to direct the location of the impacts away from priority areas onsite. The second, a forest conservation plan (FCP), follows a priority sequence concerning impacts to and retention of priority areas identified in the FSD. Thresholds for clearing, afforestation, and reforestation are established based on the net tract area, land-use category, existing forest cover, and proposed clearing area. Forest and tree protective measures are required for stand edges and specimen trees. Long-term protective instruments are required to ensure that the retained area will remain forested. In its first five years, FCA has been responsible for the retention of more than 22,000 ac (10,000 ha) of forest, and 120% more forest retained and planted than has been cleared for development.

Genet structure and determinants of clonal structure in a temperate deciduous woodland herb,Uvularia perfoliata

1 We used isozyme variation to examine the genet structure of Uvularia perfoliata patches in gap and closed canopy habitats in a temperate deciduous forest in Maryland, USA. 2 A large patch in a gap habitat was composed of a small number of widely spread genets with many ramets, and a large number of genets with more restricted distribution and few ramets. Genets with many ramets were patchily distributed at a metre scale. Analysis of genet structure on a scale of square centimetres, however, revealed that the genets were highly intermingled with no clear boundaries between them. The presence at both scales of sampling of many genets with unique multilocus genotypes indicated continuing genet recruitment within the population. 3 In the closed canopy habitat, the patches examined were each composed of a single unique multilocus genotype, suggesting that each had developed by asexual propagation following the establishment of a single genet. 4 The clonal structure of U. perfoliata patches in both gap and closed canopy habitats therefore appears to depend on recruitment patterns of genets. Populations in closed canopy habitats are characterized by a ‘waiting’ strategy, in which asexual ramet production maintains populations until genet recruitment by seed production can occur under the more optimal conditions associated with canopy gaps. Extended sampling suggests that the genetic diversity of U. perfoliata populations is primarily controlled by the disturbance regime of the forest canopy.

Does Long-Term Elevation of CO2 Concentration Increase Photosynthesis in Forest Floor Vegetation? (Indiana Strawberry in a Maryland Forest).

As the partial pressure of CO2 (pCO2) in the atmosphere rises, photorespiratory loss of carbon in C3 photosynthesis will diminish and the net efficiency of light-limited photosynthetic carbon uptake should rise. We tested this expectation for Indiana strawberry (Duchesnea indica) growing on a Maryland forest floor. Open-top chambers were used to elevate the pCO2 of a forest floor habitat to 67 Pa and were paired with control chambers providing an ambient pCO2 of 38 Pa. After 3.5 years, D. indica leaves grown and measured in the elevated pCO2 showed a significantly greater maximum quantum efficiency of net photosynthesis (by 22%) and a lower light compensation point (by 42%) than leaves grown and measured in the control chambers. The quantum efficiency to minimize photorespiration, measured in 1% O2, was the same for controls and plants grown at elevated pCO2. This showed that the maximum efficiency of light-energy transduction into assimilated carbon was not altered by acclimation and that the increase in light-limited photosynthesis at elevated pCO2 was simply a function of the decrease in photorespiration. Acclimation did decrease the ribulose-1,5-bisphosphate carboxylase/oxygenase and light-harvesting chlorophyll protein content of the leaf by more than 30%. These changes were associated with a decreased capacity for light-saturated, but not light-limited, photosynthesis. Even so, leaves of D. indica grown and measured at elevated pCO2 showed greater light-saturated photosynthetic rates than leaves grown and measured at the current atmospheric pCO2. In situ measurements under natural forest floor lighting showed large increases in leaf photosynthesis at elevated pCO2, relative to controls, in both summer and fall. The increase in efficiency of light-limited photosynthesis with elevated pCO2 allowed positive net photosynthetic carbon uptake on days and at locations on the forest floor that light fluxes were insufficient for positive net photosynthesis in the current atmospheric pCO2.