A Love of Science and the Excitement of Discovery

Professor Albert Burky retires from UD in May 2022 with 49 years of teaching, fieldwork, publishing and professional service. His impact is beyond measure, writes colleague Ryan McEwan

A Review on the Invasion Ecology of Amur Honeysuckle (Lonicera maackii, Caprifoliaceae), A Case Study of Ecological Impacts at Multiple Scales

Invasive species are of global importance because of their impacts on ecological communities, habitat structure, native community dynamics, and ecosystem processes and function. Scientists and conservation managers are increasingly focusing on the biological impacts of invasive species and on devising management practices that emphasize the health of ecosystems based on measured biological processes. Amur honeysuckle (Lonicera maackii (Rupr.) Herder) is a highly successful invasive shrub in forests of eastern North America. The scientific literature surrounding this species has grown in the past several decades as researchers have investigated L. maackii impacts across multiple ecological scales. In this review we synthesized literature on (a) the key traits related to this species\u27 invasion success, (b) the impacts this invasive species has at various ecological scales, (c) the outcomes of restoration efforts for this species, and (d) the connections of this weed to invasion ecology theories. Lonicera maackii impacts are complex and vary across ecosystems and spatial scales; we report findings from studies demonstrating a wide range of effects on species composition, community structure, ecosystem function, and successional trajectories. We end by providing a working ecological framework that may help guide future research and conservation efforts

The Role of Environmental Filtering in Structuring Appalachian Tree Communities: Topographic Influences on Functional Diversity Are Mediated through Soil Characteristics

Identifying the drivers of community assembly has long been a central goal in ecology, and the development of functional diversity indices has provided a new way of detecting the influence of environmental gradients on biotic communities. For an old-growth Appalachian forest, we used path analysis to understand how patterns of tree functional diversity relate to topography and soil gradients and to determine whether topographic effects are mediated through soil chemistry. All of our path models supported the idea of environmental filtering: stressful areas (high elevation, low soil moisture, low soil nutrients) were occupied by communities of low functional diversity, which suggests a selective effect for species with traits adapted to such harsh conditions. The effects of topography (slope, aspect, elevation) on functional diversity were often indirect and moderated through soil moisture and fertility. Soil moisture was a key component of our models and was featured consistently in each one, having either strong direct effects on functional diversity or indirect effects via soil fertility. Our results provide a comprehensive view of the interplay among functional trait assemblages, topography, and edaphic conditions and contribute to the baseline understanding of the role of environmental filtering in temperate forest community assembly

Lethal Effects of Leaf Leachate from the Non-Native Invasive Shrub Amur Honeysuckle (Lonicera maackii) on a Model Aquatic Organism (Hyalella azteca)

The invasive shrub Lonicera maackii (Amur honeysuckle) is a problematic species in the eastern United States and there is growing evidence that materials from this species have toxic effects on some organisms. We used a sequence of microcosm bioassays to assess the influence of L. maackii leaf leachate on the macroinvertebrate Hyalella azteca, which is a standard aquatic organism for toxicity assessment. In a laboratory setting, H. azteca were exposed to a leaf leachate dilution series (6.25%, 12.5%, 25%, 50%, 100%) in 48-h toxicity tests. This was repeated throughout the growing season to assess the potential for changes in leaf toxicity due to phenology. Strong toxic effects were found when H. azteca was exposed to a L. maackii leachate from autumn (P \u3c 0.05) and, in fact, all organisms died when exposed to any level of concentration in most trials. Mean percent survival also decreased significantly in all dilutions in the spring (P \u3c 0.05 for all treatments); however, little toxicity was detected in growing season trials. These results suggest (a) strong toxic effects of L. maackii foliage on a model aquatic organism that (b) varies throughout the year, potentially in relationship to biochemical changes associated with phenology

Lethal and Sublethal Effects of Novel Terrestrial Subsidies from an Invasive Shrub (Lonicera maackii) on Stream Macroinvertebrates

The biology of headwater streams is intimately linked to that of the surrounding terrestrial environment through organic matter subsidies. Lonicera maackii, an invasive shrub that is becoming abundant in headwater stream riparian areas, deposits substantial quantities of organic matter into the aquatic system. This organic material has allelopathic effects on terrestrial plants and insects, and a growing body of work suggests strong connections between L. maackii invasion and aquatic biota. Lonicera maackii deposits fruit and flowers in quantities and timings that are unique, and we tested the hypothesis that these subsidies would negatively affect survival and growth of laboratory-cultured Hyalella azteca and field-collected Anthopotamus verticis and Allocapnia spp. Invertebrates were exposed to a gradient of fruit (reference sediment + 0, 0.31, 0.62, 1.25, or 2.5 g dry mass [DM]) and flower (reference sediment + 0, 0.30, 0.60, 1.2, or 2.4 g DM) biomass in laboratory and field sediment exposure tests. Hyalella azteca survival was significantly reduced by exposure to L. maackii fruit in the laboratory and in the field exposures, and a negative effect was observed for A. verticis (p\u3c 0.05). Lonicera maackii flower biomass was associated with negative effects on survival of H. azteca in the field and laboratory exposures and of A. verticis in the laboratory exposure. During the laboratory exposures, dissolved O2 (DO) and pH were /L and 5.5, respectively. In the field exposures, DO and pH were comparable to stream conditions during fruit exposures, declining significantly with increasing flower biomass. Our results suggest that L. maackii fruit and flowers, novel subsidies in these systems, can negatively affect benthic organism survival and growth. Research focused on verifying this novel subsidy hypothesis for L. maackii and other species could enhance our understanding of invasion biology and terrestrial–aquatic linkages

Leaf phenology and freeze tolerance of the invasive tree Pyrus calleryana (Roseaceae) and potential native competitors

Pyrus calleryana is one of the most problematic invasive species in the eastern United States. The mechanisms that enable Py. calleryana to establish and outcompete native plants are not fully understood but likely include a profile of advantageous traits. Extended leaf phenology is a characteristic noted in many woody invasive plants. Leaf phenology of Py. calleryana and two native woody species, Populus deltoides and Platanus occidentalis, was observed in natural areas near Dayton, OH from December 2019 to November 2020. A frost event in May also gave us the serendipitous opportunity to assess frost tolerance of these species. We found that Py. calleryana began leafing out almost a month before its native competitors in the spring and kept its leaves on significantly longer than both Po. deltoides and Pl. occidentalis throughout the fall. After the frost event, almost every leaf on Pl. occidentalis died and almost 70% of the leaves on Po. deltoides were damaged; however, Py. calleryana exhibited damage on only 6% of its leaves. Our study suggests that Py. calleryana has a nearly 1-mo advantage in leaf phenology in both spring and fall, and much greater frost tolerance, as compared with native species. These attributes likely contribute to its capacity to outcompete native trees in early successional habitats

Herb-Layer Dynamics in an Old-Growth Forest: Vegetation–Environment Relationships and Response to Invasion-Related Perturbations

Temperate forests of eastern North America are subject to multiple invasions from non-native species that have the potential to drive long-term dynamics in biodiversity. Garlic mustard (Alliaria petiolata (M. Bieb.) Cavara and Grande) is an invasive plant in many deciduous forests, and management efforts often focus on removing this species to initiate native species restoration. Agrilus planipennis Fairmaire (emerald ash borer; Coleoptera: Buprestidae) is a non-native insect pest that has caused substantial loss of ash trees (Fraxinus spp. L.) in North America. Our goal was to understand how the herbaceous layer in an old-growth forest responded to the removal of a significant invasion of A. petiolata and the loss of Fraxinus spp. due to A. planipennis. Herbaceous diversity and environmental parameters were measured in 32 permanent plots (1 m2 each) from 2012 to 2020 in an old-growth forest remnant that had experienced A. petiolata invasion and subsequent removal as well as mortality of Fraxinus spp. due to A. planipennis. Near-total loss of Fraxinus spp. as a canopy tree was not associated with changes in the understory light environment, possibly due to rapid canopy closure by adjacent trees not susceptible to the insect. Alliaria petiolata removal was associated with changes in herbaceous species richness and possibly shifts in individual species importance. Vegetation–environment relationships remained stable throughout the sampling period, suggesting that resource-related factors that structure the herb layer prevailed throughout the changes associated with Fraxinus spp. mortality and A. petiolata management. From a natural area management perspective, our data offer support for the idea that A. petiolata removal influences herb-layer diversity and indicate that in stands with a diverse tree community, the loss of Fraxinus spp. may not directly influence understory biodiversity

Microbial Biofilm Community Variation in Flowing Habitats: Potential Utility as Bioindicators of Postmortem Submersion Intervals

Biofilms are a ubiquitous formation of microbial communities found on surfaces in aqueous environments. These structures have been investigated as biomonitoring indicators for stream heath, and here were used for the potential use in forensic sciences. Biofilm successional development has been proposed as a method to determine the postmortem submersion interval (PMSI) of remains because there are no standard methods for estimating the PMSI and biofilms are ubiquitous in aquatic habitats. We sought to compare the development of epinecrotic (biofilms on Sus scrofa domesticus carcasses) and epilithic (biofilms on unglazed ceramic tiles) communities in two small streams using bacterial automated ribosomal intergenic spacer analysis. Epinecrotic communities were significantly different from epilithic communities even though environmental factors associated with each stream location also had a significant influence on biofilm structure. All communities at both locations exhibited significant succession suggesting that changing communities throughout time is a general characteristic of stream biofilm communities. The implications resulting from this work are that epinecrotic communities have distinctive shifts at the first and second weeks, and therefore the potential to be used in forensic applications by associating successional changes with submersion time to estimate a PMSI. The influence of environmental factors, however, indicates the lack of a successional pattern with the same organisms and a focus on functional diversity may be more applicable in a forensic context

Long-term drought sensitivity of trees in second-growth forests in a humid region

Classical field methods of reconstructing drought using tree rings in humid, temperate regions typically target old trees from drought-prone sites. This approach limits investigators to a handful of species and excludes large amounts of data that might be useful, especially for coverage gaps in large-scale networks. By sampling in more “typical” forests, network density and species diversity would increase in ways that could potentially improve reconstructions. Ten nonclassical tree-ring chronologies derived from randomly selected trees, trees from logged forests, or both were compared to more classical chronologies and an independent regional drought reconstruction to determine their usefulness for dendrohydroclimatic research. We find that nonclassical chronologies are significantly correlated to classical chronologies and reconstructed drought over the last 2–3 centuries. While nonclassical chronologies have spectral properties similar to those from classical dendroclimatic collections, they do lack spectral power at lower frequencies that are present in the drought reconstruction. Importantly, our results show that tree growth is strongly dependent on moisture availability, even for small, randomly selected trees in cut forests. These results indicate that there could be more data available in areas with few current tree-ring collections for studying climate history and that drought plays an important role in humid forests

Recovery of Forest Floor Diversity After Removal of the Nonnative, Invasive Plant Euonymus fortunei

The vine Euonymus fortunei (Turcz.) Hand.-Mazz. is invading forests of the eastern United States; as a result, removal of E. fortunei has become a priority of resource managers. This study examined the effectiveness of five techniques for eliminating E. fortunei, restoring plant species richness, and enhancing recolonization by woody species. In 2003, the following five treatments were applied: burn with a propane torch, light exclusion by plastic tarp, burn and glyphosate application, cut (simulated grazing) and glyphosate application, mow and glyphosate application, plus an untreated control. Each treatment was replicated four times in a randomized block design located in a heavily E. fortunei–invaded forest remnant in Lexington, KY. Vegetation was surveyed in 2004, 2005, 2006, 2007, and 2013. Across years, most treatments were associated with reduced E. fortunei cover and increased total species richness. Over time, E. fortunei cover increased across treatments, such that by 2013, no difference in E. fortunei cover was detectible among treatments. Some differences in total and native species richness among treatments were still perceptible by 2013. Increased E. fortunei cover was correlated with decreased ground-layer species richness, native species richness, sapling richness, and sapling density. Light exclusion by plastic tarp, a method absent from many management recommendations, was unique in its long-term reduction of E. fortunei cover and its association with increased total species richness, but use of plastic tarps may have drawbacks. This study quantified the long-term community effects of removing an established invasive species from a mature, urban forest. Removal allowed native plants, notably woody species, to reestablish. Because richness continues to decline as E. fortunei reinhabits plots, land managers seeking to conserve biodiversity under conditions similar to those within our study site should maintain proactive E. fortunei removal plans