Bryant C. Scharenbroch

The unseen invaders: introduced earthworms as drivers of change in plant communities in North American forests (a meta-analysis).

Abstract Globally, biological invasions can have strong impacts on biodiversity as well as ecosystem functioning. While less conspicuous than introduced aboveground organisms, introduced belowground organisms may have similarly strong effects. Here, we synthesize for the first time the impacts of introduced earthworms on plant diversity and community composition in North American forests. We conducted a meta‐analysis using a total of 645 observations to quantify mean effect sizes of associations between introduced earthworm communities and plant diversity, cover of plant functional groups, and cover of native and non‐native plants. We found that plant diversity significantly declined with increasing richness of introduced earthworm ecological groups. While plant species richness or evenness did not change with earthworm invasion, our results indicate clear changes in plant community composition: cover of graminoids and non‐native plant species significantly increased, and cover of native plant species (of all functional groups) tended to decrease, with increasing earthworm biomass. Overall, these findings support the hypothesis that introduced earthworms facilitate particular plant species adapted to the abiotic conditions of earthworm‐invaded forests. Further, our study provides evidence that introduced earthworms are associated with declines in plant diversity in North American forests. Changing plant functional composition in these forests may have long‐lasting effects on ecosystem functioning.

Biochar and Biosolids Increase Tree Growth and Improve Soil Quality for Urban Landscapes

Urban soil quality is often degraded and a challenging substrate for trees. This study was conducted to assess the impacts of biochar (BC), biosolids (BS), wood chips (WC), compost (COM), aerated compost tea (ACT), and a nitrogen plus potassium fertilizer (NK) for improving three typical urban soils and tree sapling growth. Across the three soil types, the most significant changes in soil properties were observed with BS and BC. Biosolids decreased soil pH and increased available N, N mineralization, and microbial respiration. Biochar increased total organic C. Increases in microbial respiration were also observed with NK, COM, and WC in only the sand soil. Leachate concentrations of dissolved organic C were greater with BS and COM, but nitrate in leachates did not differ among the treatments. The greatest and most significant increases in and growth were found with BS and BC. Tree growth was modeled from plant-available N and microbial respiration. The N content in the treatments appeared to be a strong determinant of tree growth for all treatments except BC. Nitrogen fertilizer, COM, and WC are the most common urban soil amendments and mulches in use today. This study provides evidence that BS and BC are acceptable, and possibly preferred, alternatives for improving urban soil quality and tree growth.

Tree Species Suitability to Bioswales and Impact on the Urban Water Budget.

Water movement between soil and the atmosphere is restricted by hardscapes in the urban environment. Some green infrastructure is intended to increase infiltration and storage of water, thus decreasing runoff and discharge of urban stormwater. Bioswales are a critical component of a water-sensitive urban design (or a low-impact urban design), and incorporation of trees into these green infrastructural components is believed to be a novel way to return stored water to the atmosphere via transpiration. This research was conducted in The Morton Arboretums main parking lot, which is one of the first and largest green infrastructure installations in the midwestern United States. The parking lot is constructed of permeable pavers and tree bioswales. Trees in bioswales were evaluated for growth and condition and for their effects on water cycling via transpiration. Our data indicate that trees in bioswales accounted for 46 to 72% of total water outputs via transpiration, thereby reducing runoff and discharge from the parking lot. By evaluating the stomatal conductance, diameter growth, and condition of a variety of tree species in these bioswales, we found that not all species are equally suited for bioswales and that not all are equivalent in their transpiration and growth rates, thereby contributing differentially to the functional capacity of bioswales. We conclude that species with high stomatal conductance and large mature form are likely to contribute best to bioswale function.

Effects of Phylogenetic Diversity and Phylogenetic Identity in a Restoration Ecology Experiment

Our understanding of the effects of plant biodiversity on ecosystem function rests in large part on experiments that have disentangled environmental variables from local diversity. Yet phylogenetic diversity (PD) effects can be confounded by phylogenetic identity effects in such experiments if assemblages with low or high PD tend to be dominated by a single clade. We illustrate this problem in a 127-species experiment designed to test the effects of angiosperm PD and trait diversity on tallgrass prairie restoration outcomes. In this experiment, the taxon pool exhibits a phylogenetic bias: if species were randomly assigned to experimental assemblages, low PD plots would frequently be dominated by a single clade (the sunflower or daisy family, Asteraceae). We present a visualization tool for examining phylogenetic experiments for this bias and propose a taxonomically constrained experimental design to reduce the most egregious causes of bias. We then present the experimental design we developed using the constrained approach and summarize initial findings from this large-scale restoration experiment. Entanglement of phylogenetic diversity and phylogenetic identity is an underappreciated and likely widespread challenge for PD experiments, particularly those that draw upon a large number of candidate species. By recognizing, quantifying, and counteracting this bias, researchers can better differentiate the effects of PD per se from phylogenetic identity effects.