Entomology

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Legacy effects of long-term autumn leaf litter removal slow decomposition rates and reduce soil carbon in suburban yards
(Wiley, 2024-02-22) Ferlauto, Max; Schmitt, Lauren; Burghardt, Karin T.
Societal Impact Statement As cities grow, it is essential to understand how landscape management decisions in urban spaces alter ecosystem function. This study demonstrates that the ubiquitous practice of long-term leaf litter removal in suburbs, even in relatively small patches of a yard, reduces the soil's ability to cycle nutrients in plant litter and results in lower amounts of carbon stored in the soil. Even two years of retaining leaves where they previously were removed is insufficient to restore decomposition rates or carbon pools. This research is an important step in creating best practices for litter management to maintain essential ecosystem functions, like carbon sequestration, water holding capacity, and soil fertility. Summary Seasonal senesced leaf litter removal eliminates considerable organic material from suburban soils annually. We test if this disturbance alters decomposition and carbon cycles and depletes soils of organic matter over time, creating persistent legacy effects. We used a factorial experimental design to implement 1–2 years of current leaf litter manipulations (remove or retain fallen leaves) within historically raked and unraked areas in suburban Maryland yards. We then compared total organic soil carbon and decomposition using a standardized substrate decomposition methodology (Tea Bag Index) across treatment plots. Long-term litter removal in suburban yards reduced decomposition rates by 17% and total soil organic carbon concentration by up to 24% compared to areas where leaf litter was retained in situ. In contrast, short-term management changes (1–2 years) did not significantly impact decomposition rates or total organic soil carbon concentrations. Our findings suggest that long-term suburban litter raking creates legacy effects that alter decomposition and carbon storage process trajectories that are not easily reversed. This is important in understanding urban ecosystem function and sustainable management.
Positive tree diversity effects on arboreal spider abundance are tied to canopy cover in a forest experiment
(Wiley, 2023-06-01) Butz, Elizabeth M.; Schmitt, Lauren M.; Parker, John D.; Burghardt, Karin T.
Human actions are decreasing the diversity and complexity of forests, and a mechanistic understanding of how these changes affect predators is needed to maintain ecosystem services, including pest regulation. Using a large-scale tree diversity experiment, we investigate how spiders respond to trees growing in plots of single or mixed species combinations (4 or 12) by repeatedly sampling 540 trees spanning 15 species. In 2019 (6 years post-establishment), spider responses to tree diversity varied by tree species. By 2021, diversity had a more consistently positive effect, with trees in 4- or 12-species plots supporting 23% or 50% more spiders, respectively, compared to conspecifics in monocultures. Spiders showed stronger tree species preferences in late summer, and the positive impact of plot diversity doubled. In early summer, the positive diversity effect was tied to higher canopy cover in diverse plots, leading to higher spider densities. This indirect path strengthened in late summer, with an additional direct effect of plot diversity on spiders. Prey availability was higher in diverse plots but was not tied to spider density. Overall, diverse plots supported more predators, partly by increasing available habitat. Adopting planting strategies focused on species mixtures may better maintain higher trophic levels and ecosystem functions.
Current street tree communities reflect race-based housing policy and modern attempts to remedy environmental injustice
(Wiley, 2022-10-05) Burghardt, Karin T.; Avolio, Meghan L.; Locke, Dexter H.; Grove, J. Morgan; Sonti, Nancy F.; Swan, Christopher M.
Humans promote and inhibit other species on the urban landscape, shaping biodiversity patterns. Institutional racism may underlie the distribution of urban species by creating disproportionate resources in space and time. Here, we examine whether present-day street tree occupancy, diversity, and composition in Baltimore, MD, USA, neighborhoods reflect their 1937 classification into grades of loan risk—from most desirable (A = green) to least desirable (D = “redlined”)—using racially discriminatory criteria. We find that neighborhoods that were redlined have consistently lower street tree α-diversity and are nine times less likely to have large (old) trees occupying a viable planting site. Simultaneously, redlined neighborhoods were locations of recent tree planting activities, with a high occupancy rate of small (young) trees. However, the community composition of these young trees exhibited lower species turnover and reordering across neighborhoods compared to those in higher grades, due to heavy reliance on a single tree species. Overall, while the negative effects of redlining remain detectable in present-day street tree communities, there are clear signs of recent investment. A strategy of planting diverse tree cohorts paired with investments in site rehabilitation and maintenance may be necessary if cities wish to overcome ecological feedbacks associated with legacies of environmental injustice.

Entomology

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