Forest patch size predicts seed bank composition in urban areas

Abstract

Questions: As urban areas expand around the world, understanding how to restore and maintain forests within the urban environment becomes increasingly important. Given that a comprehensive understanding of regeneration dynamics is critical to designating appropriate management interventions we ask the following: how does regeneration, vis-à-vis the buried seed bank, vary in heterogenous urban forests? And, can forest patch size be used to predict regeneration and consequent management interventions? Location: Vacant lots and public parks throughout New Haven, CT, USA. Methods: We sampled buried seed banks in 131 plots distributed across three forest patch sizes ranging from large intact parks (95-126 ha), to small parks (1-19 ha), and vacant lots (0.05-0.65 ha). We collected soil samples from the surface mineral soil and stratified them over sand in a greenhouse over a period of five months to record germination. Results: By examining seed bank floristics in a range of forest patch sizes we found that species composition, nativity, and dominance of specific functional groups shifted with patch size representing a spectrum of urbanization within just one city. Seed bank floristics in large parks more closely resembled results from seed bank studies in rural forests with over 85% native germinants on average. In contrast, vacant lots were dominated by non-native germinants and more ruderal species indicative of earlier successional stages. Seed banks in small parks were variable and in some cases were more similar to large parks or vacant lots. Conclusions: Our findings suggest that large parks in urban areas may be largely selfsustaining whereas smaller parks may require more intensive management for site rehabilitation, especially in early states of succession. Furthermore, our results confirm the highly heterogenous nature of urban forest patches and call for more systematic sampling of urban areas to capture this variation and improve management prescriptions and outcomes.

Diverging conditions of current and potential future urban forest patches

“…Results from our regeneration regression models also confirmed that more isolated plots (i.e., further from adjacent forest) harbored higher proportions of non‐native tree seedlings—a trend also detected in the buried seed banks of the same plots (Doroski, Duguid, & Ashton, 2020). Isolation was also was highly correlated with edge‐to‐interior ratio, area, and forest age (correlation coefficient > 0.50; Appendix S1: Figure S2).…”

“…The most important canopy tree and sapling species in small patches included a mixture of native and non‐native species. Two of these non‐native species (black locust and tree of heaven) were also the most abundant and frequent germinants in a buried seed bank study conducted at the same sites just a year prior (Doroski, Duguid, & Ashton, 2020). When canopy tree composition is similar to composition in the buried seed bank, forests are presumed to be in an earlier successional stage (Grime, 1989).…”

“…New Haven city center is starred, and all parks and lots fell within 8 km of this point. Green polygons designate forested areas in large patches, yellow designates forest cover in medium patches, and blue points are small patches (map adapted from Doroski, Duguid, & Ashton, 2020)…”

“…Notably, patch size should influence the nature of disturbance regimes (Pickett et al, 2001), edge effects (LaPaix et al, 2012; Reinmann & Hutyra, 2017), and seed supplies and sources (Johnson et al, 2017; Lopez et al, 2018)—all of which will impact aboveground vegetation and regeneration potential. Indeed, in a study of urban forest patches throughout the city of New Haven, CT, Doroski, Duguid, and Ashton (2020) found that both the species composition and life history traits of germinants in the buried seed bank shifted with forest patch size. In another study of small regenerated forest patches and large remnant forests within the city of Syracuse, NY, Zipperer (2002) and Zipperer and Guntenspergen (2009) similarly observed shifts in stand structure and vegetation community types depending on patch size.…”

Paying for nature‐based solutions: A review of funding and financing mechanisms for ecosystem services and their impacts on social equity

“…In some cases, the studies took an environmental justice or environmental equity approach, seeking to understand how access Beaulieu et al, 2014;Biehler et al, 2019;Carmichael et al, 2019;Harada et al, 2020;Larson & Perrings, 2013;Prudencio & Null, 2018;Reisinger et al, 2019;Sicard et al, 2018;Taguchi et al, 2020;Wang et al, 2014;Zhang et al, 2020 Crompton, 2007;Davis et al, 2017;Dronova et al, 2018;Evenson et al, 2013;Gerken Golay et al, 2016;Larson et al, 2016;Loeb, 2006a Doroski, Duguid, & Ashton, 2020;Escobedo et al, 2010;Jennings et al, 2019;Johnson & Handel, 2016;Lovasi et al, 2013;Nesbitt et al, 2017;Roman et al, 2021;Sicard et al, 2018;Watkins et al, 2017 Vacant land Wildlife habitat, biodiversity, climate regulation, stormwater management Physical disorder, poor health outcomes, safety concerns Anderson & Minor, 2019;Gardiner et al, 2013;Kremer et al, 2013 Other green space (turf, prairies, urban greening, urban green space)…”