Practical and Innovative: A Design for a New Field Nursery at the Morris Arboretum

The Morris Arboretum is an exceptionally beautiful place to learn about and appreciate trees from around the world. Before these incredible specimens make their way out to the garden, many of these plants will spend at least part of their life in the field nursery. Unlike commercial nurseries where large quantities of relatively few species are grown, the field nursery at the Morris Arboretum serves a more dynamic role hosting a wide array of tree and shrub species from all over the world. The purpose of the nursery at the Arboretum is threefold: to offer a more hospitable growing environment for plants that do not grow well in pots; to provide a space for trees to grow larger in size before being planted out; and to test the hardiness of a tree species. Some of the important considerations in designing a new field nursery are location, spacing, irrigation, weed control, fertilization, fencing, and shade structure. Given these considerations, a new nursery will be designed to minimize maintenance and environmental impact while at the same time creating an optimal environment for the young plants of the Morris Arboretum to thrive until they reach their ultimate destination in the landscape

Stand Dynamics and Diversity Patterns in Planted and Naturally Regenerating Urban Forests

The world is becoming an increasingly urban planet with 68% of the global population expected to live in cities by 2050 and urban land cover expected to increase by 40%. This urban expansion brings with it a host of environmental and health consequences such as the urban heat island effect, reduced air and water quality, and biodiversity losses. In forested biomes, trees and forests growing within the urban matrix offer a valuable opportunity to offset many of these negative impacts and to provide a suite of additional benefits. In recognition of this opportunity, there is mounting interest in investing in urban forests as a form of green infrastructure. Effectively directing these investments will depend on baseline knowledge of current and potential future conditions, however, urban forest dynamics are poorly understood. In this dissertation, I help to overcome knowledge gaps in urban forest dynamics by examining patterns of nativity, diversity, and species composition in planted and naturally regenerating urban forests. To do this, I draw from two datasets that capture the two sources of future trees in urban settings: natural regeneration and tree planting.In my first two chapters, I use field data from forested natural areas throughout the city of New Haven, CT, USA to examine successional trajectories and regeneration potential in urban forest patches. While previous work has focused on discerning the differences between urban and rural forests, in this work, I focus instead on discerning the range of urban forest types that can be found within a single city. Using patch size as a framework I examine naturally regenerating forests in large (95-126 ha), medium (1-19 ha), and small forest patches (0.05-0.65 ha). In my first chapter, I find that forest structure, composition, and the proportion of native species shifts significantly with forest patch size and by relating these shifts to regeneration patterns in the seedling layer I highlight a suite of distinct successional trajectories. In my second chapter, I build on these findings by examining the regeneration potential of the buried seedbank at these same plots. Similar to findings from my first chapter, I find that the proportion of native species and dominance of individual tree species in the buried seedbank shifts with forest patch size. Together, these two chapters suggest that large patches are following similar successional trajectories to analogous rural forests in the region whereas small patches are exhibiting more distinct and novel successional trajectories. Medium patches are the most challenging patch size to characterize and in some cases resemble large patches and in other instances, small patches. Challenges in distinguishing forests in this patch size highlight the potentially important role that landscape structure, age, land-use history, and anthropogenic impacts – in addition to patch size – play in shaping urban forest dynamics. Indeed, results from regeneration regressions in these two chapters indicate that proximity to surrounding forest cover is a significant positive predictor of the number of native seedlings and germinants in the buried seedbank. This finding suggests that native tree planting may be necessary in more isolated forest patches in order to sustain future cohorts of native trees. Tree planting is the focus of my third chapter. In this chapter, I use survey data from municipalities and non-profit organizations throughout the Northeastern USA to understand how local tree planting programs contribute to regional diversity patterns. I find that cities in the Northeast rely heavily on a narrow suite of species and genera for specific ecosystem services. Specifically, nearly 20% of all shade trees planted in the region are oak species and over 50% of ornamental trees are either cherry species or tree lilac. This overreliance on individual taxa may have implications for future forest resilience. Moreover, tree planting palettes in the region included invasive tree species, one of which (Norway maple) was also a prolific species regenerating in the urban forest patches from chapters one and two. This finding underscores the importance of considering natural regeneration and tree planting in the context of one another as planted trees may serve as seed sources for naturally regenerating trees in natural areas. Collectively, this dissertation illuminates potential future forest conditions in planted and naturally regenerating urban forests. Insights into the future forest are the cornerstone to effective and appropriate forest management and findings from this dissertation can be leveraged to inform management in urban forests throughout the Northeastern, USA. Beyond management, this dissertation also introduces frameworks that can be further honed and developed to enhance our understanding of forest dynamics in urban areas around the world

Leveraging Community Support to De-vine New Haven’s Natural Areas

This case study discusses the Urban Resources Initiative’s efforts to remove invasive vines from natural areas in New Haven, CT. The Urban Resources Initiative (URI) is the primary urban forestry organization in New Haven, and community engagement is a key feature of their programming. Working with a combination of local stewardship groups (“Community Greenspace”) and a workforce program (“GreenSkills”) for previously incarcerated individuals and teens, URI began hosting vine removal workdays in New Haven’s parks as a way to both protect critical components of the city’s forest canopy and build interest and investment in the city’s natural areas

Positive long-term impacts of restoration on soils in an experimental urban forest

As urbanization increases worldwide, so too are investments in nature-based solutions that aim to mitigate urban stressors and counter the impacts of global climate change. Tree planting on degraded urban lands—or afforestation—is one form of nature-based solution that has been increasingly implemented in cities around the world. The benefits of afforestation are, however, contingent on the capacity of soils to support the growth of planted trees, which poses a challenge in some urban settings where unfavorable soil conditions limit tree performance. Soil-focused site treatments could help urban areas overcome impediments to afforestation, yet few studies have examined the long-term (> 5 years) effects of site treatments on soils and other management objectives. We analyzed the impacts of compost amendments, interplanting with shrubs, and tree species composition (six species vs. two species) on soil conditions and associated tree growth in 54 experimental afforestation plots in New York City, USA. We compared baseline soil conditions to conditions after six years and examined changes in the treatment effects from one to six years. Site treatments and tree planting increased soil microbial biomass, water holding capacity, and total carbon and nitrogen and reduced soil pH and bulk density relative to baseline conditions. These changes were most pronounced in compost-amended plots, and the effects of the shrub and species composition treatments were minimal. In fact, compost was key to sustaining long-term changes in soil carbon stocks, which increased by 17% in compost-amended plots but declined in unamended plots. Plots amended with compost also had 59% more nitrogen than unamended plots, which was associated with a 20% increase in the basal area of planted trees. Improvements in soil conditions after six years departed from the initial trends observed after one year, highlighting the importance of longer-term studies to quantify restoration success. Altogether, our results show that site treatments and tree planting can have long-lasting impacts on soil conditions and that these changes can support multiple urban land management objectives.This dataset is comprised of three tabs in a single excel file. See the "MetaData" tab for information pertaining to the variables measured and analyzed. The "SoilData" tab includes values for all the soil variables analyzed and reported on and "TreeData" includes values for all the tree growth variables analyzed and reported on in the manuscript.This study was conducted within long-term research plots (NY-CAP) located in Kissena Corridor Park, a 40-ha urban park in Queens, New York, USA. The NY-CAP experimental plots test the impacts of three treatments on planted tree growth and soil conditions over time. Treatments include: tree species composition (two species or six species), compost addition (compost-amended or unamended), and interplanting with shrubs (presence or absence). We sampled soils four times over the course of the experiment in 2009, 2010, 2011 and 2016. In 2011 and 2016 we measured DRC and DBH, respectively, for all planted trees in experimental plots. Soils were processed and analyzed at Yale University