Promoting Biodiversity Through Tree Selection and Planting
Urban forests play a crucial role in promoting biodiversity, but choosing the right trees is key. This article explores how hybrid trees, diverse understory plants, and native species contribute to building resilient ecosystems in our cities. Drawing on expert insights, we'll discover how thoughtful diversity in tree selection can create vibrant urban forests that support a wide range of plant and animal life.
- Hybrid Trees Nurse Native Plants
- Diverse Understory Supports Tree Regeneration
- Native Species Build Resilient Urban Ecosystems
- Thoughtful Diversity Creates Vibrant Urban Forests
Hybrid Trees Nurse Native Plants
Native restoration and carbon sequestration were the main objectives of a recent installation in a hot, dry area of Southern California. The soil was highly sodic, with salt and boron impacts, and probably some levels of contamination. After non-native allelopathic trees were removed from the site, we planted hybrid salt- and boron-tolerant poplars to act as nurse trees for very slow-growing native plants. The sterile trees will grow quickly and begin to improve the soil health and quality, providing wind and heat protection to the understory without any risk of becoming invasive. The root systems will begin to develop a rhizosphere that will support the successional planting. After the end of the hybrid trees' lifespan, the native understory will grow in successfully.
Diverse Understory Supports Tree Regeneration
We have focused on more than just tree selection and planting. Trees, shrubs, and the diversity of ground story vegetation have all been taken into account. Even in urban areas, we have used native ground story wildflowers, sedges, grasses, and other native plants that support the regeneration of future generations of trees.
Most lawns and many non-native cool-season grasses (e.g., Kentucky bluegrass, Hungarian brome, Orchard grass, Tall fescue, etc.), often used as plant materials in urban areas, are typically shallow-rooted and able to live in dense sods. Sod-forming plants can restrict or eliminate the diversity of other ground story plants able to compete, and also restrict the germination of acorns, hickory nuts of native trees, and native shrubs such as American hazel, sumac, haws, viburnum, and others.
On hundreds of urban projects, from yards with large remnant bur oak trees growing in highly maintained lawns, to historic oak savanna and forests where invasive shrub colonization has shade-suppressed native ground story vegetation, we have reduced the lawns and the invasive shrubs and replanted seeds of the native understory shrubs, and ground story wildflowers, sedges, and native shade-tolerant grasses.
Many examples can be found, including what we have done on our own farm in southern WI (See "Nature's Second Chance" - Beacon Press). See the USEPA oak savanna recovery plan (Region 5, USEPA). See oak savanna restoration publications on ResearchGate.
Native Species Build Resilient Urban Ecosystems
When selecting and planting trees to promote biodiversity and ecological health, I always focus on choosing a wide mix of native species suited to the local soil and climate. Native trees not only adapt better and require less maintenance but also provide essential habitat and food sources for local wildlife like birds, bees, and butterflies. I also avoid monocultures, as they're more vulnerable to pests and disease. Instead, I create layered plantings using understory shrubs and groundcovers to support a more complete ecosystem. The goal is to build resilience through diversity, so that each part of the planting supports the health of the whole. Proper site preparation and aftercare are just as important to ensure that every tree gets off to a healthy start and continues to thrive.
A standout project was a streetscape renewal we did in a suburban Melbourne neighbourhood where the local council had been struggling with declining tree health and low wildlife activity. Drawing on my horticulture training and more than 15 years of experience, I designed a planting strategy that replaced old exotics with a mix of indigenous species including Eucalyptus leucoxylon, Acacia melanoxylon, and Banksia marginata. We paid close attention to spacing, companion planting, and long-term canopy cover. Within 18 months, we saw a visible return of native birds and pollinators, improved soil health, and stronger community engagement with the space. What made this a success was not just the plant selection but the hands-on knowledge of how each species behaves over time, how they interact with each other and the environment, and how to build an ecosystem instead of just planting trees.
Thoughtful Diversity Creates Vibrant Urban Forests
When promoting biodiversity and ecological health through tree selection, I prioritize native species that support local wildlife and adapt well to urban conditions. For example, in a recent urban reforestation project, I selected a mix of oaks, maples, and serviceberries—each providing different food sources and habitats for birds and pollinators. I avoided monocultures to reduce vulnerability to pests and disease, ensuring long-term resilience. The site also included understory shrubs and ground covers to enhance structural diversity. By considering soil type, sunlight, and water availability, I tailored the mix to maximize survival and ecological benefits. This approach not only created a healthier urban forest but also improved air quality and community well-being. From this experience, I learned that thoughtful diversity and local ecological knowledge are key to sustaining vibrant, resilient green spaces in cities.
