Societal Impact Statement Trees play a critical role for people and the planet. Numerous studies have demonstrated that the presence of trees and urban nature can improve people's mental and physical health, children's attention and test scores, the property values in a neighborhood, and beyond. Trees cool our urban centers. Trees are essential for healthy communities and people. The benefits that trees provide can help cities and countries meet 15 of the 17 internationally supported United Nations Sustainable Development Goals. This critical review provides a comprehensive argument that trees should be considered an important part of the equation by project managers and civic leaders as we collectively work toward reaching these sustainability goals. Summary We live in an era influenced by humans to the point that the Earth's systems are now altered. In addition, a majority of the world's population live in cities. To meet the needs of people in a changing world, The United Nations General Assembly created the United Nations Sustainable Development Goals (UN SDG) to improve the quality of life for people. These broad goals outline the greatest challenges of our time. An effective strategy to assist in meeting these goals is to plant and protect trees, especially in cities where the majority of people live. This paper serves as a critical review of the benefits of trees. Trees promote health and social well‐being by removing air pollution, reducing stress, encouraging physical activity, and promoting social ties and community. Children with views of trees are more likely to succeed in school. Trees promote a strong economy and can provide numerous resources to the people that need them. While cities are getting hotter, trees can reduce urban temperatures. They provide habitat and food for animals. Finally, trees are valuable green infrastructure to manage stormwater. Money spent on urban forestry has a high return on investment. As we navigate this human‐dominated era, we need skilled people who understand the nuances of the built environment and trees as we strategically plan the cities of the future. The overwhelming evidence from the scientific literature suggests that investing in trees is an investment in meeting the UN SDG, and ultimately an investment for a better world.

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With % of trees (. , species) threatened with extinction there is an urgent need for botanical gardens to protect threatened trees in dedicated conservation collections. Species conservation is mentioned in the mission statements of most major botanical gardens, yet the actual conservation value of existing ex situ tree collections is low. We conducted interviews with members of the botanical garden community and organized a symposium at the th Global Botanic Gardens Congress to identify challenges and collect recommendations to improve living ex situ tree collections. We summarize and evaluate this information to facilitate gardens becoming more effective agents for global tree conservation. Experts agree that gardens offer valuable strengths and assets for tree conservation. Some challenges exist, however, including a lack of strategic conservation focus, collection management limitations, gaps in fundamental biological information for trees, and a lack of global coordination. Solutions are offered to facilitate gardens and arboreta of all sizes to participate more effectively in tree conservation. Prioritizing genetically diverse tree collections, participating in conservation networks, developing tree-specific conservation models and guidelines, and strengthening tree science research efforts are a few examples. Most importantly, a more coordinated global effort is needed to fill knowledge gaps, share information, and build conservation capacity in biodiversity hotspots to prevent the loss of tree species.

Societal Impact Statement The need for urban greening increases with global urbanization. Trees are major assets to livable urban areas, providing valuable environmental services to combat challenges such as pollution, urban heat, and flooding, as well as to improve social cohesion, human health, and well‐being. Investments in tree planting and arboriculture yield valuable returns, but trees face many challenges in the unnatural and stressful urban environment and in a rapidly changing climate. Botanical gardens have expertise in growing plants in designed landscapes. We urge their increased involvement with urban forestry to improve sustainability of cities and human lives. Summary Improving urban forests is one of the solutions to achieving several of the United Nations Sustainable Development Goals and making cities healthier and more livable for people. Priority should be given to protecting mature trees and promoting long‐lived trees in the future. Achievement of this goal requires recognition of the myriad stresses trees face in built landscapes as well as the challenges related to climate change. Because all people living in communities are affected by the urban forest, developing solutions and forestry action plans should be a social endeavor and include diverse partnerships. Botanical gardens and arboreta can provide key resources in support of these efforts. They have a significant public reach, maintain a strong professional network, and can make important contributions to address key priorities including (a) protecting existing trees; (b) improving tree selection, diversity, and age structure; and (c) improving planning, standards, training, and management. A focus on below‐ground aspects, such as root development and soil composition, is a critical component for success. Horticultural and scientific knowledge combined with extensive public reach make botanical gardens and arboreta important potential partners in achieving urban forest objectives, but a greater call to action is needed.

A manual and software for common statistical methods for ecological and biodiversity studies