Governments increasingly collaborate with residents and nongovernment organizations (NGOs) in urban forest management because of the underlying belief that these groups improve the delivery of local forest services. However, in practice, the successes, challenges, and outcomes vary drastically by collaborative arrangement; solely documenting positive outcomes in NGO-government collaborations may hinder the ability to mitigate their associated downsides rather than biasing collaborative behaviours towards success. This study draws on the experiences of urban forest professionals across nine Canadian cities who have participated in or observed NGOs and local governments engage in collaborative urban forest management. We employed semi-structured interviews with 32 participants from three groups: leaders of NGOs, municipal government officials, and urban forest experts who have observed the two parties interact. Our results demonstrate that the addition of NGOs in municipal forest management is associated with positive outcomes and the characteristics of relationships, individual personnel, and community support contribute to their success. We also characterize the barriers that collaborators are tasked with navigating in order to achieve positive outcomes, including high employee turnover, siloed departments, competing priorities, shifting politics, and precarious funding and contracts. Our recommendations for successful NGO-government collaborations include arming stakeholders with a thorough knowledge of civic processes, diversifying political relationships, fostering "champions" among a greater number of involved parties, and participating in longer-term contracts and funding agreements. Further, involved parties should ensure they work towards the equitable distribution of the benefits and outputs of urban forest collaborations. Moving forward, because of the insular nature of NGO-government collaborations and a low capacity among NGOs to share the outputs of these collaborations, we recommend researchers continue to study the successes and shortcomings under varying governance arrangements so that groups may benchmark their collaborative activities against others and determine the most effective means of participating in co-management. • The addition of NGOs in forest management is associated with ecological and social benefits. • Champions, sociocultural backdrops, and knowledge of civic processes contribute to success. • Funding, shifting politics in government, turnover, and censorship are vulnerabilities to success. [ABSTRACT FROM AUTHOR]