Governments can use three ways to maintain biodiversity: spatial planning, planning of processes (management) and communication. Good communication between scientists, planners, managers and users of urban green areas may be essential to achieve success in maintaining urban biodiversity. In this case study, we have tried to find answers to the question of whether public participation fosters biodiversity by comparing a city in The Netherlands (The Hague), where citizens can participate in decision-making processes, with its twin city in Poland (Warsaw), where the authorities traditionally have not involved its citizens in the planning and management of green areas. The policy plan for green areas in The Hague offers a framework for realizing a sustainable green infrastructure by means of planning, management and use of urban green space. The policy plan describes the status and management of the most important green areas: nature reserves and parks. In this city, it is easy for citizens to obtain information about the management of green areas, but this is very difficult in a city like Warsaw, where management plans are lacking. In Warsaw, much useful information is collected by biologists but only a very small part of the data is provided to, and can be obtained through, the offices of the districts' Department of Environmental Protection. In The Hague, fewer data about the presence of species are collected than in Warsaw, but most of this data can be obtained easily from the Service City Management. Several NGOs in The Hague regularly publish articles about the status of nature within their town and local environment. This stimulates people to observe species and to collect data. The number of volunteers who are active in collecting data on the status of species is still increasing. The collected data are passed to a databank or directly to the managers of the park concerned. The last option will often be consultative, which may lead to empowerment concerning park management. It appears that public participation in the management of green areas will foster recruitment of volunteers who can help to maintain urban biodiversity.