Urban trees are thriving : an explanation of the innovation of the Stockholm soil system

Abstract: The situation for urban trees is often highly problematical. Due to the high proximity between different functions in cities, space is often quite limited which makes it hard for plants to establish and grow. To overcome these challenges, the City of Stockholm’s tree officers have been developing ways to make plants thrive even in hardscape environments with only small volumes of space available below as well as over-ground. To a larger extent, this is done by using structural soils. These are soils that combine a load-bearing structure of some kind that are able to sustain the hard surfaces often used in cities, with a more porous soil or volume of air. In the porous part, roots are able to grow and receive the water, air and nutrients that they need to survive. The City of Stockholm have been developing their own kind of structural soils, and also experiment with different substrates as alternatives to more traditional soils. In particular, the use of biochar has been very successful and gained the city an international reputation. The technical function and construction of this system are documented in several journalistic magazines, books and in a technical manual provided by the City of Stockholm. Literature explaining the process of how the organisation adopted this innovation is limited, though, and this study therefore aims to identify and explain the key factors for the innovation of the Stockholm soil system and to facilitate an understanding for how it has been adopted by the City of Stockholm. The research question is: Which is the most distinguishing factor for the innovation of the Stockholm soil system? It can be valuable for landscape architects and city officials with a responsibility for street trees in other cities to understand how a new system for planting and establishing trees in Stockholm has been created and implemented. Transferable similarities from the experiences in Stockholm may act as an aid in how such a process can be managed elsewhere too. The scientific approach in this study was hermeneutic, abductive and explorative. The data gathering was performed as an interview study with experts selected for their particular insight and knowledge of the subject. This was combined with a review of journalistic articles. The data was then analysed using a content analysis, structured according to Innovation Adoption Theory and finally analysed by Complexity Theory. On one hand, this shows that factors related to individual/staff characteristics have been an important part in the innovation of the Stockholm Soil system. On the other hand, it also shows that there are factors related to the Innovation, the Organisation, External/Socio-political- and Client-factors that are important as well. The main findings and conclusion to this study is that the most important factor for the success of the Stockholm soil system is a working method of constant experimentation and evaluation, and that the organisation has self-organised itself to incorporate this approach. The main contribution that the study makes is that it shows how a multitude of different factors have been important to the development of the Stockholm soil system. The main part of this is that the organisation seems to accept changes to the soil system as a key ingredient of constant innovation. It also shows that innovation in how urban trees are established might be most successful when it is closely related to practice, as urban environments are hard to emulate in other research situations. For landscape architects, this is valuable as it shows how having an innovative approach to their field can help to improve on current conditions and working methods.