Review

First, a review and synthesis of existing scientific knowledge about the relation between tree biodiversity and ecosystem functioning was executed. The results were presented in a white paper as a special issue of the Bosrevue, in Dutch, and Forêt Wallonne, in French (outputs). 

Overall, it is hard to draw conclusions. Scientific knowledge is patchy and mostly based on mixtures with only two species. Moreover the effects of confounding factors were not always controlled for. In general, tree species mixtures seem to favour forest biodiversity, but the relation with other aspects of ecosystem functioning is less clear. Expansion of scientific knowledge on this topic is essential (and large-scale forest biodiversity experiments can help to understand some of the mechanisms) (outputs).

Questionnaire

Second, a questionnaire on the role of forest biodiversity was held in Flanders and Wallonia amongst two big groups of forestry stakeholders: scientists and ‘practitioners’ (comprising owners and managers). The goals were to determine (1.) which management objectives are thought to be most important, (2.) to find out how forest stakeholders perceive ecosystem services in mixed forests compared to monocultures. In addition, differences in perception between the stakeholders types and the two regions were looked at. The results of the questionnaire and the in depth synthesis were published in the final report of FORBIO for SSD (outputs).

1. There were significant differences between stakeholder types and regions. Yet, in general higher importance was attributed to the management objectives related to maintaining the diversity of associated species, preserving soil and water quality and providing an environment in which it is pleasant to live. Lowest importance was attributed to the management objectives related to maintaining the game population, providing protection against fire, ensuring wood supply for individuals and ensuring the production of non-woody products.

2. The ecosystem services were classified in accordance to their relationship to human wellbeing (see figure). For the perception on ecosystem services in mixed forests and monocultures there were also significant differences between type and region of stakeholders, but there was a general agreement that supporting, regulating and cultural services are higher in mixed forest in comparison with monocultures. On provisional services, the perception of the stakeholders is mixed and rather neutral.

Analysis

Finally, the opinion of the stakeholders in the questionnaire was compared with the scientific knowledge from the review. The most striking conclusion is that stakeholders have a quite strong opinion on the functioning of ecosystems in mixed stands versus monocultures, which contrasts the lack of specific scientific information.