Do you think that invasive potential of introduced tree species in general is considered at the time of their introduction?
Actually, I think that historically the potential of introduced tree species to escape and naturalize has hardly been considered, when species were introduced for forestry or ornamental purposes. However, this attitude has recently been changing and full opportunities and risks of introduced tree species are increasingly taken into account.
Bearing in mind climate change, do you think we will need to accept introduced tree species in the native species composition?
Primarily, I believe that while some introduced tree species will continue to play a certain and likely even expanding role in European forests, I don’t believe that the severe risks of climate change on forests and forestry can be addressed adequately by large-scale planting of introduced tree species. Instead, I believe that severe and rapid climate change will exceed the resilience of many forest ecosystems, and will cause major problems for nature conservation and forestry alike, irrespective which tree species are planted in the decades to come. Thus, it is imperative to avoid severe climate change, and terrestrial ecosystems (such as forests) are particularly important in this regard, as they are important pools of carbon. Thus, there is a substantial potential for synergies between forestry, nature conservation and climate change mitigation.
Do you think introduced tree species can substitute native ones while providing necessary habitats?
My a bit simplistic answer is: no. Of course, there will be a large variation if and in how far introduced tree species can provide the same role and services than native ones, but overall the potential of introduced tree species to do so is quite limited.
Do you believe it is necessary to provide stricter legislation with regards to introduced tree species in European forest ecosystems?
Yes, I believe so – I think there is a need for taking the full long-term consequences of introduced tree species into account. In the end, any decision on the extant of planting introduces tree species will have to weigh the pros and cons of doing so. Although this may be difficult, such an approach would allow for a transparent decision process, which would be favourable.
Do you think some countries are more open to tree species introductions than others?
I don’t know, but I would suspect so. For instance, the paucity of silviculturally productive conifer species in the British Isles may have contributed to the wide-scale plantation of introduced conifer species. 
Dr. Franz Essl
Senior lecturer
Vienna University
Vegetation ecologist
Austrian Environment Agency