Forest owners reluctant to protect infected woods with no economic value

Globalization is in many regards shrinking our world. This is not unproblematic, especially in regards to the increasing transports of living plants. Such carry populations of microbes, which even though possibly harmless in their natural environment might act as pathogens in the new one. The reason for this is that they have not co-evolved with the potential hosts they are being introduced to, which thus have not developed any resistance towards the microbes. Species introduced in this way, usually by the hand of man, are called invasive and may cause massive devastation. Examples of such in Sweden the last decades are the notorious ash and elm declines.

These outbreaks are often spectacular and attract much attention. This leads to political and societal outrage and demands for action, and the scientific community correspondingly mobilizes in order to develop pesticides or biological control agents against the aggressor. Much less effort, not to say none at all, is put into investigating to what extent such agents will be used by the land owner. It is more or less taken for granted that anyone whose forest is being assailed by an invasive species will use every mean to his disposal to mitigate the damages.

Abandoned forests

In reality, this is a modified truth, as has become apparent in Catalonia in north eastern Spain. This region has for a long time been covered by chestnut forests. Some foresters grow the trees for chestnut fruit, whereas others harvest the trees for low-diameter timber. Since the 70’s however, price on the fruit has increased, while demand for chestnut logs has dropped significantly. During this period, chestnut orchards have been plagued by the fungal disease chestnut canker. Since 1994, a biological control agent against the fungus is available. This is a virus called CHV-1 that successfully infects the pathogen, and in most parts of Europe has spread naturally among the chestnut stands after introduction. Not so in Spain, however, which is why the Catalonian government subsidized use of CHV-1 between 2006 and 2011, in hopes that this would help establishing the virus in the environment.

Chestnut canker and the mentioned fluctuations on the chestnut market has since the 70’s driven the foresters down three different pathways. Almost two-thirds have chosen to abandon their forests, control agent and subsidies notwithstanding. The remainder has pushed on as before, or substituted their forests for an exotic species, usually Monterrey pine or Douglas fir. Naturally, only those willing to continue managing their chestnut plantations has opted for CHV-1 treatment. But on what grounds were these critic decisions being made? Under what circumstances are there reasons to believe that land owners will use novel control agents, and when it is more likely that the forest will be abandoned regardless of what treatments become available? This is the topic of a new study from the Department of Forest Mycology and Plant Pathology at the Swedish University of Agricultural Sciences.

Economy the deciding factor

Jonas Oliva is the first author of the study. “We have investigated the chestnut case through in-depth interviews with 26 land owners”, he says. “The most striking result was that it is four times commoner to continue managing the forest among foresters keeping their orchards for the expensive fruit, compared to those keeping them for the lumber, for which there is no strong demand presently. These managers were also four times more likely to apply for biological control with CHV-1. Thus, it is the potential for economic revenue that decides whether land owners keep managing their forests. To those who see no financially rewarding management options, the availability of subsidized biological control agents is not a critical factor.”

Economy was however not the sole driver affecting whether a foresters abandoned the forest or pressed on, albeit the strongest. The study also showed that self-taught foresters, without family traditions or contact with other mentors, were more prone to abandon management than others. This also held for foresters that saw dangers in substituting the chestnut trees for exotic species.

Social pressure important

“Our interviews also show that a forester that faces a threat, such as a disease, will only act when the threat lowers or threatens to lower land value”, Jonas says. “This value is a subjective measure and a sub-conscious weighting of economic, aesthetic, social and personal factors. Once this has happened, the land owner will only decide on actions from his personal experience, or from such already practiced within his social cluster. If an action such as abandonment or substitution to exotic species is not viewed as accepted within this cluster, it will very rarely be taken.”

The will to put effort into aiding tree species threatened by invasive pathogens seems, at least in the present case, strongly linked to a perceived future revenue. These might well be important lessons for those seeking to develop expensive biological control agents against other invasive species, such as the fungi causing elm and ash decline in Sweden. These tree species are hardly considered economically important to most foresters. If use, and especially costs, of a future control agent is to be tasked to the forest owner, it would be well advised to investigate his motivation for such an undertaking before spending vast resources on the development of such agents.