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| S. siberica |
A friend of mine asked me a question this week that has no easy answer: Is S. siberica an invasive species? There are now some places in the United States where S. siberica is certainly listed as an invasive species [1], though there also appears to be some debate about this listing. At present S. siberica is not found on Canadian invasive species lists [2].
Disagreement about whether or not to list a species as 'invasive' arises from the difficulty of determining what precisely an 'invasive' species is, and the philosophical and moral debate about what we should do about it. In ecological terms, in order to qualify as invasive, a species must be (a) outside of its native range and (b) spreading to the detriment of native species. The first criterion is easy enough to judge, provided there is a historical record or some other straightforward evidence of the species' native status. The second criterion is much harder. It takes a lot of research to establish that (a) native populations are suffering and (b) the suffering is caused by the introduced species.
For example, in some places S. siberica is forming high-density populations in sites which have been previously occupied by native spring ephemerals (eg Trillium spp, Sanguinaria canadensis, etc). These native spring ephemerals are showing drops in population density and other metrics of health.
Knowing these two facts does not establish a causal link; because we're dealing with an open system, it's not so easy to tease apart potential causes of observed effects. Maybe the native spring ephemerals are suffering because of deer predation, or habitat disturbance, climate change, insect predation, fungal infection, or any number of other potential causes -- and more likely several causes including competition from the introduced species. It will take time effort to determine what, precisely, is the cause of the documented decline.
And this is where we get to the non-scientific aspect of this whole issue: deciding at what level of proof we should take action. Listing a plant as an invasive species is not just a scientific statement: it's a policy decision, too. So we have to consider the policy; while scientific standards of proof shouldn't be overly impacted by practical concerns, practicality is central to policy decisions and will affect how evidence is assessed.
On the one hand, we don't want to take action without understanding the causes. This could lead to wasted or misdirected efforts, or unintended harm. But by the time we meet the scientific standards for proof, it may be too late to take any useful action. We must find ways to balance the need for good evidence with the unfortunate reality of haste, financial limitations, and culture.
All species which meet the scientific criteria for invasiveness are invasive in both senses (as this is the stricter definition), but some species which do not yet meet the scientific criteria may still qualify as invasive for the purposes of policy-making. The degree of proof to qualify for policy-oriented 'invasiveness' is in principle less strict. Exactly where we draw the line is currently unclear, and may always have to be decided on a case-by-case basis (this is never an attractive option politically; nobody likes to hear the answer "it depends" when we talk about rules, policy, and enforcement).
I believe that this issue will eventually have to be settled politically, as part of a much broader public discussion about what we, as a society, will do to address environmental issues.
So: Is S. siberica an invasive species?
Yes. And no. And we don't all agree what to do about it.
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| S. siberica |
For example, in some places S. siberica is forming high-density populations in sites which have been previously occupied by native spring ephemerals (eg Trillium spp, Sanguinaria canadensis, etc). These native spring ephemerals are showing drops in population density and other metrics of health.
Knowing these two facts does not establish a causal link; because we're dealing with an open system, it's not so easy to tease apart potential causes of observed effects. Maybe the native spring ephemerals are suffering because of deer predation, or habitat disturbance, climate change, insect predation, fungal infection, or any number of other potential causes -- and more likely several causes including competition from the introduced species. It will take time effort to determine what, precisely, is the cause of the documented decline.
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| S. siberica flower - note the blue anthers and central stripe along the petals; I certainly can't dispute the aesthetic appeal of this species |
On the one hand, we don't want to take action without understanding the causes. This could lead to wasted or misdirected efforts, or unintended harm. But by the time we meet the scientific standards for proof, it may be too late to take any useful action. We must find ways to balance the need for good evidence with the unfortunate reality of haste, financial limitations, and culture.
All species which meet the scientific criteria for invasiveness are invasive in both senses (as this is the stricter definition), but some species which do not yet meet the scientific criteria may still qualify as invasive for the purposes of policy-making. The degree of proof to qualify for policy-oriented 'invasiveness' is in principle less strict. Exactly where we draw the line is currently unclear, and may always have to be decided on a case-by-case basis (this is never an attractive option politically; nobody likes to hear the answer "it depends" when we talk about rules, policy, and enforcement).
I believe that this issue will eventually have to be settled politically, as part of a much broader public discussion about what we, as a society, will do to address environmental issues.
So: Is S. siberica an invasive species?
Yes. And no. And we don't all agree what to do about it.
 |
| Naturalized S. siberica population in a public park in Montreal |
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