Vascular plants outside their natural home range – assessment of consequences for biodiversity
Report no: 2021:15
When planting vascular plants, using seeds harvested from local populations has the lowest risk of negative impact on biodiversity. A good rule of thumb as to what can be considered “local” is within a radius of ten kilometres from the site of planting, but this varies between species.
Thus concludes the Norwegian Scientific Committee for Food and Environment (VKM) in an assessment of possible negative impact on biodiversity when sowing species sourced from local, regionally alien, or other populations.
The assessment was commissioned by the Norwegian Environment Agency.
Seeds have been spread by domestic animals across habitats for a very long time. This has probably resulted in some loss of local adaptation for many vascular plants.
In Norway today, planting of vascular plants is conducted in a large scale, for reasons other than to produce food and feed. For almost every intrusion in natural habitats, such as building roads and other infrastructure, restoration of military training facilities, reestablishment and maintenance of semi-natural meadows, or of green roofs on houses and cabins, nearly all involve some sort of revegetation.
Difficult to define
Local plants that already occur naturally in the area, are best adapted to growing in that area, and pose the lowest risk of negative repercussions to the environment. It is, however, difficult to define “the area” as vascular plants have different modes of growing, different environmental requirements, and varying reproductive strategies. This means that the size of “the area” varies between species.
Even closely related species can have vastly different characteristics, for instance in terms of forms of growth and of spreading.
Various negative effects
When locally adapted plants are to be mixed with plants from other areas, it is important to take the genetics of the species into account. Genetic change can lead to loss of local adaptation, which again can lead to the species succumbing to competition from other species.
Genetic change can also stem from changes in the ploidy level (different number of chromosomes between populations of the same species), or hybridization with other species or subspecies.
Avoid problem species
VKM concludes, since there is limited knowledge about the genetic structure of most vascular plants, it is not possible to define a clear set of species, without known risks, that can be used for planting.
“The most important thing is to avoid problematic species, and to find a way for every species to be evaluated on the basis of a simple set of criteria,” says Anders Nielsen, Scientific Leader of the project group.
VKM has created a flow chart with five criteria to guide everyone involved in restoration of rehabilitation of natural habitats following human impingement. The flow chart aids in assessing which species of populations is suited for planting and identifies aspects of the species that need further evaluation prior to planting.
Nielsen points out the set of criteria also can be used to identify potential problems prior to planting in any given area, and with plants from any population.
“In sum, VKM found that it is safe to plant species that are not defined as invasive or problematic in any other way, which are already present in the region. This assumes that one uses local populations, or populations from similar habitats. It is also important to assess whether there is a potential for hybridization with other species in the specific area and whether the seeds to be planted have a different ploidy level than those that already occur in the region,” explains Nielsen.
The VKM Panel on Alien Organisms and Trade in Endangered Species (CITES) is responsible for the assessment.