1.9 billion invertebrates and 800 million seeds. That’s the number of stowaways arriving to Norway via garden plants every year. The costs could be sky high.
Thuja, belonging to the Cupressaceae (cypress family) is one of the imported garden plants bringing the most stowaways to Norway. Here, two Rhaphigaster nebulosa are brought along. Photo credit: Anders Endrestøl, NINA
Invasive species are considered one of the five most important drivers of global biodiversity loss, a threat growing at an unprecedented rate. The ecological and socioeconomic costs are dramatic, with a global economic cost exceeding $423 billion annually in 2019.
Early detection is key
Eradication measures are often expensive, and their success and cost effectiveness rely heavily on early detection and rapid response, says Research Director Jørgen Rosvold at the Norwegian Institute for Nature Research (NINA).
Commissioned by the Norwegian Government, NINA is monitoring and assessing risks associated with the introduction of alien species via garden plant imports to Norway. The results of 10 years of monitoring is now summarized.
The import of plant products to Norway over the last 30 years has increased greately, and more than 20 000 metric tons of garden plants were imported in 2023 alone. Both soil and plant material have been subjected to analyses by NINA experts.
700 kilograms of soil containing 850 000 insects
More than 700 kilograms of soil have been analyzed in the period 2014-2023, showing large amounts of germinating seeds, insects and other invertebrates introduced to the country as stowaways.
As many as 857 199 insects have been identified and assessed according to the Norwegian Invasive Species List. At least 65 of the 764 species detected in either soil, foliage or flying in between plants do not belong in Norway. NINA experts also identified and assessed 35 913 vascular plants, of which 39 species were alien to Norway.
Strumigenys rogeri is one of several alien ant species arriving to Norway with garden plant import from Costa Rica. Photo credit: Arnstein Staverløkk, NINA
Estimates gave answers in the billions
Random samples made by the experts add up to only 0.0001 percent of the total volume of garden plants imported during the monitoring period.
Based on the samples, however, we have estimated imports of 800 million germinating seeds and 1.9 billion insects and other invertebrates annually along with garden plants, explains senior researcher Marie Davey at NINA.
Detects alien species in Norwegian ecosystems
NINA also runs a program to detect and report alien species at an early stage in the wild. Experts have mapped plants and insects at 90 locations around the Oslofjord, chosen because of being a hotspot for alien species.
We have found 24 species listed on the Norwegian Invasive Species List through this monitoring. Several of them are insects and other invertebrates that have not previously been recorded in Norwegian nature, says Davey.
Call for earlier warning
We have a unique opportunity to follow the invasion process through our monitoring programs. Ideally, we would like to be able to report new alien species detections immediately so that measures can be implemented with the aim of halting a possible invasion. In this way, major negative impacts on nature and society can be prevented, says Rosvold.
As an important step, NINA therefore recommends intensifying sampling of garden plant imports, in order to provide more accurate estimates. The experts also recommend using environmental DNA for a more precise mapping of possible alien species.
Chlorophorius varius is an alien species arriving to Norway via vines. Photo credit: Arnstein Staverløkk, NINA
Read the report here (Summary in English): Davey, M.L., Westergaard, K.B., Endrestøl, A., Fossøy, F., Hanssen, O., Brandsegg, H., Laugsand, A.E., Opsahl, N.N., Dahle, S., Andersskog, I.P.Ø., Staverløkk, A., Åström, J. 2024. Monitoring the invasion pathway of imported horticultural plants. Basic monitoring 2023 and a ten year summary of results. NINA Rapport 2484. Norwegian Institute for Nature Research.
Learn more about the monitoring of garden plant import here
Contact: Jørgen Rosvold