Transportation of non-indigenous species via soil on international aircraft passengers’ footwear
The potential for transported soil to harbour and spread non-indigenous species is widely recognized and many National Plant Protection Organizations restrict or prohibit such movement. A study was undertaken on organisms present in soil that had been removed from footwear being carried in the baggage of international aircraft passengers arriving in New Zealand. This study highlighted the high incidence and diversity of viable bacteria, fungi, nematodes and seeds, as well as several live arthropods occurring in this soil. Among the genera detected, it is noted that species belonging to these genera are regulated in New Zealand. The organisms detected included bacteria (found in 100% of samples), fungi (98%), seeds (57%), nematodes (65%) and other mesofauna (38%).
Concerning seeds, a total of 446 seeds was recovered from 155 samples (this is considered to underestimate the total number as some were missed during searches). Seeds occurred in 57% of samples, and on average 1 g of soil contained 2.5±0.37 seeds. Overall, 69% of the seeds were found to be viable, 9 plant types dominated, in particular grass and tree seed.
The type, number of seeds found and the genera were as follows:
- Climber (1 seed): Clematis;
- Creeper (2 seeds): Vitis;
- Grass (160 seeds): Agrostis, Andropogon, Dactylactenium, Deschampsia, Digitaria, Eragrostis, Festuca, Glyceria, Hordeum, Lachnagrostis, Lolium, Paspalum, Poa, Setaria, Sporobolus, Triticum, Vulpia (Poaceae);
- Herb (46 seeds): Amaranthus (Amaranthaceae), Arctotheca (Asteraceae), Asperugo (Boraginaceae), Capsicum (Solanaceae), Cleome (Cleomaceae), Fragaria (Rosaceae), Galium (Rubiaceae), Ipomoea (Convolvulaceae), Medicago (Fabaceae), Polygonum (Polygonaceae), Rumex (Polygonaceae), Trifolium (Fabaceae), Tropaeolum (Tropaeolaceae);
- Sedge (2 seeds): Scirpus (Cyperaceae);
- Shrub (4 seeds): Rubus (Rosaceae);
- Tree/shrub (4 seeds): Alnus (Betulaceae), Sambucus (Adoxaceae);
- Tree (137 seeds): Betula (Betulaceae), Platanus (Platanaceae).
Sampling period and type of footwear had a significant impact on seed counts. Seed counts in both January and October were significantly higher than those in March-April. Furthermore, among footwear types, golf shoes had the highest seed counts.
Sources
McNeill M, Phillips C, Young S, Shah F, Aalders L, Bell N, Gerard E ; Littlejohn R (2011) Transportation of nonindigenous species via soil on international aircraft passengers’ footwear. Biological invasion 13, 2799-2815.