St John's-wort
Hypericum perforatum
Family: Hypericaceae
Fire effect on plant
Fire likely top kills St John’s Wort (Zouhar, 2004) , but the woody root crown and lateral roots likely survive fire (Agee, 1994).
Key traits
Woody base, with vertical and lateral roots that extend to depths of 0.5-1.5m (Clark, 1953; Zouhar, 2004). Lateral roots capable of producing buds from which new crowns develop.
The seeds are long-lived remaining viable in seed banks for ‘longer than 50 years’ and with a high seed density in UK woodland soils reported (Warr et al, 1994). Seed germination may increased by brief exposure to heating of the range 100-140oC (Sampson and Parker, 1930)
This species lacks any specific dispersal features, with dispersal distance being short (1–5 m; Lososová et al, 2023).
Plant response to fire
Fire is noted to encourage the establishment of St John’s wort. Fire has been indicated to enhance the vegetative spread and formation of patches of St John’s wort and brief exposure to heating of the range 100-140°C has been shown to significantly increase germination (Sampson and Parker, 1930), which Crompton et al, (1988) conclude may in part account for their abundance following fire. Tisdale et al (1959) noted a ‘flush’ of seedlings after fire and Sampson and Parker (1930) described an increase in vegetative reproduction following both grazing and fire. Fire appears to increase stand density in St John’s wort (Campbell and Delfosse, 1984).
Timing of life history
Perennial species. Seeds likely produced from second growing season. Flowering June to September.
Conservation status
None.
References
Agee, J.K. 1994. Fire and weather disturbances in terrestrial ecosystems of the eastern Cascades. Gen. Tech. Rep. PNW-GTR-320. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 52 p. (Everett, Richard L., assessment team leader; Eastside forest ecosystem health assessment; Hessburg, Paul F., science team leader and tech. ed., Volume III: assessment). [Empirical evidence; Grey literature]
Clark, N. 1953. The biology of Hypericum perforatum L. var. angustifolium DC (St. John's wort) in the Ovens Valley, Victoria, with particular reference to entomological control. Australian Journal of Botany. 1: 95-120. [Empirical evidence; Academic literature]
Crompton, C.W., Hall., I.V., Jensen, K.I.N., Hildebrand, P.D. 1988. The biology of Canadian Weeds. 83. Hypericum perforatum L. Canadian Journal of Plant Science, 68: 149-162 [Empirical evidence; Academic literature]
Lososová Z., Axmanová I., Chytrý M., Midolo G., Abdulhak S., Karger D.N., Renaud J., Van Es J., Vittoz P. & Thuiller W. (2023). Seed dispersal distance classes and dispersal modes for the European flora. Global Ecology and Biogeography, 32(9), 1485–1494 [Empirical evidence; Academic literature]
Warr, Susan J.; Kent, Martin; Thompson, Ken. 1994. Seed bank composition and variability in five woodlands in south-west England. Journal of Biogeography. 21(2): 151-168 [Empirical evidence; Academic literature]
Zouhar, Kris. 2004. Hypericum perforatum. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.usda.gov/database/feis/plants/forb/hypper/all.html [Expert opinion; Grey literature]