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Research article2012Peer reviewed

Seed dynamics of two fire-dependent Geranium species in the boreal forest of southeastern Sweden

Risberg, Lotta; Granström, Anders

Abstract

We analyzed critical life-history variables for two rare fire-dependent annual Geranium species in southern Sweden, which are today threatened because of effective fire suppression. At recently burned sites with abundant recruitment, seedlings occurred only where the humus layer had been completely removed by smoldering fire. Emergence depths ranged 1-6 cm in the mineral soil. Soil sampling at four sites revealed that in unburned soil Geranium seeds were located only in the mineral soil. Surprisingly, residual seeds were still present where fire had burned away the humus layer. An experiment showed that both species deposit seeds relatively evenly within a radius of 5-6 m, through ballistic dispersal. Repeated sampling in the field over a 2-year period after seed dispersal at one site indicated a low rate of seed depletion, corroborated by an indoor incubation of seeds. Our results show that successful management of these species depend on deep-burning prescribed fire, which can only result after severe drought. On the other hand, the seed bank is extremely long-lived, as viable seeds were present at a site last burned 200 years ago. This well-protected seed bank will likely buffer against both ill-timed fires and occasional failure in the recruiting seedling populations.

Keywords

Geranium bohemicum; Geranium lanuginosum; seed bank; heat triggered; fire regime

Published in

Botany
2012, Volume: 90, number: 9, pages: 794-805 Publisher: CANADIAN SCIENCE PUBLISHING, NRC RESEARCH PRESS