Stream bryophyte recovery after extreme flood disturbance takes several years
2025
Virtanen, Risto | Huttunen, Kaisa‐Leena | Muotka, Timo | Suomen ympäristökeskus | The Finnish Environment Institute
1. The recovery rates and assembly processes of stream bryophyte communitiesafter severe disturbances are not well known. 2. Breaking of an ice dam caused an extreme flood that completely removedbryophyte cover along several hundreds of metres of a boreal stream (StreamUopajanpuro, Koillismaa, NE Finland). We monitored recolonization rates and suc-cessional processes of stream bryophytes in the disturbed stream section over8 years. 3. In the first two summers after the disturbance, the disturbed section remainedlargely unvegetated. The initial recovery of the bryophyte community resultedmainly from colonization of vegetative moss fragments of the dominant, perennialspecies present in the undisturbed upstream section, whereas typical early suc-cessional colonist species remained scarce. 4. The recovery of total cover, richness and community composition of stream bryo-phytes took 5–6 years after the disturbance event, even though bryophyte veg-etation supplying fragments was located in the immediate vicinity upstream of thedisturbance site. 5. Bryophyte species showed differences in the colonization–recovery rates. Meanspatial segregation among species showed no trend during recovery, whereas sev-eral species pairs showed both segregation and aggregation trends. 6. Our results indicate that extreme flooding can have devastating effects on bryo-phyte cover, and the recovery of bryophytes is slow compared to other stream or-ganisms, with full recovery taking up to several years. This recovery time estimatemay only apply if there is an immediate upstream source of vegetative propagulesfrom undisturbed populations. Where such populations are absent, recovery ofbryophyte communities can take decades.
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