STAND DYNAMICS, REGENERATION PATTERNS AND LONG-TERM CONTINUITY IN BOREAL OLD-GROWTH PICEA-ABIES SWAMP-FORESTS

The occurrence of macrofossil charcoal (long axis greater than or equa l to 0.5 mm) and Picea abies (Norway spruce) pollen in peat stratigrap hies, in combination with size and age data from 2976 P. abies trees w ere used to analyse ecosystem continuity and stand-structure in ten ol d-growth swamp-forests in northern Sweden. All stands were dominated b y P. abies, a species whose abundance increased westwards in Sweden be tween 3000 and 2000 yr B.P. In three stands no macrofossil charcoal wa s found and the maximum age of the peat, determined by C-14 dating, va ried from 1800 to 3600 yrB.P. In the other seven stands the number of levels containing charcoal varied from 1 to 23, but only between 1 and 7 levels were found after the appearance of spruce. Here the maximum age of the peat varied from 400 to 7900 yr B.P. The ten stands had an all-sized stand structure and a stand continuity of ca. 300 yr. The sh ape of the age structure was similar to an inverse J-curve. This indic ates a continuous recruitment over time in a self-perpetuating ecosyst em. In a short-term perspective (< 300 yr), the swamp-forests are char acterized by individual trees continually emerging while others are dy ing. It is suggested that internal dynamics of continuous small-scale disturbances in combination with local site-specific factors determine the structure of these forests. In a long-term perspective, some of t he present spruce swamp-forests within the northern boreal zone have f unctioned as true fire-free refugia since the establishment of P. abie s populations while others have been affected by recurring fires, alth ough not as frequently as forests on surrounding drier sites. The hypo thesis that Scandinavian spruce swamp-forests in general have function ed as true long-term fire-free refugia is thus modified by the present results.