Stand dynamics, regeneration patterns and long‐term continuity in boreal old‐growth Picea abies swamp‐forests

Abstract

Abstract. The occurrence of macrofossil charcoal (long axis > 0.5 mm) and Picea abies (Norway spruce) pollen in peat stratigraphies, in combination with size and age data from 2976 P. abies trees were used to analyse ecosystem continuity and stand‐structure in ten old‐growth swamp‐forests in northern Sweden. All stands were dominated by P. abies, a species whose abundance increased westwards in Sweden between 3000 and 2000 yr B.P. In three stands no macrofossil charcoal was found and the maximum age of the peat, determined by 14C dating, varied from 1800 to 3600 yr B.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 shape of the age structure was similar to an inverse J‐curve. This indicates a continuous recruitment over time in a self‐perpetuating ecosystem. In a short‐term perspective (< 300 yr), the swamp‐forests are characterized by individual trees continually emerging while others are dying. 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 the present spruce swamp‐forests within the northern boreal zone have functioned as true fire‐free refugia since the establishment of P. abies populations while others have been affected by recurring fires, although not as frequently as forests on surrounding drier sites. The hypothesis that Scandinavian spruce swamp‐forests in general have functioned as true longterm fire‐free refugia is thus modified by the present results.

Forest age distribution under mixed-severity fire regimes – a simulation-based analysis for middle boreal Fennoscandia

“…The peak at high cohort age consists of climax-type old-growth spruce forests that occur on rarely burning spruce swamps or on sites that are isolated by mires. Such old-growth spruce forests are important in actual landscapes with intermediate fi re frequencies (Zackrisson and Östlund 1991, Hörnberg et al 1995, Esseen et al 1997.…”

“…Studies suggest fi re intervals of 40-70 y in the 1800s, about 130 y in the 1600s and about 200 y around 1700 y BP, but it is not clear over what regions such fi gures could be extrapolated (Pitkänen and Huttunen 1999, Niklasson and Granström 2000, Pitkänen and Grönlund 2001. The longest fi re intervals have been observed on spruce swamps (Hörnberg et al 1995), in northern high-elevation forests (Steijlen andZackrisson 1987, Hyvärinen andSepponen 1988), and in European Russia outside Fennoscandia (Syrjänen et al 1994, Wallenius 2002.…”

“…In pine bogs the respective probabilities were 1.0 and 0 after fi res, and 0.5 and 0 later. The fl ammability of swamp and bog forests was assumed to be 10 times lower, and the fl ammability of mesic sites 2 times lower than the fl ammability of dryish sites (Engelmark 1987, Hörnberg et al 1995. Flammability corresponds to the probability of a site being burnable during a fi re (Pennanen and Kuuluvainen 2002).…”

Forest age distribution and traces of past fires in a natural boreal landscape dominated by Picea abies

“…Several studies have shown that even peatlands can burn fairly frequently (Tolonen 1985, Segerström et al 1994, Pitkänen et al 1999. Nevertheless, some studies indicate that there are forested sites, which have not been burnt for very long periods (Steijlen and Zackrisson 1987, Zackrisson et al 1995, Kuuluvainen et al 1998. Some evidence exists that Picea forest probably burn more seldom than Pinus forests (Zackrisson 1977, Engelmark 1987).…”

Spruce regeneration on woody microsites in a subalpine forest in the western Carpathians

“…In areas with harsh climate the occurrence of suitable microsites for seedlings and saplings, providing better conditions for their survival and growth, is an important aspect of phytocoenosis regeneration (Harmon et al 1986;Kuuluvainen 1994;Hörnberg et al 1995;Kupferschmid and Bugmann 2005a). The presence of different types of microsites creates diverse environmental conditions in terms of temperature, moisture, and light.…”