Cataclysmic response to recent cooling of a natural boreal pine (Pinus sylvestris L.) forest in northern Sweden

Abstract

SII M M A R YInstant stand-level dieback occurred in boreal coniferous forests of northern Sweden in 1 087. A population of pine (Finns sylvestri.s L,) and subdominant spruce (Picea abies (L.) Karst,) was analysed witb respect to defoliation, age structure, ladial increment and soil conditions. Defoliation and mortality were due to frost and drought in response to an early winter witb abnormal cold and a tbin snow cover, A tbick mor bumus layer preconditioned ground frost preservation. Annual radial increment bad declined steadily over c, 40 years, in variance witb climatic cooling and local exposure. Possibly, tbe growtb decline depleted energy reserves and lowered tbe tolerance to climatic stress during extreme conditions. It is obvious tbat tbe structure of nortbem boreal forests responds perceivably to sbort-term tbermal decline, Tbe outlined mecbanism of dieback may prevent tbe evolution of climax in tbe absence of otber exogenous disturbances, Tbe present event may be a small-scale analogue of forest response.s to rapid cooling during, for example, tbe Younger Dryas period and tbe Little Ice Age,

Natural regeneration of Scots pine and Norway spruce close to the timberline in northern Finland

“…Basically, trees in the timberline and tree line respond more sensitively to climate warming than to climate cooling (Kullman 1990). The most sensitive response to climate warming is the establishment of new seedlings and closer spacing of seedling populations.…”

“…Some studies show that high seedling mortality in climatically extreme areas might constitute the crucial obstacle to the advance of the timberline (Hustich 1978, Kullman 1993, Körner 1998, Lloyd 1998, Stöcklin and Körner 1999, Holtmeier 2000, Paulsen et al 2000. Unfortunately, seedling mortality as a controlling factor of timberline dynamics has been neglected in many analyses.…”

“…Recent studies show that tree species respond individualistically to climatic variation (Brooks et al 1997, Kullman 2001, Juntunen et al 2002. Moreover, the responses are often regionally variable in magnitude and direction (Kullman 2001, Juntunen et al 2002. Follow-up measurements on permanent plots since 1983 in Finnish Lapland have revealed that regeneration of Norway spruce (Picea abies (L.) Karst.)…”

“…Responses of different models vary from drastic positive effects on boreal forests and the coniferous timberline (Kellomäki andVäisänen 1995, Kellomäki et al 1997) to catastrophic incidents of dieback and regression of the timberline (Gates 1990, Hänninen 1991, Juday et al 1997. Recent studies show that tree species respond individualistically to climatic variation (Brooks et al 1997, Kullman 2001, Juntunen et al 2002. Moreover, the responses are often regionally variable in magnitude and direction (Kullman 2001, Juntunen et al 2002.…”

Rise and demise of cold‐climate Picea abies forest in Sweden

“…The study combines monitoring of tree health and local air and soil temperatures during a 7 3^r period, with retrospective age-structure analysis of the extant spruce population and radiocarbon dating of macrofossil wood remains. Previous case studies (Kullman, 1989(Kullman, , 1991aKullman & Engelmark, 1991), suggest that ground frost conditions constitute a critical determinant of crown conditions and stand dynamics in this particular type of forest ecosystem, which may be structurally and functionally sensitive to annual-decadal weather variations. STUDY …”