An Atlas of Past and Present Pollen Maps for Europe: 0-13000 Years Ago, and The Overlay Maps.

Vegetation research in boreal forests has tended to focus on the tree component, while little attention has been paid to understory components such as dwarf shrubs, mosses, and reindeer lichens. However, the productivity of understory vegetation is probably comparable to that of the trees. We review recent research in the boreal forest of northern Sweden to highlight the ecological importance of understory vegetation, both in the short term by influencing tree seedling regeneration, and in the longer term by affecting belowground processes such as decomposition, nutrient flow, and buildup of soil nutrients. Wildfire resulting from lightning strike is a primary determinant of understory vegetation, and as such is a major driver of forest community and ecosystem properties. Forest management practices that alter the fire regime and the composition of understory vegetation may have long-term consequences for both conservation goals and commercial forest productivity.

Understory vegetation as a forest ecosystem driver: evidence from the northern Swedish boreal forest

Coarse woody debris and stand characteristics in mature managed and old-growth boreal mesic forests in southern Finland

Questions: Did the forest area in the Swiss Alps increase between 1985 and 1997? Does the forest expansion near the tree line represent an invasion into abandoned grasslands (ingrowth) or a true upward shift of the local tree line? What land cover / land use classes did primarily regenerate to forest, and what forest structural types did primarily regenerate? And, what are possible drivers of forest regeneration in the tree line ecotone, climate and/or land use change? Location: Swiss Alps. Methods: Forest expansion was quantified using data from the repeated Swiss land use statistics GEOSTAT. A moving window algorithm was developed to distinguish between forest ingrowth and upward shift. To test a possible climate change influence, the resulting upward shifts were compared to a potential regional tree line. Results: A significant increase of forest cover was found between 1650 m and 2450 m. Above 1650 m, 10% of the new forest areas were identified as true upward shifts whereas 90% represented ingrowth, and we identified both land use and climate change as likely drivers. Most upward shift activities were found to occur within a band of 300 m below the potential regional tree line, indicating land use as the most likely driver. Only 4% of the upward shifts were identified to rise above the potential regional tree line, thus indicating climate change. Conclusions: Land abandonment was the most dominant driver for the establishment of new forest areas, even at the tree line ecotone. However, a small fraction of upwards shift can be attributed to the recent climate warming, a fraction that is likely to increase further if climate continues to warm, and with a longer time-span between warming and measurement of forest cover.

Tree line shifts in the Swiss Alps: Climate change or land abandonment?

In this review, we focus on the biotic parameters that are crucial to an understanding of the recruitment dynamics of North American boreal tree species following natural (fire, budworm infestation, windthrow) or human-induced (clearcut, partial cut) disturbances. The parameters we emphasize are (i) the production of seeds and asexual stems (both of which, we argue, are a function of basal area density), (ii) the dispersal of seeds by wind (or the dispersion of asexual stems) as a function of distance from source, (iii) dormant seed bank capacity, (iv) organic layer depth as a determinant of germinant mortality and asexual bud response, and (v) shade tolerance as a partial arbiter of the density of advanced regeneration. Having identified the gaps in our knowledge, we conclude by suggesting a short-term research agenda whose completion would lead to the parameterized functions that would constitute the recruitment subroutine in a landscape-scale forest dynamics simulator.

https://www.nrs.fs.fed.us/pubs/jrnl/1999/nc_1999_Greene_001.pdf

A review of the regeneration dynamics of North American boreal forest tree species

1 Age and diameter distributions of nonpyrogenic, virgin Scots pine (Pinus sylvestris) populations were studied at six different sites of the Empetrum-Vaccinium type along a latitudinal gradient (65?54'-68?15'N) in northern Sweden. 1910 trees, including saplings and seedlings, were aged at their root collars in order to reconstruct regeneration patterns. 2 All populations had multimodal age structures. Obvious regeneration pulses occurred in the 1770s-80s and 1950s-70s. The three southernmost stands exhibited an additional regeneration pulse in the 1870s-80s. A regeneration cycle of about 100 years in the south and 200 years in the north were thus clearly expressed. Correlation with temperature changes over the past 300 years showed that recruitment peaks of Scots pine lagged 20-30 years behind the warm climate periods and fell to zero in the intervening cold periods. 3 A much smaller number of experimentally planted pine and spruce seeds established and survived in vegetation dominated by Empetrum hermaphroditum than in that dominated by Cladina spp. After two growing seasons, fresh weights of pine seedlings were also much lower in E. hermaphroditum vegetation than in Cladina spp. Spruce established less frequently than pine in both vegetation types. Naturally established pine seedlings were found almost exclusively in vegetation dominated by Cladina spp. 4 The wave-like regeneration pattern of pine may therefore result from successful establishment in periods with good seed production on ground dominated by Vaccinium spp. and Cladina spp. This vegetation type is favoured by warm dry conditions but its establishment possibly lagged behind climate change. The extreme amplitude between regeneration failures and successes found over the period studied may be caused by the specific complex of vegetation responses to climate variability found in this forest type. 5 The results have implications for predicting the effect of climatic warming.

Regeneration Pulses and Climate-Vegetation Interactions in Nonpyrogenic Boreal Scots Pine Stands

The natural age and stand structure of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.), and birch (Betula pubescens Ehrh.) was studied in a virgin forest stand in northern Sweden. The stand has been unaffected by fire during the past 500 years. It is suggested that the variations in age structure and invasion pattern are the result of low-frequency climatic fluctuations influencing seed production, germination, and early survival of seedlings. The periods of climatic amelioration that occurred during the 1870s and during this century have been especially favourable to pine, resulting in a pine-dominated regeneration underneath a tree layer where spruce and birch are the most abundant species. This is contrary to generally accepted theories concerning postfire successional trends in this part of the boreal zone. It is concluded that small gap-phase replacement of trees by climatically induced regeneration and mortality events probably is the reason for the general weak correlation...

Long-term regeneration dynamics and successional trends in a northern Swedish coniferous forest stand

Six old-growth, late postfire Scots pine (Pinussylvestris L.) dominated forest stands of the Vaccinium–Cladina type were selected along a latitudinal gradient in northern Sweden. In two of the stands, Scots pine seedlings that had naturally regenerated during the last 40 years were surveyed in relation to field- and bottom-layer vegetation. The most abundant forest floor species, viz. Cladina spp., occupied 41% of the ground cover and dominated the microhabitat of Scots pine seedlings 10 years), however, the cover of Cladina spp. significantly decreased and the cover of P. schreberi and various ericaceous species slightly increased. Thus Scots pine seedlings initially establish in lichen-dominated vegetation but as they devel...

Seed regeneration of Scots pine in boreal forest stands dominated by lichen and feather moss

Scots pine (Pinussylvestris L.) were selectively seeded in 1990, 1991, 1992, and 1994 in bottom layer vegetation of Pleuroziumschreberi (Bird.) Mitt, in a clearcut created in 1989 and in an adjacen...

Ingeborg Steijlen

Papers

Regeneration Pulses and Climate-Vegetation Interactions in Nonpyrogenic Boreal Scots Pine Stands

Long-term regeneration dynamics and successional trends in a northern Swedish coniferous forest stand

Seed regeneration of Scots pine in boreal forest stands dominated by lichen and feather moss

Time-restricted seed regeneration of Scots pine in sites dominated by feather moss after clear-cutting