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  • 1
    Electronic Resource
    Electronic Resource
    Above-ground biomass and structure of pristine Siberian Scots pine forests as controlled by competition and fire (1999)
    Springer
    Oecologia 121 (1999), S. 66-80 
    Details
    ISSN: 1432-1939
    Keywords: Key wordsPinus sylvestris ; Siberia ; Biomass ; Self-thinning ; Forest fire
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The study presents a data set of above-ground biomass (AGB), structure, spacing and fire regime, for 24 stands of pristine Siberian Scots pine (Pinus sylvestris) forests with lichens (n = 20) or Vaccinium/mosses (n = 4) as ground cover, along four chronosequences. The stands of the “lichen” site type (LT) were stratified into three chronosequences according to stand density and fire history. Allometric equations were established from 90 sample trees for stem, coarse branch, fine branch, twig and needle biomass. The LT stands exhibited a low but sustained biomass accumulation until a stand age of 383 years. AGB reached only 6–10 kgdw m−2 after 200 years depending on stand density and fire history compared to 20 kgdw m−2 in the “Vaccinium” type (VT) stands. Leaf area index (LAI) in the LT stands remained at 0.5–1.5 and crown cover was 30–60%, whereas LAI reached 2.5 and crown cover was 〉100% in the VT stands. Although nearest-neighbour analyses suggested the existence of density-dependent mortality, fire impact turned out to have a much stronger effect on density dynamics. Fire scar dating and calculation of mean and initial fire return intervals revealed that within the LT stands differences in structure and biomass were related to the severity of fire regimes, which in turn was related to the degree of landscape fragmentation by wetlands. Self-thinning analysis was used to define the local carrying capacity for biomass. A series of undisturbed LT stands was used to characterise the upper self-thinning boundary. Stands that had experienced a moderate fire regime were positioned well below the self-thinning boundary in a distinct fire-thinning band of reduced major axis regression slope −0.26. We discuss how this downward shift resulted from alternating phases of density reduction by fire and subsequent regrowth. We conclude that biomass in Siberian Scots pine forests is strongly influenced by fire and that climate change will affect ecosystem functions predominantly via changes in fire regimes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050908
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  • 2
    Electronic Resource
    Electronic Resource
    Dibutyrylic cyclic AMP and theophylline inhibit proliferation of accessory cells in primary cultures of adrenomedullary cells (1982)
    Springer
    Cell & tissue research 223 (1982), S. 73-86 
    Details
    ISSN: 1432-0878
    Keywords: Adrenal medullary cells ; Culture ; Growth control of non-chromaffin cells ; Dibutyrylic cyclic AMP ; Theophylline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Studies on isolated adrenal chromaffin cells in primary cultures may be seriously hampered by the presence of non-chromaffin, mainly fibroblast-like cells, which always occur in dissociates of adrenal medullary tissue and often outnumber the chromaffin cells by the end of the first week of culture, when no measures are taken to control their proliferation. The present study offers a new means to inhibit effectively the proliferation of these accessory cells by treating the cultures with dibutyrylic cyclic AMP (dbcAMP, 0.1 or 0.01 mM) and equimolar amounts of the phosphodiesterase inhibitor theophylline. With this treatment cultures of young rat adrenal chromaffin cells remain virtually free of accessory cells for two weeks of culture. Cultures of bovine adrenomedullary cells retain their initial amounts of non-chromaffin cells, which largely depends upon whether the primary cell suspensions have undergone differential plating prior to seeding. Suppression of accessory cell proliferation with dbcAMP and theophylline is partly due to maintaining differentiation of cortical cells, which otherwise dedifferentiate into rapidly dividing fibroblast-like elements. However, a more direct action of dbcAMP on accessory cells in terms of growth control is also conceivable. DbcAMP and theophylline in the doses applied do not impair the viability, ultrastructure and catecholamine-storing capacity of cultured chromaffin cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00221500
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