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- Asplund, Johan, et al.
(författare)
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Lichen Specific Thallus Mass and Secondary Compounds Change across a Retrogressive Fire-Driven Chronosequence
- 2012
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- In the long-term absence of major disturbances ecosystems enter a state of retrogression, which involves declining soil fertility and consequently a reduction in decomposition rates. Recent studies have looked at how plant traits such as specific leaf mass and amounts of secondary compounds respond to declining soil fertility during retrogression, but there are no comparable studies for lichen traits despite increasing recognition of the role that lichens can play in ecosystem processes. We studied a group of 30 forested islands in northern Sweden differing greatly in fire history, and collectively representing a retrogressive chronosequence, spanning 5000 years. We used this system to explore how specific thallus mass (STM) and carbon based secondary compounds (CBSCs) change in three common epiphytic lichen species (Hypogymnia phsyodes, Melanohalea olivacea and Parmelia sulcata) as soil fertility declines during this retrogression. We found that STMs of lichens increased sharply during retrogression, and for all species soil N to P ratio (which increased during retrogression) was a strong predictor of STM. When expressed per unit area, medullary CBSCs in all species and cortical CBSCs in P. sulcata increased during retrogression. Meanwhile, when expressed per unit mass, only cortical CBSCs in H. physodes responded to retrogression, and in the opposite direction. Given that lichen functional traits are likely to be important in driving ecological processes that drive nutrient and carbon cycling in the way that plant functional traits are, the changes that they undergo during retrogression could potentially be significant for the functioning of the ecosystem.
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| 2. |
- Asplund, Johan, et al.
(författare)
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The influence of tree-scale and ecosystem-scale factors on epiphytic lichen communities across a long-term retrogressive chronosequence
- 2014
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 25, s. 1100-1111
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Tidskriftsartikel (refereegranskat)abstract
- Questions: We tested the relationship between total cover, species richness and composition of epiphytic lichens on trunks of Betula pubescens and ecosystem retrogression (i.e. prolonged absence of major disturbance). We then investigated how the relationships changed when also accounting for tree-scale factors (aspect, height and bark characteristics) and ecosystem-scale factors (e. g. light transmission, tree species diversity and soil fertility).Location: Thirty forested islands in northern Sweden differing in fire history, which collectively represent a retrogressive chronosequence spanning ca. 5000 yr.Results: Total lichen cover responded negatively to long-term absence of major disturbance, but only at exposed positions on the tree trunk, indicating that lichen cover on substrates with more favourable microclimates is less susceptible to environmental change at the ecosystem scale. Further, although there was no overall effect of island size on lichen species richness, we did find a significant interactive effect between island size and height on trunk on species richness. This emerged because species richness decreased with retrogression for lichen communities at breast height, but showed a hump-shaped response to retrogression at the trunk base. Shifts in ecosystem properties with retrogression explained some of the variation in lichen community composition, but most of the variation could be explained by tree-scale factors, notably height on the trunk.Conclusions: While it has frequently been shown that lichens increase in abundance and richness during the first two or three centuries of succession, our results highlight that over a much longer time scale, encompassing soil aging and declining soil fertility, the lichen flora can be negatively affected. However, these effects are heavily mediated by tree-scale factors. These changes in the lichen community may be of potential importance for ecosystem processes and higher trophic level interactions driven by lichen communities.
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