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Verifying an Extinction Debt among Lichens and Fungi in Northern Swedish Boreal Forests
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
2005 (English)In: Conservation Biology, ISSN 0888-8892, E-ISSN 1523-1739, Vol. 19, no 2, 338-348 p.Article in journal (Refereed) Published
Abstract [en]

Destruction and fragmentation of natural habitats results in small species populations that face increased risk of extinction. A time delay may be involved in the regional extinction of species, and the number of species that eventually may go extinct in the future is called the “extinction debt.” In boreal Sweden, we examined whether the number of epiphytic crustose lichens and wood-inhabiting fungi in old-growth forest remnants diverges from species richness levels in forest patches that have been naturally isolated for millennia. An excess of species in forest remnants could indicate the presence of an extinction debt. Observed species richness in 32 old-growth forest remnants (also called woodland key habitats [WKHs]) was compared with predicted species richness. To predict species richness we used regression models based on data from 46 isolated old-growth forest patches in a forest-wetland matrix. The reference landscape is ancient and assumed to reflect the conditions of insular floras in dynamic equilibrium. Stand factors constituted predictive variables in the models. The observed number of lichen species was higher than expected (i.e., an extinction debt among lichens may exist). By contrast, there was no significant difference between observed and expected species richness among wood-inhabiting fungi. The species richness of wood-inhabiting fungi has adjusted to the changes in forest and landscape structure more rapidly than the species richness of lichens. Differences in substrate dynamics between epiphytes on living trees and species growing on decaying logs might explain the difference between species groups. The results also indicate that population densities of red-listed species were low, which may result in continuing extinctions of red-listed species. The importance of WKHs might be overvalued because species may be lost if conservation efforts consider only protection and preservation of WKHs.

Abstract [es]

La destrucción y fragmentación de hábitats naturales provoca que poblaciones de especies pequeñas enfrenten mayores riesgos de extinción. Puede haber retraso en la extinción regional de especies, y el número de especies que eventualmente podrán extinguirse en el futuro es denominado la “deuda de extinción.” Examinamos, en Suecia Boreal, si el número de líquenes epifitos y de hongos de la madera en remanentes de bosques maduros difiere de los niveles de riqueza de especies en parches de bosque que han estado naturalmente aislados por milenios. Un exceso de especies en los remanentes de bosque podría indicar la presencia de una deuda de extinción. La riqueza de especies observada en 32 remanentes de bosque maduro (también denominados hábitats boscosos clave [HBC]) fue comparada con la riqueza de especies predicha. Para predecir la riqueza de especies utilizamos modelos de regresión basados en datos de 46 parches aislados de bosque maduro en una matriz de bosques-humedales. El paisaje de referencia es antiguo y se asume que refleja las condiciones de floras insulares en equilibrio dinámico Atributos de los bosques fueron las variables predictivas en los modelos. El número observado de especies de líquenes fue más alto que el esperado (i. e. puede existir una deuda de extinción). En contraste, no hubo diferencia significativa entre la riqueza de especies de hongos de la madera observada y esperada. La riqueza de especies de hongos de la madera se ha ajustado más rápidamente a los cambios en la estructura del bosque y del paisaje que la riqueza de especies de líquenes. La diferencia entre grupos de especies se pude explicar por diferencias en la dinámica del sustrato entre epifitas sobre árboles vivos y especies que crecen en troncos en descomposición. Los resultados también indican que las densidades poblacionales de especies enlistadas fueron bajas, lo que puede resultar en extinciones de estas especies. La importancia de HBC se puede sobrevaluar porque se pueden perder especies si los esfuerzos de conservación sólo consideran la protección y preservación de los HBC.

Place, publisher, year, edition, pages
John Wiley & Sons, 2005. Vol. 19, no 2, 338-348 p.
National Category
Biological Sciences
URN: urn:nbn:se:umu:diva-3817DOI: 10.1111/j.1523-1739.2005.00550.xOAI: diva2:142695

Article first published online: 23 MAR 2005

Available from: 2004-03-26 Created: 2004-03-26 Last updated: 2012-05-15Bibliographically approved
In thesis
1. Biodiversity in fragmented boreal forests: assessing the past, the present and the future
Open this publication in new window or tab >>Biodiversity in fragmented boreal forests: assessing the past, the present and the future
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aims of this thesis are to (1) analyze the predictability (indicators) of plant and fungal species diversity in old-growth forests, and (2) assess the history and biodiversity of woodland key habitats (WKHs) and their potential to maintain species diversity in fragmented boreal forest landscapes.

Predictability was explored in Granlandet nature reserve, an unexploited landscape composed of discrete old-growth Picea forest patches of varying size isolated by wetland, reflecting conditions of insular biota at stochastic equilibrium. Data from 46 patches (0.2-12 ha) showed that most species were rare. However, species richness and composition patterns exhibited a high degree of predictability, which strengthen the possibility to apply biodiversity indicators in old-growth forest stands. Area was a key factor. The increase in species richness starts to level out at 2-3 ha. Large patches host more Red-list species in their interiors than do small ones, i.e. stand size is an important qualitative aspect of old-growth habitat. Nestedness emerged in relation to area but also in equal-sized plots. Structural complexity and habitat quality were important for species richness and compositional patterns, and small habitats of high quality could harbor many rare species. Monitoring of wood-fungi on downed logs showed that species diversity on downed logs changed over periods of 5-10 years and that the occurrences of annual species were unpredictable. It is suggested that monitoring of species with durable fruit bodies (mainly polypores) is likely to be a feasible approach to obtain comparable data over time.

Assessments of biodiversity of WKHs were performed in two areas with contrasting histories of forest exploitation, namely in south boreal and north boreal Sweden. Analyses of the history of 15 south boreal WKHs showed that fire-suppression, selective logging until mid-20th century and abandonment by modern forestry has shaped their forest structure. These WKHs are not untouched forests, they lack key structural components and harbor few Red-list species. Artificial interventions to restore natural processes and patterns are needed to further increase their suitability for threatned species. Modeling analyses of species richness in 32 WKHs in north boreal Sweden, some of which have not been isolated by modern forestry until recently, indicated an excess of crustose lichen species, i.e. WKHs may face delayed species extinctions. By contrast, the results indicate that wood-fungi have tracked the environmental changes. Differences in substrate dynamics between epiphytes on living trees and species growing on decaying logs may explain the diffeence between species groups. The results indicate that population densities of Red-list species were low, which may result in further depletion of species diversity.

Continuing species declines and extinctions are likely if not conservation of WKHs are combined with other considerations in th managed forest landscape. Both WKHs and their surroundings must be managed and designed to maintain biodiversity over time. For a successful future conservation of boreal forest biodiversity monitoring of WKHs must be combined with monitoring of refeence areas.

44 p.
Ecology, bryophytes,  CWD,  edge effects,  fragmentation,  fungi,  habitat destruction,  historical records,  indicator,  lichens,  regression,  species-area relationship,  value pyramids,  woody debris , Ekologi
National Category
Research subject
Ecological Botany
urn:nbn:se:umu:diva-220 (URN)91-7305-610-3 (ISBN)
Public defence
2004-04-23, Fälldinsalen (N109), Mälthuset, Mitthögskolan, Sundsvall, 10:00
Available from: 2004-03-26 Created: 2004-03-26Bibliographically approved

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