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Biological diversity values in semi-natural grasslands: indicators, landscape context and restoration
Stockholm University, Faculty of Science, Department of Botany.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Semi-natural grasslands, which are a declining and fragmented habitat in Europe, contain a high biodiversity, and are therefore of interest to conservation. This thesis examines how plant diversity is influenced by the landscape context, and how plant and fungal diversity can be targeted by practical conservation using indicator species and congruence between species groups. Reproduction and recruitment of the dioecious herb Antennaria dioica was also investigated, providing a case study on how fragmentation and habitat degradation may affect grassland plants.

Grassland size and heterogeneity were of greater importance for plant diversity in semi-natural grassland, than present or historical connectivity to other grasslands, or landscape characteristics. Larger grasslands were more heterogeneous than smaller grasslands, being the likely reason for the species-area relationship.

A detailed study on A. dioica discovered that sexual reproduction and recruitment may be hampered due to skewed sex-ratios. Sex-ratios were more skewed in small populations, suggesting that dioecious plants are likely to be particularly sensitive to reduced grassland size and fragmentation.

A study on indicators of plant species richness, used in a recent survey of remaining semi-natural grasslands in Sweden, revealed several problems. A high percentage of all indicator species were missed by the survey, removing an otherwise significant correlation between indicator species and plant species richness. Also, a null model showed that the chosen indicator species did not perform significantly better than species chosen at random from the available species pool, questioning the selection of the indicators in the survey. Diversity patterns of the threatened fungal genus Hygrocybe were not congruent with plant species richness or composition. Plants are thus a poor surrogate group for Hygrocybe fungi, and probably also for other grassland fungi. Implications from this thesis are that conservation of semi-natural grasslands should target several species groups, and that an appropriate scale for plant conservation may be local rather than regional.

Place, publisher, year, edition, pages
Stockholm: Botaniska institutionen , 2006. , 41 p.
Keyword [en]
Biodiversity, connectivity, Hygrocybe, indicators, landscape history, plants, pollen limitation, species-area effects, surrogate species
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:su:diva-1352ISBN: 91-7155-341-X (print)OAI: oai:DiVA.org:su-1352DiVA: diva2:189934
Public defence
2006-12-15, föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 13:00
Opponent
Supervisors
Available from: 2006-11-23 Created: 2006-11-23Bibliographically approved
List of papers
1. Size and heterogeneity rather than landscape context determine plant species richness in semi-natural grasslands
Open this publication in new window or tab >>Size and heterogeneity rather than landscape context determine plant species richness in semi-natural grasslands
2007 (English)In: Journal of Vegetation Science, ISSN 1100-9233, E-ISSN 1654-1103, Vol. 18, no 6, 859-868 p.Article in journal (Refereed) Published
Abstract [en]

Question: Is plant diversity in fragmented semi-natural grasslands related to present and historical landscape context?

Location: Southern Sweden.

Methods: Plant diversity was described at 30 semi-natural grassland sites in terms of total and specialist plant species richness at the site and species density at different scales (0.5–10 m2). These measures are commonly used to assess conservation value of semi-natural grasslands. Landscape context was measured as contemporary connectivity to other semi-natural grasslands, historical connectivity 50 years ago, amount of linear elements potentially suitable for dispersal (road verges, power line clearings), and amount of forest (inverse of the openness of the landscape).

Results: The diversity measures were generally correlated with each other, implying that species richness in a subset of the grassland can predict the total richness. Plant species density at three scales (0.5 m2, 10 m2 and total) was related to the landscape context using an information theoretic approach. Results showed that total species richness increased with increased size of grasslands, contrary to earlier diversity studies in semi-natural grasslands. Larger grasslands were more heterogeneous than smaller grasslands, and this is a likely reason for the species-area relationship. Heterogeneity was also of high importance at the smaller scales (0.5 m2, 10 m2). With increased amount of forest, total species richness increased but species density on 10 m2 decreased. There was no influence of connectivity in either the contemporary or the historical landscape, contrary to previous studies.

Conclusions: Grassland size and heterogeneity are of greater importance for plant diversity in semi-natural grassland, than grassland connectivity in the landscape.

Keyword
AIC, Akaike's Information Criterion, Biodiversity, Connectivity, Landscape history, Road verge, Species-area effect, Species density
National Category
Botany
Identifiers
urn:nbn:se:su:diva-23022 (URN)10.1111/j.1654-1103.2007.tb02602.x (DOI)000250089400010 ()
Available from: 2006-11-23 Created: 2006-11-23 Last updated: 2013-06-05Bibliographically approved
2. Sex-ratio mediated pollen limitation in the dioecious herb Antennaria dioica
Open this publication in new window or tab >>Sex-ratio mediated pollen limitation in the dioecious herb Antennaria dioica
2007 (English)In: Ecoscience, ISSN 1195-6860, Vol. 14, no 3, 387-398 p.Article in journal (Refereed) Published
Abstract [en]

We examined how population structure affects seed set and recruitment in the dioecious plant Antennaria dioica, which is a declining species inhabiting semi-natural grasslands in Sweden. Flowering and sex ratio in A. dioica were studied over 4 y at a local (1.2 km2) scale and over 1 y at a regional (742 km2) scale in southern Sweden. Antennaria dioica was also hand-pollinated during 2y to examine whether sex ratios, male abundance, and distance to nearest male influence the degree of pollen limitation. Seed-sowing experiments were conducted to assess whether recruitment is limited by seed or microsite availability. There was a considerable spatio-temporal variation in both flowering and sex ratios. The regional scale survey showed that patch size and number of patches per site were positively correlated, and small patches of A.dioica tended to have biased sex ratios. Experimental hand-pollinations showed that the degree of pollen limitation increased with increasingly female-biased sex ratios in the closest vicinity of the experimental plants. Thus, even though A. dioica is pollinated by many different insects, a fragmented population structure has a large influence on reproductive performance of A. dioica. The seed-sowing experiments showed that recruitment is limited by a combination of seed and microsite availability. It is therefore plausible that reduced seed production due to pollen limitation translates into reduced recruitment. The results from the local and the regional scale indicate that a large fraction of local patches and populations of A. dioica have decreased sexual reproduction. The conclusion is that A. dioica is likely to be particularly sensitive to habitat fragmentation.

Keyword
dioecy, habitat fragmentation, hand-pollination, pollen limitation, seed sowing, sex ratio
National Category
Botany
Identifiers
urn:nbn:se:su:diva-23023 (URN)10.2980/1195-6860(2007)14[387:SRMPLI]2.0.CO;2 (DOI)000250040400016 ()
Available from: 2006-11-23 Created: 2006-11-23 Last updated: 2011-03-11Bibliographically approved
3. Validation of plant diversity indicators in semi-natural grasslands
Open this publication in new window or tab >>Validation of plant diversity indicators in semi-natural grasslands
2008 (English)In: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 125, no 1-4, 65-72 p.Article in journal (Refereed) Published
Abstract [en]

The use of plant biodiversity indicators in a nationwide survey of semi-natural grasslands in Sweden was examined by comparing results from the survey with additional in-depth studies of plant diversity at the same 30 sites in southern Sweden. Additional grasslands, that were not subjected to the nationwide survey (i.e. rejected after an initial site selection), were also investigated in order to examine the quality of the initial site selection and to assess to what extent they harboured species rich plant communities. Results showed that grasslands that were not included in the nationwide survey were generally smaller in size and that they contained significantly lower plant diversity than sites that were included by the survey. However, some indicator species, including indicators for poor management, were abundant in both types of sites. Biodiversity indicators correctly indicated both plant species richness and plant species density when using data from the in-depth study. However, by comparing indicator species found by the nationwide survey and by the in-depth study, it was shown that the survey overlooked 42% of all indicator species occurrences, which removed the significant relationship between indicator richness and total plant species richness. Furthermore, a null model showed that the chosen indicator species did not perform significantly better than species chosen at random from the available species pool. The conclusion was that validation of indicators is crucial, because even though real correlations exist between taxa or between a subset of species and overall diversity, poor precision of surveys might make these indicators useless. This also suggests that the effort put into searching for the indicator species may have to be so high, that it may be more efficient to go directly into assessing the biological values they are supposed to indicate.

Keyword
Bioindicators; Species subsets; Surrogate species; Validation; Vascular plants
National Category
Botany
Identifiers
urn:nbn:se:su:diva-23024 (URN)10.1016/j.agee.2007.11.006 (DOI)000255134500007 ()
Available from: 2006-11-23 Created: 2006-11-23 Last updated: 2011-03-11Bibliographically approved
4. Low congruence between the diversity of Waxcap (Hygrocybe spp.) fungi and vascular plants in semi-natural grasslands
Open this publication in new window or tab >>Low congruence between the diversity of Waxcap (Hygrocybe spp.) fungi and vascular plants in semi-natural grasslands
2008 (English)In: Basic and Applied Ecology, ISSN 1439-1791, Vol. 9, no 5, 514-522 p.Article in journal (Refereed) Published
Abstract [en]

The diversity of fungi in semi-natural grasslands is poorly known, partly due to difficulties in species identification in the field but also because there are few specialists available. Diversity assessments of grassland fungi would be facilitated if a potential surrogate group for fungal diversity could be identified. The aim of this study was to assess whether plant diversity patterns in semi-natural grasslands are congruent with diversity patterns of Waxcap (Hygrocybe spp.) fungi. Waxcaps, together with several other groups of fungi (e.g. the genera Entoloma, Dermoloma, Camarophyllopsis, and the families Clavariaceae and Geoglossaceae) have habitat requirements similar to many plants typical for semi-natural grasslands and they are all threatened by ceased management and nutrient enrichment. Diversity data from 31 semi-natural grasslands in southern Sweden were used to examine if there is congruence in species richness, nestedness, β-diversity and species composition between plants and Hygrocybe fungi. Species richness of Hygrocybe was significantly positively correlated with plant richness, although the relationship was not strong (r2=0.14). Both plant and Hygrocybe species composition was significantly nested, i.e. species-poor sites contain a subset of species from species-rich sites, which suggests that rare species mostly occur in the species-rich sites. A species similarity analysis between the grassland sites showed that there is low overlap between species composition of plants and Hygrocybe, indicating that conservation decisions based solely on plants may not fulfil the requirements of the Hygrocybe species. The conclusion is that there is low congruence between plant and Hygrocybe species diversity, making plants a poor surrogate group for Hygrocybe fungi, and probably also for other grassland fungi.

Abstract [de]

Die Diversität von Pilzen in halbnatürlichen Grünländern ist kaum bekannt, z. T. aufgrund der schwierigen Artbestimmung im Gelände, aber auch weil nur wenige Spezialisten verfügbar sind. Die Einschätzung der Diversität von Grünlandpilzen würde gefördert, wenn eine potenzielle Ersatzgruppe zur Bestimmung der Pilzdiversität identifiziert werden könnte. Das Ziel dieser Untersuchung war daher, ob die Muster der Pflanzendiversität in halbnatürlichen Grünländern mit den Mustern der Saftlingpilze (Hygrocybe spp.) kongruent sind. Saftlinge haben zusammen mit einigen anderen Gruppen von Pilzen (z. B. die Gattungen Entoloma, Dermoloma, Camarophyllopsis sowie die Familien Clavariaceae und Geoglossaceae) Habitatansprüche, die vergleichbar sind mit denen von vielen Pflanzen, die typisch für halbnatürliche Grünländer sind und die alle durch die Aufgabe der Bewirtschaftung und die Nährstoffanreicherung bedroht sind. Es wurden die Diversitätsdaten von 31 halbnatürlichen Grünländern in Südschweden genutzt, um zu untersuchen, ob eine Kongruenz im Artenreichtum, der Schachtelung, der β-Diversität und der Artenzusammensetzung zwischen den Pflanzen und den Saftlingpilzen existiert. Der Artenreichtum der Hygrocybe war mit der Pflanzenartenvielfalt signifikant positiv korreliert, obwohl die Beziehung nicht stark war (r2=0.14). Die Artenzusammensetzungen der Pflanzen und Hygrocybe waren signifikant geschachtelt, d. h. artenarme Standorte enthielten einen Teil der Arten artenreicher Standorte, und lässt vermuten, dass seltene Arten vor allem an den artenreichen Standorten vorkommen. Eine Analyse der Artenähnlichkeiten zwischen den Grünlandstandorten zeigte, dass es nur eine geringe Überlappung zwischen den Artenzusammensetzungen der Pflanzen und den Hygrocybe gibt. Dies zeigt, dass Entscheidungen, die ausschließlich aufgrund der Pflanzen getroffen werden, die Anforderungen der Hygrocybe-Arten nicht erfüllen. Die Schlussfolgerung ist, dass es eine geringe Kongruenz zwischen der Pflanzen- und Hygrocybe-Artendiversität gibt und Pflanzen eine wenig geeignete Ersatzgruppe für Hygrocybe-Pilze und wahrscheinlich auch für andere Grünlandpilze sind.

Keyword
Biodiversity, BINMATNEST, Fungi, Jaccard similarity index, Nested subset, RANDNEST, Species richness, Surrogate species
National Category
Ecology
Identifiers
urn:nbn:se:su:diva-23025 (URN)10.1016/j.baae.2007.11.006 (DOI)
Available from: 2006-11-23 Created: 2006-11-23 Last updated: 2011-03-16Bibliographically approved

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