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Small remnant habitats: Important structures in fragmented landscapes
Stockholm University, Faculty of Science, Department of Physical Geography. (Biogeography and geomatics)ORCID iD: 0000-0001-7219-4359
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The world-wide intensification of agriculture has led to a decline in species richness due to land use change, isolation, and fragmentation of natural and semi-natural habitats in agricultural and forestry landscapes. As a consequence, there is a current landscape management focus on the importance of green infrastructure to mitigate biodiversity decline and preserve ecosystem functions e.g. pollination services and pest control. Even though intensification in agriculture has been ongoing for several hundreds of years, remnant habitats from earlier management practices may still be remaining with a surprisingly high plant richness. Preserving these habitats could help conserving plant species richness in agricultural landscapes, as well as other organisms that are dependent on plants for food and shelter.

In this thesis I focus on two small remnant habitats; midfield islets and borders between managed forest and crop field in southeastern Sweden. In the past, both habitats were included in the grazing system and therefore often still have remnant population of grassland specialist species left today. I have used these two remnant habitats as model habitats to investigate the effect of landscape factors and local factors on species richness of plants, flower morphologies and plants with fleshy fruits. Additively, I analysed the effect of surrounding landscape and local openness on the functions; pollination success, biological pest control of aphids and seed predation on midfield islets.

One of my studies showed that spatial distribution and size of the habitat affected plant species richness. Larger habitat size and higher connectivity between habitats increased species richness of plants in the habitats. Openness of the habitats was shown to be an important factor to increase species richness and richness of flower morphologies, both on midfield islets and in forest borders. Even though midfield islets had the highest species and morphology richness, both habitat types are needed for habitat complementary as forest borders have more plants with fleshy fruits and a higher richness of plant species that flowers in spring/early summer. It was also shown that a more complex forest border, not just with gaps in the canopy, but also with high variation in tree stem sizes increases plant species richness in the field layer. The conclusion is that by managing small remnant habitats to remain or become more semi-open and complex in their structure, would increase species richness of plants, grassland specialist species, and flower morphologies. It would also increase some ecosystem functions as seed predation and biologic pest control of aphids are more effective close to trees. If both midfield islets and forest borders would be managed to be semi-open, the area and connectivity of semi-open habitat would increase in the agricultural landscape, which may also improve pollination success as the connectivity between populations has a possibility to increase. Grassland specialist species are clearly abundant in the small remnant habitats. As the decline of semi-natural grasslands is causing a decline in grassland specialists’ species, not only plants, I recommend that small remnant habitats are included in conservation and management plans and strategies to improve habitat availability and connectivity for grassland species in agricultural landscapes.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography, Stockholm University , 2017.
Series
Dissertations from the Department of Physical Geography, ISSN 1653-7211 ; 70
Keywords [en]
Alpha-diversity, Beta-diversity, Biological pest control, Canopy cover, Connectivity, Ecosystem function, Fleshy fruits, Forest edge, Forest management, Forest specialist species, Fragmentation, Functional diversity, Gamma-diversity, Grassland specialist species, Green infrastructure, Habitat amount hypothesis, Island biogeography, Midfield islets, Plant diversity, Plant-pollinator interaction, Pollination, Remnant habitat, Seed predation, Small habitats, Species richness, Structural heterogeneity
National Category
Ecology Environmental Sciences related to Agriculture and Land-use Physical Geography
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-148653ISBN: 978-91-7797-057-6 (print)ISBN: 978-91-7797-058-3 (electronic)OAI: oai:DiVA.org:su-148653DiVA, id: diva2:1154654
Public defence
2017-12-20, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

Research funder Ekoklim. Project:4339602.

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2017-11-27 Created: 2017-11-03 Last updated: 2018-01-13Bibliographically approved
List of papers
1. Island biogeography theory outweighs habitat amount hypothesis in predicting plant species richness in small grassland remnants
Open this publication in new window or tab >>Island biogeography theory outweighs habitat amount hypothesis in predicting plant species richness in small grassland remnants
2017 (English)In: Landscape Ecology, ISSN 0921-2973, E-ISSN 1572-9761, Vol. 32, no 9, p. 1895-1906Article in journal (Refereed) Published
Abstract [en]

Context

The habitat amount hypothesis has rarely been tested on plant communities. It remains unclear how habitat amount affect species richness in habitat fragments compared to island effects such as isolation and patch size.

Objectives

How do patch size and spatial distribution compared to habitat amount predict plant species richness and grassland specialist plant species in small grassland remnants? How does sampling area affect the prediction of spatial variables on species richness?

Methods

We recorded plant species density and richness on 131 midfield islets (small remnants of semi-natural grassland) situated in 27 landscapes in Sweden. Further, we tested how habitat amount, compared to focal patch size and distance to nearest neighbor predicted species density and richness of plants and of grassland specialists.

Results

A total of 381 plant species were recorded (including 85 grassland specialist species). A combination of patch size and isolation was better in predicting both density and richness of species compared to habitat amount. Almost 45% of species richness and 23% of specialist species were explained by island biogeography parameters compared to 19 and 11% by the amount of habitat. A scaled sampling method increased the explanation level of island biogeography parameters and habitat amount.

Conclusions

Habitat amount as a concept is not as good as island biogeography to predict species richness in small habitats. Priority in landscape planning should be on larger patches rather than several small, even if they are close together. We recommend a sampling area scaled to patch size in small habitats.

Keywords
Connectivity, Fragmentation, Habitat amount hypothesis, Island biogeography, Species richness, Remnant habitat
National Category
Earth and Related Environmental Sciences
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-147045 (URN)10.1007/s10980-017-0544-5 (DOI)000406962100010 ()
Available from: 2017-09-20 Created: 2017-09-20 Last updated: 2017-11-03Bibliographically approved
2. Local conditions in small habitats and surrounding landscape are important for pollination services, biological pest control and seed predation
Open this publication in new window or tab >>Local conditions in small habitats and surrounding landscape are important for pollination services, biological pest control and seed predation
2018 (English)In: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 251, p. 107-113Article in journal (Refereed) Published
Abstract [en]

Small semi-natural and natural habitats in agricultural landscapes are important for biodiversity. With modern and more intensive agricultural practices they have become smaller (less than 1600 m2) and more isolated study which also affects ecosystem functions. Most ecosystem function studies using field experiments focus on a single function. Here, we investigate three functions in the same landscape at the same time. We investigated how local (trees, shrubs and grass-cover in small remnant habitats) and landscape factors (amount of and distance from key habitats i.e. forest and semi-natural grasslands) affect pollination, biological pest control and seed predation. We applied a multifunctional approach using different organisms to analyze pollination success (Primula veris), predation on aphid pests (Rhopalosiphum padi) and seed predation (of Helianthus annuus). A set-up of 3 different experiments were placed in situ on 12 midfield islets. Pollination was more affected by local factors than landscape factors, although pollination success was improved by a smaller proportions of surrounding crop fields. Seed predation was higher on islets with more surrounding forest and also with more trees on the habitat, especially close to shrubs, compared to more open areas of habitat. Predation on aphids decreased on midfield islets with a larger amount of nearby forest but was positively affected by increasing local tree cover on the habitat.

We show that managing semi-open habitats that are connected to other natural or semi-natural habitats can improve pollination success and biological pest and weed control, thus potentially increasing yield in surrounding crop fields.

Keywords
biological pest control, ecosystem function, midfield islets, pollination, seed predation, small habitats
National Category
Ecology
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-148632 (URN)10.1016/j.agee.2017.09.025 (DOI)000414880300011 ()
Available from: 2017-11-02 Created: 2017-11-02 Last updated: 2017-12-12Bibliographically approved
3. The complexity of forest borders determines the understory vegetation
Open this publication in new window or tab >>The complexity of forest borders determines the understory vegetation
2018 (English)In: Applied Vegetation Science, ISSN 1402-2001, E-ISSN 1654-109X, Vol. 21, no 1, p. 85-93Article in journal (Refereed) Published
Abstract [en]

Questions: What are the most important drivers of plant species richness (γ-diversity) and species turnover (β-diversity) in the field layer of a forest edge? Does the tree and shrub species richness structure and complexity affect the richness of forest and grassland specialist species?

Location: South-eastern Sweden.

Methods: We sampled 50 forest edges with different levels of structural complexity in agricultural landscapes. In each border we recorded trees, shrubs and herb layer species in a 50 m transect parallel with the forest. We investigated species composition and species turnover in relationship to the proportions of gaps the border, the diversity of trees and shrubs and distance to semi-natural grasslands.

Results: Total plant species richness in the field layer was mainly explained by the proportion of gaps to areas with full canopy cover, and tree diversity. Increasing number of gaps promoted higher diversity of grassland specialist species within the field layer, resulting in open forest borders with the highest overall species richness. Gaps did however have a negative impact on forest species richness. Conversely, increasing forest species richness was positively related to tree diversity but number of grassland specialist species was negatively affected by tree diversity.

Conclusions: Managing forest borders, and therefore increasing the area of semi-open habitats in fragmented agricultural landscapes, gives future opportunities to create a network of suitable habitats for both grassland and deciduous forest specialist species. Such measures therefore have the potential to increase functional connectivity and support dispersal of species in homogeneous forest/agriculture landscapes.

Keywords
Alpha-diversity, Beta-diversity, Canopy cover, Forest border, Forest management, Forest specialist species, Gamma-diversity, Grassland specialist species, Plant diversity, Species richness, Remnant habitat, Structural heterogeneity
National Category
Ecology
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-148648 (URN)10.1111/avsc.12344 (DOI)000425120600010 ()
Available from: 2017-11-02 Created: 2017-11-02 Last updated: 2018-03-22Bibliographically approved
4. Habitat complementary supports pollinators and frugivores in agricultural landscapes
Open this publication in new window or tab >>Habitat complementary supports pollinators and frugivores in agricultural landscapes
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Context: Homogenization of land uses causes a decline in biodiversity in agricultural landscapes. The species composition of plants in small remnant habitats may overlap to some extent with species composition in decreasing species-rich key habitats, e.g. semi-natural grasslands, and therefore buffer the decline of species in intensively managed landscapes. Since plant species composition determines many ecosystem functions, small remnant habitats may provide essential contributions to ecosystem services in agricultural landscapes where semi-natural grasslands are rare.

Questions: To what extent does the plant community in forest edges and on midfield islets (remnant habitats of grasslands) overlap in composition with the plant species composition in semi-natural grasslands?

How important are these two types of remnant habitats for harboring plant communities utilized by a diversity of pollinators and frugivores, and does this importance vary during the growing season? And finally, does surrounding landscape type (agricultural intensity) or local environment (canopy openness) affect the function of the plant community characteristic’s associated with attracting frugivorous and pollinators?

Methods: We sampled plants, including trees and shrubs, and in 13 semi-natural grasslands, 50 forest edges and 132 midfield islets in agricultural landscapes in south-eastern Sweden. We investigated distribution and richness of plant traits (fleshy vs. dry fruits, flower morphology) in relation to habitat type, openness and surrounding agricultural management.

Results: Midfield islets had higher richness of plant species and flower shapes, and were more similar in composition to semi-natural grassland than forest edges. Species richness in midfield islets increased with habitat openness and in more intensively used (more open) agricultural landscapes. Midfield islets are important habitats for a diversity of nectar/pollen providing flowers from mid-summer and later in the growing season. Forest edges have a higher frequency of fleshy fruits and are an important source of nectar/pollen early in the season.

Conclusions: In landscapes with few other semi-natural habitats, small remnant habitats can contribute to species richness of plants, fleshy fruits and flower shapes. However they are not able to fully compensate for the decrease of semi-natural grasslands. Viewed over the whole growing season, several different habitats are needed to maintain foraging possibilities for pollinators in the landscape. Through habitat complementarity, midfield islets and forest edges with deciduous trees and shrubs, contribute to this function.

Keywords
biodiversity, fleshy fruits, flowering time, forest edge, functional diversity, grassland, midfield islets, plant-pollinator interaction, seed dispersal, small remnant habitat
National Category
Ecology
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-148650 (URN)
Available from: 2017-11-02 Created: 2017-11-02 Last updated: 2017-11-03Bibliographically approved

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