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Plant community assembly during succession from arable fields to semi-natural grassland

Schmid, Barbara Christine LU (2016)
Abstract (Swedish)
Popular Abstract in Swedish

Vi vill bevara naturbetesmarker och deras skönhet, vilken bland annat utgörs av de olika växtarter som förekommer där. Men idag finns det tyvärr inte många betesmarker kvar. Naturbetesmarkerna har under de senaste två sekelerna försvunnit på grund av ökad eller minskad markanvändning, där betesmarker blivit omvandlade till antingen åkermark eller skog. Bristen på betesmarker hotar mångfalden och överlevnaden av typiska betesmarksväxter. För att på lång sikt skydda dessa betesmarksväxter, skapar man idag betesmarker på mark som tidigare varit åkermark. Dessutom prövar man att sammankoppla olika betesmarker till varandra för att förbättra växternas spridningsmöjligheter.

Vi undersökte hur... (More)
Popular Abstract in Swedish

Vi vill bevara naturbetesmarker och deras skönhet, vilken bland annat utgörs av de olika växtarter som förekommer där. Men idag finns det tyvärr inte många betesmarker kvar. Naturbetesmarkerna har under de senaste två sekelerna försvunnit på grund av ökad eller minskad markanvändning, där betesmarker blivit omvandlade till antingen åkermark eller skog. Bristen på betesmarker hotar mångfalden och överlevnaden av typiska betesmarksväxter. För att på lång sikt skydda dessa betesmarksväxter, skapar man idag betesmarker på mark som tidigare varit åkermark. Dessutom prövar man att sammankoppla olika betesmarker till varandra för att förbättra växternas spridningsmöjligheter.

Vi undersökte hur ett växtsamhälle, det vill säga hur en karakteristisk grupp av olika växtarter, utvecklades på betesmark som tidigare har varit åker. Växtsamhällens utveckling över tid kallas successionen. Vår studie visade att successionen från ett växtsamhälle på åkermark till ett typiskt växtsamhälle i betesmark är en långsam process som kan ta mer än hundra år. För att kunna studera en så lång succession, använder man olika gamla betesmarker i ett landskap. Först undersöker vi förekommande växtarter och markegenskaper som till exempel växtnäringsämnen i jorden. Sedan ordnades de olika betesmarkerna efter deras ålder, vilket kallas ”chronosequence”, som representerade utvecklingen av en åkermark till en betesmark över tid. Metoden kallas ”space-for-time approach” (”rum-för-tid metodiken”).

För att bilda ett växtsamhälle på tidigare åkermark måste växtarterna invandra, etablera sig och stanna kvar i betesmarken under successionens förlopp. Vi undersökte vilka processer som bidrog till att ett typiskt betesmarks-växtsamhälle utvecklades. Dessutom studerade vi vilka processer som hade störst påverkan på successionen. Ekologiska teorier föreslår tre till fyra huvudprocesser på landskapsnivå som driver utvecklingen av ett växtsamhälle: störnings-processer, utbrednings-processer, miljöpåverkan (abiotiska processer) och inflytandet av andra växter eller djur (biotiska processer). Betning av tamboskap visade sig att vara ”huvudaktören” i utvecklingen av växtsamhället i betesmarker. Betningen kan man betrakta som en störnings-process, där betesdjur kontinuerligt skadar växterna, eller man kan se det som ett samspel mellan växt och betesdjur, alltså en biotisk process. Vi drog slutsatsen att betningen hade en direkt påverkan på växterna. Huvudsakligen etablerades växter som hade en viss anpassning emot bladförlust. Betesdjur är inte enbart skadliga för betesmarksväxter, de kan även förbättra växternas utbredning genom att sprida fröer. Dessutom påverkade betningen på långt sikt växtnäringsämnena i jorden. Över lång tid kan det ske en minskning av näringsämnen i betesmarken om betesdjur transporterar näringen till andra platser i landskapet, så som, till stallen, där betesdjur övernattar, eller andra platser som de har tillgång till. Näringen kan även omvandlas till kött- och mjölk-produkter och på så vis försvinna från betesmarkerna. Vår studie visade att det tar lång tid, mer än två hundra år, för jorden att bli magrare och innan typiska växtsamhällen för naturbetesmarker utvecklas.

Vi var också intresserade av hur man kan uppskatta hur många växtarter som sprids från gamla till unga betesmarker. På så vis kan man bättre förstå hur snabbt successionen är. För att uppskatta växternas spridning använde vi en modell som tar hänsyn till de gamla betesmarkernas areal, avståndet mellan unga och gamla betesmarker och det genomsnittliga spridningsavstånd av växtarterna. Klassiska modeller och det flesta betesmarksstudier uppskattar arealen av gammal betesmark i abstrakta cirklar. I vår studie testade vi en mer realistisk metod genom att ersätta de abstrakta cirklarna med arealen som betesdjuren var inhägnade i. Detta gav sedan en bättre uppskattning. Vidare var det en utmaning att kunna uppskatta det genomsnittliga spridningsavståndet för flera olika växtarter. Vi löste detta genom att bedöma det maximala avståndet som tamboskapen kunde förflytta sig inom sitt inhägnade område.

Till sist ville vi även ta reda på när under successionen det specialiserade växterna på betesmarkerna hade sin största frekvens. Successions-teorier och andra ekologiska teorier antar att karakteristiska växter för betesmarker, som gynnas av betning, etablerar sig sent och därför har högst frekvens i de äldsta betesmarkerna. Men är det verkligen så? Vår undersökning visade att några växtarter istället hade sin högsta frekvens i övergångsfasen mellan unga och gamla betesmarker, det vill säga efter cirka 50 år. Därefter gick deras frekvens tillbaka. Detta betyder att det är viktigt att inte bara bevara gamla betesmarker utan även andra betesmarker med yngre ålder för att gynna samtliga växtarter. (Less)
Abstract
Large areas of grazed, species rich semi-natural grassland were lost in Europe during the last two centuries and as a consequence led to decreases in grassland specialist species. Therefore, today the “restoration” of grassland on previously arable fields is recommended for the protection of grassland specialists. Even “substitute habitats” for lost grasslands are discussed as temporary alternative habitats for grassland specialists. During the “restoration” of grasslands on previously arable fields, the grazing management interrupts the progress of succession (to forest) at an intermediate stage, the semi-natural grassland which is maintained as an alternative endpoint of succession. Within this type of “truncated” arable-to-grassland... (More)
Large areas of grazed, species rich semi-natural grassland were lost in Europe during the last two centuries and as a consequence led to decreases in grassland specialist species. Therefore, today the “restoration” of grassland on previously arable fields is recommended for the protection of grassland specialists. Even “substitute habitats” for lost grasslands are discussed as temporary alternative habitats for grassland specialists. During the “restoration” of grasslands on previously arable fields, the grazing management interrupts the progress of succession (to forest) at an intermediate stage, the semi-natural grassland which is maintained as an alternative endpoint of succession. Within this type of “truncated” arable-to-grassland succession the disturbance filter by grazing management may have a strong influence on plant communities, next to the dispersal, abiotic and biotic filters which may influence plant community assembly during succession. Ecological theory suggests that arable-to-grassland succession may be mainly driven by deterministic or by stochastic processes and that plant communities either diverge or converge during succession. Specialist species are expected to be most common in the final stage of succession. Spatial dispersal processes may be estimated by connectivity measures, but simple, biological meaningful measures are still missing.

The overall aim of the thesis is to understand plant community assembly during a long-term (≥ 280 years) arable-to-grassland succession with a special focus on i) changes in different facets of diversity and ii) the underlying processes (assessed as filters of plant community assembly) leading to the changes. We further investigated how to improve the estimation of dispersal processes from old to young grasslands by incorporating basic movement patterns into connectivity measures and we examined changes in the species frequencies during succession and its implications for grassland specialist conservation.

GIS analyses were used to detect grassland ages (t_5: 5-14, t_15: 15-49, t_50: 50-179 and t_280: ≥ 280 years old) and land-use changes over the last 280 years. The differently aged grasslands on previously arable fields were arranged to a chronosequence of succession. Null model analysis and hierarchical partitioning were used to identify processes influencing plant community assembly during the arable-to-grassland succession. Within an information-theoretic framework different IFM connectivity measures were compared with the help of specialist richness (actual connectivity) models to examine whether modification in the support area, the mean dispersal distance or the edge:area transformed the IFM connectivity into a simple functional connectivity measure. Finally ordination and indicator species analyses were used to investigate frequency-changes of typical grassland species during succession.

At present-day most of the grasslands on previously arable fields are early-successional (5-49 years old) grasslands. Mid-successional (50-279 years old) grasslands are very rare (3% of the grasslands on previously arable fields). 22.5% of the grasslands are old semi-natural grasslands. Taxonomic and functional alpha diversity increase with grassland age, but show different patterns during the succession, whereas taxonomic and functional beta diversity decrease during succession. Taxonomic beta diversity was significantly associated with the disturbance (grazing), the dispersal (realised connectivity) and the abiotic (phosphorus, nitrogen) filters of plant community assembly during succession. A connectivity measure based on the “realised support area” including an edge:area ratio and a short-intermediate mean dispersal distance approximated actual connectivity best. Mid-successional grasslands host typical grassland species in intermediate frequencies and some of the so-called typical grassland species have even their highest within-plot frequencies in these transient grasslands.

Our results suggest that plant communities converge in terms of their species composition and species frequencies during the arable-to-grassland succession. The disturbance filter seems to be the main driver during the succession. The disturbance by grazing animals influences plant community assembly directly and also indirectly via the dispersal and abiotic filter, because the grazing animal may also contribute to species dispersal and may remove nutrients from the grasslands. The dispersal filter in grazed grassland systems may, in a simple functional way, be estimated by a modified IFM connectivity measure that is based on a realised support area, reflecting where the main dispersal vector of plant species actually can move. The mean dispersal distance of the main dispersal vector seems to function as an estimate for the mean dispersal distance of multiple species. Our results further suggest that mid-successional grasslands may make a valuable contribution to the protection of typical grassland species and that they may function as “substitute habitat” for lost old semi-natural grasslands. Rather than focussing solely on high-quality old semi-natural grassland fragments, the incorporation of land-use dynamics in species protection schemes seems to be desirable, because some of the so-called typical grassland species seem to have found a temporal niche in the transient and slightly more nutrient rich mid-successional grasslands. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Zobel, Martin, Plant Ecology Laboratory, University of Tartu, Estonia
organization
publishing date
type
Thesis
publication status
published
subject
keywords
diversity, arable-to-grassland succession, space-for-time approach, land-use history, plant community assembly, grazing management, connectivity measures, dispersal vector, vascular plants, grassland specialist conservation
pages
165 pages
publisher
Department of Biology, Lund University
defense location
Blå Hallen, Ekologihuset
defense date
2016-02-05 09:30
ISBN
978-91-7623-608-6 (print)
978-91-7623-609-3 (pdf)
language
English
LU publication?
yes
id
7f3e808f-eb48-441e-bd6c-c106272acb80 (old id 8626040)
date added to LUP
2016-02-12 17:49:50
date last changed
2016-09-19 08:45:06
@phdthesis{7f3e808f-eb48-441e-bd6c-c106272acb80,
  abstract     = {Large areas of grazed, species rich semi-natural grassland were lost in Europe during the last two centuries and as a consequence led to decreases in grassland specialist species. Therefore, today the “restoration” of grassland on previously arable fields is recommended for the protection of grassland specialists. Even “substitute habitats” for lost grasslands are discussed as temporary alternative habitats for grassland specialists. During the “restoration” of grasslands on previously arable fields, the grazing management interrupts the progress of succession (to forest) at an intermediate stage, the semi-natural grassland which is maintained as an alternative endpoint of succession. Within this type of “truncated” arable-to-grassland succession the disturbance filter by grazing management may have a strong influence on plant communities, next to the dispersal, abiotic and biotic filters which may influence plant community assembly during succession. Ecological theory suggests that arable-to-grassland succession may be mainly driven by deterministic or by stochastic processes and that plant communities either diverge or converge during succession. Specialist species are expected to be most common in the final stage of succession. Spatial dispersal processes may be estimated by connectivity measures, but simple, biological meaningful measures are still missing.<br/><br>
The overall aim of the thesis is to understand plant community assembly during a long-term (≥ 280 years) arable-to-grassland succession with a special focus on i) changes in different facets of diversity and ii) the underlying processes (assessed as filters of plant community assembly) leading to the changes. We further investigated how to improve the estimation of dispersal processes from old to young grasslands by incorporating basic movement patterns into connectivity measures and we examined changes in the species frequencies during succession and its implications for grassland specialist conservation.<br/><br>
GIS analyses were used to detect grassland ages (t_5: 5-14, t_15: 15-49, t_50: 50-179 and t_280: ≥ 280 years old) and land-use changes over the last 280 years. The differently aged grasslands on previously arable fields were arranged to a chronosequence of succession. Null model analysis and hierarchical partitioning were used to identify processes influencing plant community assembly during the arable-to-grassland succession. Within an information-theoretic framework different IFM connectivity measures were compared with the help of specialist richness (actual connectivity) models to examine whether modification in the support area, the mean dispersal distance or the edge:area transformed the IFM connectivity into a simple functional connectivity measure. Finally ordination and indicator species analyses were used to investigate frequency-changes of typical grassland species during succession.<br/><br>
At present-day most of the grasslands on previously arable fields are early-successional (5-49 years old) grasslands. Mid-successional (50-279 years old) grasslands are very rare (3% of the grasslands on previously arable fields). 22.5% of the grasslands are old semi-natural grasslands. Taxonomic and functional alpha diversity increase with grassland age, but show different patterns during the succession, whereas taxonomic and functional beta diversity decrease during succession. Taxonomic beta diversity was significantly associated with the disturbance (grazing), the dispersal (realised connectivity) and the abiotic (phosphorus, nitrogen) filters of plant community assembly during succession. A connectivity measure based on the “realised support area” including an edge:area ratio and a short-intermediate mean dispersal distance approximated actual connectivity best. Mid-successional grasslands host typical grassland species in intermediate frequencies and some of the so-called typical grassland species have even their highest within-plot frequencies in these transient grasslands.<br/><br>
Our results suggest that plant communities converge in terms of their species composition and species frequencies during the arable-to-grassland succession. The disturbance filter seems to be the main driver during the succession. The disturbance by grazing animals influences plant community assembly directly and also indirectly via the dispersal and abiotic filter, because the grazing animal may also contribute to species dispersal and may remove nutrients from the grasslands. The dispersal filter in grazed grassland systems may, in a simple functional way, be estimated by a modified IFM connectivity measure that is based on a realised support area, reflecting where the main dispersal vector of plant species actually can move. The mean dispersal distance of the main dispersal vector seems to function as an estimate for the mean dispersal distance of multiple species. Our results further suggest that mid-successional grasslands may make a valuable contribution to the protection of typical grassland species and that they may function as “substitute habitat” for lost old semi-natural grasslands. Rather than focussing solely on high-quality old semi-natural grassland fragments, the incorporation of land-use dynamics in species protection schemes seems to be desirable, because some of the so-called typical grassland species seem to have found a temporal niche in the transient and slightly more nutrient rich mid-successional grasslands.},
  author       = {Schmid, Barbara Christine},
  isbn         = {978-91-7623-608-6 (print)},
  keyword      = {diversity,arable-to-grassland succession,space-for-time approach,land-use history,plant community assembly,grazing management,connectivity measures,dispersal vector,vascular plants,grassland specialist conservation},
  language     = {eng},
  pages        = {165},
  publisher    = {Department of Biology, Lund University},
  school       = {Lund University},
  title        = {Plant community assembly during succession from arable fields to semi-natural grassland},
  year         = {2016},
}