Plant trait responses to grassland management and succession [Elektronische Ressource] / vorgelegt von Stefanie Kahmen

Stefanie Brandt

Informations

• Publié par: universitat_regensburg
• Publié le: 01 janvier 2004
• Nombre de lectures: 18
• Poids de l'ouvrage: 1 Mo

Extrait

PLANT TRAIT RESPONSES TO
GRASSLAND MANAGEMENT AND
SUCCESSION






DISSERTATION ZUR ERLANGUNG DES DOKTORGRADES DER
NATURWISSENSCHAFTEN (DR. RER. NAT.)
DER NATURWISSENSCHAFTLICHEN FAKULTÄT III –
BIOLOGIE UND VORKLINISCHE MEDIZIN DER UNIVERSITÄT REGENSBURG








VORGELEGT VON STEFANIE KAHMEN
REGENSBURG
JUNI 2003


















Veröffentlichung:
Kahmen, S. (2004) Plant trait responses to grassland management and succession.
Dissertationes Botanicae 382, pp. 123.






Promotionsgesuch eingereicht am 18. Juni 2003
Mündliche Prüfung am 10. Oktober 2003

Prüfungsausschuss: Prof. Günter Hauska
Prof. Peter Poschlod
Prof. Michael Kleyer
Prof. Jürgen Heinze
Die Arbeit wurde angeleitet von Prof. Peter Poschlod



Contents

CHAPTER 1 GENERAL INTRODUCTION...................................................................1
CHAPTER 2 PLANT FUNCTIONAL TRAIT RESPONSES TO GRASSLAND
SUCCESSION OVER 25 YEARS..............................................................7
CHAPTER 3 CONSERVATION MANAGEMENT OF CALCAREOUS GRASSLANDS.
CHANGES IN PLANT SPECIES COMPOSITION AND RESPONSE OF
PLANT FUNCTIONAL TRAITS DURING 25 YEARS.................................23
CHAPTER 4 EFFECTS OF GRASSLAND MANAGEMENT ON PLANT FUNCTIONAL
TRAIT COMPOSITION .........................................................................35
CHAPTER 5 COMPARISON OF UNIVARIATE AND MULTIVARIATE ANALYSIS OF
PLANT TRAIT RESPONSES TO MANAGEMENT TREATMENTS................49
CHAPTER 6 DOES GERMINATION SUCCESS DIFFER WITH RESPECT TO SEED
MASS AND GERMINATION SEASON? EXPERIMENTAL TESTING OF
PLANT FUNCTIONAL TRAIT RESPONSES TO MANAGEMENT.................59
CHAPTER 7 EVALUATION OF PLANT TRAIT RESPONSES TO DIFFERENT
GRAZING INTENSITIES USING A MECHANISTIC, SPATIALLY
EXPLICIT SIMULATION MODEL ..........................................................73
SUMMARY .........................................................................................................99
ZUSAMMENFASSUNG ..................................................................................................103
REFERENCES .......................................................................................................107
APPENDIX116
DANK123


Chapter 1

General Introduction

Grassland management and succession
Semi-natural grasslands with their specific flora and fauna are of high conservation
value in Central Europe. They became threatened when intensification of agricultural
practice increased in the middle of the last century. From this time on, semi-natural
grasslands have been fertilised, afforested or, alternatively, been abandoned owing to
their low agricultural productivity (Poschlod & Schumacher 1998, WallisDeVries et
al. 2002). A major goal of nature conservation is to ensure the protection and
maintenance of these semi-natural grasslands and their unique floristic and faunistic
diversity by conservation management. Aiming to find the best management, i.e.
optimal maintenance of the species composition at the lowest cost possible, several
studies on management treatments have been started in the last decades (e.g.
Schreiber 1977, Krüsi 1981, Schmidt 1981, Kapfer 1988, Bakker 1989, Bobbink &
Willems 1993, Huhta & Rautio 1998, Huhta et al. 2001, Fischer & Wipf 2002). Most
of these studies investigated the impact of management-induced shifts in fertility on
changes in species composition. Due to different environmental conditions and
species sets, however, the transfer of conservation knowledge between sites or
regions remains difficult.
When management ceases and a site is abandoned, grassland succession leads to the
establishment of shrubs and trees until the site is entirely covered by forest. The
course of succession, however, differs greatly among sites. Species composition,
environmental conditions, but also site characteristics like the history of a site,
determine the succession process to a large extent, thus preventing the generation of
one general, unifying theory (Clements 1916, Margalef 1963, Odum 1969, Connell &
Slatyer 1977, Miles 1987, Pickett et al. 1987, Glenn-Lewin & van der Maarel 1992).
Without such a theory, predictions of the effects of grassland management or
abandonment for the purpose of nature conservation require individual studies for
each region and grassland type. As this approach is both unaffordable and time
consuming, conservationists have been forced to explore other methods of
assessment. In recent years, there has been a growing interest in the role of biological
characteristics of plants (plant functional traits) for vegetation changes induced by
management or succession (Hodgson 1990, Briemle & Schreiber 1994, Olff et al.
1994, Hobbs 1997, Prach et al. 1997, Poschlod et al. 1998, Dupré & Diekmann 2001,
Pywell et al. 2003). Focusing on plant functional traits instead of species is promising
since more general processes can be exposed. This thesis investigates plant functional
trait responses to grassland management and succession in order to identify regulating
mechanisms.2
Plant functional traits
Plant functional trait responses to ecosystem processes are of increasing interest in
plant ecology (Gitay & Noble 1997, Lavorel et al. 1997, Grime 2001). Plant traits are
biological characteristics like morphological or regenerative features. These features
may determine whether a plant species is able to establish, survive or increase in
abundance under specific environmental conditions or processes like disturbance,
land use, climate change, fire etc. A plant trait that is sensitive to an environmental
factor is defined as functional. As a consequence, plant functional traits are biological
characteristics of plant species that respond to environmental conditions or processes
in an ecosystem (Keddy 1992b, Kelly 1996, Gitay & Noble 1997, Lavorel et al.
1997). The benefit of knowing about the relationship between plant functional traits
and specific processes is twofold. Firstly, by interpreting trait responses ecologists
gain a better understanding of the mechanisms underlying the processes. Secondly,
examining traits instead of species is useful for predictive purposes. Predictions based
on species responses to a specific process are of a limited validity because most sites
differ with respect to the species set and these differences increase with increasing
spatial scale. In contrast to that, trait responses are more general, and sites with
different environmental conditions or different species sets are thus rendered
comparable. In a valuable study, Díaz et al. (2001) found similar trait responses to
grazing for two geographic regions with completely different floras (Argentina and
Israel).
Functional groups versus functional traits
There is a great variety of studies on functional trait responses (e.g. Boutin & Keddy
1993, Kelly 1996, Noble & Gitay 1996, Skarpe 1996, Thompson et al. 1996, Díaz &
Marcelo 1997, Kleyer 1999, Lavorel et al. 1999b, Leishman 1999, Díaz et al. 2001,
Thompson et al. 2001, Pywell et al. 2003). This has led to an equally great variety of
methods used in plant functional trait analyses. According to their methodology,
studies may, however, be broadly grouped into two categories, as they either focus on
single plant traits or plant groups.
Lavorel et al. (1997) as well as Gitay & Noble (1997) gave an overview of the
approaches to identifying plant groups, functional types sensu Lavorel et al. (1997)
and response groups sensu Gitay & Noble (1997). Based on a set of common plant
traits, plant functional types are defined as non-phylogenetic groups of species that
exhibit similar responses to ecosystem processes (Kelly 1996, Gitay & Noble 1997,
Lavorel et al. 1997). Reducing the high amount of species to some plant functional
types is appealing for comparative as well as for predictive reasons. Unfortunately,
plant functional types are highly context-specific so that a set of specific types has to
be defined for each process. Although a lot of studies identified similar plant
functional types that respond to grazing (Díaz et al. 1992, Lavorel et al. 1998, Hadar
et al. 1999, Landsberg et al. 1999, Lavorel et al. 1999a, Sternberg et al. 2000), until
now each study has used its own specific types. Gitay & Noble (1997) devised four
criteria for plant functional types, namely uniqueness, repeatability, congruency and
convergence but these criteria are seldom met.
In the temperate zone, widely applied functional concepts comprise the life form
groups of Raunkiaer (1934) and the CSR-strategy scheme proposed by Grime (1974).
GENERAL INTRODUCTION 3
‘Life form’ classifies plants with respect to the location of the regeneration buds as
strategy to survive cold winters (Raunkiaer 1934). It encapsulates sets of correlated
traits