Rainfall partitioning and soil water dynamics along a tree species

168 Pages·2010·8.53 MB·English

by  Inga Krämer

GÖTTINGER ZENTRUM
FÜR BIODIVERSITÄTSFORSCHUNG UND ÖKOLOGIE
− GÖTTINGEN CENTRE FOR BIODIVERSITY AND ECOLOGY −

Rainfall partitioning and soil water dynamics along a tree
species diversity gradient in a deciduous old-growth forest
in Central Germany

Dissertation zur Erlangung des Doktorgrades der
Mathematisch-Naturwissenschaftlichen Fakultäten der
Georg-August-Universität Göttingen

vorgelegt von
Diplom Landschaftsökologin und MSc Environmental Sciences
Inga Krämer
aus
Eckernförde

Rostock, 2009/2010
Referent: Prof. Dr. Dirk Hölscher
Korreferent: Prof. Dr. Wolfgang Schmidt
Tag der mündlichen Prüfung: 30.11.2009
There is no life without water. It is a treasure indispensable to all human activity.

(European Water Charter, Strasbourg 1968)

Contents

1 Introduction 1
1.1 Forests: biodiversity and ecohydrology 3
1.2 The hydrological cycle in a forest 4
1.3 Biodiversity research in forests 6
1.4 Umbrella project and study design 7
1.5 Study objectives and chapter outline 10
1.6 References 12

2 Rainfall partitioning along a tree diversity gradient in a deciduous old-growth
forest in Central Germany 17
2.1 Abstract 19
2.2 Introduction 19
2.3 Methods 21
2.4 Results 29
2.5 Discussion 35
2.6 Conclusion 38
2.7 Acknowledgement 40
2.8 References 40

3 Soil water dynamics along a tree diversity gradient in a deciduous forest in
Central Germany 47
3.1 Abstract 49
3.2 Introduction 49
3.3 Methods 51
3.4 Results 57
3.5 Discussion 62
3.6 Conclusion 66
3.7 Acknowledgement 67
3.8 References 67

4 Deposition and canopy exchange processes in central-German beech forests
differing in tree species diversity 73
4.1 Abstract 75
4.2 Introduction 75
4.3 Material and Methods 78
4.4 Results 86
4.5 Discussion 90
4.6 Conclusion 96
4.7 Acknowledgement 96
4.8 References 97

5 Modeling stand water budgets of mixed temperate broad-leaved forest stands
by considering variations in species-specific drought response 103
5.1 Abstract 105
5.2 Introduction 105
5.3 Material and Methods 107
5.4 Results and Discussion 114
5.5 Conclusion 128
5.6 Acknowledgement 129
5.7 References 129

6 Discussion 137
6.1 Observed effects along the tree species diversity gradient: did biodiversity play a role? 139
6.2 Relationships among the studied subjects 142
6.3 Relations to other studies in the umbrella project 143
6.4 Conclusion 148
6.5 References 148

Summary 153

Zusammenfassung 157

Acknowledgements 161
C
HAPTER
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Introduction

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1.1 FORESTS: BIODIVERSITY AND ECOHYDROLOGY
Forests play an essential role in the global water, nutrient, and carbon cycle. From a
hydrological point of view forests act as a water reserve, regulate water flow, and prevent soil
erosion. Due to their large canopy surface area they also filter particles, such as nutrients,
from the air (BMVEL, 2001). Owing to their multiple functions, forests provide services and
goods as for example improved water quality and biodiversity (Anderson et al., 2000; FAO,
2008). Before humans started to impact the landscape considerably, forests formed the natural
vegetation on a broad scale. Nowadays they are often important relicts of the former species
assemblages and biodiversity and therefore subject to conservation efforts.
In Central Europe, beech forest communities, including other deciduous tree species, compose
the potential natural vegetation in large areas. Beech (Fagus sylvatica L.) even tends to form
monospecific stands over a wide range of site conditions (Ellenberg, 1996). However, during
the past two centuries mainly coniferous species were used for reforestations (BMELV,
2004). The present forest cover in Germany accounts for 31% of the land area, whereof 62%
is dominated by coniferous species and only 38% is broadleaved deciduous forest. Mono-
specific beech forests represent merely 2.4% of the total forest area while 4.9% of the total
forest area consists of beech forest with admixture of other broadleaved deciduous species
(BMELV, 2004). Recently, the establishment of mixed and deciduous forests has been
promoted and increased in areas where site conditions are suitable (BMVEL, 2001; BMELV,
2004; Röhrig et al., 2006). Reasons for this change are supposedly higher stability against
storms and diseases, and economical assurances. Additionally, this process supports the goals
of the Convention on Biological Diversity (1993).
Biological diversity, also referred to as biodiversity, has been defined in many ways. The
Convention on Biological Diversity (1993) declared biological diversity as ‘the variability
among living organisms from all sources including, inter alia, terrestrial, marine, and other
aquatic ecosystems and the ecological complexes of which they are part: this includes
diversity within species, between species, and of ecosystems’. Next to its intrinsic value,
biological diversity has among others ecological, genetic, economic, scientific, and
recreational values. However, biodiversity is significantly reduced by human activities and
further biodiversity loss will diminish the positive effects on the provision of ecosystem
services (Hooper et al., 2005; Balvanera et al., 2006).
Interdisciplinary research on the interrelationship between ecology and hydrology received
recently renewed attention under the term ‘ecohydrology’. Ecohydrology seeks to understand
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the interactions between the hydrological cycle and ecosystems (Porporato and Rodriguez-
Iturbe, 2002). This includes the influence of hydrological processes on ecosystem patterns,
diversity, structure, and functions and how feedbacks from biological communities affect the
hydrological cycle (Newman et al., 2006; Smettem, 2008). The importance of ecological and
hydrological interrelationships is increasingly recognized as a central aspect in predicting and
managing ecosystem dynamics (Zou et al., 2008). Major topics of ecohydrology are for
example the role of the vegetation in rainfall interception processes (van Dijk, 2004), soil
water and plant relations (Rodriguez-Iturbe, 2000; Porporato and Rodriguez-Iturbe, 2002;
Dolman, 2003; Rodriguez-Iturbe and Porporato 2004; van Dijk, 2004), and the interrelation-
ship between the hydrological cycle and other biogeochemical cycles such as the central role
of water as a transport mechanism for nutrients (Dolman, 2003).

1.2 THE HYDROLOGICAL CYCLE IN A FOREST
The water budget of a forest includes the rates of input and output as well as the storage
changes of water in the system. The main components are shown in Figure 1.1. Some rain-
water is temporarily stored (intercepted) on surfaces such as leaves, branches, and stems of
trees and on the herb- and litter layer and evaporates back into the atmosphere. Rainfall passes
the canopy directly through gaps or indirectly after contact with the canopy as throughfall and
stemflow. The water which finally reaches the soil surface can evaporate from the soil
surface, occur as surface runoff, or infiltrate into the soil. Infiltrated water can be stored in the
soil, taken up by the vegetation for transpiration, or may leave the rooted soil volume as
drainage water or as slope parallel interflow.
Closely coupled to the forest hydrological cycle are the deposition and transportation of ions
such as nitrogen and phosphorus by the rainwater. The deposition of ions in forests depends
among others on the leaf area, the physical and chemical properties of the leaf surface, and the
structural properties of the canopy (Erisman and Draaijers, 2003). The canopy can act as a
source or a sink for deposited ions due to canopy exchange processes. Next to litterfall, both
throughfall and stemflow transport ions to the forest floor.

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