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Biodiversity and ecosystem functioning: The effects of tree and litter diversity


Haase, J U. Biodiversity and ecosystem functioning: The effects of tree and litter diversity. 2009, University of Zurich, Faculty of Science.

Abstract

Global changes and declines in biodiversity at all taxonomic levels have intensified the scientific effort to understand the functional role of biodiversity as a regulator of ecosystem processes. Although evidence for a positive relationship between biodiversity and ecosystem functioning is accumulating from studies mainly performed in grasslands, little is known about the importance of this relationship in forest ecosystems, despite their huge ecological and socioeconomic importance. In this thesis I therefore assessed the effects of tree diversity on above- and belowground productivity and on litter decomposition along an experimentally manipulated diversity gradient in a temperate forest system, using different approaches including field and pot experiments.
In chapter 1, I quantified the relative contributions of complementarity and selection to net effects of tree diversity on above- and belowground productivity, and assessed whether this relationship is influenced by planting density. I found that total productivity was increased in mixed compared with monospecific stands and that tree diversity effects on productivity occurred below rather than above ground and were density-dependent. Positive effects of tree diversity were related to complementarity rather than selection and were more pronounced at low planting density. This study demonstrates the potential role of niche separation in driving the biodiversity ecosystem functioning relationship in trees, and highlights the significance of belowground processes for driving this pattern.
Chapter 2 looks deeper into the role of belowground competition in affecting root allocation of saplings. I tested whether trees increase root allocation in response to the presence of neighbours, and whether this response is more pronounced in the presence of con- compared with heterospecific competitors. Although belowground competition in tree pairs led to increased root production and root allocation, this effect was independent of the identity of the competitor, perhaps because neighbour recognition mechanisms are absent in trees. Increased root production more generally may have implications for carbon storage and nutrient retention within forest systems.
In chapter 3, I examined the functional importance of "after-life" effects of tree species diversity and its interaction with soil fauna on a crucial ecosystem process, leaf litter decomposition. In particular I investigated the relative importance of different direct and indirect pathways through which litter species diversity can influence decomposition. Different litter species compositions varied greatly in decomposition rates, which interactively with soil fauna was more important than litter diversity per se for litter decomposition. However, decomposition in mixtures resulted in synergistic effects only in the absence of soil fauna, suggesting that small litter diversity effects may be masked by soil fauna activity.
In chapter 4, I quantified intraspecific variation in litter quality and decomposition and the ecological consequences of intraspecific diversity on decomposition rates. Using European beech as a model species, I showed that there was considerable intraspecific variation in litter decomposition rates, although this was not related to litter quality. However, I also found synergistic effects on decomposition of mixing litter from different individuals, demonstrating the significance of intraspecific variation on this ecosystem process.
Overall this study demonstrates the importance of biodiversity both among and within species for ecosystem functioning. However, diversity effects were relatively weak, and species composition was a consistently better predictor of variation in productivity and decomposition. This underscores the importance of specific species traits in driving ecosystem processes in tree communities.

Abstract

Global changes and declines in biodiversity at all taxonomic levels have intensified the scientific effort to understand the functional role of biodiversity as a regulator of ecosystem processes. Although evidence for a positive relationship between biodiversity and ecosystem functioning is accumulating from studies mainly performed in grasslands, little is known about the importance of this relationship in forest ecosystems, despite their huge ecological and socioeconomic importance. In this thesis I therefore assessed the effects of tree diversity on above- and belowground productivity and on litter decomposition along an experimentally manipulated diversity gradient in a temperate forest system, using different approaches including field and pot experiments.
In chapter 1, I quantified the relative contributions of complementarity and selection to net effects of tree diversity on above- and belowground productivity, and assessed whether this relationship is influenced by planting density. I found that total productivity was increased in mixed compared with monospecific stands and that tree diversity effects on productivity occurred below rather than above ground and were density-dependent. Positive effects of tree diversity were related to complementarity rather than selection and were more pronounced at low planting density. This study demonstrates the potential role of niche separation in driving the biodiversity ecosystem functioning relationship in trees, and highlights the significance of belowground processes for driving this pattern.
Chapter 2 looks deeper into the role of belowground competition in affecting root allocation of saplings. I tested whether trees increase root allocation in response to the presence of neighbours, and whether this response is more pronounced in the presence of con- compared with heterospecific competitors. Although belowground competition in tree pairs led to increased root production and root allocation, this effect was independent of the identity of the competitor, perhaps because neighbour recognition mechanisms are absent in trees. Increased root production more generally may have implications for carbon storage and nutrient retention within forest systems.
In chapter 3, I examined the functional importance of "after-life" effects of tree species diversity and its interaction with soil fauna on a crucial ecosystem process, leaf litter decomposition. In particular I investigated the relative importance of different direct and indirect pathways through which litter species diversity can influence decomposition. Different litter species compositions varied greatly in decomposition rates, which interactively with soil fauna was more important than litter diversity per se for litter decomposition. However, decomposition in mixtures resulted in synergistic effects only in the absence of soil fauna, suggesting that small litter diversity effects may be masked by soil fauna activity.
In chapter 4, I quantified intraspecific variation in litter quality and decomposition and the ecological consequences of intraspecific diversity on decomposition rates. Using European beech as a model species, I showed that there was considerable intraspecific variation in litter decomposition rates, although this was not related to litter quality. However, I also found synergistic effects on decomposition of mixing litter from different individuals, demonstrating the significance of intraspecific variation on this ecosystem process.
Overall this study demonstrates the importance of biodiversity both among and within species for ecosystem functioning. However, diversity effects were relatively weak, and species composition was a consistently better predictor of variation in productivity and decomposition. This underscores the importance of specific species traits in driving ecosystem processes in tree communities.

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Additional indexing

Item Type:Dissertation
Referees:Hector A, Prati D, Auge H, Schmid B, Scheu S
Communities & Collections:07 Faculty of Science > Institute of Evolutionary Biology and Environmental Studies
Dewey Decimal Classification:570 Life sciences; biology
590 Animals (Zoology)
Language:English
Date:2009
Deposited On:07 Oct 2009 14:44
Last Modified:05 Apr 2016 13:22
Number of Pages:135

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