Fragmentqualität prägt Waldregeneration eher als Matrixhabitat in einer südafrikanischen Mosaikwaldlandschaft

Land-use change and agricultural intensification are responsible for a global decline of forest cover entailing the fragmentation of forests. Landscapes are increasingly shaped by a mosaic of forest fragments within variable matrix habitat. It is thus essential to understand how these habitat alterations influence function and stability of forest ecosystems. However, the complex relationships between anthropogenic disturbance of forests, concurrent species loss and ecosystem functions are not fully clarified yet. In the present thesis, I investigated the impact of structural forest fragment quality and variable matrix habitat on biodiversity and ecological processes of forest regeneration. For this purpose, I conducted three studies in a fragmented mosaic-forest landscape in KwaZulu-Natal, South Africa. In particular, I assessed (1) seed predation by rodents, (2) establishment of woody seedlings and saplings, and (3) leaf damage on woody seedlings and saplings by insects and pathogens in 24 study plots in scarp forest fragments. These fragments were embedded in four variable matrices: two natural, heterogenous (forest, grassland) and two modified, homogenous matrices (eucalypt plantations, sugarcane fields). In the first field study I assessed rodent diversity and conducted seed predation experiments. As a measure for forest fragment quality important for rodents, I estimated herbal ground vegetation cover. For the second study I identified all trees on 500 m², seedlings on 10 m² and saplings on 50 m² per study plot. I categorized trees, seedlings and saplings as either early- or late-successional species. Moreover, I differentiated between seedlings and saplings of external and local origin depending on the presence of conspecific adult tress within fragments to be able to identify potential seed influx by seed dispersers. Additionally, I measured canopy cover, light intensity and vegetation complexity as parameters of forest fragment quality relevant to seedling establishment. In the third study I used beating samples to collect the arthropod community. Furthermore, I estimated proportions of leaf damage by insect herbivory and leaf pathogens on woody seedlings and saplings. I determined tree diversity, canopy cover and vegetation complexity in terms of forest fragment quality. My investigations showed an increase of rodents and seed predation in small forest fragments, potentially caused by enhanced ground vegetation cover. Especially in fragments with sugarcane matrix rodent abundance and seed predation were significantly higher than in fragments with forest matrix. Further, I found reduced seedling and sapling establishment in forest fragments with modified homogenous surroundings. In particular, these fragments consisted of less late-successional species. This could predominantly be ascribed to reduced canopy cover and increased light intensity. However, seed influx occurred in all forest fragments indicating high matrix permeability for seed dispersers. Moreover, forest fragment quality amplified arthropod predator abundance and reduced arthropod herbivore abundance. Fragment quality effects on herbivory were variable. This mismatch might be related to weak trophic interactions. Matrix habitat had merely marginal effects on the investigated factors. Overall, my results illustrate that forest fragment quality as well as matrix habitat have the potential to alter biodiversity and ecological processes of forest regeneration, but effects on the observed processes differed in strength. Yet, I generally found that forest fragment quality appears to be of high relevance for regeneration, indicating its potential for conservation management of the remaining fragments. Further, the rather weak overall effects of matrix habitat indicate a comparable and generally high permeability for the investigated groups of species. This emphasizes the significant value of forest fragments for the connectivity of remaining forests and the conservation of biodiversity and ecological processes at a landscape scale. Nevertheless, conclusions have to be treated with care. Due to the historical natural fragmentation of scarp forests in KwaZulu-Natal, which might have caused a higher robustness of species towards human-induced fragmentation, my findings might not be transferable to other regions. The scarp forest fragments are characterized by high habitat quality for the different species groups. However, potential shifts in the plant community from late- to early-successional species in fragments enclosed by modified matrices might entail unforeseen cascading effects and negative feedback loops within the ecosystem that still need to be examined. Thus, the value of natural forest as a source of propagules and as habitat for forest specialists remains indisputable.Weltweit werden Wälder in alarmierender Geschwindigkeit zerstört und fragmentiert. Landschaften bestehen zunehmend aus Mosaiken mit Waldfragmenten in variablem Matrixhabitat. Es ist daher essentiell zu verstehen, inwiefern diese Habitatveränderungen Funktion und Stabilität von Waldökosystemen beeinflussen. Die komplexen Zusammenhänge zwischen anthropogener Störung von Wäldern, Artenverlust und Ökosystemfunktionen sind jedoch noch nicht hinreichend geklärt. In der vorliegenden Arbeit untersuchte ich den Einfluss von Waldfragmentqualität und Matrixhabitat auf Biodiversität und ökologische Prozesse der Waldregeneration. Ich führte drei Studien in einer fragmentierten Waldlandschaft in KwaZulu-Natal, Südafrika durch. Ich erfasste 1) Samenprädation durch Nager, 2) Etablierung von Baumkeimlingen und -schösslingen sowie 3) Blattschäden an Baumkeimlingen und -schösslingen durch Insekten und Pathogene auf 24 Untersuchungsflächen in Fragmenten so genannter Hangwälder („scarp forests“). Die Waldfragmente waren von vier verschiedenen Matrixhabitaten umgeben: Zwei natürliche, heterogene (Wald, Grassland) und zwei modifizierte, homogene Matrices (Eukalyptus-Plantagen, Zuckerrohrfelder). Für die erste Studie nahm ich die Nagerdiversität auf und führte Samenprädationsexperimente durch. Zudem schätzte ich als Maß für die Fragmentqualität die Bodenbedeckung durch krautige Pflanzen. Für die zweite Studie bestimmte ich die Diversität der Bäume auf 500 m² pro Fläche, die der Keimlinge auf 10 m² und die der Schösslinge auf 50 m². Ich unterteilte Bäume, Keimlinge und Schösslinge in Pionier- und Klimaxarten. Des Weiteren differenzierte ich zwischen Keimlingen und Schösslingen mit externer und lokaler Herkunft, abhängig von der Präsenz artgleicher Bäume im Fragment, um so auf eventuellen Sameneintrag durch Samenausbreiter rückschließen zu können. Außerdem nahm ich Kronenbedeckung, Lichtintensität und Vegetationskomplexität als Parameter der Fragmentqualität auf. Für die dritte Studie ermittelte ich mit einem Klopfschirm die Arthropoden-Gemeinschaft. Zusätzlich schätzte ich den Blattschaden durch Insektenherbivorie und Pathogenbefall an Baumkeimlingen und -schösslingen. Bezüglich der Fragmentqualität nahm ich Baumdiversität, Kronenbedeckung und Vegetationskomplexität auf. Meine Untersuchungen deuteten auf ein erhöhtes Nagervorkommen und verstärkte Samenprädation in kleinen Fragmenten hin, was vermutlich mit der höheren krautigen Bodenbedeckung zusammenhing. Speziell in Fragmenten im Zuckerrohr waren Nagervorkommen und Samenprädation signifikant höher als in Fragmenten mit Waldmatrix. Ferner konnte ich eine reduzierte Keimlings- und Schösslingsetablierung in den Waldfragmenten mit modifizierten Matrices feststellen. Es kam außerdem zu einer Verringerung von Klimaxarten in diesen Fragmenten. Dies wurde hauptsächlich durch abnehmende Kronenbedeckung und erhöhte Lichtintensität bedingt. Jedoch fand Sameneintrag in allen Waldfragmenten statt, was auf die Matrixdurchlässigkeit für Samenausbreiter hindeutete. Des Weiteren kam es zu einem Anstieg an Arhtropoden-Prädatoren und einem Rückgang an Arhtropoden-Herbivoren mit zunehmender Fragmentqualität. Der Einfluss der Fragmentqualität auf Herbivorie war variabel. Diese Abweichungen könnten mit schwachen trophischen Interaktionen zusammenhängen. Das Matrixhabitat hatte nur marginale Effekte auf die untersuchten Faktoren. Insgesamt zeigen meine Ergebnisse, dass Waldfragmentqualität und Matrixhabitat Biodiversität und ökologische Prozesse der Waldregeneration beeinflussen, jedoch waren die Effekte dabei unterschiedlich. Generell schien die Fragmentqualität jedoch eine wichtige Bedeutung für die Regeneration zu haben, was ihr Potential für den Naturschutz hervorhebt. Ferner lassen die schwachen Effekte der variablen Matrices in unserem Untersuchungsgebiet eine vergleichbar hohe Durchlässigkeit für die untersuchten Artengruppen erkennen. Das unterstreicht den Wert der Waldfragmente als Habitatinseln in modifizierten Landschaften und für den Erhalt von Biodiversität und ökologischen Prozessen auf der Landschaftsebene. Nichtsdestotrotz ist bei der Verallgemeinerung der Aussagen Vorsicht angebracht. Aufgrund der historischen, natürlichen Fragmentierung der Hangwälder, die zu einer hohen Robustheit der Artengruppen gegenüber menschlich verursachter Fragmentierung beigetragen haben könnte, sind die Ergebnisse eventuell nur eingeschränkt auf andere Regionen übertragbar. Die Fragmente zeichnen sich zwar durch ihre hohe Habitatqualität für verschiedene Artengruppen aus, jedoch könnten die Verschiebungen in den Pflanzengemeinschaften von Klimax- zu Pionierarten in Fragmenten mit modifizierten Matrices unvorhersehbare Kaskadeneffekte mit sich bringen. Das macht den Erhalt von großen zusammenhängenden Wäldern als Quelle für Klimaxarten und Habitat für spezialisierte Arten unerlässlich

Do contaminants originating from state-of-the-art treated wastewater impact the ecological quality of surface waters?

Since the 1980s, advances in wastewater treatment technology have led to considerably improved surface water quality in the urban areas of many high income countries. However, trace concentrations of organic wastewater-associated contaminants may still pose a key environmental hazard impairing the ecological quality of surface waters. To identify key impact factors, we analyzed the effects of a wide range of anthropogenic and environmental variables on the aquatic macroinvertebrate community. We assessed ecological water quality at 26 sampling sites in four urban German lowland river systems with a 0–100% load of state-of-the-art biological activated sludge treated wastewater. The chemical analysis suite comprised 12 organic contaminants (five phosphor organic flame retardants, two musk fragrances, bisphenol A, nonylphenol, octylphenol, diethyltoluamide, terbutryn), 16 polycyclic aromatic hydrocarbons, and 12 heavy metals. Non-metric multidimensional scaling identified organic contaminants that are mainly wastewater-associated (i.e., phosphor organic flame retardants, musk fragrances, and diethyltoluamide) as a major impact variable on macroinvertebrate species composition. The structural degradation of streams was also identified as a significant factor. Multiple linear regression models revealed a significant impact of organic contaminants on invertebrate populations, in particular on Ephemeroptera, Plecoptera, and Trichoptera species. Spearman rank correlation analyses confirmed wastewater-associated organic contaminants as the most significant variable negatively impacting the biodiversity of sensitive macroinvertebrate species. In addition to increased aquatic pollution with organic contaminants, a greater wastewater fraction was accompanied by a slight decrease in oxygen concentration and an increase in salinity. This study highlights the importance of reducing the wastewater-associated impact on surface waters. For aquatic ecosystems in urban areas this would lead to: (i) improvement of the ecological integrity, (ii) reduction of biodiversity loss, and (iii) faster achievement of objectives of legislative requirements, e.g., the European Water Framework Directive

Fragment quality rather than matrix habitat shapes forest regeneration in a South African mosaic-forest landscape

Land-use change and agricultural intensification are responsible for a global decline of forest cover entailing the fragmentation of forests. Landscapes are increasingly shaped by a mosaic of forest fragments within variable matrix habitat. It is thus essential to understand how these habitat alterations influence function and stability of forest ecosystems. However, the complex relationships between anthropogenic disturbance of forests, concurrent species loss and ecosystem functions are not fully clarified yet. In the present thesis, I investigated the impact of structural forest fragment quality and variable matrix habitat on biodiversity and ecological processes of forest regeneration. For this purpose, I conducted three studies in a fragmented mosaic-forest landscape in KwaZulu-Natal, South Africa. In particular, I assessed (1) seed predation by rodents, (2) establishment of woody seedlings and saplings, and (3) leaf damage on woody seedlings and saplings by insects and pathogens in 24 study plots in scarp forest fragments. These fragments were embedded in four variable matrices: two natural, heterogenous (forest, grassland) and two modified, homogenous matrices (eucalypt plantations, sugarcane fields). In the first field study I assessed rodent diversity and conducted seed predation experiments. As a measure for forest fragment quality important for rodents, I estimated herbal ground vegetation cover. For the second study I identified all trees on 500 m², seedlings on 10 m² and saplings on 50 m² per study plot. I categorized trees, seedlings and saplings as either early- or late-successional species. Moreover, I differentiated between seedlings and saplings of external and local origin depending on the presence of conspecific adult tress within fragments to be able to identify potential seed influx by seed dispersers. Additionally, I measured canopy cover, light intensity and vegetation complexity as parameters of forest fragment quality relevant to seedling establishment. In the third study I used beating samples to collect the arthropod community. Furthermore, I estimated proportions of leaf damage by insect herbivory and leaf pathogens on woody seedlings and saplings. I determined tree diversity, canopy cover and vegetation complexity in terms of forest fragment quality. My investigations showed an increase of rodents and seed predation in small forest fragments, potentially caused by enhanced ground vegetation cover. Especially in fragments with sugarcane matrix rodent abundance and seed predation were significantly higher than in fragments with forest matrix. Further, I found reduced seedling and sapling establishment in forest fragments with modified homogenous surroundings. In particular, these fragments consisted of less late-successional species. This could predominantly be ascribed to reduced canopy cover and increased light intensity. However, seed influx occurred in all forest fragments indicating high matrix permeability for seed dispersers. Moreover, forest fragment quality amplified arthropod predator abundance and reduced arthropod herbivore abundance. Fragment quality effects on herbivory were variable. This mismatch might be related to weak trophic interactions. Matrix habitat had merely marginal effects on the investigated factors. Overall, my results illustrate that forest fragment quality as well as matrix habitat have the potential to alter biodiversity and ecological processes of forest regeneration, but effects on the observed processes differed in strength. Yet, I generally found that forest fragment quality appears to be of high relevance for regeneration, indicating its potential for conservation management of the remaining fragments. Further, the rather weak overall effects of matrix habitat indicate a comparable and generally high permeability for the investigated groups of species. This emphasizes the significant value of forest fragments for the connectivity of remaining forests and the conservation of biodiversity and ecological processes at a landscape scale. Nevertheless, conclusions have to be treated with care. Due to the historical natural fragmentation of scarp forests in KwaZulu-Natal, which might have caused a higher robustness of species towards human-induced fragmentation, my findings might not be transferable to other regions. The scarp forest fragments are characterized by high habitat quality for the different species groups. However, potential shifts in the plant community from late- to early-successional species in fragments enclosed by modified matrices might entail unforeseen cascading effects and negative feedback loops within the ecosystem that still need to be examined. Thus, the value of natural forest as a source of propagules and as habitat for forest specialists remains indisputable

Contrasting taxonomic and phylogenetic diversity responses to forest modifications : comparisons of taxa and successive plant life stages in South African scarp forest

The degradation of natural forests to modified forests threatens subtropical and tropical biodiversity worldwide. Yet, species responses to forest modification vary considerably. Furthermore, effects of forest modification can differ, whether with respect to diversity components (taxonomic or phylogenetic) or to local (α-diversity) and regional (β-diversity) spatial scales. This real-world complexity has so far hampered our understanding of subtropical and tropical biodiversity patterns in human-modified forest landscapes. In a subtropical South African forest landscape, we studied the responses of three successive plant life stages (adult trees, saplings, seedlings) and of birds to five different types of forest modification distinguished by the degree of within-forest disturbance and forest loss. Responses of the two taxa differed markedly. Thus, the taxonomic α-diversity of birds was negatively correlated with the diversity of all plant life stages and, contrary to plant diversity, increased with forest disturbance. Conversely, forest disturbance reduced the phylogenetic α-diversity of all plant life stages but not that of birds. Forest loss neither affected taxonomic nor phylogenetic diversity of any taxon. On the regional scale, taxonomic but not phylogenetic β-diversity of both taxa was well predicted by variation in forest disturbance and forest loss. In contrast to adult trees, the phylogenetic diversity of saplings and seedlings showed signs of contemporary environmental filtering. In conclusion, forest modification in this subtropical landscape strongly shaped both local and regional biodiversity but with contrasting outcomes. Phylogenetic diversity of plants may be more threatened than that of mobile species such as birds. The reduced phylogenetic diversity of saplings and seedlings suggests losses in biodiversity that are not visible in adult trees, potentially indicating time-lags and contemporary shifts in forest regeneration. The different responses of taxonomic and phylogenetic diversity to forest modifications imply that biodiversity conservation in this subtropical landscape requires the preservation of natural and modified forests

Contrasting taxonomic and phylogenetic diversity responses to forest modifications: comparisons of taxa and successive plant life stages in South African scarp forest.

The degradation of natural forests to modified forests threatens subtropical and tropical biodiversity worldwide. Yet, species responses to forest modification vary considerably. Furthermore, effects of forest modification can differ, whether with respect to diversity components (taxonomic or phylogenetic) or to local (α-diversity) and regional (β-diversity) spatial scales. This real-world complexity has so far hampered our understanding of subtropical and tropical biodiversity patterns in human-modified forest landscapes. In a subtropical South African forest landscape, we studied the responses of three successive plant life stages (adult trees, saplings, seedlings) and of birds to five different types of forest modification distinguished by the degree of within-forest disturbance and forest loss. Responses of the two taxa differed markedly. Thus, the taxonomic α-diversity of birds was negatively correlated with the diversity of all plant life stages and, contrary to plant diversity, increased with forest disturbance. Conversely, forest disturbance reduced the phylogenetic α-diversity of all plant life stages but not that of birds. Forest loss neither affected taxonomic nor phylogenetic diversity of any taxon. On the regional scale, taxonomic but not phylogenetic β-diversity of both taxa was well predicted by variation in forest disturbance and forest loss. In contrast to adult trees, the phylogenetic diversity of saplings and seedlings showed signs of contemporary environmental filtering. In conclusion, forest modification in this subtropical landscape strongly shaped both local and regional biodiversity but with contrasting outcomes. Phylogenetic diversity of plants may be more threatened than that of mobile species such as birds. The reduced phylogenetic diversity of saplings and seedlings suggests losses in biodiversity that are not visible in adult trees, potentially indicating time-lags and contemporary shifts in forest regeneration. The different responses of taxonomic and phylogenetic diversity to forest modifications imply that biodiversity conservation in this subtropical landscape requires the preservation of natural and modified forests

River systems with respective streams, abbreviations (abbr.), and number of sampling sites (no.).

<p>River systems with respective streams, abbreviations (abbr.), and number of sampling sites (no.).</p

NMDS biplot of taxa and environmental variables.

<p>Displayed are variables with a significant impact (p<0.05) for sampling campaign in spring (A) and autumn (B). HM, components of the principal component analysis (PCA) with heavy metals; OC, components of the PCA with organic contaminants; structure, structural degradation. Spring: two convergent solutions, two dimensions, stress = 0.17; autumn: two convergent solutions, two dimensions, stress = 0.21).</p

Effects of forest disturbance, forest loss, and spatial trends (easting and northing of the study plots) on the taxonomic and phylogenetic α-diversity of species groups.

<p>Separate models were calculated for (a) plants and (b) birds. The coefficients from model averaging of equivalently likely models (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118722#sec002" target="_blank">Methods</a>) are shown. Akaike weights yield information on the relative importance of multiple predictors per model. Statistically significant predictors (p < 0.050) are shown in boldface type. With the exception of life stage, all predictors were Z-transformed to facilitate comparisons of effect sizes.</p><p>^a Note that these are t-values from the single “best” multiple linear regression model; no model averaging was necessary and Z-values are reported for averaged models only.</p><p>Effects of forest disturbance, forest loss, and spatial trends (easting and northing of the study plots) on the taxonomic and phylogenetic α-diversity of species groups.</p

Analyzed contaminants.

<p>Analyzed contaminants.</p

Number of EPT taxa (Ephemeroptera, Plecoptera, Trichoptera) correlating with the first component of the PCA with organic contaminants (OC1).

<p>Displayed are results for sampling campaign in spring (A) and autumn (B). Please note different scaling of y-axes in A and B.</p