Topics for student research

Below I briefly describe a few topics for student research. Some of the student projects include field work  in Singapore. Others consist of data analyses using data from long-term research on the dynamics of secondary forests in Panama and elsewhere (see page ‘Research‘). To take on one of the latter projects, you should have some background in statistical analyses and be interested in writing a publication. These topics are by no means the only possibilities. Come talk with me to disscuss other ideas or to explain me your own ideas.

Topic 1 | Plant functional traits

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Description | A plant functional trait is a well-defined property of a plant that can be measured from an individual and that can be used comparatively across species. Examples of such traits are specific leaf area, leaf toughness, wood density and seed mass. Functional traits tell us something about the ecological strategies of species, i.e., how they acquire and utilize resources to grow, reproduce and disperse, and defend against or tolerate herbivores, pathogens, and mechanical damage. These ecological strategies are governed by fundamental trade-offs in the resource economics of plants. The best-understood leaf-level trade-off is the so-called leaf economic spectrum (LES), which runs from cheap-to-construct and short-lived leaves that maximize resource capture rate to expensive-to-construct leaves that tolerate stress and better conserve acquired resources. At our lab, we collect leaf traits for a high number of regional plant species to (1) better understand the trade-offs that govern the relationships between traits and (2) to study how different plant communities re-assemble after disturbance.

The study on variation in leaf trait relationships offers various options for student projects.  For example, in tropical forests, traits are overwhelmingly collected from trees and (to a much lesser extent) lianas. Other growth forms such as forbs, ferns and palms, are largely ignored. However, functional trait relationships are not necessarily similar among species. For one, differences in whole-plant morphology may impose specific constraints on leaf-level attributes and how they relate. Within this context, you could look at trait variation in a specific plant group, or contrast two specific groups. You could also zoom in on specific traits and ecological processes, such as leaf toughness and herbivory pressure during different phases of leaf development. If you are interested, let me know and we can discuss ideas.

Activities | (1) Field work: Collecting data in gardens and forests across Singapore. (2) Lab work: Processing of leaf samples. (3) Data analysis.

Duration | Summer internship (3 months), independent research project (1 semester) or capstone/honours thesis (2 semesters)

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Topic 2 | Forest and light

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Description | Light is one of the main limiting factor for plant growth in forest understories.  In mature tropical forests, light availability at the forest floor is typically < 5% and complex interactions among canopy trees and understory vegetation cause significant spatial heterogeneity of the light environment. In forest succession, it has been shown that average light levels in the understory decline rapidly and may reach mature forest values within a decade. This change in light environment is one of the principle drivers of succesional species turnover. It is less clear, however, how spatial patterns in light environment change during succession and if these changes can be related to canopy structure, understory density or an interaction between both.

You can address this question using available data on light levels at 0.5, 3.0 and 4.5 meters above ground level in a series of plots in humid tropical forests of 1-15 years old. We also collected data on the size of all trees in these plots. This data provides an unique opportunity to assess the influence of understory vegetation on light availability in the understory and how this changes during the first years of succession.

Another option is to do a field study in which you investigate the effects of successional forest age, wind disturbance, understory vegetation and the interaction between these variables on variation in light availability across a forested landscape in Singapore. An additional option is to focus on the effects of specific species or plant groups such as large-leaved forbs on the micro-environment below their canopies.

Activities | (1) Field work (first option): taking hemispherical photographs and PAR sensor readings in different forest patches across Singapore. (2) Lab work: Processing and analysis of hemispherical photographs. (3) Data analysis.

Duration | Summer internship (3 months), independent research project (1 semester) or capstone / honors project (2 semesters)

Topic 3 | Secondary forest succession and dynamics

Description | The Secondary Forest Dynamics study in the Panama Canal Watershed  monitors changes in the community structure of 54 0-35 year old secondary forests that were randomly selected from across the Agua Salud landscape. Plots were established in 2008-2009 and annually censused for tree growth, mortality and recruitment. Since 2010, we also monitor seedling recruitment and mortality. See this article for more information. We have also data on light, soil moisture and nutrients in all plots; plant functional traits of over 80% of the trees; and vegetation structure and composition of vegetation along streams and in pastures.

This study design allows us to investigate factors and processes that drive predictability and variation in successional dynamics on both local and landscape scales. Recently, different publications have examined this on the scale of individual plots (e.g., here). However, often the focus is the conservation or restoration of diversity and ecosystem services in human-modified landscapes, in which case we rather need to understand the predictability and uncertainty of successional trajectories on the scale of the whole landscape.  So you could ask (1) how predictable successional dynamics is on landscape scale?

Other examples of questions you could focus on are: (2) What are the strongest demographic drivers (growth, mortality or recruitment) of succesional change in the community structure of secondary forests? (3) Does variation in functional composition and/or diversity affect the productivity of young secondary forests? (4) Time-series of secondary forest dynamics show that chronosequences do a poor job in predicting successional trajectories on individual plot level, but is this also true on landscape-level? To what extent does the answer depend on the response variable (e.g., species diversity or biomass)? (5) How is diversity of the secondary forests of the Agua Salud landscapes partitioned at multiple scales (within-plot, site, landscape) and does this change during succession? (6) Is the composition of the seedling community a good predictor of tree recruitment later in succession? (7) Is there a tradeoff between maximum growth and the sensitivity of trees to neighborhood competition?

Activities | (1) Field work: none. (2) Lab work: none. (3) Data analysis: a lot.

Duration | Independent research project (1 semester) or capstone / honors project (2 semesters)

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Topic 4 | Trees and shade

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Description | Singapore is often called the ‘Garden City’, thanks to a decades-long efforts to greening the city’s landscape through a network of parks and gardens, park connectors, tree-lined roads, and other types of greenery. Street trees may have all kinds of beneficial effects on the urban environment in tropical cities. One obvious example is that they provide shade for the pedestrian, thus creating a more comfortable walking environment. Assessing the effect of street plantings on physical comfort levels are of special interest in the context of the park connectors, that are set up to offer opportunities for recreation and leisure. Characteristics of the street, the urban settings and the planting will influence the microclimate, and the effects of each will differ depending on the weather conditions and time of the day.

In our lab, we are interested in the role of trees and differences among tree species. The size and intensity of a tree’s shadow depends the height of the tree and on the size and foliage density of its crown. In this study, you would explore ways to quantify and relate measurements of shade, temperature and humidity below tree crowns – which directly influence physical comfort – to the species, size and other characteristic of tree species that are commonly planted along streets and in parks in Singapore, in interaction with easy-to-measure characteristics of the urban surroundings.

Activities| (1) Field work in Singapore: Measuring light, temperature and humidity, taking hemispherical photographs below street trees , measuring tree size and crown dimensions of street trees; (2)  Lab work: Processing and analysis of hemispherical photographs. (3) Data analysis.

Duration | Summer internship (3 months) or independent research project (1 semester)

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