In this post, Svenja Kleinschmidt talks about her recent paper, Potential growth more than functional traits explain successional habitat filtering in rainforest trees.

About the paper

In tropical forest ecology, the relationships between succession, growth rates and several functional traits appear to be well-established. Commonly studied functional traits in tree species, like wood density or specific leaf area, are easy to measure and often data is already available. This may create incentives to primarily investigate relationships with these easily measurable traits as proxies to describe differences in the ecology of species. Although, many studies showed that these correlations sometimes are weak and not always plausible.

We examined the relationships between leaf and wood traits, growth and successional habitat, and asked if growth and habitat are related because both are driven by a similar set of traits, or if growth is the main trait explaining habitat, while relationships with other traits are indirect.

Our results indicate that correlations between habitat and leaf or wood functional traits can be indirect and may suggest misleading interpretations. Potential growth rate appears to be the most important successional habitat filter, while traits such as wood density are linked to habitat indirectly, via growth rates. We suggest that analysing traits that are more directly functional, including shade tolerance, drought resistance and growth rates, in the case of the successional gradient, might be more informative and would improve our understanding of what ecological strategies and niche specialization of hyperdiverse tree communities in tropical forests are based on, although such data is often more laborious to obtain.

About the research

The study was conducted as part of a reforestation project in Costa Rica, where more than 100 local tree species were planted under uniform light conditions. The planting design aims to serve for long-term studies contributing to local biodiversity conservation. We used exclusively seeds and seedlings collected from the local forest and grown in the project’s nursery. The plots were set up as a long-term study on the effect of variable functional diversity at constant species diversity on processes and ecosystem functions. However, during the first years of the trees’ growth no plot effects were to be expected, and so I mainly analysed differences in growth rates among species and relationship with functional traits. This had been done before, but we combined our data with information on successional habitat preference to better understand what makes a tree a pioneer or late successional species.

Regeneration of tropical forests, whether by active reforestation or natural succession, is of huge importance for conservation and could make an important contribution to carbon sequestration. I think that a sound understanding of how succession works and of the role of the many different trees is very important here.

Personally, I was particularly surprised by the growth rate of some tree species. I could practically watch the trees grow. On the other hand, the regular maintenance of the large area was difficult and labour-intensive. The grass and understory vegetation grew very quickly and had to be cleared regularly to avoid competition and shading of the juvenile trees.

About the author

When I was about to finish my bachelor’s degree, I decided to complete my work placement, which was a compulsory part of my studies, abroad. First, I wanted to go to the Netherlands. I have been to the Netherlands a few times and really liked it. But then I wondered why I shouldn’t complete my internship in a country I didn’t know – something far away. I chose Costa Rica.

In the Tropical Research Station La Gamba, I worked for a reforestation project financed by the NGO ‘Regenwald der Österreicher’. My family and friends watched me for 3 months sunburned, terribly bitten all over and sweaty, planting and measuring trees in an unshaded pasture at about 35°C. Few have been able to understand why I extended my stay by another 2 months. – The experience was unique and probably only those who experience this fascination with ecological research themselves will understand me. – For my master’s thesis, I had the opportunity to return several times to Costa Rica to continue the research with Peter Hietz and the priceless help of many students, without whom this work would not have been possible. If you ask me about the best thing for me of being an ecologist, then it’s about the fascination of better understanding some little pieces of the world that surrounds us, to learn countless new things, such as using a machete, categorize one hundred tree species you’ve never seen before, manage data collection and statistical analysis and – most importantly – work with a great team of highly motivated people who share your passion.

Read the paper here and the free plain language summary here.