Editor’s note

The Harper Prize 2015 for the best paper published in Journal of Ecology by a young author has been awarded to Dr. Yuuya Tachiki, currently postdoctoral researcher at Kyushu University in Japan. His paper entitled “A spatially explicit model for flowering time in bamboos: long rhizomes drive the evolution of delayed flowering” provides novel evolutionary insights into the reproductive strategy of clonal plants by using a spatially explicit mathematical model. This paper was also selected as the Editor’s Choice for Issue 103:3 – check out Associate Editor Richard Shefferson’s interesting commentary here.

Yuuya has kindly agreed to describe his research findings and share his view on the topic in the blog post below “Seeking the peculiar flowering habit of bamboo”. The Editors of Journal of Ecology and myself congratulate Yuuya, Winner of the Harper Prize 2015.

Coming soon: Laura Martin and Courtney Stepien, both authors of highly commended papers for the Harper Prize, will also present their study and research findings through video podcasts.

Pierre Mariotte
Blog Editor, Journal of Ecology

Seeking the peculiar flowering habit of bamboo

Study of demography and phenology of perennial plants requires perpetual effort over many plant generations. Bamboo has long fascinated many ecologists with its distinctive flowering habit – most bamboos are monocarpic and thus die after reproducing, but also reproduce vigorously through clonal propagation before flowering. The study of population ecology over the whole life cycle of bamboo requires surprisingly long-term observations due to the long delay before reproduction. Although exact flowering interval is still unknown in many species, it can be longer than 100 years for some species (Numata 1970), with a record of 120 years for madake (Phyllostachys bambusoides) (Kawamura 1927).

In this blog post, I would like to introduce a field site of bamboo research, where great efforts to reveal bamboo’s demography have been invested. It is situated in an old-growth beech forest located at the South of Lake Towada, Akita prefecture in the northern Honshu Island in Japan. The canopy layer is dominated by beech (Fagus crenata) with the understorey covered by the dwarf bamboo (Sasa kurilensis). A flowering of the bamboo took place in 1995 (Makita et al. 1995), but the exact flowering interval is not known. Although flowering and subsequent withering occurred over a broad spatial range, more than 1,000 ha, some patchy populations did not flower and remained as vegetative growth. The area was therefore ideal to observe the effects of bamboo flowering on the forest ecosystem and regeneration processes. Two decades of long-term observation provided information on several topics, including the changes in light availability, the regeneration of tree canopy (Abe et al. 2002), and the interplay among trees, bamboo, and herbivorous rodents (Abe et al. 2001).

The first census of dwarf bamboos in Towada in 1996. Bamboos are all withering as far as we can see with beeches covering the canopy layer, credit: Akifumi Makita.

One of the purposes of long-term observation is to understand the evolutionary significance of the extraordinary reproductive strategy in bamboos from a demographic point of view. “Why bamboos wait so long to flower” is the title of an article by Janzen in 1976. After this monumental paper, many ecologists tackled this topic and proposed many hypotheses to explain the advantage of the bamboo’s strategy. For example, the relationship between fire cycle and flowering interval is one of the most famous hypotheses for tropical bamboo (Keeley & Bond 1999). A game theory model that explains the multiplication of flowering interval was also proposed more recently (Veller et al. 2015).

Yuuya Tachiki during the fieldwork in 2015, credit: Akifumi Makita.

Our study, published in Journal of Ecology, tackles the evolutionary significance of long flowering intervals, but also shows how the geographic cline emerged (Tachiki et al. 2015). Geographic trend in flowering interval, which is short in tropical regions and becomes longer as we move toward north, has long been recognized (Campbell 1985). Interestingly, another correlational geographic tendency has also been reported, in which rhizome extension patterns and resulting spatial arrangements of ramets are also different between tropical and temperate bamboos (Makita 1998). To understand how dispersal traits (i.e. rhizome length, seed dispersal range) affect the evolution of flowering interval, we developed a spatially explicit simulation model. The results of stochastic simulation showed that flowering interval increased with rhizome length but decreased with seed dispersal range. A major cause of this dependence could be intra-genet competition. If a rhizome is short, each genet forms a clumping structure by clonal reproduction. Such structure favours strong intra-genet competition, which can be reduced by early flowering. I believe that our hypothesis on intra-genet competition as mediator of flowering interval should be tested through the study of bamboo demography. This emphasises the importance of long-term field observation and I hope that the findings of our paper will attract more ecologists into the fantastic and unique Asian bamboo forests.

Yuuya Tachiki
Winner of the Harper Prize 2015