The importance of early-stage dynamics in rainforests

For 50 years scientists have been monitoring the rainforest trees at Dinden and Lamington National Parks in Queensland.  Established by Prof Joseph Connell in 1963 and funded by USA’s National Science Foundation until 2003 and by TERN’s Long Term Ecosystem Research Network since 2012, the Connell Rainforest Plot Network facilitates important long-term research into the development and life-cycle dynamics of tropical rainforests – home to about half the world’s biodiversity despite covering less than 6% of the Earth’s surface.

The site’s research infrastructure is being used by both Australian and international scientists to conduct research into how our tropical and subtropical rainforests develop and sustain themselves.  Among those using the site are Dr Peter Green of La Trobe University and Prof Kyle Harms of Louisiana State University. Dr Peter Green, LTERN Plot Leader of the Connell Rainforest Plot Network, assumed responsibility for this important research infrastructure after Prof Connell retired. The story of this succession is told in LTERN’s recent publication on insights and lessons from long-term research.

This international research team has recently published 50 years worth of rainforest research from the plot network in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) journal.

Between 1971 and 2013 the study monitored about 8,000 trees of 186 different species and conducted 13 mortality censuses during the 42-year period. The sample of trees included all size classes, from tiny seedlings large canopy trees. As expected the team found that smaller trees die more often than larger ones, but the really interesting result was that their deaths had a major diversifying influence on the whole rainforest.

‘Species richness of the survivors was up to 30% greater than expected in the two smallest size classes, but not greater than expected in the larger size classes,’ write Green and his co-authors.

The paper’s findings support, for the first time, a long-standing paradigm in forest ecology that says that rainforest diversity is driven by early life-cycle dynamics. The processes that occur at the plants’ earliest life cycle stages largely determine forest diversity and the abundance of mature trees down the track. Put simply, what happens now in rainforests will continue to impact on their development for hundreds of years.

Researchers take a break from collecting data on the final day of the fiftieth-anniversary census of the Connell Rainforest Plot Network

Without long-term data and research infrastructure, like what is available to researchers at the Connell Plots, it would be impossible to study the developmental stages of forests and understand how they change over time as a result of natural and human-induced factors.

‘Tropical trees can live for hundreds if not thousands of years, so if we are to understand the development of these trees we need to do very long-term studies to capture the dynamics,’ says Green during a recent interview about the study on ABC Radio National.

The paper’s findings corroborate the importance that tropical ecologists have traditionally assigned to early-stage dynamics, and calls for greater and more widespread inclusion of the smallest size classes into large, plot-based tropical forest dynamics projects worldwide.

Data from the Connell Rainforest Plot Network are accessible via either the Long Term Ecological Research Network (LTERN) data portal or the TERN Data Discovery Portal. A selection of this data is also featured in this month’s Data Update.

Click here or on the image below to listen to the ABC Radio National interview.

Published in TERN newsletter January 2015

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