Evolutionary stable states in 3D

Although the current literature abounds with ecological and forestry based models of individual tree and forest canopy growth, all such models are notable either for their general omission of any consideration of the carbon costs associated with what are a range of different possible reproductive strategies and/or the glossing over of key ecologically and evolutionary relevant concepts [1]. For example, for a stand of leaf area index greater than 0.5, trees must compete with each other and hence with a growth and life-cycle strategy not necessarily the same (in fact almost certainly different) than if they were to grow in isolation [2]. Moreover, we know that different tree species may take on a wide variety of growth forms (e.g. tropical pioneer trees are often 'umbrella types", whereas late successional trees tend to have a much denser leaf area density within a smaller volume canopy) but with little knowledge of the consequences of these different architectures for light interception or how they link to known variations in physiologically important plant properties such as leaf lifetimes and the growth stage at which the tree first allocates its resources to reproduction rather than new growth [3, 4]. And, reiterating a point already made, how these strategies should differ between an isolated tree vs. the evolutionary stable strategies which must occur when competing with other trees of both the same and different species.

Such questions have traditionally been considered impossibly difficult to answer, with most results to date being limited to 'toy models' where the above processes have been represented in an extremely simplistic manner. Nevertheless, with recent advances in computing power allowing the development of new spatially implicit models of tree carbon acquisition and growth with the development of 3-D functional-structural plant models such as "lignum" (see http://www.metla.fi/metinfo/kasvu/lignum/\\index-en.htm) we are now in a position to make a first attempt to answer these very interesting questions [5, 6].
This PhD project will parameterise the LIGNUM model for a range of tropical trees species of well-defined growth form - using existing and specially collected data from the Caatingas, Brazil. We can then explore how - for both an isolated tree and trees in competition - different growth and reproductive allocation strategies (from seed to grave) should impact on the long-term success of the individual, species and community.

1. Risto Sievanen, Eero Nikinmaa, Pekka Nygren, and Harry Ozier-lafontaine. Sievnen et al. - 2000 - Components of functional-structural tree models.pdf. 57:399-412, 2000.
2. Nathan J.B. Kraft, Renato Valencia, and David D. Ackerly. Functional traits and niche-based tree community assembly in an Amazonian forest. Science, 322(5901):580-582, 2008.
3. W. Koenig and J. M. H. Knops. Scale of mast-seeding and tree-ring growth. Nature, 396(6708):225, 1998.
4. Juan M. Posada, Risto Sievanen, Christian Messier, Jari Perttunen, Eero Nikinmaa, and Martin J. Lechowicz. Contributions of leaf photosynthetic capacity, leaf angle and self-shading to the maximization of net photosynthesis in Acer saccharum: a modelling assessment. Annals of botany, 110(3):731-741, 2012.
5. H. Salminen, H. Saarenmaa, J. Perttunen, R. Sievanen, J. Vakeva, and E. Nikinmaa. Modelling trees using an object-oriented scheme. Mathematical and Computer Modelling, 20(8):49-64, 1994.
6. J. Perttunen, R. Sievanen, E. Nikinmaa, H. Salminen, H. Saarenmaa, and J. Vakeva. LIGNUM: A tree model based on simple structural units. Annals of Botany, 77(1):87-98, 1996.