Towards a unifying theory of vegetation dynamic

The thesis to be argued is that vegetation dynamics is a unified, complex chaotic process, hierarchically unfolding over spatio-temporal scales, where determinism and randomness convolute, shifting in dominance through sequential phases. Conventional theory, known as the Clements-Gleason controversy, views determinism and randomness as mutually exclusive phenomena. My goal is to prove conventional theory wrong.;I use the language of dynamical systems theory to conceptualize vegetation dynamics as an analytical space-time trajectory. The phase space coordinates are derived from compositional data. Two case studies are presented. The first short-term dynamics in an Atlantic heathland recovering from fire and grazing. Dynamics is observed to be transient, beginning with linear determinism and then collapsing into a chaotic nonlinear phase. The stationary Markov chain serves as an excellent reference set for detecting determinism, and the model fits the observed process quite well. However, this simple linear model cannot account for the phase transition defining the natural process.;Interestingly, simulation experiments on the stationary Markov chain with various levels of random perturbation recover the observed two-phase structure surprisingly well. The simulated process is deterministically chaotic, possessing a positive Lyapunov exponent and high fractal dimension. This verifies that passage between dominant determinism and dominant randomness is a distinctly possible event and suggests that the heathland process is highly complex and unpredictable in the long-term.;The second case study of long-term postglacial vegetation dynamics revealed a surprising repetition of the pattern seen in the heathland. The two-phase complex chaotic structure re-emerged, revealing the hierarchical nature of vegetation dynamics.;Against better intuition, apparently random effects can enhance the appearance of determinism through a synergistic accumulation of small feedback effects. Determinism is thus not always dominant, but rather appears as an underlying wave which may at times be overwhelmed by randomness. The fact that determinism and randomness are not easily teased apart suggests that both Clements' and Gleason's views are necessary.;"Chaos" provides the basis for a unified theory of vegetation dynamics. Classical theories are reconciled and in fact reside as special cases.