Growth and survival of plants in patchy environments
Plants, as sessile organisms, have evolved many strategies to survive in a changing environment. Three key phenomena are considered in the present study: (1) morphological changes associated with C allocation to roots and shoots in favour of the most limiting resource; (2) differential C allocation to root pieces growing in relatively high nutrient patches and (3) physiological adjustment to the nutrient environment by up- or down regulating specific nutrient uptake rates. Plants exist as individuals within populations or communities. The aim of this study was to explore some of the dynamics, with respect to the above phenomena, that even-aged monocultures display. To this end, an individual-based modelling approach was developed (Chapter 2). A Moore neighbourhood cellular automation was designed so that each plant had nine roots (eight in its eight neighbouring cells and one in the central cell below the shoot). Roots could deplete N and P from neighbouring cells. A diffusion term was introduced to allow the movement of N and P between cells following a concentration gradient. To avoid edge effects, a 30 x 30 cell array was implemented with a toroidal configuration. As well as homogenous nutrient distribution, heterogeneity was introduced into the array at fine, medium or coarse grain. The total N available within the array (either high or low) remained constant but was distributed differently according to the grain of heterogeneity. The individual unit of the cellular automation was a single plant growth model (SPM) that incorporates the three phenomena listed above (Chapter 3). Plants (SPM) were randomly allocated to cells within the array from a Gaussian distribution of initial plant weights. Each plant could grow and interact with its eight immediate neighbours. The SPM growth followed an expo-logistic curve.