The Leaf as a Sustainable and Renewable System

Leaves play a critical role in the Earth's biosphere, regulating weather, renewing mineral nutrients and maintaining biotic processes to support both flora and fauna. Leaves also form an important resource for consumers. Together, plant hosts and consumers represent complex adaptive selection. We used systems dynamic and holon models to understand the ability of the leaf to meet both host plant and host consumer criteria resulting in socio-ecological system sustainability. We first identified dynamic cycles facilitated by the leaf as a component of both plant and consumer systems. Each of the variables in these loops serves a critical role in the production and function of the leaf, recycling energy and matter through plant and consumer systems. Control feedback balances the system, optimizing opposing selective forces to meet criteria for viability of host plants and usability by consumers, which return benefits through various services. We then examine the organization of the leaf host system, revealing mutually closed sub-systems corresponding to a definition of ‘component life’. We thus show the leaf host relation to be a theoretically ‘whole’ system having positive, sustainable impacts on biomass, food, energy, etc. These results may inform more general sustainability assessments by offering a mathematical definition of sustainability as emergent, cyclical organization in ecosystems.