By Ranil Senanayake –

There is a mathematical ratio that defines the sustainability of ecosystems, it is called the ratio of biomass to biodiversity (B:B).  Growth towards sustainability means that, if one is increased, there must be a concommitent increase in the other. What is biomass and what is biodiversity?

Biomass is the component of every ecosystem that signifies the action of life on any environmental substrate. The quantity of which is measured by weight and can be presented as three fractions, termed photosynthetic, respiring and inert. Biodiversity or the measure of variability of life at any geographical point, represents the patterns of species wrought in biomass over time

Photosynthetic biomass

The photosynthetic component is that part of the global biomass stock that contains chlorophyll and performs the act of primary production or ecosystem initiation. This is act of capturing the energy of the sun to power the biological processes on the planet and is termed primary productivity. Photosynthetic biomass can be represented by a simple algal cell containing chlorophyll or a complex leaf structure with chlorophyll bearing cells within its matrix. The photosynthetic biomass of cells in a liquid medium, such as marine phytoplankton are the most efficient because they have little respiration costs to maintain structures. This is why the simple cells in the ocean account for 70% of the global Oxygen production. On land, the complex structures of a leaf have a higher respiration cost because the energy demand of a functioning leaf is much greater and therefore use up much of the Oxygen produced  for their own respiration.

Water cleansing is the movement of water through a plant collected  by tree roots in polluted groundwater and released out of its leaves and other aerial parts into the atmosphere as clean water.  Plants cool when they transpire. As plants release water into the atmosphere from their leaves via transpiration, the surrounding air is cooled as water goes from liquid to a vapor form. 

Transpirative cooling  happens when  water that is released by the leaves and moves from a liquidin its gas vapor has a cooling effect on the surrounding air. An individual tree can transpire hundreds of litres of water per day. Transpiring 100 litres is equivalent to a cooling power of 70 kWh. In other words, a large tree provides the cooling effect that 8 room sized air conditioners will produce in a day of operation, a cooling factor of about 1.2 million British thermal units

Respiring Biomass

Plants use the energy gathered by photosynthesis to grow and maintain their physical structures through the process of respiration, in which glucose breaks down in the presence of oxygen to form carbon dioxide and water with the release of energy. All biomass that is not photosynthetic and is participating in the process of life is respiring biomass, Thus the life activity of plant growth, animals and microorganisms are all considered respiring biomass. Respiration is a key factor in accounting for net – primary productivity of a given plant of land.

Inert Biomass

Inert biomass is that portion of biomass that does not actively participate in electron transfer between molecules and are composed of extra cellular polymeric substances (EPS), A wide range of microorganisms produce EPS, a mix of highly hydrated polymers that are mainly comprised of polysaccharides, proteins and DNA. Inert biomass is commonly seen in anoxic, wet ecosystems such as peat bogs and is the major part of the long-lived fraction of Soil Organic Matter (SOM) found in undisturbed forests and other mature ecosystems.

Biodiversity

Biodiversity is often expressed as ‘the measure of the variability of living organisms at any spatio-temporal point’, i.e. the number of different species at any place at any given time. It does not mean wild, endemic, rare or even native, it is merely a measure of the diversity of life, expressed as Linnean species, measured at any place. This measure has various meanings, from indicating a potential for conservation to indicating changes in the environment.

But in considering the management of biodiversity on any landscape, it has to be evaluated by the stated goals for that land. If conservation is the goal, exotic species in native ecosystems are an anathema and need to be removed. If production or human habitation is the goal, exotic species are an important component of the local biodiversity and must be counted. Therefore, biodiversity on any landscape must be measured as two distinct states, natural and anthropogenic

Natural biodiversity exists as a product of a long history of interactions between organisms, landscape and climate at any given place. It is high in some ecosystems and low in others.  The natural biodiversity of stable ecosystems provide the indicators and measurements that define the sustainable state for that ecosystem. A loss of biodiversity, means a loss of the variety of organisms that comprise that ecosystem and suggests disturbance and unstable states.

Anthropogenic ecosystems are those influenced by humans in such a manner that their natural evolutionary processes are massively disrupted. Most rural land other than natural ecosystems are regions where exotic species replace native species to some degree. However all agricultural and other anthropogenic land use systems, also have a biodiversity measure or value as represented by its biological components. If the frequency or intensity of disturbance in any area is high there is a loss of biodiversity. If the frequency and intensity of disturbance is low there is a corresponding gain in biodiversity. This gain is obtained through a hybrid population of natural and exotic organisms.

Such an understanding suggests that the relationship between biodiversity and biomass is an important feature in defining the stability of any ecosystem. If the biomass of an area increases, there should be an corresponding increase in the biodiversity within it. This simple B:B ratio can help land managers evaluate the sustainability  potential in their designs.