Understanding: PLANT SUCCESSION

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duane
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Understanding: PLANT SUCCESSION

Postby duane » Sun Dec 19, 2010 4:10 pm

This is the second in a series of articles written by Ian Sutton.

Co-operation is the key: PLANT SUCCESSION

Once you understand the seriousness of the situation, it becomes necessary to begin co-operating, not only with each other, but with the environment. Nature is a self repairing system that naturally moves towards equilibrium. The current problem is that we have vastly increased the amount of energy entering the system, disrupting the feedback loop network, and driving the cycles away from equilibrium.

Remember, everything is energy, so inputs of all kinds constitutes an energy source. Whenever we create order in a system it requires the input of energy. Equilibrium is maximum disorder or infinite possibilities, and all systems move away from disorder when there is an energy imbalance. For a system to find balance again it must re-establish a high degree of disorder.

When we look at the environment, what constitutes disorder? Bio- Diversity creates disorder. The higher the level of diversity, the greater the disorder, and what you should all understand by now is that there is function in the disorder, complexity allows energy to flow unrestricted.

How can we work with the natural process of systems moving towards equilibrium? We must firstly reduce our energy inputs entering the systems. Our human footprint is very heavy and we need to begin treading lightly on the earth. Many of these issues can be effectively addressed through holistic approaches to sustainable development.

Farming is perhaps the single most destructive practice we carry out. Current methods require the removal of all bio-diversity over large areas of land, to create an ordered system (monoculture). The resulting loss of fertility and increasing pest and disease problems have lead to the increasing use of chemical inputs. This input of excess energy then devastates the soil biology further, creating more pestilence and plague.

Irrigation and storm water runoff from farmlands poison our water systems with excessive salts/nutrients and chemicals, wiping out much of the diversity within our rivers and streams. Tilling the ground destroys soil structure and leads to the loss of organic matter, this intern leads to the further loss of fertility and the loss of our top soils.

With vastly reduces vegetation cover, flooding rains become destructive, and scour deep channels in our hills and flood plains. Once the flooding has past, these channels left behind act like a drainage system carrying all of our water to the ocean, and in the process draining the landscape of its precious ground tables. Modern farming practices have input massive amounts of energy into the natural system, resulting in the destruction of the landscape functions and the desertification of much of our once fertile lands.

I will look at farming in a future paper, but keep in mind every landscape function you are learning about needs to be incorporated into the management system of any farm. Let’s just focus on regenerating natural systems for the moment.
Arguably the largest energy increase mans impact has created is the input of solar radiation. We have cleared much of the landscape and have vastly increased the suns intensity reaching our soils. Where before the plants insulated the landscape, and shaded the soils, the sun now bakes them dry and heats the air above them. Between the ultra violet light and the lack of moisture the soil diversity is decimated.

If diversity decreases within the soil then energy cannot flow unrestricted to the plants. The result of infertile soils is an energy imbalance causing plant communities, the first trophic level, to move away from equilibrium, impacting on all trophic levels above them. If the landscape functions have broken down and there is no secondary feedback loops functioning, then the end result will be a desert.

So how do we get plant communities to begin their natural succession process back towards equilibrium? We begin by reducing the amount of solar energy entering the system. This can be done using a combination of rehydrating the landscape and layering. I will do a future paper on rehydrating the landscape but for now I will focus on using plant successions to develop layering.

There is a natural succession process that plant communities cycle through. When soils are impacted by high energy inputs such as wind and sun, this evaporates soil moisture and decreases fertility. Areas such as exposed ridges, sand dunes and headlands, and further afield the semi arid and arid zones are all dominated by heath scrub and or dry grassland communities. If water availability drops, these systems become deserts.

As we have drained the landscape and baked it dry in the sun, heath communities and other dry plant communities, such as woodlands and dry forests have greatly expanded their territories. Much of what was wetlands, rainforest and wet forests have become dry forests and even woodlands. Our impact on the environment has driven the plant succession process away from equilibrium, towards desertification, and in the process has enabled fire to rampage out of control.

If the energy imbalance is a negative one, in other words water in the soil freezers for long periods of time, tundra plant communities will dominate. Essentially heath and tundra plant communities are the same and both are adapted to low fertility, exposed conditions and lack of available water. In cold climates, removing the insulating vegetation layers sends the succession process towards an ice desert.

At the other end of the scale is the rainforests, plant communities that can only dominate in ideal conditions with optimum water availability and fertility. In these conditions maximum bio-diversity within the soil can develop, allowing energy to flow unrestricted between the trophic layers of the plants and soil biota. This allows maximum diversity to also develop within the plant community. If water availability increases further, then a wet grassland / wetland system will result.
The natural plant succession from the least fertile, driest soils, to the most fertile, moist soils, is; 1- HEATH SCRUB / DRY GRASSLANDS: Single layered systems, least bio-diversity, highest number of repair plants, 2- WOODLANDS: two layered systems, 3- DRY FORESTS: Three layered systems, 4- WET FORESTS: four layered system, 5- RAINFORESTS: five layered systems, most bio-diversity, lowest number of repair plants.

All these plant communities exist in different microclimates throughout the central coast. Our temperate climate, unique geological features and proximity to the ocean create dramatic variations in the amount of available water in our soils. Exposure to wind, aspect, degree of slope, height on slope and distance from the ocean are all determining factors in creating our microclimates. The result is a mosaic patch work of different plant communities, giving the central coast region one of the highest levels of diversity left in the country. This makes our region one of high priority when it comes to diversity protection.

Weeds can encroach into any of the succession stages, but only if there has been a disturbance in the layers of the system. Weeds are categorised as primary succession plants and are the first repair plants to re-establish in a disturbed ecosystem. They are the secondary feedback loop that absorbs some of the excess available energy, increased sun intensity, and converts it into bio-mass. It is this efficient conversion of solar energy into chemical energy that gives weeds their ability to quickly re-build soil fertility.

Primary succession plants are opportunist, fast growing ,short lived and have effective distribution mechanism that allow them to spread quickly. They will also have specialised root systems and other adaptation that enable them to grow well in poor conditions. Their function is to cover the soil quickly by creating a layer of vegetation, reducing sun intensity, trapping humidity and allowing soil moisture and fertility to begin to rebuild.

An equation Peter Andrews taught me in order to determine the effectiveness of a repair plant, is to, calculate the green surface area over time and space. In other words the green surface area of the plant is- divided by-(the time the plant takes to mature- times- the space the plant takes up at ground level). The weed that has the largest green surface area, grows the quickest and takes up the least amount of space will be the most effective repair plant.

The large green surface area can convert more of the suns energy into bio-mass. The short life cycle means that the plant can quickly pass on that bio-mass to the soil biota, when it dies and decomposes. This enabling the soil biology to more quickly rebuild in diversity, and repair the soil structure. The smaller the area the plant takes up at the soil surface the greater the number of plants can grow in any one place and the more effective the repair process becomes.

By observing weeds we can come to understand the natural repair process that plants facilitate in the landscape. Developing layers of vegetation quickly, using specialised repair plants. At no point within natural cycles is any plant removed from the system until their function has been completed.

We need to recognise that weeds are not the problem and in fact are part of the solution. They are simply the repair mechanisms, the secondary feedback loop, that has been initiated by our impact on the landscape. Where ever human impact contributes a high energy input into an ecosystem the weed succession will simply continue to dominate in a desperate attempt to correct the imbalance.

Landscape repair will only become effective when we begin co-operating with the weeds. This will allow the network of secondary feedback loops to begin to re-establish and initiate the natural plant succession process back towards layering and diversity.

As the soil moisture and fertility increases, due to the weeds, the plant communities above increase in both layering and diversity. As the layering and diversity increases within the plant community, the soil biota below increases in both layering and diversity. If the microclimate is suitable, this feedback loop will drive the plant succession all the way back to a rainforest.

So vegetation layering is one of the keys to landscape function. It reduces the amount of solar radiation entering the system, by shading and insulating the soil. It converts much of the excess available solar energy into bio-mass for distribution throughout the food web. It traps lost soil moisture as humidity within the layers of vegetation, which in the cool of the evening condenses and returns to the soil (micro water cycle). And it also protects the soil from erosion.
However, probably the most important function of vegetation is its moderation of the climate. Plants are not only responsible for filtering CO2 out of the atmosphere, they also manage the hydrological systems on land, and are influential in developing and maintaining both ground and surface water systems. The transpiration of water from their leaves provides cool moist air above the landscape, and as this air contracts it draws low pressure systems in off the ocean, bringing more regular and less extreme rain events to the inland.

I will discuss these last two points in my next paper because I am going to attempt to explain the most important landscape function of all, the hydrological system. This is what I have learnt most about from Peter Andrews, and this will be my first attempt to explain it. The process of rehydrating the landscape is the key to both landscape repair and sustainable farming practices, and because of this I can’t really go into any more details on either point until you understand about water.


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Ian Sutton

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