Plant Succession: How Mother Nature Rearranges Her Landscape, and How We Are Involved
Think about a volcano emerging from the surface of the ocean and forming a new island, new land. At first, there is no life of any kind on the island. Eventually, however, after the lava has cooled, there may be some bacteria and fungi begin to grow on the lava at the edge of the water, and these microorganisms begin a very long, slow process of breaking down the rock. Then, algae can begin to colonize the rocks, growing on the decomposed rock material.
As the algae and other lower forms of life grow, die and decay, organic matter is added to the decomposed rock, and we have the beginnings of soil. This is followed by the higher plants, some arriving at the island by sea, some in bird droppings. As the amount of vegetation increases, insects blown by the wind and other small animals arriving on drifting seaweed begin to colonize the island. The pace of change increases as larger and larger plants and animals become established and the amount of soil increases, and eventually you have Hawaii, or Trinidad or Puerto Rico, with trees and jungles.
This process is called “plant succession,” and it has gone on and continues to go on everywhere. Plant succession is the natural process by which one group of plants succeeds or takes over from another group. When this process stops and the plant composition remains stable, it is referred to as the climax plant community. The climax plant community will continue until some major event (climate change or major human activity) occurs in the environment that changes which plant(s) are fa-vored over others. If this occurs, plant succession will begin again and may take the community in a different direction.
Before Europeans arrived in large numbers in the Hill Country, we had more open grasslands with fewer trees than we do now. The grasslands were made up of a larger percentage of taller grasses such as little bluestem, big bluestem, yellow indiangrass and switchgrass, and these grasses were grazed by large herds of bison on a regular, but infrequent, basis. These grasslands also burned every few years, caused by either lightning or the Native Americans. This was the climax plant community prior to the early 1800s.
When the European settlers moved in, they brought livestock with them which grazed the same area constantly, thus greatly reducing the amount and species composition of the grass, and they fought fires with all their might. This changed the area from one where the grasses were denser and larger and burned every few years, which kept the numbers of trees and shrubs controlled, to one of smaller, less dense grasses with fewer fires, thus allowing woody plants to increase in number. This human-induced change in the environment caused plant succession to take the Hill Country from one with many areas of open grasslands to more savanna-like areas with significant woody plant populations.
But it turns out that cedar is more capable of expanding into this new environment than hardwoods are, and so the percentage of cedar has increased, relative to hardwoods. And to exacerbate things further, in more recent times, say the 1960s to the present, the significant increase in white-tailed deer populations, again caused by man’s activities, has shifted the plant succession yet again to slow the population growth of hardwoods, but allow the cedar to increase largely unchecked, thus our current cedar overabundance.
But we have found that the cheapest and most effective way to keep cedar under control, once an area has been cleared of the larger bushes, is to conduct periodic (every five-10 years) prescribed burns. Prescribed burns are very effective in killing small (3’ or less) cedar bushes and keeping once-cleared areas free of cedar, and to a lesser extent, hardwoods also.
In other words, man’s activities caused the encroachment of cedar in the first place by altering the environment, allowing plant succession to take the landscape in a different direction, and now we are reversing the process by reintroducing fire where it had once been largely eliminated and again allowing plant succession to change the landscape more to our liking.
You may argue whether all of this is good, bad, or inevitable, but it does tell us a lot about how to manage land to achieve our desired result. Or as Aldo Leopold famously observed, habitat “can be restored by the creative use of the same tools which have heretofore destroyed it-ax, cow, plow, fire and gun.”
The main point being that this is just one example of where man can work with Mother Nature to achieve our desired result, as long as we know what we are doing!
Until next time…