Overstory #22 - Pioneering Difficult Sites
In past editions of The Overstory we covered observing patterns of nature to help design agroforestry systems (Overstory #9), and using plant succession to make more efficient use of space over time (Overstory #10). This issue uses both concepts of observation of nature and natural succession to pioneer disturbed or severely degraded lands.
"Pioneering" is a natural process that takes place in the first stage of succession after land is disturbed. Natural pioneering begins on land that is newly formed or newly exposed, such as lava flows or land exposed after a glacier retreats, when there is no organic matter, seeds, or vegetation on the site. On these sites, nature has to start from scratch. Pioneering can also be observed following severe man-made or natural disturbances, such as deforestation, fire, landslides, etc.. On these of sites, there are still some (usually minimal) resources such as certain seeds, some organic matter and soil microbes.
To ponder: In which of the following environments could pioneering be observed?
A) recent lava flow
B) abandoned sugarcane land
C) downtown Los Angeles
D) an ancient rainforest
The best place to learn species and techniques you can use to restore your area is to start out by observing how nature pioneers land in your area. Here on the Island of Hawaii (also known as The Volcano Island), we have the privilege of observing first hand the natural processes that occur on new lava flows. Because there are lava flows of many different ages bordering one another, one can observe how bare expanses of lava are converted to a forest. The process of pioneering on lava flows is instructive for pioneering other area.
Lava flows in Hawaii are always colonized by plants (except at extremely high elevations). The kind of plants and length of time in which colonization takes place depends mainly on rainfall and elevation, and, of course, which plants are present in the area. There is a succession of plants involved in the process of forest establishment. Initially without plant cover, the lava field lays exposed to sun and wind, and presents a very hostile environment for most plants. Certain plants such as lichens, ferns and a pioneering native tree species (ohia-lehua) can tolerate these harsh conditions and often appear first on the lava. These early pioneers establish themselves in the most sheltered pockets and crevasses, where they can gather scarce moisture and nutrients.
The early colonists begin to form deposits of organic matter in the lava, laying a foundation for other plants to get a foothold. Organic matter plays an essential role in lava: it is the basis for soil fertility and moisture retention. Soon, a sparse litter layer appears in the protected pockets, consisting of the residues of early pioneers. Over time, other plants will find their way to these fertile niches and become established underneath the cover of the original plants. This represents the beginning of the forest, when plants begin to grow in layers, each succeeding plant making use of the increased fertility and protection offered by earlier pioneers, until a forest is established.
To ponder: If you were working with pioneering a difficult site, where would you start?
A) on the windy, exposed ridges
B) in sheltered depressions/crevasses
The key players in the process of succession described above are pioneering plants. These plants have the ability to establish themselves in harsh, difficult conditions. Pioneers lend shade and fertility to the environment, altering it and ultimately facilitating the establishment of plants that can thrive in the improved conditions. Eventually, as the more tender plants become established and the environment continues to diversify and improve, the pioneers will be succeeded.
Pioneering is a pattern of nature, and it can be aided and accelerated by people to restore productivity to damaged or degraded lands. If you are starting from a cleared or damaged area or young lava flow, you may encourage this process by planting species which are natural pioneers. Such species tend to have common characteristics: they grow rapidly, tolerate poor soils, are often drought tolerant, are relatively short lived, prefer full sun, and can survive in rocky, exposed soils. There are no universal pioneer species--instead of going by a list, we suggest using the species that grow spontaneously in your area.
Pioneer plants change the environment by:
- adding organic matter
- regulating temperatures (less extremes of hot/cold)
- providing shade
- protecting from winds
- breaking up physical barriers to extensive root growth (rock and hard pan)
About the Authors
Kim M. Wilkinson is the Education Director for Permanent Agriculture Resources and editor of The Overstory. She has B.A. degrees in Anthropology and Ecology from Emory University.
Craig R. Elevitch is an agroforestry specialist with more than ten years of public and private sector experience in tropical agroforest and forest management. He has a M.S. degree in Electrical Engineering (Dynamical Systems) from Cornell University.
Related Editions to The Overstory
- The Overstory #70--Rhizosphere
- The Overstory #61--Effects of Trees on Soils
- The Overstory #27--Foster Ecosystems
- The Overstory #20--Five Fertility Principles
- The Overstory #10--Sequential Planting
- The Overstory #8--Mycorrhizae
- The Overstory #4--Nitrogen Fixing Trees--A Brief Introduction