Pit-and-mound Topography Fosters Biodiversity

a forest floor with large fir trees is dappled with sunlight

Biological Strategy

Douglas fir forests

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Image: Patrick Alexander / Flickr / CC BY - Creative Commons Attribution alone

Manage Disturbance in a Community

When environmental conditions change, they can disrupt an ecosystem’s equilibrium. Excessive rain can cause flooding and drought can cause forest fires. An ecosystem must be resilient to such disturbances. Disturbances are unpredictable in location, size, and intensity, so ecosystems must be able to regrow and must have a variety of duplicate forms, processes, or systems that are dispersed in location. For example, a forest ecosystem can recover from fire because diverse organisms play different roles in different ways and in different locations. Many organisms can resprout or grow from seeds triggered by fire, and their dispersed distribution ensures that an entire population isn’t decimated. Though the recovered ecosystem may look totally different from the pre-fire one, the ecosystem as a whole remains healthy.

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Maintain Biodiversity

The greater the amount of genetic and species variation in an ecosystem, the more resilient that ecosystem is to disturbances. Variation in ecosystems across the Earth also contributes to the Earth’s resilience to unpredictable changes. This variation is called biodiversity. Because living systems compete with each other for scarce resources, maintaining biodiversity involves creating conditions for a large variety of species to successfully co-occur and reproduce. For example, within a wetland, there are different vegetation types. This diversity results in a complex mosaic of microenvironments as the vegetation types alter air flows, light regimes, and water temperatures and chemistry. Because organisms vary in their ideal environmental conditions, these micro-environments increase the diversity of plants in the wetland. In turn, having a wetland in an otherwise dry area increases biodiversity at an even larger scale.

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Conifers and Others (Pines, Spruce, Gingko)

Clade Gymnosperms (“naked seeds“): Conifers, cycads, Gingko, gnetophytes

There are approximately 1,000 known species of Gymnosperms. These include well known needle-bearing plants like pines, firs, and spruce, as well as some with broad leaves like the Gingko and the gnetophytes. Instead of flowers, gymnosperms produce unenclosed (“naked”)seeds exposed on the surface of cone scales. Economically, conifers make up 45 percent of the world’s lumber production. The first gymnosperms evolved over 390 million years ago in the Paleozoic Era and dominated landscapes for a quarter of a billion years before the evolution and diversification of flowering plants.

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The pit-and-mound surface microtopography of the forest floor in Douglas fir forests helps create and maintain diversity by creating microhabitats.

“When you look closely at the surface of the forest floor, it becomes apparent that there is no such thing as a smooth slope. The forest floor is roughened by the scattered pieces and stumps of collapsed snags and by whole fallen trees, their uprooted butts, and the pits and mounds left after their uprooting. Living trees roughen the surface of the forest floor by sending roots outward along slopes, often near the litter layer. Tree trunks also distort the surface by sloughing bark and by arresting creeping soil at their bases…Of all of the factors that affect the soil of the forest near the spring, surface microtopography, particularly the pit-and-mound topography, is the most striking. The effects of this topography have a major influence on creating and maintaining species richness of the herbaceous understory and on the success of tree regeneration. Pit-and-mound topography, for example, has been, is, and will be a major factor in mixing the soil of the forest floor as the forest evolves through time.” (Maser 1989:95)

Last Updated August 18, 2016

References

Book

Forest Primeval: The Natural History of an Ancient Forest

Sierra Club Books | 01/02/2001 | Chris Maser

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