Brosofske, K.D., J. Chen, R.J. Naiman, and J.F. Franklin. “Harvesting Effects on Microclimate Gradients from Small Streams to Uplands in Western Washington.” Ecological Applications 7 (1997): 1188-1200. (reviewed by Heather Daniel)
Summary:
We have already identified the complex relationships within the Columbia watershed. This study examines in depth the insufficient regulations governing riparian buffer zones. Numerous studies have suggested the importance of riparian buffer areas along stream areas. They provide plant and wildlife habitat as well as protect water quality. Since the 1990's, there have been many regulations at a state level to protect riparian zones to meet environmental protection goals. However, riparian zones differ dramatically in their placement and influence on basin ecology. State regulations often do not take “individual site characteristics” into account. As a result, many scientists disagree with requiring a fixed buffer width (1188). The question becomes how wide should a riparian buffer zone be for a stream?
Past researchers have identified four criteria when assessing the need for the width of riparian buffers.
1. Resource functional value.
2. Adjacent land use
3. Buffer characteristics.
4. Buffer functions desired.
Assessing the ecology of a particular stream and riparian system and examining the ecosystem processes will help to decide how much buffer area is required. Variables such as nutrient cycling, air temperature, humidity, decomposition and solar radiation can influence habitat restoration and management. Too much buffer zone will result in a loss of harvestable timber.
The study examined 15 streams in western Washington and examined microclimate characteristics before and after clear-cutting. The results of the study found that there are statistically significant riparian gradients. Gradient lengths were defined as distances from stream where statistical differences in microclimate values stopped. Riparian areas were detected at 31-47 meters for air and soil temperatures to 31-62 meters for surface temperature and humidity. Deforestation in the sites resulted in increased temperatures and decreased humidity along the gradient. “Changing the microclimate near the stream through harvesting in the upland can alter some functions of the riparian zone, including maintenance of high biodiversity. Amphibians rely on cooler temperatures, higher humidity, and reduced wind velocity of near-stream environments to prevent dehydration and allow respiratory functions (1196).
In addition, the study revealed the strong influence of soil temperature in the surrounding land area on water temperature. This result is probably associated with the streams examined in the study receiving much of the water through groundwater sources rather than from upstream. Small streams in steeply graded forests influenced by water moving through the soil and buffer zones and into the stream.
The discussion at the end of the study examined several solutions as well as a call for more research on riparian buffer zones in steep gradient forests. One solution would encourage selected harvesting rather than clear cutting. Such practices would mitigate factors that affect water quality and microclimate characteristics. In addition, the study called for reassessment of regulations over riparian buffer zones so that these areas are allowed to function as a true buffer zone.
Critique:
I found this document to be very helpful, well written and original. Other scientific papers have suggested that riparian buffer zone regulations are so meager that they are no longer functional as biological, physical and chemical buffers between upland areas (clear-cut areas) and the stream. This paper is the first scientific study I have seen that measures riparian zone gradients. In addition this study examines what factors should be included when assessing riparian buffer zones and riparian regulations.
I was surprised to learn that ground temperature was a greater factor in influencing water temperature than canopy cover over streams. In Western Washington, where many streams receive their water from groundwater sources, higher land temperature directly correlate to higher stream temperatures. I assumed that riparian buffer zones are important because they keep streams cool by shading them. This study shows, at least in some cases, that riparian buffer zones are crucial in keeping the soil itself cool, which in turn influences stream temperature.
This study would be particularly useful to researchers interested in riparian buffer zones and how vital these buffer zones are to maintaining the ecological integrity of a forest.
Robert D. Clark Honors College, University of Oregon
HC 441: Science Colloquium, Columbia River Ecology
Fall term, 2005
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