- Elgar original reference
U ultraviolet (UV) radiation. Electromagnetic energy which has a wavelength just beyond the visible light spectrum. Much of the sun’s UV radiation is blocked in the earth’s atmosphere by stratospheric ozone, but a proportion still reaches the earth’s surface. Long-term exposure to UV radiation can reduce immune responses in humans and cause skin cancers and other ailments. Ultraviolet A, B and C radiation have wavelengths of 320-400,280-320 and 200-280 nanometers. uncertainty. A situation where many possible events or outcomes may occur, but it is not possible to assign probabilities to these events in advance. underemployment. Persons who have some form of employment, parttime or seasonal, but who are willing and able to work more. understory. The layer of vegetation made up of shrubs and plants on the forest floor. undervaluation. Placing too low an economic value upon an activity or resource without taking into account all the economic benefits associated with that activity or resource. For example, tropical forests yield not only timber products that tend to be underpriced for institutional reasons, but also yield a variety of non-timber products and other environmental values (such as biodiversity and carbon sequestration) that are not captured in timber prices. unemployment rate. A measure of the number of people out of work but willing to work and looking for work. The unemployment rate is measured as a proportion of the total workforce. UNESCO. See United Nations Educational, Scientijic and Cultural Organization. uneven-aged stand. A forest in which at least three stands are...
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