9 2.1 Why Tree Height?
Forests of the Pacific Northwest can produce very tall trees. Fertile soils, a mild climate, and a long growing season west of the Cascade Mountains yield old-growth Douglas-fir (Pseudotsuga menziesii) forests that rise 250 feet in the air (Franklin 1988). East of the Cascades, ponderosa pines (Pinus ponderosa) are no less impressive, reaching over 150 feet (Burns and Honkala 1990). Tree height is an important ecological trait, as the competition for sunlight determines which trees flourish, and which trees become suppressed and eventually die out. It also influences shade in streams, changes in understory vegetation over time and cover for wildlife. As such, it is an important part of many natural resource data collections.
Here are some examples of where height measurements are used:
- Stand exams. Stand exams are conducted to characterize forest vegetation. They provide basic, baseline data on species composition, forest structure, and condition for a variety of stand management uses, ranging from wildlife habitat to timber production.
- Riparian/stream surveys. Height of the vegetation and physical landforms (such as bluffs) along streams can be used to predict the amount of shade a stream will receive throughout the day and year. This in turn, can determine the width of streamside vegetation buffers reserved during any logging activity.
- Nesting sites. Some birds and cavity nesters prefer to nest and/or feed at particular heights in the forest canopy. Assessing tree and snag heights can help determine nesting suitability of forest stands.
- Site quality. Tree height is the most widely used indicator of a site’s ability to grow trees.
- Timber cruises. Forest inventories that determine the volume and value of wood require a height measurement – the most important factor for estimating wood volume.