In a survey of 112 canopy researchers, examples of problems cited include: bias in the selection of study species or sampling locations; difficulties in obtaining adequate replication; problems in collecting data in a three-dimensional, complex environment; logistical constraints in moving between canopy sampling points; and, disturbance, sometimes including interference of the object being studied (i.e., `demonic intrusion') caused by access. Designing experimental protocols for work in the canopy requires at the outset the allocation of time and resources for anticipating and overcoming the particular sampling problems associated with the work.
This paper present includes a study of 100 trees to compare this measurement method to four alternatives�two field instruments, ocular estimates, and regression models. Using the taping method as the standard of comparison, accuracy of the tested alternatives was adequate for softwood species, but short of the specified measurement quality objective for estimating the mean crown diameter of hardwoods. Due to savings in field costs, ocular estimation and regression models were the best alternatives to direct measurement with logger's tapes (from abstract).
With the increased use of variables such as canopy cover, phytosynthetically active radiation (PAR) and overstorey leaf area index (LAI) in forestry research.
Tree crown shapes are integral to a variety of models because volume estimates, surface area estimates, or various types of two dimensional crown projections are directly related to crown shape.
This paper presents a new method for assessing crown radii at different tree heights, using a simple mechanical device, the crown window. It described briefly about the manufacturing of device and the equipment is more useful than other sophisticated techniques, such as digital photo analysis or laser based instruments in estimating crown radii and their corresponding heights with acceptable accuracy.
This paper presents a crown cover chart for estimating the crown coverage of open-grown oaks and hickories in oak savannas and similar plant communities.
Tree crown information contributes to the investigation of several key forest ecosystem attributes: biodiversity, productivity, sustainability, aesthetics, forest environment, and wildlife. It describe about how crown are measured and why crown are measured.
The estimation of vegetation cover or canopy closure can be difficult and costly. The utilization of a vertical sampling tool, such as a canopy densitometer, along linear transects provides a reasonable means of generating reliable cover estimates. Estimates represent both the horizontal and vertical diversity of sample areas and may represent description of species composition, size, and canopy structure as well as non-tree characteristics, such as ground surface condition and shrub or herbaceous cover.
dernière mise à jour: lundi 15 novembre 2004