Forest canopy research: sampling problems and some solutions

Conducting research in forest canopies is accompanied by both opportunities and difficulties. Opportunities occur because the canopy is important in overall forest structure and function, for example in containing a high proportion of species richness, being the site of forest-atmosphere fluxes, and in strongly influencing understory microclimate. However, despite this importance, the canopy has been largely neglected by researchers, until recently. Many difficulties in forest canopy research apparently arise from problems related to access. 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. Many of these problems have at least partial solutions. These include: using multiple access techniques to give greater sampling flexibility; identifying appropriate units of replication within the canopy; using ground-operated canopy sampling methods; and, using protocols for unbiased and systematic data collection in three-dimensional sampling space. 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.