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 o verall forest structure and function, for example in containing a high prop ortion of species richness, being the site of forest-atmosphere fluxes, and in strongly influencing understory microclimate. However, despite this imp ortance, the canopy has been largely neglected by researchers, until recent ly. Many difficulties in forest canopy research apparently arise from probl ems related to access. In a survey of 112 canopy researchers, examples of p roblems cited include: bias in the selection of study species or sampling l ocations; difficulties in obtaining adequate replication; problems in colle cting data in a three-dimensional, complex environment; logistical constrai nts in moving between canopy sampling points; and, disturbance, sometimes i ncluding 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 u nbiased and systematic data collection in three-dimensional sampling space. Designing experimental protocols for work in the canopy requires at the ou tset the allocation of time and resources for anticipating and overcoming t he particular sampling problems associated with the work.