The SERC Forest Ecology Lab has long been concerned with the structure of forest canopies. To make these measurements in an objective and repeatable way, we developed a portable, ground-based LIDAR system, called the Portable Canopy LIDAR (PCL) [link to publication – Parker et al. 2004.] In the past our principle focus was on the canopies of forests of different ages in the neighborhood of SERC. But more recently we have concentrated on forests throughout the world. Ultimately we hope to measure examples of most of the dominant types of forests in all the climate zones where forests are common. This global-scale information can then help us to understand the components of canopy structure and their dependence on major climate patterns.
Geographic and climatic coverage of the project
The PCL system has been deployed at more than 60 regions throughout world in more than 100 distinct stands, covering about half of all climates supporting forests. It has been used by about a dozen different groups of researchers. Many of the researchers using our system have been trained in our lab and have shared their field data with us.
Most of the studies are of intact mature forests, but some projects focused on younger stands. At every site the studies cooperate closely with local investigators to choose appropriate stands, to share the methodology and to analyze the data. Currently the distribution of studied forests is incomplete—it is biased towards well-developed regions in the northern temperate zone and some intensively-studied sites in the tropics.
To operate, researchers carry the PCL along lines on the forest floor, while the upward-looking laser rangefinder makes high-frequency distance measurements. The system yields a wealth of information, including a visual slice of the canopy surfaces above the route walked. This representation shares several similarities with the CAT-scans (Computerized Axial Tomography) used in medical imaging. Among the specific measures we extract are:
- the height of the canopy (useful for estimates of biomass and carbon)
- the texture of the canopy surface (useful in studies of atmospheric-surface exchanges)
- the internal complexity of the forest (useful for assessments of habitat and biodiversity)
- the porosity of the canopy
- the fraction of ground open to the sky (useful in understanding radiation balance)
Taken in combination these measures help identify the forest type, its developmental state and its disturbance condition.
Data from this study will allow, for the first time, direct comparisons at a global scale using a standard methodology (sampling system, data reduction and metrics). The results will be useful for:
- researchers concerned with canopy structure and climate-forest interactions,
- public audiences concerned with environmental matters, and
- calibrating global-scale studies of forest characteristics acquired from airborne or space-borne vantages.
For a complete global picture, we need samples from forests in underrepresented regions. The highest priority regions are: the taiga (boreal forests), tropical savannas and dry forests, and tropical montane forests.