Table 1 Overview of the methods referred to in the text and their characteristics, advantages and disadvantages (in three parts)
From: Review of ground-based methods to measure the distribution of biomass in forest canopies
 | Approach group | Measured parameters | Requirements according to the investigated object | Accuracy/resolution | Needed computer resources | Required weather conditions | Expenditure of time | Postprocessing effort | Price for instruments | Advantages | Disadvantages |
|---|---|---|---|---|---|---|---|---|---|---|---|
Allometric relations | Direct | LAI, PAI, individual tree biomass; AGBM; tree height; DBH; biomass repartition; crown form; vertical changes in branch inclination; vertical changes in foliage density; | Enough statistically independent samples available; small destructions must be allowed | High/middle (usually not finer than tree or branch level) | Low (simple calculations) | Calm wind during the destructive part | Long (days) | Middle | Low | Once established formulas can be applied to other trees/canopies | Sometimes statistical requirements cannot be met (e.g. number of samples); characteristics of individuals hard to separate from species-specific; laborious |
Stratified clipping/Scaffolding harvest | Direct | 3D foliage distribution; AGBM | No dense understory; small area of interest; not protected area | High/middle (usually not finer than tree or branch level) | Low (simple calculations) | Calm wind | Long (days) | Very high | Middle | Accuracy | Destructive; not suitable for large areas; difficult setup; not usable in dense understory; laborious |
Litter trap | Direct | LAI; dry-weight-to-leaf area ratio; leaf decay | None | High/very low (canopy level) | Low (only simple calculations, scanner) | No snow cover; no frost | Very long (autumn leaf fall) | Very high | Low | Simple instruments | Geographically averaging; analysis is laborious; difficulty to relate the data to a single tree; no data for a certain point in time |
Point quadrat | Indirect contact | LAI; Green area index; PAI; cover percentage; approximated vertical foliage distribution | Low-vegetation canopies; only small trees | e.g. Levy and madden 1933; Dufrêne and Bréda 1995/low (usually not more than canopy level) | Low (simple calculations) | Calm wind | Long (days) | Middle | Low | No postprocessing; not based on inversion formulas | Laborious; limited to low vegetation canopies; assumes random distribution of foliage elements |
Inclined point quadrats | Indirect contact | LAI; Green area index; PAI; cover percentage; approximated vertical foliage distribution | Low-vegetation canopies; only small trees | e.g. Wilson 1960/low (usually not more than canopy level) | Low (simple calculations) | Calm wind | Long (days) | Middle | Low | No postprocessing; not based on inversion formulas | Laborious; limited to low vegetation canopies; assumes random distribution of foliage elements |
MacArthur and Horn photography | Indirect non contact | Foliage profile; canopy cover; 3D foliage distribution | None | e.g. Fukushima et al. 1998; MacArthur and Horn 1969/low (canopy level) | Low (only simple calculations, flatbedscanner) | Calm wind; no rain; uniform sky conditions (overcast; dusk; dawn) | Short (minutes) | Middle | Low | Fast; permanent image record; portability | Lens distortions; camera settings difficult; analysis sometimes subjective |
Hemispherical photography | Indirect non contact | PAI; canopy cover; transmitted light; 3D biomass distrubution | None | e.g. Welles and Cohen 1996; Jonckheere et al. 2004/low (canopy level) | Middle (special software, advanced calculations) | Calm wind; no rain; uniform sky conditions (overcast; dusk; dawn) | Short (minutes) | High | Low | Fast; permanent image record; portability | Lens distortions; camera settings difficult; analysis sometimes subjective |
Terrestrial 3D laser scanners (TLS) | Indirect non contact | Architectural information (DBH; height and others); 3D structure; light interception; PAI; alia; AGBM | None | e.g. Lovell et al. 2003; Henning and Radtke 2006; Takeda et al. 2008/very high(precise leaf level) | High (strong pc, large ram and hard disk, strong graphics, special software) | Calm wind; no rain | Middle (hours) | Very high | Very high | Comprehensive data; permanent image record; resolution | Expensive instrument; early stage of development (less experience), less standardized ways for the data analysis |
LI-Cor Line Quantum sensor | Indirect non contact | Canopy transmittance; par; canopy closure; LAI | Above/beneath canopy data must be available (tower or open field close to the study side) | e.g. Welles and Cohen 1996; Martens et al. 1993/low (canopy level) | Low (only simple calculations) | Calm wind; no rain; direct sunlight (clear sky) | Middle (hours) | Middle | Middle | Simple instrument; portability | Above canopy data sometimes hard to get; accuracy; single tree related data difficult to extract; additional data needed for analysis; assumes random distribution of foliage elements |
Sunfleck Ceptometer | Indirect non contact | Canopy transmittance; par; canopy closure; LAI; sunfleck distribution | None | e.g. Welles and Cohen 1996; Fassnacht et al. 1994/low (canopy level) | Low (only simple calculations) | Calm wind; no rain; direct sunlight (clear sky) | Middle (hours) | None | Middle | Portability | Single tree related data difficult to extract; assumes random distribution of foliage elements |
SunScan SS1 | Indirect non contact | Canopy transmittance; PAR; canopy closure; LAI; sunfleck distribution | None | e.g. Dufrêne and Bréda 1995; Welles and Cohen 1996/low (canopy level) | Low (only simple calculations) | Calm wind; no rain; direct sunlight (clear sky) | Middle (hours) | None | Middle | Portability | Single tree related data difficult to extract; additional data needed for analysis; assumes random distribution of foliage elements |
LI-Cor LAI 2000 | Indirect non contact | LAI; canopy transmittance | Above/beneath canopy data must be available (tower or open field close to the study side) | e.g. Machado and Reich 1999; Fassnacht et al. 1994/low (canopy level) | Middle (advanced calculations) | Calm wind; no rain | Middle (hours) | None | High | Comprehensive information on the canopy light climate in one measurement; portability | Above canopy data sometimes hard to get; accuracy; assumes random distribution of foliage elements |
TRAC | Indirect non contact | Clumping index; canopy reflectance; LAI | None | e.g. Chen and Cihlar 1995a; Leblanc et al. 2005/low (canopy level) | Low (only simple calculations) | Calm wind; no rain | Middle (hours) | None | Middle | Portability, offers clumping data; | Single tree related data difficult to extract |