Comparing direct and indirect methods of assessing canopy structure in a northern hardwood forest

Abstract

Several methods exist for measuring forest canopies following disturbance, and the biases and differences among them are unclear. We compared techniques for measuring the northern hardwood forest's canopy structure at the Hubbard Brook Experimental Forest, New Hampshire, following the severe ice storm of January 5–10, 1998. Methods included leaf area index (LAI) using LI-COR's LAI-2000, visual damage assessments based on tree branch loss, radiation estimates from hemispherical photographs, and LAI determined from litterfall. LAI-2000 measurements were not significantly related to visual damage class estimates, but were strongly correlated with radiation estimates from hemispherical photographs and average LAI values from litterfall. LAI from the LAI-2000 and litterfall differed on a point-by-point basis, but were similar at the stand scale. The LAI-2000 has the highest precision for large-scale measurements. Visual damage estimates appear adequate for assessing large-scale patterns of disturbance intensity in the northern hardwood forest, but the LAI-2000 is more accurate at quantifying canopy structure at large plot or stand scales. Hemispherical photographs may also accomplish this, but are better suited to characterizing the distribution of canopy gaps and light availability patterns over time. Litterfall provides accurate and precise measurements of small-scale LAI patterns in deciduous forests and reveals species-specific patterns.

Decreased water flowing from a forest amended with calcium silicate

“…S2 and S3). The LAI data were collected by measuring the area of freshly fallen leaves (50). The median LAI for three W1 plots was subtracted from the median LAI for seven reference plots to calculate the deviation of W1 LAI from the reference.…”

Estimating canopy structure of Douglas-fir forest stands from discrete-return LiDAR

“…Understanding canopy structure is critical to provide insights into functional characteristics and processes of tree growth, and can reveal important information on the forests' response to disturbance at the individual tree, stand, community, and ecosystem level (Parker et al 2004, Rhoads et al 2004. The horizontal and vertical arrangement of forest canopies have been shown to strongly control the absorption of photosynthetically active radiation (PAR) and subsequently overall stand net primary productivity (Chason et al 1991, Brokaw and Lent 1999, Hall et al 2005).…”

“…Canopy closure (or percent cover) can be defined as the fraction of the sky obscured by foliage within a crown ) and often relies on visual canopy assessments (Whitney andJohnson 1984, Seischab et al 1993). Whilst being a relatively fast technique, this method suffers from subjectivity and imprecision (Rhoads et al 2004). LAI (m 2 m -2 ), is typically defined as the ratio of the single-sided surface area of leaves to the projected ground area (Barclay andGoodman 2000, Lefsky et al 1999) and has proved useful in measuring the impacts of natural and anthropogenic disturbances on forest ecosystems (Rhoads et al 2004).…”

“…Whilst being a relatively fast technique, this method suffers from subjectivity and imprecision (Rhoads et al 2004). LAI (m 2 m -2 ), is typically defined as the ratio of the single-sided surface area of leaves to the projected ground area (Barclay andGoodman 2000, Lefsky et al 1999) and has proved useful in measuring the impacts of natural and anthropogenic disturbances on forest ecosystems (Rhoads et al 2004). The direct measurement of LAI can involve destructive sampling of the canopy (Gower and Norman 1991), the use of litterfall traps, and the measurement of individual leaf area using planimeters (Rhoads et al 2004).…”

“…LAI (m 2 m -2 ), is typically defined as the ratio of the single-sided surface area of leaves to the projected ground area (Barclay andGoodman 2000, Lefsky et al 1999) and has proved useful in measuring the impacts of natural and anthropogenic disturbances on forest ecosystems (Rhoads et al 2004). The direct measurement of LAI can involve destructive sampling of the canopy (Gower and Norman 1991), the use of litterfall traps, and the measurement of individual leaf area using planimeters (Rhoads et al 2004). More commonly, indirect methods are applied, as they are nondestructive and rapid, and include systems that detect the relative penetration of solar radiation under the canopy such as the LI-COR LAI 2000 plant canopy analyzer (LI-COR Incorporated, Lincoln, Nebraska) and the TRAC LAI meter (Chen et al 1997).…”