Leaf-Area Index and Light Attenuation in Rapidly Expanding Shrub Thickets

Abstract

There is increasing interest in the changes in ecosystem services that accompany the conversion of grasslands to shrub-dominated communities. Shrub structure and associated effects on the light environment may be especially important in affecting productivity and diversity. Leaf-area index (LAI) and understory light levels of Morella cerifera shrub thickets were assessed on Hog Island, Virginia, USA, at four sites along a soil chronosequence. LAI was estimated from annual leaf litter, with allometric models relating stem diameter to leaf area, with a portable integrating radiometer (LI-COR LAI-2000), and from photosynthetically active radiation (PAR) using the Beer-Lambert law. For the two youngest thickets, LAI estimates from leaf litter (approximately 10.0) approached levels often associated with tropical rain forest. Allometric models estimated LAI values at 9.8 and 12.5 for the same thickets. High LAI in thickets also results in high light attenuation. Light levels within thickets were as low as 0.7% of above-canopy PAR in the youngest thicket. These data suggest that M. cerifera shrub thickets have a very high potential for annual net primary production. Furthermore, extreme modification of the light environment, coupled with heavy shrub litter fall, may exclude potential competitors during thicket establishment and rapidly alter community structure and ecosystem function.

Effects of Vegetation and Background Noise on the Detection Process in Auditory Avian Point-Count Surveys

“…In forest systems, direct and indirect measures of LAI are available. Indirect measures provide simple, easy ways to collect large amounts of data with minimal effort and have been found to provide rapid means of comparison for spatial and seasonal changes in leaf area (Brantley and Young 2007). Indirect measures of LAI can be made with a portable integrating radiometer, which uses canopy gap fraction to estimate LAI (Gower and Norman 1991).…”

Application of hyperspectral vegetation indices to detect variations in high leaf area index temperate shrub thicket canopies

“…Because of a fundamental importance to ecosystem processes, accurate estimation of LAI is necessary for monitoring changes in ecosystem C stocks (SanchezAzofeifa et al, 2009). Collection and analysis of leaf litterfall biomass and a dry weight/leaf area conversion factor can provide an accurate and direct physical measurement of LAI (Brantley & Young, 2007;Gower et al, 1999;Newbold, 1967). While direct measurement of LAI is most accurate, techniques such as litter collection, or alternatives such as direct destructive sampling or allometry, that rely on harvest of leaf biomass are labor intensive and do not reflect seasonal or interannual variations unless repeated for each period of interest.…”

Modeling the distributed effects of forest thinning on the long-term water balance and streamflow extremes for a semi-arid basin in the southwestern US

“…tRIBS computes short-and long-wave radiation fluxes using geographic location, time of the year, cloudiness, aspect, emissivity, slope and albedo at each computational element. Incoming solar radiation is reduced by vegetative shading according to the Beer-Lambert law (Brantley and Young, 2007;Marshall and Waring, 1986) (see Appendix B). Effects of distant landscape on the amount of incoming radiation are accounted through radiation scattering and sheltering functions that are controlled by landview factors and hillslope albedo (Rinehart et al, 2008).…”

“…The Beer-Lambert law was adopted to account for the reduction in radiative transmittance due to dense canopies (Brantley and Young, 2007;Marshall and Waring, 1986) following…”