Dear Juan and others, Let's keep in mind that a substantial number of samples will be needed to characterize any site ... especially those under patchily open canopies, such as savannas.
For a given site, I'd recommend a stratified random set of ca. 50 fisheye lens photographs (Nikon Coolpix has a high quality but surprisingly inexpensive fisheye lens extender, and ample electronic storage). Use a tripod; level the "film plane" (that is, the plane of the CCD, or the camera front) and orient the top of the camera dead north. Stratified random sampling is relative easy to accomplish, and is widely documented. The images will need to be normalized in Photoshop (write me for details if you need them) to correct for differences in exposure), and then you can use one of several free webware programs for analyzing the photos for % cover and estimated direct and indirect radiation (moles m-2 day PPFD). If you want, you can calibrate one of your data points as Jordan indicates. But if you want to datalog the dynamic light regime (say at 10 s intervals), then you should assemble a fleet of galium arsenide sensors (ca. 30-50 per plot) ... see Givnish, Montgomery, Goldstein 2004 or Lopez et al. 2008. Those sensors need to be calibrated against PAR sensors. OR you can invest in a fleet of HOBO sensors ... not so good sensors of photosynthetically active radiation, alas, but you don't need to fuss with cables and problems incident thereto (e.g., bears love certain kinds of insulation!). If you go the low-tech, densiometer route, remember that the measurement error per point will be somewhat greater, and that you still have to sample an adequate number of points per site (see Leach and Givnish 1999 for an implementation of the fisheye photograph approach for Midwestern savannas. Cheers, Tom Thomas J. Givnish Henry Allan Gleason Professor of Botany University of Wisconsin [email protected] http://botany.wisc.edu/givnish/Givnish/Welcome.html On 08/09/13, Jordan Marshall wrote: > Juan > > Are you wanting shade as in percent cover or shade as in reduction in light > intensity/quality? If you want percent cover, I'd use a densiometer or canopy > image to calculate coverage of canopy. If using a camera to take images, it > would be recommended to use a fisheye lens. If you want light intensity, I've > used PAR sensors with data loggers. One sensor goes out in a field of full > sunlight and the other goes in the forest for sampling a points. The sensor > in full sun logs data at 100% open (i.e. 0% shade). Since light is variable > over a sampling period, you can then link the point samples from in the > forest to time stamps on the open sensor and calculate percent PAR values in > the forest. I typically do both cover and PAR measurements. > > Jordan > > > -- > Jordan M. Marshall, PhD > Assistant Professor > Department of Biology > Indiana University-Purdue University Fort Wayne > 2101 E. Coliseum Blvd. > Fort Wayne, IN 46805 > > Office (260) 481-6038 > Mobile (865) 919-9811 > Fax (260) 481-6087 > > www.jordanmarshall.com > > > >>> On 8/9/2013 at 12:00 AM, ECOLOG-L automatic digest system > > Date: Thu, 8 Aug 2013 10:28:11 -0400 > > From: Juan Alvez <[email protected]> > > Subject: Percent shade methodology? > > > > Dear ECOLOG-L, > > > > I would like to know what are the best methods to determine different > > percent gradients of shade on forested lands (including savannas and > > grasslands). > > > > Thank you for your consideration! > > Juan > > > > > > > > -- > > Juan P. Alvez, PhD > > Pasture Program Technical Coordinator > > Center for Sustainable Agriculture, UVM Extension > > 23 Mansfield Avenue > > Burlington, VT 05401-5933 > > Phone: 802-656-6116 > > Fax: 802-656-8874 > > [email protected] | www.uvm.edu/sustainableagriculture > > > > UVM Extension helps individuals and communities put research-based > > knowledge to work > > --
