GEOG/ES&P 330

California Ecosystems

Field Data Collection in Quadrat Frames

Quadrats

The first lab had you do "virtual transects" in La Jolla Valley, based on field work done there by various Biogeography Lab group projects. This lab will familiarize you with another way of collecting biogeographical data in the field: quadrats.

In transecting, you run lines into vegetation and identify plants directly below (or in some cases beside) points spaced on a regular interval along that line (e.g., the plants found directly under points every one meter along a 20 m tape). This is a kind of quick 'n' dirty way of building up a census of the plants in a landscape. It is especially useful when you are trying to find out about plants growing in an ecotone or boundary situation. For example, you might be recording the sequence of species found in a coastal wetland across the fresh, briny, and salty water transition. Or maybe you are recording the increasing presence of halophyte (salt tolerant) species bordering an inland playa in the Mojave Desert. Or maybe you are investigating the change in species found behind an expanding boundary between CSS and grassland.

Sometimes, you want a bit more detail, not just about plants that are present or absent but about how well they cover the ground. Maybe you also want to collect other relevant information, such as perhaps the compaction of soil, its pH, its moisture content, its carbon:nitrogen ratios, or anything else that you think might affect species' presence and their ground cover patterns. This is a job that can be handled with quadrats.\

Quadrats are sampling frames that can be made up in a range of sizes, depending on the sizes of the plants involved or the spatial scale of any regularity in their patterning. So, the Biogeography Lab here has a lot of 1 m frames (made of PVC pipes and joints! DIY equipment design!) that can easily be put together or taken apart during fieldwork and during the schlep into the field. We also have a few 3 m frames (~10 ft. long pipes) and some 30 cm ones (when you're sampling bitty little things, such as lichens or tiny seedlings). Most quadrats are square in shape (convenience), though some are rectangular.

Here're some students setting up a 3 m quadrat frame in Peacock Valley, Portuguese Bend Reserve, Palos Verdes in the "Great Mustard Forest." The student in the background to the left is using a GPS unit to record the latitude, longitude, and elevation of one corner of the frame.

Here is a photo of a 1 m quadrat all ready to go, somewhere in New Jersey:

Your Data

Here is a map (now you know why "they" will never let me teach a cartography class!) of a 3 m or 10 ft. quadrat set up in an area dominated by two species, Salvia mellifera (black sage) and Bromus diandrus (ripgut brome, a common invasive annual Mediterranean grass) and a fair amount of bare ground (possibly due to sage allelopathy, or chemical warfare). The map is plotted on a grid to help you with your estimations: There are 100 1 ft. squares (bolder lines), each subdivided into nine 1/3 ft. subsquares (n=900). You can use these to figure out what percentage of the ground is covered by the black blobs/grey shading (black sage patches), cross-hatched areas (brome), and blank areas (these would be bare soil or rock, perhaps with some dead litter).

Under field conditions, we usually use the eyeball guesstimation method with a group conferring and converging on a decision -- and then make sure that our collective guessed percentages reach exactly 100%. If they don't, you go back and adjust one or more species estimates to bring the sum to 100%. This system works well if you are confining yourself to just the top layer of growth, the species visible from above. If your study is interested in plants under other plants, then the totals will be more than 100% because of the layering of canopies. That's not the case here.

Procedure

Your first step:

Look at the map and come up with ballpark estimates of how much of the quadrat is covered by sage, by brome, and by bare ground. Enter those estimates on the data entry form.

Your second step:

You have a resource here to help you improve your estimates. After you use the eyeball method, redo everything by using the 100 1 ft. squares (or if you're really, er, "retentive," you could go for it and use the 900 subsquares).

A trick to using sub-quadrat units like this is to count the complete squares covered by a given species. Then, count the partially covered squares (some may be 10% covered; others may be 90% covered; and all sorts of values in between). Count up the partial squares and simply divide them by two, using the idea that the variation will settle somewhere around an average of 50%. Then, add the partial square half-counts to the complete squares covered by the same species and you have an estimate of how many square-quivalents out of 100 are covered by the species in question. That just happens to equal the percentage! (If you are truly dedicated and used the 900 subsquares, you'd count the subsquare-equivalents for each species' coverage, divide it by the 900 subsquares, and then multiply by 100 to get the percentage).

You don't need to do the 900 subsquare method, unless you're curious (and have a lot of time and patience). You do need to do both the eyeball and the 100 square-equivalent methods. You'll see the modified "field data entry" form has two columns: one for your eyeball estimates and one for your square counting measurements. I'm trying to get you to refine your field eyeball skills!

Your data entry form is here: https://home.csulb.edu/~rodrigue/geog330/labs/quadrat/quadratlabform.ods. When you're done, upload it to the Dropbox for Lab 6.

Document maintained by Dr. Rodrigue
First placed on web: 09/28/20
Last revision: 09/28/20