How many quadrats to use

Grid Survey : Let's say we want to estimate the number of dandelions in a vacant lot. We will set up a square 10 meter by 10 meter grid square meters and count all of the dandelions in ten randomly selected one-meter squares, called quadrats. Optional for Overachievers : Using a plant identification guide, identify and count the number of individual plants of each species in each of the quadrats. This data can later be used to do a species diversity calculation.

Humans aren't good at sampling randomly, so we're going to let Microsoft Excel pick our sample locations. Download this excel spreadsheet and print out the randomly assigned sample grid it generates. Note: since Excel is randomizing the sample grid locations, you may get incomplete or complete overlaps. If so, you'll have to decide how you want to handle that issue. As variability in plant community increases: Necessary sample size increases Plot size increases Need for stratification increases The Size-Variability Trade Off: Small quadrats or plots tend to have higher variability or express greater differences from plot to plot.

Small plots are usually faster to read. But, the number of plots you must examine depends on variability. The more variation among plots, the more plots you need to estimate. Therefore, there is a trade-off between number needed and quadrat size.

Sources of Uncertainty One of the main sources of error in quadrat based sampling occurs when deciding whether an individual is within or outside the quadrat frame. These types are errors are called "boundary decisions" and protocols should be discussed to ensure consistent decisions Elzinga et al. For example, would you include a species that entered the quadrat or just those species with roots in the quadrat.

What then happens with species that roots cross the quadrat but terminate outside it? Can you achieve this assessment without damaging the plant?

A further common source of error is due to differences in observers opinion. Again this can be minimized by having clear consistent standards. For more details on boarder decision study figure above and text in Elzinga et al. Assume that each quadrat is 50 by 50 cm. The "white daisy" plants are: »» Click here to see answer and calculations. Web Design - CTI. Plot-based or Quadrat Techniques.

Quadrats are required for estimating several vegetation attributes including: Density - for counting the number of objects within the unit area of the quadrat. Using quadrats in sampling Quadrats are square frames of wire usually 0. When looking at plants in a quadrat, the following sampling can be used: Number of an individual species - the total number of individuals of one species eg daisies is recorded. Species richness - the number of different plant or animal species is recorded but not the number of individuals within a species.

Percentage cover - the percentage of the quadrat area that is covered by one species eg grass. This is easier to estimate if a quadrat has wires making smaller sections. Percentage cover rather than number of individuals is used when estimating plant frequencies if it is difficult to identify individual plants, such as grasses or moss. Download 0 items.

Twitter Pinterest Facebook Instagram. Email Us. See our newsletters here.