Can you decrease the size of the Eco plots?

Section for FAQs regarding i-Tree Eco (UFORE)

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Can you decrease the size of the Eco plots?

Post by i-Tree Support » Fri Jan 05, 2007 2:55 pm

Yes. The Eco model can analyze a data set that was collected using smaller or larger plot sizes than 1/10 acre. Results based on that data would have a certain standard error that depends on the number of samples and the variance from plot to plot. The errors below for total tree count have been provided by the Forest Service for different numbers of plots.

30 plots = 32% SE
60 plots = 23% SE
100 plots = 18% SE
200 plots = 12% SE
400 plots = 9% SE

The i-Tree User’s Manual recommends 1/10 acre plots but also offers a range of possible plot size/radius options:

1/75 acre/ 13.6 ft
1/24 acre/ 24.0 ft
1/10 acre/ 37.2 ft
1/6 acre/ 48.1 ft

Note that the error tends to go down as the plot size increases, because larger plot sizes usually produce smaller variance.

Please also refer to the technical Journal article Effect of Plot and Sample Size on Timing and Precision of Urban Forest Assessments http://www.itreetools.org/eco/resources ... 20size.pdf
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