Comparing Sample & Complete Inventory of same plot, problems

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greenspaceintern
Posts: 9
Joined: Wed Jun 03, 2015 7:29 am

Comparing Sample & Complete Inventory of same plot, problems

Post by greenspaceintern » Wed Jul 22, 2015 11:18 am

Hello!

For my ECO project, I compared the complete inventory and a 'random' sample inventory for the same site. The sample was actually a complete with plots arranged to encase each tree cluster. The small site meant that a complete inventory would provide better data, but it did not come with Written Report so we wanted to see what a 'random' sample would say. When the plots overlapped, I calculated how much and entered this number as percent unmeasured for one plot while measuring its overlapping neighbor at 100%.

There were some discrepancies between Sample's and Complete's numbers. One was population estimation but I discovered that 4 entries for Sample were never entered. With 131 total trees and 4 entries accidentally left out I should have had 127 (and after triple checking, I do only have 127 entered) but the Sample's Written Report says I have 137. I assume this is because of iTree calculating for trees in the 'unmeasured area' in Sample's plots. If I don't fully measure a sample plot, will iTree add in a few trees? How much per percentage unmeasured? What does it do for calculating benefits?

Another problem is different pricing. I chose the default Benefit Prices for both Sample and Complete. Both have the same pollution removal values for CO2 but their pricing for other pollutants are widely different:

Complete has $1136 per ton (CO), $2112 per ton (O3),$483 per ton (NO2), $146 per ton (SO2), $12596 per ton (PM10), $100591 per ton (PM2.5).

Sample has $1136 per ton (carbon monoxide), $4278 per ton (ozone),$1079 per ton (nitrogen dioxide), $314 per ton (sulfur dioxide), $22588 per ton (particulate matter less than 10 microns and greater than 2.5 microns), $185151 per ton (particulate matter less than 2.5 microns).

I do not know how this happened. All defaults were chosen and each had English units, it couldn't be a rise in prices that steep since there was only a week or so between results. Does anyone have any idea what happened and how to fix this?

One last odd thing I noticed was that while energy saving price values were close enough ($10.81 per MBTU vs. $11.068/MBTU) the units actually changed ($111.6 per MWH vs. $0.112/Kwh). I don't know why.

Thank you for your time and patience.

*7/23/15 UPDATE*

I entered the four missing trees for Sample and resubmitted it for analysis yesterday. Today the reports says that I have 172 trees. The new Sample has the same location and time period as the previous so I clicked 'Yes' on the automatic pop-up to overwrite the previous Sample's data. Even if these two accidentally combined trees instead of overwriting them, I would not have 172 trees.

Is this part of sampling's standard error, even though my sampling wasn't random?
Jason.Henning
i-Tree Team
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Joined: Fri Dec 21, 2012 7:45 am

Re: Comparing Sample & Complete Inventory of same plot, prob

Post by Jason.Henning » Thu Jul 23, 2015 8:56 am

It does sound like that sampling statistics are probably what are causing the issue. Essentially, the software is taking the information on your measured plots and applying it to the whole area of interest entered in the map land use table. So if for example your plots covered 50% of the total area of interest then the software would multiply all of your measurements, numbers of trees, benefits, etc. by 2 to get the totals for your area of interest. When you do a sample based project none of the estimates are for individual trees they are always summarized at the project or strata level.

It is possible that there may be some other issues with the project set-up and possibly an alternative method for getting the written report. If you can send your packed projects for the sample and complete inventory to info@itreetools.org we can help troubleshoot and offer some more guidance. You can create the packed project .zip files from the "File" menu within i-Tree Eco.

For future versions of i-Tree Eco we are trying to make it so that the same outputs are available for sample based projects and complete inventories. So hopefully this won't be an issue once those software updates are available.
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azelaya
i-Tree Team
Posts: 345
Joined: Fri Jun 27, 2008 10:50 am

Re: Comparing Sample & Complete Inventory of same plot, prob

Post by azelaya » Thu Jul 23, 2015 9:57 am

Here are some additional thoughts on this topic. It is possible to create a sample project in Eco version 5 with 1 plot that is the same size of the project area. The plot can then be populated with all the trees in your inventory and you will be able to generate the canned written report and other reports not available for the standard complete inventory project. The population is basically a complete inventory shoe-horned into a sample project framework to allow for more reporting.

So, if you do a simulation of the same set of trees in a sample project as described above and a complete inventory, the population estimates should be identical 1:1. However, the ecosystem service results will not be the same. This is due to limitations of how the Eco model functions and was later adapted for doing complete inventories. Some of the plot variables that are required for a sample project affect ecosystem services estimates. For example, the % tree cover for a plot affects pollution, rainfall, energy climate effects and BVOC estimates. This plot variables is not entered for complete inventory projects though.

The Eco model is a lumped population model and was later adapted to produce results for individual trees. As a result, the pollution modeling for inventories is first completed at the population level based on the inventory canopy cover & leaf area and then values are partitioned into individual trees. So, a change in 1 tree in a complete inventory can affect the individual pollution contributions of all trees based on the overall pollution modeling effect that is later distributed to each inventoried tree. This will also affect monetary values for the BenMap modeled pollutants (O3, PM2.5, NO2 & SO2) based on the population affected by polluntant reduction and the overall amount of pollutant reduction.

Some of the Eco reference material is older and doesn’t adequately capture the newer integration of the BenMap pollution estimates in Eco. I found a better description in one of the i-Tree Canopy papers and copied in below which describes the modeling and valuation for a national study.

2.4. Air pollutant removal valuation
The U.S. EPA’s BenMAP was used to estimate the incidence of adverse health effects and associated monetary values resulting from changes in NO2, O3, PM2.5 and SO2 concentrations (US EPA 2012). The pollutant removal value for CO and PM10* were CO = $1,470 t-1 and PM10* = $6,910 t-1 for urban and CO = $27 t-1 and PM10* = $126 t-1 for rural areas. Urban values were estimated using national median externality values (Murray et al. 1994) adjusted to 2010 values using the producer price index (U.S. Department of Labor 2012), while rural values were derived from urban values adjusted based on the rural to urban value ratio for all four BenMAP pollutants (NO2, O3, PM2.5, and SO2).

For each rural and urban area in counties, calculated total removal amount and monetary value were divided by the area’s total tree cover to derive the removal amount and monetary value multipliers, respectively. For the entire county, the multipliers were derived by aggregating rural and urban areas in the county. In i-Tree Canopy, the air pollutant amount annually removed by trees and the associated monetary value can be calculated with the tree cover in the area of interest multiplied by these multipliers based on the county-level values in the United States. For countries outside the United States, county multipliers derived from the Unites States’ total removal amount, monetary value and tree cover can be used. Table 1 presents national values for the entire rural and urban areas as well as counties in the conterminous United States.


This may give you a better understanding of potential differences that you may see in inventory & sample projects.
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greenspaceintern
Posts: 9
Joined: Wed Jun 03, 2015 7:29 am

Re: Comparing Sample & Complete Inventory of same plot, prob

Post by greenspaceintern » Thu Jul 23, 2015 10:30 am

Jason.Henning, I would have assumed that it was the percent coverage compensation, but I only added 1 plot at 100% for two missing trees. The two remaining plots with one tree each are at 100% as well. So all plots whose areas of interest covered less than 100% remained the same between the first and second Sample reports.

azelaya, it could be that I didn't do a 1:1. For Sample, I have 41 plots in a 8.19 acre area since I kept the 1/10 acre standard but wanted to cover every tree. Yet if having more plots was a problem, I don't see how the first Sample report could have been so close in total trees. I only added trees to Sample inventory and resubmitted it alone since the Complete inventory had all entries.

Thank you for the breakdown in pricing for pollutant removal. My different prices make a lot of sense now. Complete inventory just goes off the nearest weather station results, but I gave iTree the city's entire population when Sample asked for population.

I've packaged and sent my data, thank you so much for your help.
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