Carbon Dioxide Emissions

Estimation of weight of CO2 can be locked up by a tree annually
Southern Pine Coastal plane
Diameter 5" Height 7'
Weight 36lb = 16.4kg
assume 700kg per m^3
may absorb 43kg of CO2 per year
Hard Hardwoods
Diameter 5" Height 7'
Weight 44.5lb = 20kg
assume 700kg per m^3
may absorb 53kg of CO2 per year
Reference
The algorithms require the two measurements you have made: Diameter at breast height = D (in inches), Height of tree = H (in feet). The lesson's calculators convert the tree's height to inches so the units agree.
For each kind of tree there are two different algorithms. One is for trees with a small diameter and a second for trees with a large diameter.

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ASL Tree species
Size
Algorithm (calculates weight in pounds)

Southern Pine Coastal plane
< 5 inches　　0.32214(D^2 * H)^0.91330
> 5 inches　　0.19821(D^2)^1.06419 (H)^0.91330

Southern Pine Piedmont
< 5 inches　　0.28557(D^2 * H)^0.92236
> 5 inches　　0.18703(D^2)^1.05385 * (H)^0.92236

Hard Hardwoods
< 11 inches　　0.38315(D^2 * H)^0.92045
> 11 inches　　0.11710(D^2)^1.16763 * (H)^0.92045

Soft Hardwoods
< 11 inches　　0.26153(D^2)^1.12422 * (H)^0.93871
> 11 inches　　0.10743(D^2)^1.12422 * (H)^0.93871

Sweet gum
< 11 inches　　0.24512(D^2 * H)^0.95220
> 11 inches　　0.09605(D2)^1.14754 * (H)^0.95220

Yellow Poplar
< 11 inches　　0.16258(D^2 * H)^0.99008
> 11 inches　　0.12701(D^2)^1.04157 * (H)^0.99008
http://www.shodor.org/succeedhi/succeedhi/weightree/math1.html
expert opinion that 1 cubic m of timber can absorb 1.83 tons of CO2 and release 1.62 tons of oxygen every year.
http://www.chinadaily.com.cn/china/2007-06/06/content_887865.htm
For the past 25 years, Zhou Guoyi and his colleagues have carried out researches on the mature forests located in the Dinghu Mountain National Nature Reserve. Their research shows that the amount of organic carbon stored in the soil layer 0-20 centimeters under ground increases at a rate of 0.61 ton per hectare every year. In other words, mature forests are capable of absorbing large amounts of organic carbon. Based on these findings, Zhou estimates that half or two-thirds of the carbon is absorbed by the soil in mature forests.
http://www.chinanews.cn/news/2005/2006-12-06/31087.html
With 30 years of orientation investigation on the forests of Dinghu Mountain, calculation proves that 1 hectare of forest can absorb 500 kg of carbon. Monsoon evergreen broad-leaved forest, mixed coniferous broad leaved forest and pine forest rank downtrend in the order of carbon absorption capacity, which vary in different seasons. In Oct. and Nov., carbon absorption capacity of forests is the highest, while from Dec. to Mar. the lowest. Although forests in different regions might have different functions, such research is broadly representative on account of the fact that monsoon evergreen broad-leaved forest is mainly distributed in subtropics in south China.
http://www.china.org.cn/english/environment/134150.htm

Because rate of people cut down tree is higher than plant tree, tree know that they may be cut down eventually, so they will not take up carbon dioxide as efficient as before, so their yield may be lowered.