Preparations for the Agroforestry External Tree Inventory

For agroforestry, a parcel is defined as a unique/uniform management practice, and soil type with various tree species and diameters.

Estimating carbon storage in agroforestry practices using the external tree survey requires additional information about the size and number of trees in your parcel(s) that you will need to gather before starting COMET-VR.

The external tree survey replaces the average aboveground carbon values calculated automatically by the CENTURY model.  This survey requires additional detailed information about the size and number of trees in your parcel(s) and provides a more accurate carbon footprint for the aboveground carbon.  You will need to gather this information before starting COMET2 to use the external tree survey.

• Determine the acreage of each Homogenous forest stand;
• The tree species in each forest stand;
• Measure and record the diameter (DBH) of each tree;
• Count each tree species at that size;
• Determine the Trees Per Acre for each species in that size group.

Please click here to see additional information on determination of acreage for specific practices and sampling methods.

External Tree Inventory

The parcel Tree Inventory is a detailed tree survey which records information about your trees like the number of trees, the diameter of your trees, and the tree species.  The goal of the survey is to provide useful information to describe the trees so that External Tree Survey Model can determine the aboveground carbon associated with each species and size group in greater detail and with more accuracy than the generalized calculations obtained from COMET-VR.  Once you have this information you will be able to enter it on the "External Tree Screen".  There are two different data collection units for Agroforestry parcels:

• Row-Type Practices that include Alley Cropping, Windbreaks and Riparian Buffers and;
• Forest-Type Practices that include Farm Woodlots, Multi-Story Cropping/Forest Farming, and Silvopasture.

For more information on the tree survey, refer to the document:

Inventory guidelines and sampling methods.  For your convenience, we have included several Inventory worksheets to facilitate the data collection.

• Row-Type Practices: Survey Instructions - PDF File
  circumference method - Excel spreadsheet diameter method - Excel spreadsheet
• Area-Type Practices: Survey Instructions - PDF File
  forest method - Excel spreadsheet

What is Agroforestry?

A land use system involving deliberate introduction or mixture of trees in crop and/or animal production systems to take advantage of economic or ecological interactions among the components. It is essentially, the right trees planted in the right places for the right reasons that add value to land-use systems.

The most common practices supported in COMET2 are:

• Alley Cropping: is an agroforestry practice intended to place trees within agricultural cropland systems (sample photo).  Alley Cropping is an linear feature and considered a Row-Type practice.  Click Here for the USDA practice specification.

• Farm Woodlot: is a managed wooded area on your farm composed entirely of trees (sample photo).  This practice includes Multi-Story Cropping/Forest Farming.  Farm Woodlot is an area feature and considered a Forest-Type practice.  Click Here for additional practice specification.

• Multi-Story Cropping/Forest Farming: In Multi-Story Cropping/forest farming, high-value specialty crops are cultivated under the protection of a forest canopy that has been modified and managed to provide the appropriate conditions. It is a way of utilizing forests for short-term income while high-quality trees are being grown for wood products.  Currently, COMET2 processes forest farming as a Farm Woodlot.

• Riparian Buffer: is land next to streams, lakes, and wetlands that is managed for perennial vegetation (grass, shrubs, and/or trees) to enhance and protect aquatic resources from adverse impacts of agricultural practices (sample photo) .  Riparian Buffer is an linear feature and considered a Row-Type practice.  Click Here for the USDA practice specification.

• Silvopasture: is specifically designed and managed for the production of trees, tree products, forage, and livestock. Silvopasture results when forage
  crops are deliberately introduced or enhanced in a timber production system, or timber crops are deliberately introduced or enhanced in a forage production system. As a silvopasture, timber and pasture are managed as a single integrated system (sample photo).  Silvopasture is an area feature and considered an Forest-Type practice.  Click Here for the USDA practice specification.

• Windbreak: are strips of trees and/or shrubs planted and maintained to alter windflow and microclimate, thereby protecting a specific area. They are often planted and managed as part of a crop and/or livestock operation (sample photo).  Windbreaks are a linear feature and considered a Row-Type practice.  Click Here for the USDA practice specification.

To determine the parcel size you should consider the net area that is occupied by the agroforestry practice. Subtract large areas within the agroforestry practice area that are in crops, pasture, brush, buildings, etc.  To assist with measuring the dimensions of your agroforestry parcel, you could use aerial photos (available at your county Soil & Water Conservation District office) or an online mapping program such as Google Earth (http://earth.google.com/).

For Row-Type practices, calculate the parcel size as follows:

• Riparian Buffer: buffer length * (avg. width on bank side A + avg. width on bank side B) / 43560

• Windbreaks: ∑ (tree row length * avg. crown spread) / 43560

Carbon Sequestration

Trees and shrubs can be used to produce social, economic, and conservation benefits.  Agroforestry practices can lead to substantial storage of carbon and removal of atmospheric carbon dioxide.  Trees and shrubs on agricultural lands can take carbon dioxide out of the air and "store" it in stems and roots. By taking steps to help protect our future quality of life, landowners can also enhance current production and achieve conservation objectives.

• If 4.6 million acres of the tilled crop land were managed as a 30-foot-wide tree windbreak, based on 20-year-old plantings, the carbon accumulation would exceed:80 million metric tons. 
• USDA has committed to planting 2,000,000 miles of conservation buffers. If one-fourth of these buffers were 100 foot wide forested riparian buffers, CO2 removal would exceed:110 million metric tons.

Estimated Carbon Dioxide Removal in 35-year-old Loblolly Pine Stand
Metric tons CO2 per acre
(To convert CO2 to C, divide by 3.67)

* U.S. Department of Energy 1999.
**Louisiana State University, Hill Farm Research Station 1999.

Aboveground Tree Biomass

Overstory trees: Virtually, all the registries require aboveground tree biomass estimation. In fact, most registries only accept aboveground live tree C.  This forest carbon pool has been measured frequently since this is the “merchantable timber” of the forester and the timber and paper industry. In-field inventory methods are standardized and well developed. There are also a number of available mathematical models as well as look-up tables.

Below Ground Root Biomass

Studies of tree growth physiology across a broad range of tree species on many sites indicate that there is a relatively constant relationship between above and belowground living tree biomass.  This ratio of the above to belowground biomass (often referred to as the shoot to root ratio) is approximately 4:1 or, in other words, ~20% of total tree biomass is belowground.  As such, estimation of the carbon in belowground coarse root biomass (including tap root) is easily achieved by utilizing aboveground biomass estimates and multiplying by 1.25.

Belowground coarse root biomass = aboveground tree biomass x 0.25

Participants in a carbon registries can utilize the data they have generated under the aboveground accounting schemes to include belowground coarse root biomass.

Actually, direct measurements of belowground coarse root biomass are extremely difficult and costly, have high uncertainty, and lack a standard protocol.  As such, direct measurements made by registry participants is unlikely.

Diameter at Breast Height (DBH)

Diameter at breast height is measured at 55 inches (4.5 feet) or 1.4 meters above the ground.  Valid diameters vary by species.  You should enter between 0.78 and 39 inches for sugar maple, beech or yellow birch, and between 0.78 and 20 inches for the other species. There are no fir, spruce or white birch with a DBH larger than about 20 inches.

Trees per Acre

In natural resources many management concepts, as well as an evaluation and control methods, utilize tree numbers per acre as a quantitative measure. The number of trees per acre vary by the distance between each tree and the distance between tree rows. In plantations, the number of trees per acre would be determined by knowing the spacing within a row and the spacing between rows. In planting systems, the initial number of trees per acre can be estimated by their spacing.

Below are presented two tables that determine the number of trees per acre based upon tree spacing in two directions (along two axes perpendicular to each other). The spacing distances are in feet. The table shows the number of trees per acre when trees are on square or equal spacings.

Approximate number of trees per acre based upon the distance in feet between stems in a square grid rounded to the nearest whole tree*.

spacing (feet)	number of trees/acre	spacing (feet)	number of trees / acre
11	43,560	3030	48
22	10,890	3535	36
33	4,840	4040	27
44	2,723	4545	22
55	1,742	5050	17
66	1,210	5555	14
77	889	6060	12
88	681	6565	10
99	538	7070	9
1010	436	7575	8
1111	360	8080	7
1212	303	8585	6
1313	258	9090	5
1414	222	9595	5
1515	194	100100	4
1616	170	125125	3
1717	151	150150	2
1818	134	175175	1
1919	121	200200	1
2020	109	225225	1
2525	70	250250	1

*Kim D. Coder, The University of Georgia, 1996 TPA

Coarse Woody Debris (CWD) Carbon Pool

Lying dead wood: This pool (also referred to as coarse woody debris or downed woody debris) is required by a number of registries and can be a substantial carbon pool. CWD is defined as the wood biomass that consists of standing dead trees (snags), fallen trees, and large decomposing roots composed of logs and larger diameter branches >1 inch (2.5 cm) on the forest floor. CWD not only stores carbon but also provides habitat for plants, animals, and insects and is a slow release source of nutrients. 

Forest Floor Carbon Pool

Tree Identification

red maple	red spruce
Sugar Maple: one of the dominant canopy species of the northern hardwood forest found at all but the highest elevations.	American Beech: is one of the dominant canopy species of the northern hardwood forest found at all but the highest elevations.
white ash	white birch
pin cherry	yellow birch: one of the dominant canopy species of the northern hardwood forest found at all but the highest elevations. It has intermediate shade intolerance and can live to be 300 years old or more.
striped maple	beech