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
- 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:
guidelines and sampling methods. For your convenience, we
have included several Inventory worksheets to facilitate the data
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
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
Click Here for additional
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
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
Click Here for the USDA practice
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
Parcel Size Calculations By Practice
For agroforestry, a parcel is defined as a unique/uniform
management practice, and soil type with various species and diameters. If a sizeable portion of your agroforestry practice has a different planting design, a different mix of species, was planted in a different year, has a different soil or moisture regime resulting in very different tree growth rates, etc., then you
may want to treat it as a separate parcel for the purposes of carbon storage estimation using COMET-VR.
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
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.
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
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
Approximate number of trees per acre based upon the
distance in feet between stems in a square grid rounded to the
nearest whole tree*.
||number of trees/acre
||number of trees / acre
*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
Forest floor: This pool is required by a
number of the registries and may account for a fairly substantial amount
of carbon. This pool typically is one that can grow rapidly during early
years of afforestation and thus has some interest. This pool is not
difficult to measure in the field and there is relatively good models
and tables available for estimation.