08.01.2014 Views

Forests Sourcebook - HCV Resource Network

Forests Sourcebook - HCV Resource Network

Forests Sourcebook - HCV Resource Network

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Box 7.8<br />

Example of Defining the Sample of Interest<br />

Box 7.10<br />

Map-Based Estimation Methods<br />

If “forests on the edge” are to be included in the<br />

sample, a possible way of defining them would be<br />

to<br />

■<br />

■<br />

choose watersheds (approximately 1,000) with<br />

– at least 10 percent forest cover, and<br />

– at least 50 percent of forest in private ownership;<br />

and<br />

rank watersheds<br />

– by forest contributions,<br />

– by threats to forest contributions, and<br />

– by combination of contributions and threats.<br />

The inventory could be focused on watersheds<br />

with a high rank.<br />

Source: USFS 2007.<br />

Internet map-based estimation methods involve<br />

■<br />

■<br />

■<br />

selecting a map of forest attribute,<br />

drawing polygon of any shape, and<br />

developing a selection estimation type that<br />

could be<br />

– sample-based estimate and standard error, or<br />

– pixel-based estimate and standard error (for<br />

small or user-defined areas).<br />

Within this process there are two relevant sets<br />

of images: (i) a “reference set,” which is made up of<br />

satellite image pixels with associated plots, and (i)<br />

a “target set,” which is the satellite image pixels<br />

without associated plots.<br />

Source: USFS 2007.<br />

Practical considerations. Considerations to keep in<br />

mind when developing inventories include the following:<br />

■<br />

how to link the national inventory with (where available<br />

and relevant) existing stand (management) inventory.<br />

■<br />

■<br />

difficulty of access to plots in large, remote areas;<br />

continuity of estimates when transitioning from a statelevel<br />

inventory to a national level inventory; and<br />

Box 7.9<br />

Initial plot observation and stratification can assist<br />

in identifying the areas that need to be measured<br />

and those that can be excluded. If initial plot<br />

observation indicates an area is obviously a nonforest<br />

area, it does not need to be observed in the<br />

field. This type of information can help classify<br />

satellite imagery into homogeneous strata to<br />

increase the precision of estimates.<br />

When stratifying forests, stratification must be<br />

distinguished from classification. It is possible to<br />

have large numbers of classifications and few stratification,<br />

or vice versa. For example, there may be<br />

21 classifications, stratified into forest and nonforest<br />

land; or the classification can be forest land and<br />

nonforest land, with four stratifications: forest,<br />

forest edge, nonforest edge, nonforest.<br />

Source: USFS 2007.<br />

Plot Stratification<br />

It is helpful to identify regions where different sampling<br />

and attribute intensities can be applied, such as remote or<br />

reserved areas. The same level of precision is not required in<br />

such areas. If such an approach is adopted, it is important to<br />

■<br />

■<br />

■<br />

decide whether aerial or ground sampling or both are to<br />

be used, by region;<br />

ensure that a core set of compatible results is available<br />

across all regions; and<br />

clarify the responsibilities of all groups involved.<br />

Cost of inventory. Cost is an important consideration in<br />

inventories. It is important when promoting forest inventories<br />

to<br />

■<br />

■<br />

■<br />

determine the most cost-effective data collection and<br />

processing approaches;<br />

develop needed operational experience in the relevant<br />

department or unit so that the inventory can be scaled up<br />

on a cost-effective and timely basis; and<br />

provide an estimate of the cost for implementing the<br />

inventory.<br />

Use of new technologies can help with cost concerns.<br />

However, cost should not be the sole driving force for<br />

NOTE 7.1: NATIONAL FOREST INVENTORIES 259

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!