Productivity is a measure of overall forest growth¾the amount of sunlight converted to plant growth¾and is considered a basic indicator of ecosystem functioning. We present several measures of forest productivity, because no single measure provides a complete picture. Most of these measures are based on timber inventory, growth, and harvest. Timber growth, although only a portion of overall plant productivity, is the most accurate measure widely available today. Satellite information is presented as a key future measure.

Timber inventory, harvest, and growth, as measures of overall status and change. (Fig. 1)

Harvest and growth by region (Fig. 2)

Wood grown on lands with different owners. Differences in land quality, management, and average forest age can result in different growth patterns. (Fig. 3)

Satellite measurements of vegetation growth, as a means of locating large-scale changes in forest condition. (Fig. 4)

Changes in carbon storage in forests, products, and landfills, because such changes affect atmospheric concentration of carbon dioxide, a key greenhouse gas. (Fig. 5)

Annual timber growth is more than annual timber harvest. About 2 percent of the Nation's timber is cut annually, and growth adds a slightly larger amount. Nationally, the extent to which growth exceeds harvest has declined from a peak in the 1970s, although regional differences are significant.

Industry timber lands produce more timber per acre than do other private or public lands. Growth rates are higher now than they were in the 1950s and 1960s, for all types of ownership.

Carbon stored in forests has been increasing for several decades, but the amount added per year is declining. The amount of carbon stored in products and landfills is increasing.

Net Growth & Harvest (1) Technical Note	Regional Growth/Harvest Ratios (2) Technical Note
Source: USDA Forest Service, Forest Inventory & Monitoring	Source: USDA Forest Service, Forest Inventory & Monitoring
	A growth-to-harvest ratio of 1 indicates that timber cutting equals net growth; a ratio of 2 indicates that only one-half of net growth is being harvested. Mature forests have very low net growth rates, whereas younger forests have high growth rates.

Growth Per Acre By Major Owner (3) Technical Note	Changes in Plant Growth (4) Technical Note
Source: USDA Forest Service, Forest Inventory & Monitoring
	Source: USGS, EROS Data Center
	This image shows changes over 10 years in the normalized difference vegetation index (NDVI), a satellite-derived measure of plant growth. Dark areas exhibited a trend toward more growth, whereas lighter areas grew less. Gray areas showed no significant trend.

Carbon Stored Per Year (5) Technical Note

Source: USDA Forest Service

Forest growth removes carbon dioxide from the air. Carbon is stored in trees, roots, soil, the forest floor, and wood products and paper discarded in landfills.