Growing stock is a common term used to describe timber volume. The volume of growing stock trees is a subset of all live trees in a forest or stand. Growing stock includes sawtimber, pole timber, saplings, and seedlings, but excludes rough, rotten, and cull trees. It is a fundamental element in determining the productive capacity of an area identified as forest available for timber production. Knowledge of growing stock of the various species that make up the forest and how growing stock changes over time is central to considerations of a sustainable supply of wood for products and the sustainability of the ecosystems that provide them.
Between 1984 and 2006, the total volume of growing stock on timberland increased from 6.1 billion cubic feet to 8.4 billion cubic feet, an increase of 38 percent. The volume of growing stock increased by 39 percent on private lands and 35 percent on public lands. Positive trends in growth on timberland are attributable to maturation of forests cut in the early 1900’s, investments in fire protection, land owner education, and silviculture.
Volume of Growth and Removals
Net growth on timberlands is defined as gross growth minus mortality. Removals include trees removed from the inventory by harvesting, cultural operations such as timber-stand improvement, land clearing, or changes in land use. While comparing net growth to removals conveys no information about quality, biodiversity, other attributes of ecology, or management objectives, it does allow us to look at implications of forestry operations over time.
From 1984 to 2006, average annual net growth almost doubled, increasing from 174.3 million cubic feet to 324.3 million cubic feet. In this same period, total average annual removals doubled from 38.8 million cubic feet to 76.7 million cubic feet. To put this in perspective, just 24 percent of growth was removed annually on average. Moreover, average annual removals drained less than 1 percent of the total inventory of growing stock trees, while average annual net growth contributed 3.9 percent to the total growing stock inventory. From a timber supply standpoint, therefore, the region’s forests are managed sustainably.
There has been a net increase in growth and removals for hardwoods and softwoods over the study period. The decrease in hardwood average annual net growth from 1984 to 1990 is almost certainly due to the effects of the longest and most severe drought in the last century (see Precipitation Patterns). Many large trees, particularly oaks, died from a scarcity of water, while other drought-stressed trees succumbed to various diseases and wind damage. The sharp decline in softwood growth from 1990-2002 reflects the devastating effects of the southern pine beetle on yellow pines, especially in the southwestern counties.