Forest Growth and Yield

1. Forest Growth and Yield Or: Knowing what and how much timber you have, how it will change over time and how to manage it Definitions Concepts Uses in Management

2. Forest Growth and YieldDefinitions Forest yield: the volume of timber in a forest at a specific point in time Forest growth: the change in volume over an interval of time

3. Forest Growth and YieldDefinitions Site quality: a loose term denoting the relative productivity of a site for a particular tree species Site index: a particular measure of site quality based on the average height of the dominant and codominant trees at a specified index age (25, 50 or 100 years – usually 50 years)

4. Site Index Curves for Eastern White Pine Height and age used as coordinates to determine site index SI correlated with soil factors and topography Curves have been developed for most commercial forest tree species

5. Forest Growth and YieldDensity vs Stocking Stand density Indicates degree of stem crowding within the stand Stocking Refers to whether the stand density meets a particular management objective These two terms are often interchanged, but they have different meanings

6. Forest Growth and YieldDensity vs Stocking Stocking chart Shows acceptable ranges of basal area for stands of different average diameters Must first determine the average basal area and number of trees per acre Use these as coordinates on chart If point falls between curves on stocking chart, stand is fully stocked Point below curve means stand is understocked; above curve means stand is overstocked

7. Forest Growth and Yield Note Height growth is affected by site quality (and genetic value) but not much by stand density (except at extremes) Basal area is affected by stand density but not well-correlated with site quality (except at extremes)

8. Yield Tables Future yields and stand conditions can be predicted using growth models and yield tables Some models allow for treatments such as thinning

9. Forest Management Regulated forest Sustained yield Allowable cut

10. Regulated forest and sustained yield A forest that produces a continuous flow of products of about the same size, quality and quantity over time is called a regulated forest Sustained yield refers to the continuous flow of timber products Regulated forests, by definition, provide sustained yield The larger the ownership, the easier it is to attain a sustained yield

11. Regulated Forest -Even-aged example Assumptions: 25 years to maturity 25-acre forest all acres of equal productivity Managed as 25 individual even-aged stands - one stand harvested each year In practice, usually not as simple as example

12. Regulated forest - Uneven-aged example Assumptions: Trees mature at some regular interval (4 years in example) Need 4 stands to be able to harvest something each year

13. Rotation vs cutting cycle Rotation age and cutting cycle are both used to designate when stands are cut. Note the difference between them. Rotation age: The length of time from final harvest cut to final harvest cut in even-aged management Cutting cycle: The length of time between major cuts (harvest entries) in uneven-aged management

14. Allowable cut The amount of timber considered available for cutting during a specified time period, usually one year

15. Rotation ageEven-aged management Rotation age is determined by first identifying the landowner’s objective Is the period of years required to establish and grow timber crops to a specific condition of maturity (or value) – refers to even-aged management only

16. Cutting cycleUneven-aged Management Idea is to cut a volume of timber equal to the growth Example shows 5-year cycle The forest is regulated by manipulating the stands so that an equal volume of timber is due for cutting each year Concept is equivalent to living off interest from money deposited in a savings account at the bank