Tree-Gust factor measurements in Harwood Forest

This project is a cooperation together with:

Sophie Hale, Northern Research Station (NRS)
Bruce Nicoll, Northern Research Station (NRS)
Barry Gardiner, Northern Research Station (NRS)

Background

A key parameter in the calculation of wind damage of forests is the gust factor. The gust factor represents the ratio of turning moments experienced by a tree in response to the average and maximum wind loading (Gardiner et al., 1997). At the moment there are major uncertainties in the calculation of the gust factor. Values used in the ForestGALES model are based on a single set of wind tunnel measurements (Gardiner et al., 2004). However, previous work shows a discrepancy between these and field measurements.

This measuring campaign aims to improve our understanding of the gust factor by measuring the experienced turning moments of trees in varying stands.

• Gardiner BA, Stacey GR, Belcher RE, and Wood CJ, 1997: Field and wind tunnel assessments of the implications of respacing and thinning for tree stability. Forestry, 70, 233-252.
• Gardiner B, Suárez J, Achim A, Hale S, and Nicoll BC, 2004: ForestGALES. A PC-based wind risk model for British forests. Forestry Commission, Edinburgh.

Objectives

1. To quantify variation in gust factor between trees within an even-aged stand.
2. To quantify variation in gust factor with distance from the edge within an even-aged stand.
3. To investigate the use of competition indices for estimating gust factor for individual trees.

Measurement Setup

The sensors used in this experiment are strain transducers. There are two strain transducers per tree. All straintransducer are measured by CR1000 data loggers (Campbell Scientific) and the data are stored on 2GB compact flash cards. Due to the low power consumption and the hight storage capacity, it is possible to leave the system unattended for longer than a month.

Photos