Analysis of Diameter-at-Breast-Height (DBH) Measurements from Forest Watch White Pine Trees

Introduction A primary goal of Forest Watch is the monitoring and documentation of forest health. Much emphasis has been placed on determining the status of forest health by the spectral reflectance of leafs. More recently we have begun to estimate the status of forest health by examining the amount of woody tissue added each year in the form of radial growth (i.e., increased girth).

Delta = DBH2 – DBH1

Analysis Methods All DBH records were selected from the Forest Watch database and copied into an MS-Excel spreadsheet. DBH records from the same tree ID, and from consecutive years were differenced to find the DBH change (Δ) after 1 year of growth. It was arbitrarily determined that any Δ greater than +/- 2.5 cm contained too much error, and the Δ was not included in the analysis.

Small Trees and Big Trees May have the same growth (Δ DBH), but the small tree has grown proportionately more than the big tree.

White Pine Size Classes Class 0: less than 15cm DBH Class 1: 15 cm < DBH < 30 cm Class 2: 30 cm < DBH < 45 cm Class 3: greater than 45 cm DBH

Anticipated Result (and Null Hypothesis) Within each size class, the averaged Δ-values would not show a trend, either increasing or decreasing.

Relative Δ DBH Relative Δ DBH = Δ / DBH1

Δ Area Δ Area = Area2 – Area1

Relative Δ Area Relative Δ Area = Δ Area / Area1

Summary Forest Watch White Pine trees provide evidence of accelerated radial growth. On average, Class 0, Class 1, and Class 3 trees have added an additional 0.56 mm/yr, 0.38 mm/yr, and 0.58 mm/yr of wood each year. This evidence suggest that White Pine throughout New England have experienced improved increased health status.

Let’s be clear … … it’s accelerated growth

Two Hypotheses Closed Stomata Hypothesis Elevated Ozone Hypothesis Elevated summer temperatures cause stomata to close to slow water loss. Elevated Ozone Hypothesis High tropospheric ozone disrupts cellular structures and organelles.

Summer Temperatures are Good Predictors of Radial Growth

Tropospheric Ozone vs. Radial Growth

Final Summary There is greater association between radial growth and average summer temperatures than between radial growth and tropospheric ozone. This finding lends support to the Closed Stomata Hypothesis. Further analysis with more geography – specific comparisons with ozone (and additionally precipitation) are needed.