Date of Award

2004

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Forest Resources

Advisor

William H. Livingston

Second Committee Member

Jeremy Wilson

Third Committee Member

D. Bryan Dail

Abstract

White Pine Decline is characterized by thinning of the crown and mortality (26% of basal area) in pole-sized stands in southern Maine. Most dead trees had their last year of growth in 1996 or 1997. Recent studies have demonstrated that the drought of 1995 incited the decline, and that potential rooting depth of less than 30 cm is a key predisposing factor. White pine rooting depths can be limited by plow pans, high water table, shallow bedrock, or lithological discontinuities (fine texture soils overlaying coarse texture soils). Many white pines regenerated on potentially rooting restricted sandy soils after extensive farm abandonment in southern Maine. This study estimated the occurrence and distribution of white pine stands in southern Maine (York and southern Oxford counties) that are at risk to White Pine Decline due to shallow rooting depths. Digitized soil maps were overlaid with satellite cover types to indicate potential areas where white pine is growing on soil types that may have a restrictive layer. Based on this map, 39 sample sites were established in 2003 using a random selection of locations. White pine growth and productivity, as well as potential rooting depth, were measured in 4 subplots at each location. Twenty-three locations were found to have potential rooting restrictions that predispose white pine to decline incited by drought, but only eight locations had restrictions that were less than 30 cm deep, and indication of sites at high risk to White Pine Decline. Analysis of variance showed relationships between restricted rooting and growth inhibition for diameter breast height (DBH) and sapwood area. A 20% reduction in BDBH (P = 0.032) and a 33% reduction in sapwood area (P = 0.057) were observed in ca. 60 yr old trees next to soil pits showing rooting barriers within 50 cm of the surface. Soil analysis verified the field observations detecting presence of significant soil textural changes (P < 0.001) from loamy sand (81.6% sand) in the B-horizon to coarse sand (90% sand) in the C-horizon. White pine roots were rarely found (8 of 36 soil pits) below these textural changes. The conclusions of this study show that soils at risk to White Pine Decline are widely scattered across the area but can reduce diameter growth of individual white pine that grow with the localized restrictions. Stand densities should be kept low to reduce the likelihood of the onset of White Pine Decline.

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