Effects of herbaceous weed control using herbicides on a young loblolly pine plantation

Zutter, B.R.; Glover, G.R.; Gjerstad, D.H.

Forest Science 32(4): 882-899


ISSN/ISBN: 0015-749X
Accession: 001581144

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On an Upper Coastal Plain site in east-central Alabama [USA] herbicides were used to create three herbaceous vegetation treatments based on duration and degree of herbaceous vegetation control during the first two growing seasons following planting of loblolly pine(Pinus taeda L.): (1) low-near complete control for two seasons; (2) medium-single broadcast application of a herbicide at the beginning of the first growing season only; (3) high-no herbaceous vegetation control. Woody vegetation was periodically controlled on all plots. These treatments created a wide range of residual herbaceous vegetation. Soil moisture and first-year height and diameter growth of loblolly pine were negatively correlated with the level of herbaceous vegetation across treatment plots. This demonstrates the necessity for researchers examining effects of competition on pines to also assess soil moisture or soil attributes affecting water holding capacity. First-year seedling diameter was found to be more responsive than height to the level of herbaceous vegetation and associated levels of soil moisture. However, tip moth incidence was greater at the lowest levels of herbaceous vegetation, possibly reducing height growth below its potential. First-year pine growth was most highly correlated to soil moisture level in late August, when soil moisture was lowest, than any other sample date. During the first growing season, pine growth on medium and high herbaceous level plots fell behind that on low level plots (near complete control) once herbaceous biomass approached 25 to 45% of September biomass on high herbaceous level plots (no control). Effects of herbaceous weed levels on pine growth are attributed in part to differences in soil moisture and their effects on seedling water status and physiological processes.