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Initial size and competing vegetation effects on water stress and growth of Picea mariana (Mill.) BSP seedlings planted in three different environments

Summary

Published in Forest Ecology and Management 103: 293-305

Three experimental sites in Québec were planted with four different sizes of containerized black spruce seedlings (Picea mariana (Mill.) BSP). We examined the water stress experienced by each stock size of black spruce seedlings in relation to different competing vegetation covers and also the effect of the water stress on spruce growth during the first three growing seasons. The sites consisted of one abandoned agricuItural field and two forest locations. Containers of sizes 45-110, 45-340, 15-700, and 12-1000 were employed to produce the four different sizes of spruce seedlings. At each site, the experimental protocol used a split-plot in a randomized complete block design, in which the presence of a competing vegetation cover (weedy and bare plots) was assigned to the whole plot, while a specific seedling size was assigned to each subplot. At each experimental site both the predawn xylem water potentiaI Yxp and the midday value Yxm were measured three times during each of the first three growing seasons. Data were analysed as a completely randomized split-split-plot design, where selection of seedlings in time was considered as the whole plot. The competing vegetation tended to protect the spruce seedlings from excessive water loss, without depressing the soil-water potential (SWP) to the point of reducing the moisture available to the seedlings. Both Yxp and Yxm were found to decrease significantly with increasing initial seedling size. The increased water stress experienced by the large stock of spruce seedlings had an effect on the absolute growth rate (AGR) in height on only one experimental site. The AGR was impaired by the presence of a competing vegetation cover, but more severely for the smaller stock-size than the larger. The short-term effect of a competition should be based on radial growth; height growth and mortality are not early indicators of such effect. These results emphasize the need to produce a large stock of spruce seedlings with well-developed root systems and root growth capacity, even though only moderate water stress was observed during the first three years of plantation growth.

Sector(s): 

Forests

Categorie(s): 

Scientific Article

Theme(s): 

Forestry Research, Forests, Silviculture

Author(s)

JOBIDON, Robert, Lise CHARETTE and Pierre-Yves BERNIER

Year of publication :

1998

Keywords :

competition, growth, nursery grading, plantation establishment, soil water potential, SWP, stock size, transplant shock, xylem water potential, conifer, Picea mariana, black spruce, absolute growth rate, AGR, water stress, plantation, silviculture and yield of plantations

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