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Pine Growth and Nutrient Status as Related to Pine/Alder Ratio in Mixed Stands

Author(s): Miguel A. Lopez-Lopez | R.M. Reich | C. Aguirre-Bravo | A. Velazquez-Martinez

Journal: Journal of Biological Sciences
ISSN 1727-3048

Volume: 9;
Issue: 7;
Start page: 637;
Date: 2009;
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Keywords: Pinus montezumae | Alnus arguta | vector analysis | growth response | nutrient status

The relationships between varying pine/alder ratios and pine growth and nutrient status were experimentally examined in three Regeneration Areas (RA) in the Mexican State of Hidalgo. A randomized complete block design with five pine/alder ratios as pseudo-treatments was established at each of the RAs. Pine density, which varied among plots, was blocked to control its effects on pine growth. The results indicate that the effects of alder on pine growth largely depend on pine density, which affects light availability to alders. Growth variables showed saturation curves with respect to increasing alder densities in the 1987 and 1994 RAs. Pine growth was maximum for pine/alder ratios of 2666/20 and 711/267 in the 1987 and 1994 RAs, respectively. For the 1989 RA, maximum pine growth was not reached since alder densities were low. When alders were in the understory, light limitations probably impaired N-fixation, bringing about competition effects for N between alder clumps and pine trees. Management techniques that promote sunlight reduction to alders may switch alder function from beneficial to detrimental. When alder was fully exposed to sunlight, it gave up all N required by pines. Availability of P and K to pine trees was increased by alders exposed to full sunlight. When sunlight limited alder performance, P and K concentrated within pine needles due to reductions in pine growth resulting from N deficiency.
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