Growth, nutrient, and water status of Montezuma pine as affected by alder in the State of Hidalgo, Mexico

Abstract

In order to study the relationships between alders and pine trees in Pinus montezumae-Alnus arguta stands in terms of pine growth, nutrient status, needle water potential, and soil water status, a series of experiments were developed in two ejidos and one private forest in the state of Hidalgo, Mexico. Results indicated that pine growth may be either positively or negatively affected by the presence of alder. When alders were well exposed to sunlight, pine growth generally increased with increasing alder density. Contrarily, when alders were in the understory of a closed pine canopy, even the lowest alder densities exerted negative effects on pine growth. Pine nutrient status also varied depending on alder condition in terms of light exposure. Pine N requirements were fully met when alders were exposed to sunlight. When alders were in the understory, however, N status became worse as alder density increased. Competition for N between pine trees and alders occurred under this condition. Pine P showed a similar behavior as with N when alders were in the understory. Pine K status, on the other hand, was improved with increasing alder density, regardless of the alder condition. However, it seems that K status improvement when alder was in the understory came from a concentration process. Needle mass generally increased with the application of N fertilizer regardless of the area of regeneration but it decreased with the presence of understory alders in the area of regeneration 1987. Results indicate that alder clumps significantly decreased soil moisture both, during the rainy and during the dry season of the year. Nonetheless, depletion of soil water did not contribute to significant changes in pine predawn water potentials.