GROWTH OF THE APICAL SHOOT OF Pinus hartwegii LINDL. IN TLALOC MOUNTAIN, TEXCOCO, STATE OF MEXICO

Abstract

Pinus hartwegii grows approximately between 3000 and 4200 masl at the limit of tree vegetation in the mountains of Mexico and Central America. It is important to analyze growth habits of trees and the possibility to adapt to environmental changes. Accordingly, the aim of this study was to compare the growth of the apical shoot of P. hartwegii plants in sampled units at three altitudes in the Tlaloc Mountain for one year. Three sampling units of 1000 m2 were established at 3629, 3824 and 4021 masl in this mountain, in Texcoco, State of Mexico, Mexico. Diameter and length of apical shoots of plants less than 2.5 m tall were measured every 30 days. Shoot growth was recorded between May 2021 and May 2022. Significative differences (P ≤ 0.05) were detected between altitudes for the studied traits. Average diameter of shoots varied between 15.14 ± 0.59 and 22.65 ± 0.73 mm. Average shoot length ranged from 10.87 ± 0.93 to 19.53 ± 2.37 cm. The apical shoots started growing, on average, between the 74 ±2.20 and 101 ± 6.60 days of the year and ended, on average, from the 214 ± 6.57 y 263 ± 9.71 days of the year. The length of the growth period varied on average from 125 ± 13.86 to 177 ± 9.80 days. The correlation between the shoot diameter and mean annual rainfall was moderate (r = 0.605 P ≤ 0.0001). The average length and diameter of the shoot were the largest at 4021 masl. The apical shoot began growing first in plants at 3629 masl and lastly in plants at 4021 masl where the growth period was greater.