REPRODUCTIVE INDICATORS IN TWO NATURAL POPULATIONS OF Pinus hartwegii LINDL

Abstract

Pinus hartwegii Lindl. grows between 2500 and 4300 masl in the mountains of Mexico and Central America. Information on reproductive indicators in a population is useful to describe the reproductive status of a species, and may be influenced by environmental variables. The objective of this study was to evaluate the variation of reproductive indicators between altitudes in Pinus hartwegii populations. Cones were collected between 3600 and 4100 masl at Monte Tlaloc (MT) and Nevado de Toluca (NT) in Mexico. The number of potential seeds (NPS), aborted ovules in year 1 (AOY1), aborted ovules in year 2 (AOY2), empty seeds (ES), full seeds (FS), mean weight of a seed (MWS), reproductive efficiency (RE), efficiency in seed production (ESP) and endogamy depression index (EDI) were determined in each cone. The environmental variables were obtained with the Spline program. Correlation coefficients (r) were estimated between reproductive indicators and environmental variables. Significant differences were found between populations and between altitudes within populations for NPS, AOY2, ES, FS, MWS and RE, while there were no significant differences between populations for ESP and EDI, they were present between altitudes; neither were significant differences between populations and altitudes for AOY1. The correlation coefficient was high (r = 0.929) between AOY2 and precipitation in September and October; it was also high (r = -0.829) between RE and late frosts in Spring. Some r values between reproductive indicators and environmental variables were moderate; for example, the correlation coefficient was 0.786 between NSV and mean annual temperature, it was 0.714 between NSLL and mean maximum temperature of the warmest month, while it was -0.642 between NPS and mean minimum temperature in the coldest month. The values of reproductive indicators showed variation between populations and between altitudes within Pinus hartwegii populations.