Effect of seedling size on post-planting growth and survival of five Mexican species and their hybrids.

BACKGROUND

Seedling growth and survival depend on seedling quality. However, there is no experimental evidence showing that the seedling dimensions of the abundant, economically important and widely distributed tree species , , , , and and their hybrids effectively improve survival and growth in reforestations and plantations in Mexico. Therefore, the aim was to evaluate the influence of initial morphological parameters of 2,007 nursery seedlings of these species and their hybrids on their growth and survival 44 months after planting in the Sierra Madre Occidental, Mexico.

METHODS

Spearman's coefficient ( ) and the unbiased conditional pseudo coefficient of determination () between each specific predictor and each response variable and their 95% confidence interval ( ) were determined using Random Forest, generalized linear model, and bootstrapping. By bootstrapping, the potential environmental heterogeneity inside the trial fields and its impact on the results were also quantified.

RESULTS

Among the studied species and their hybrids moderate correlations were observed between the nursery seedling dimensions and the plant dimensions 44 months after planting. However, only weak significant correlations were found between survival rate () and height () ( = 0.10) and between and robustness index () both before planting ( = 0.06). Also, weak significant values of the seedlings , and were detected with respect to the corresponding and 44 months after planting, respectively. Furthermore, the predictor variable "seed provenance" (with 23 provenances) significantly explained the variation in the post-planting and of the seedlings, with values ranging from 0.10 to 0.15. The low width of the shows that the environmental conditions in the trial fields were quite homogeneous.

DISCUSSION

The results also show that the inclusion of "confounding" variables in the statistical analysis of the study was crucial. Important factors to explain this low association could be the strong damage observed caused by pocket gopher, the typically low winter-spring precipitation in both field trials and adaptation factors. The study findings provide preliminary insights and information aimed at helping to design more appropriate standards for nurseries.