Background: In La Malinche National Park (LMNP), Pinus species are exploited mainly because they are a non-woody source of products such as ocote (resinous wood chips) and wood.
Questions/Objective: Which Pinus species are subjected to wood-stripping (WS) in the LMNP? What are their dendrometric characteristics? Do WS trees present traumatic resin ducts associated with the ocoteo practice? Does the number of trees subjected to WS increase with altitude?
Study site and dates: La Malinche National Park; Tlaxcala, México, 2017-2018.
Methods: Random stratified sampling was done in a total of 33 plots in three different altitudes to quantify the number of damaged and undamaged trees and the total height and diameter per tree in each plot. Increment borers were obtained to estimate tree age, samples were taken for taxonomic determination, and tissue samples to evaluate mechanical damage.
Results: Pine species subjected to wood-stripping (ocoteo) were P. leiophylla, P. montezumae, P. pseudostrobus, and P. teocote, with P. montezumae being the most affected in high and mid altitudes. WS trees were those with the greatest diameter and with the largest number of traumatic resin ducts. The species having the highest number of traumatic resin ducts was P. teocote.
Conclusions: WS intensity in the LMNP is greater in the mid and low altitudes and in trees of greater diameter, height, and age. The species most affected by WS is P. montezumae and all WS individuals have a significantly higher number of traumatic resin ducts.
Despite the extensive distribution and use of Pinus oocarpa in Mexico, knowledge on the range of genetic variation and magnitude of quantitative parameters of the defensive structures of the species is rare. Our study attempts to fill this gap by providing a comprehensive assessment of resin duct traits in mother trees and their offsprings in an open-pollinated trial of P. oocarpa. Resin ducts are fundamental structures of the defense mechanisms of the coniferous trees. They vary depending on the age of the tree, the genotype, the species, and may be influenced by environmental factors. We investigated intraspecific variation among families of the resin duct system in secondary vascular tissues (wood and inner bark) of P. oocarpa trees. Our study attempts to explore the variance and the possible genetic control of these defensive structures. We hypothesized that the resin duct features analyzed would vary with the tree’s genetic make-up. We analyzed samples from two groups of trees. First, from mature mother trees selected as superior in resin yield. Second, from their six-year-old off-springs established in a progeny trial. Axial and radial ducts showed differences in their size and quantity, between wood and bark and between ages. The axial duct density showed differences among families, and the heritability estimates were moderate. In P. oocarpa trees selected as phenotypically superior in resin yield, the size of its constitutive resin ducts is a less variable trait, and the differences in axial duct density can be attributed to genetic factors.
The study was carried out using three objects: 1) clones of the mutational witches’ brooms and the normal crown grafted together on the same rootstock; 2) mutant seedlings of the witches’ brooms; 3) clones of the witches’ brooms mutant seedlings. It was shown that the morphological and anatomical needle characteristics are affected as by the presence and the expression of the mutation, as well as the age of the maternal tree and the presence of a rootstock. Each factor and the interaction of some factors makes a significant contribution to the differences between the groups in the main needle characteristics. The mutant seedlings and their clones formed the shortest needles; they also had smaller areas of the central cylinder, resin ducts, mesophyll and vascular cylinder. Morphological and anatomical needle traits varied between the families, the needle length was a rather conservative trait in the families. Some differences between the groups from different families of witches’ brooms were due to the natural diversity of the maternal witches’ brooms.
Conifers have evolved different chemical and anatomical defences against a wide range of antagonists. Resin ducts produce, store and translocate oleoresin, a complex terpenoid mixture that acts as both a physical and a chemical defence. Although resin duct characteristics (e.g., number, density, area) have been positively related to biotic resistance in several conifer species, the literature reporting this association remains inconclusive. Axial resin ducts recorded in annual growth rings are an archive of annual defensive investment in trees. This whole-life record of defence investment can be analysed using standard dendrochronological procedures, which allows us to assess interannual variability and the effect of understudied drivers of phenotypic variation on resin-based defences. Understanding the sources of phenotypic variation in defences, such as genetic differentiation and environmental plasticity, is essential for assessing the adaptive potential of forest tree populations to resist pests under climate change. Here, we reviewed the evidence supporting the importance of resin ducts in conifer resistance, and summarized current knowledge about the sources of variation in resin duct production. We propose a standardized methodology to measure resin duct production by means of dendrochronological procedures. This approach will illuminate the roles of resin ducts in tree defence across species, while helping to fill pivotal knowledge gaps in plant defence theory, and leading to a robust understanding of the patterns of variation in resin-based defences throughout the tree’s lifespan.