Dendrometric variables and traumatic resin ducts in pine species associated with wood-stripping: a traditional practice in the conifer forests of Central Mexico

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.

Tree-ring dating of snow avalanche history in Parâng Mountains (Southern Carpathians, Romania)

<p>In high mountainous areas worldwide, snow avalanches represent one of the main morphodynamic processes which influence the morphology of steep slopes. They usually disturb the forests, and represent a significant natural hazard that may endanger the safety of tourists exposed along the hiking trails crossing the avalanche-prone slopes. In the context of the growing tourism activities in the area where tourist become exposed to snow avalanche hazard, there is need for detailed analysis for documenting the past activity of this geomorphic process, especially in remote areas where historical data is lacking. Such mountainous area without snow avalanche monitoring and archival records is in Parâng Mountains (Southern Carpathians, Romania). On forested slopes, trees disturbed by snow-avalanches may record in their growth rings information about the past event occurrence. The main aim of this study is to improve the knowledge about the past snow avalanche history using tree-rings approach. To this end, 57 disturbed spruce (Picea abies (L.) Karst.) trees growing along an avalanche path located on the western slopes of the Parâng Mountains were sampled and their growth disturbances (scars, traumatic resin ducts, compression wood and growth suppression sequences) served to reconstruct the snow-avalanche history back to 1950. Tree-ring analyses allowed reconstructing a minimum of 14 snow avalanche events which occurred in the past along the investigated path. The tree-ring approach presented in this study proved to be a valuable tool in reconstructing snow avalanche history and compliting the snow avalanche database in Parâng Mountains. The number and spatial extent of documented snow avalanches evidence the potential snow avalanche hazards in the study area. The tree-ring data from the present study, together with those presented by the previous studies in the study area may further contribute to the snow avalanche hazard assessment. </p>

TREE-RING FEATURES: INDICATORS OF EXTREME EVENT IMPACTS

Wood anatomical features may be visible on the microscopic as well as on the macroscopic scale. While the former can often be quantified by detailed wood anatomical analyses, the latter are often treated as qualitative features or as binary variables (present/absent). Macroscopic tree-ring features can be quantified in terms of frequency, intensity, or classified according to their position within a tree ring, like intra-annual density variations (IADFs) in conifers or frost rings in earlywood or latewood. Although some of these tree-ring features, like e.g. missing rings or IADFs are often seen as anomalies, hampering dendrochronologists to perform proper crossdating of tree-ring series, many of these properties are formed under extreme environmental stress or heavy impact, and could mark these extreme events by the manifestation in the wood anatomical structures throughout the lifespan of trees. The described tree-ring features form discrete time-series of extreme events. For example, flood rings may be marked by lunar-shaped earlywood vessels or enlarged latewood vessels in ring-porous oaks. White earlywood rings and light rings indicate reduced cell wall thickness and lignification occurring in very cold years. Frost rings result from cambial cell death during abrupt cooling events in the growing season. Missing rings and IADFs are mainly caused by drought events. Characteristic variations in earlywood vessel size, shape, or number in ring-porous oak species are markers for flood events, defoliation, heat stress, or drought. Traumatic resin ducts may be triggered by a range of biotic or environmental stressors, including wounding, fires or mechanical factors. Reaction wood is indicative of mechanical stress, often related to geomorphic events. In many cases anatomical responses are unspecific and may be caused by different stressors or extreme events. Additionally, the sensitivity of trees to form such features may vary between species, or between life stages within one species. We critically evaluate the indicative value of different wood anatomical tree-ring features for environmental reconstructions.

Registration of rock blocks movements using dendrogeomorphic methods: new methodical approach in a case of localities in the Moravskoslezské Beskydy Mts.

This study proposes a new systematic procedure for the dendrochronologic dating of the movement (esp. lateral spreading, backward rotation and toppling) of large boulders with precision to seasons. The methodology is based on the dendrogeomorphic analysis of trees which have been deformed by tilting blocks. Based on the research carried out in four localities within the Moravskoslezské Beskydy Mts, we have identified 22 event years revealing deformations caused by blocks. The interaction between tree stems and tilting blocks is represented by various macroscopic changes as well as growth disturbances within tree-ring series. These most frequently involve tangential rows of traumatic resin ducts and abrupt growth suppression/release. An analysis of meteorological characteristics identifies potential triggers of movements featuring especially summer heavy rainfalls.

Seven centuries of avalanche activity at Echalp (Queyras massif, southern French Alps) as inferred from tree rings

The purpose of this study was to reconstruct spatiotemporal patterns of avalanche events in a forested avalanche path of the Queyras massif (Echalp avalanche path, southeast French Alps). Analysis of past events was based on tree-ring series from 163 heavily affected multicentennial larch trees ( Larix decidua Mill.) growing near or next to the avalanche path. A total of 514 growth disturbances, such as tangential rows of traumatic resin ducts, the onset of compression wood as well as abrupt growth suppression or release, were identified in the samples indicating 38 destructive snow avalanches between 1338 and 2010. The mean return period of snow avalanches was 22 years with a 4% probability that an avalanche occurs in a particular year. On a temporal plan, three maxima in snow avalanche frequency were reconstructed at the beginning of the 16th and 19th centuries and around 1850, correlating with below-average winter temperatures and glacier advances. Analysis of the spatial distribution of disturbed trees contributed to the determination of four preferential patterns of avalanche events. The comparison of dendrogeomorphic data with historical records demonstrate that at least 18 events – six of which were undocumented – reached the hamlet of Echalp during the last seven centuries, but no significant temporal trend was detected concerning the frequency of these extreme events.