Natural durability of timber species exposed to xylophagous fungi in southern Durango, Mexico.

Introduction: Wood is a natural resource used for construction and the manufacture of many products. This material is exposed to damage due to biotic and abiotic factors. An important biotic factor is wood-degrading fungi that generate large economic losses. The objectives of this study were to determine the effect of xylophagous fungi (Coniophora puteana and Trametes versicolor) on the natural durability of six timber species in southern Durango, Mexico, and to establish differences between fungal effects on each tree species. Materials and Methods: Samples of Pinus durangensis, P. cooperi, P. strobiformis, Juniperus deppeana, Quercus sideroxyla, and Alnus acuminata were exposed to fungi for 4 months under laboratory conditions according to European Standard EN350-1. Samples of Fagus sylvatica were used as control. Durability was determined as the percentage of wood mass loss for each species. Welch ANOVA tests were performed to establish differences among tree species. Welch t-tests were used to prove loss mass differences between fungi for each tree species. Results: The most resistant species to C. puteana were P. durangensis, J. deppeana, P. cooperi and P. strobiformis, showing mean mass losses lower than 8.08%. The most resistant species to T. versicolor were J. deppeana, P. strobiformis and P. durangensis (mean mass losses lower than 7.39%). Pinus strobiformis and Q. sideroxyla were more susceptible to C. puteana effect; in contrast, P. durangensis and P. cooperi showed more damage due to T. versicolor degradation. Conclusions: Woods of P. durangensis, P. cooperi, P. strobiformis and Juniperus deppeana are well adapted to infection by these xylophagous fungi and are therefore highly recommended for commercial use in southern Durango, Mexico.

Assisted migration and the rare endemic plant species: the case of two endangered Mexican spruces.

Background: In the projected climate change scenarios, assisted migration might play an important role in the ex situ conservation of the threatened plant species, by translocate them to similar suitable habitats outside their native distributions. However, it is unclear if such habitats will be available for the Rare Endemic Plant Species (REPS), because of their very restricted habitats. The aims of this study were to perform a population size assessment for the REPS Picea martinezii Patterson and Picea mexicana Martínez, and to evaluate the potential species distributions and their possibilities for assisted migration inside México and worldwide. Methods: We performed demographic censuses, field surveys in search for new stands, and developed distribution models for Last Glacial Maximum (22,000 years ago), Middle Holocene (6,000 years ago), current (1961-1990) and future (2050 and 2070) periods, for the whole Mexican territory (considering climatic, soil, geologic and topographic variables) and for all global land areas (based only on climate). Results: Our censuses showed populations of 89,266 and 39,059 individuals for P. martinezii and P. mexicana, respectively, including known populations and new stands. Projections for México indicated somewhat larger suitable areas in the past, now restricted to the known populations and new stands, where they will disappear by 2050 in a pessimistic climatic scenario, and scarce marginal areas (p = 0.5-0.79) remaining only for P. martinezii by 2070. Worldwide projections (based only on climate variables) revealed few marginal areas in 2050 only in México for P. martinezii, and several large areas (p ≥ 0.5) for P. mexicana around the world (all outside México), especially on the Himalayas in India and the Chungyang mountains in Taiwan with highly suitable (p ≥ 0.8) climate habitats in current and future (2050) conditions. However, those suitable areas are currently inhabited by other endemic spruces: Picea smithiana (Wall.) Boiss and Picea morrisonicola Hayata, respectively. Conclusions: Assisted migration would only be an option for P. martinezii on scarce marginal sites in México, and the possibilities for P. mexicana would be continental and transcontinental translocations. This rises two possible issues for future ex situ conservation programs: the first is related to whether or not consider assisted migration to marginal sites which do not cover the main habitat requirements for the species; the second is related to which species (the local or the foreign) should be prioritized for conservation when suitable habitat is found elsewhere but is inhabited by other endemic species. This highlights the necessity to discuss new policies, guidelines and mechanisms of international cooperation to deal with the expected high species extinction rates, linked to projected climate change.

Graft survival of Pinus engelmannii Carr. in relation to two grafting techniques with dormant and sprouting buds.

Developing methods for successfully grafting forest species will be helpful for establishing asexual seed orchards and increasing the success of forest genetic improvement programs in Mexico. In this study we investigated the effects of two grafting techniques (side veneer and top cleft) and two phenological stages of the scion buds (end of latency and beginning of sprouting), in combination with other seven grafting variables, on the sprouting and survival of 120 intraspecific grafts of Pinus engelmannii Carr. The scions used for grafting were taken from a 5.5-year-old commercial forest plantation. The first grafting was performed on January 18 (buds at the end of dormancy) and the second on February 21 (buds at the beginning of sprouting). The data were examined by analysis of variance and a test of means and were fitted to two survival models (the Weibull's accelerated failure time and the Cox's proportional hazards model) and the respective hazard ratios were calculated. Survival was higher in the top cleft grafts made with buds at the end of latency, with 80% sprouting and an estimated average survival time of between 164 and 457 days after the end of the 6-month evaluation period. Four variables (grafting technique, phenological stage of the scion buds, scion diameter and rootstock height) significantly affected the risk of graft death in both survival models. Use of top cleft grafts with buds at the end of the latency stage, combined with scion diameters smaller than 11.4 mm and rootstock heights greater than 58.5 cm, was associated with a lower risk of death.

Assessment and Models of Insect Damage to Cones and Seeds of Pinus strobiformis in the Sierra Madre Occidental, Mexico.

Insect damage to cones and seeds has a strong impact on the regeneration of conifer forest ecosystems, with broader implications for ecological and economic services. Lack of control of insect populations can lead to important economic and environmental losses. Pinus strobiformis is the most widespread of the white pines in Mexico and is widely distributed throughout the mountains of northern Mexico. Relatively few studies have examined insect damage to the cones and seeds of these pines, especially in Mexico. In this study, we therefore analyzed insect damage to cones and seeds of P. strobiformis in Mexico by using X-ray and stereomicroscopic analysis. The specific objectives of the study were (a) to characterize insect damage by measuring external and internal cone traits, (b) to assess the health of seeds and cones of P. strobiformis in the Sierra Madre Occidental, Mexico, and (c) to estimate the relative importance of the effects of different environmental variables on cone and seed damage caused by insects. We found that 80% of P. strobiformis seeds and 100% of the tree populations studied had damage caused by insects. Most seeds were affected by Leptoglossus occidentalis, Tetyra bipunctata, Megastigmus albifrons, and the Lepidoptera complex (which includes Apolychrosis synchysis, Cydia latisigna, Eucosma bobana, and Dioryctria abietivorella). The cones of all tree populations were affected by some type of insect damage, with Lepidoptera causing most of the damage (72%), followed by Conophthorus ponderosae (15%), the hemipteran L. occidentalis (7%), and the wasp M. albifrons (6%). The proportion of incomplete seeds in P. strobiformis at the tree level, cone damage by M. albifrons and seed damage in L. occidentalis were associated with various climate and soil variables and with crown dieback. Thus, cone and seed insect damage can be severe and potentially impact seed production in P. strobiformis and the reforestation potential of the species. The study findings will enable managers to better identify insects that cause damage to cone and seeds. In addition, identification of factors associated with damage may be useful for predicting the levels of insect predation on seeds and cones.

Morphological Differences in Pinus strobiformis Across Latitudinal and Elevational Gradients.

The phenotype of trees is determined by the relationships and interactions among genetic and environmental influences. Understanding the patterns and processes that are responsible for phenotypic variation is facilitated by studying the relationships between phenotype and the environment among many individuals across broad ecological and climatic gradients. We used Pinus strobiformis, which has a wide latitudinal distribution, as a model species to: (a) estimate the relative importance of different environmental factors in predicting these morphological traits and (b) characterize the spatial patterns of standing phenotypic variation of cone and seed traits across the species' range. A large portion of the total variation in morphological characteristics was explained by ecological, climatic and geographical variables (54.7% collectively). The three climate, vegetation and geographical variable groups, each had similar total ability to explain morphological variation (43.4%, 43.8%, 51.5%, respectively), while the topographical variable group had somewhat lower total explanatory power (36.9%). The largest component of explained variance (33.6%) was the four-way interaction of all variable sets, suggesting that there is strong covariation in environmental, climate and geographical variables in their relationship to morphological traits of southwest white pine across its range. The regression results showed that populations in more humid and warmer climates expressed greater cone length and seed size. This may in part facilitate populations of P. strobiformis in warmer and wetter portions of its range growing in dense, shady forest stands, because larger seeds provide greater resources to germinants at the time of germination. Our models provide accurate predictions of morphological traits and important insights regarding the factors that contribute to their expression. Our results indicate that managers should be conservative during reforestation efforts to ensure match between ecotypic variation in seed source populations. However, we also note that given projected large range shift due to climate change, managers will have to balance the match between current ecotypic variation and expected range shift and changes in local adaptive optima under future climate conditions.

Survival of side grafts with scions from pure species Pinus engelmannii Carr. and the P. engelmannii × P. arizonica Engelm. var. arizonica hybrid.

Grafting is one of the most widely used methods for vegetative propagation, particularly for multiplying trees considered important, but there has been little research done on the effect of hybridization on grafts from the genus Pinus. Sometimes hybrids show the ability to reproduce and adapt efficiently to the environment. However, they reduce the genetic gain of seed orchards. The objective in this research was to evaluate the effect of scion grafts from pure species donor Pinus engelmannii Carr. and from putative hybrid trees P. engelmannii × P. arizonica Engelm., grafted on rootstocks of pure species P. engelmannii, along with the effect of the position of the scion in the donor tree crown (upper third and middle third). The scions were collected from three trees of the pure species and three hybrids. In each tree, 20 scions were collected from each third of the crown evaluated. 120 side-veneer grafts were made at the beginning of spring (March) 2018. Variance analyses were performed to evaluate the treatments and adjustments of the Logit and Weibull models to obtain the probability of graft survival. Significant differences were found between the origins of scions (p < 0.0083, after Bonferroni correction), showing grafts with hybrid tree scions taking hold better. In addition, the probability of survival at 5 months after grafting with hybrid tree scions was greater (p < 0.0001) than in grafts with scions from trees of the pure species (Logit model), which coincides with the results of the Weibull model, which indicated that the probability of graft death with pure species donor tree scions is greater than for grafts with hybrid scions. There were no significant differences regarding the position of the scion in the donor tree crown.

Gap edge attributes in Neotropical rainforest, Ecuador / Atributos de los bordes de los fragmentos en un bosque húmedo neotropical, en Ecuador

Abstract The application of gap dynamics theory appears to be a promising option for tropical forest management and conservation. In the present study of a tree species-rich and old-growth Ecuadorian Neotropical forest, we assessed the spatial distribution of gaps and gap size in relation to: i) tree number at the gap edge, ii) number of tree species at the gap edge, iii) number of tree species per stem at the gap edge, iv) species similarity, v) species evenness at the gap edge, vi) size differentiation at the gap edge, vii) gap isolation and viii) species mingling at the gap edge. Our results demonstrated that the spatial distribution of gaps was random. Various gap attributes were strongly associated with gap size. The number of tree species per stem at the gap edge was negatively correlated to the gap size. Gap sizes up to 50 m2were mostly sufficient to generate tree species-rich forest stands. Assuming that our results were representative for an old-growth neotropical rainforest in Ecuador, our study remarks the following management recommendations: 1) Rainforests have a very complex spatial and diversity structure and logging activities should preferably be omitted because of adverse effects. 2) If logging is inevitable, this should mimic a random choice of trees and tree species, to prevent special selection of tree dimension and species; and a random distribution of trees to be logged, to produce gaps smaller than 50 m2and never larger than 400 m2. Additionally, we suggest cutting not more than 5 % of the tree biomass per 10-20 years period, to preclude stronger alterations of ecosystem processes, and the reduction of existing dead wood from the ecosystem. Rev. Biol. Trop. 66(1): 149-163. Epub 2018 March 01.

Resumen Aplicar la teoría de la dinámica de parches parece ser una opción prometedora para el manejo y conservación de los bosques tropicales. En el presente estudio se analizó la distribución espacial y el tamaño de los parches en relación con: i) el número de árboles en el borde del parche, ii) el número de especies arbóreas en el parche iii) número de especies arbóreas por tronco en el borde del parche, iv) similitud de las especies, v) uniformidad de las especies en el borde del parche, vi) separación del tamaño en el borde del parche, vii) aislamiento del parche y viii) borde del parche. Nuestros resultados demostraron que la distribución espacial de los parches fue aleatoria. Varios atributos de la vegetación se asociaron fuertemente con el tamaño del parche. El número de especies de árboles por fuste en el borde del parche se correlacionó negativamente con el tamaño del parche. Asumiendo que, nuestros resultados fueron representativos de un bosque neotropical en el Ecuador, nuestro estudio respalda las siguientes recomendaciones: 1) Este tipo de bosque húmedo tiene una diversidad espacial y estructural muy compleja; por lo tanto, las actividades de explotación forestal deberían omitirse, ya que afectarán negativamente sus estructuras. 2) Si la tala es inevitable, entonces deberían imitarse las estructuras naturales descritas en este estudio. Es decir, i) una selección aleatoria de especies de árboles a cosechar, con el fin de evitar la selección específica por dimensiones del arbolado o por especies, ii) en la distribución aleatoria de árboles debe tomarse en cuenta que los parches sean menores a 50 m2y jamás mayores a 400 m2. Adicionalmente, se recomienda no cortar más del 5 % de la biomasa arbórea en cada período de corta de entre 10 a 20 años, para evitar alteraciones mayores en los procesos del ecosistema y la reducción de madera muerta existente en estos ecosistemas.

Discrimination of Picea chihuahuana Martinez populations on the basis of climatic, edaphic, dendrometric, genetic and population traits.

BACKGROUND: Picea chihuahuana, which is endemic to Mexico, is currently listed as "Endangered" on the Red List. Chihuahua spruce is only found in the Sierra Madre Occidental (SMO), Mexico. About 42,600 individuals are distributed in forty populations. These populations are fragmented and can be classified into three geographically distinct clusters in the SMO. The total area covered by P. chihuahuana populations is less than 300 ha. A recent study suggested assisted migration as an alternative to the ex situ conservation of P. chihuahuana, taking into consideration the genetic structure and diversity of the populations and the predictions regarding the future climate of the habitat. However, detailed background information is required to enable development of plans for protecting and conserving species and for successful assisted migration. Thus, it is important to identify differences between populations in relation to environmental conditions. The genetic diversity of populations, which affect vigor, evolution and adaptability of the species, must also be considered. In this study, we examined 14 populations of P. chihuahuana, with the overall aim of discriminating the populations and form clusters of this species. METHODS: Each population was represented by one 50 × 50 m plot established in the center of its respective location. Climate, soil, dasometric, density variables and genetic and species diversities were assessed in these plots for further analyses. The putatively neutral and adaptive AFLP markers were used to calculate genetic diversity. Affinity Propagation (AP) clustering technique and k-means clustering algorithm were used to classify the populations in the optimal number of clusters. Later stepwise binomial logistic regression was applied to test for significant differences in variables of the southern and northern P. chihuahuana populations. Spearman's correlation test was used to analyze the relationships among all variables studied. RESULTS: The binomial logistic regression analysis revealed that seven climate variables, the geographical longitude and sand proportion in the soil separated the southern from northern populations. The northern populations grow in more arid and continental conditions and on soils with lower sand proportion. The mean genetic diversity using all AFLP studied of P. chihuahuana was significantly correlated with the mean temperature in the warmest month, where warmer temperatures are associated to larger genetic diversity. Genetic diversity of P. chihuahuana calculated with putatively adaptive AFLP was not statistically significantly correlated with any environmental factor. DISCUSSION: Future reforestation programs should take into account that at least two different groups (the northern and southern cluster) of P. chihuahuana exist, as local adaptation takes place because of different environmental conditions.

Degree of Hybridization in Seed Stands of Pinus engelmannii Carr. In the Sierra Madre Occidental, Durango, Mexico.

Hybridization is an important evolutionary force, because interspecific gene transfer can introduce more new genetic material than is directly generated by mutations. Pinus engelmannii Carr. is one of the nine most common pine species in the pine-oak forest ecoregion in the state of Durango, Mexico. This species is widely harvested for lumber and is also used in reforestation programmes. Interspecific hybrids between P.engelmannii and Pinus arizonica Engelm. have been detected by morphological analysis. The presence of hybrids in P. engelmannii seed stands may affect seed quality and reforestation success. Therefore, the goals of this research were to identify introgressive hybridization between P. engelmannii and other pine species in eight seed stands of this species in Durango, Mexico, and to examine how hybrid proportion is related to mean genetic dissimilarity between trees in these stands, using Amplified Fragment Length Polymorphism (AFLP) markers and morphological traits. Differences in the average current annual increment of putative hybrids and pure trees were also tested for statistical significance. Morphological and genetic analyses of 280 adult trees were carried out. Putative hybrids were found in all the seed stands studied. The hybrids did not differ from the pure trees in vigour or robustness. All stands with putative P. engelmannii hybrids detected by both AFLPs and morphological traits showed the highest average values of the Tanimoto distance, which indicates: i) more heterogeneous genetic material, ii) higher genetic variation and therefore iii) the higher evolutionary potential of these stands, and iv) that the morphological differentiation (hybrid/not hybrid) is strongly associated with the Tanimoto distance per stand. We conclude that natural pairwise hybrids are very common in the studied stands. Both morphological and molecular approaches are necessary to confirm the genetic identity of forest reproductive material.