Pinus Pseudostrobus Lindl Research Articles

Study of the Spatial Distribution of the Bark Beetle in the Ejido Tixtlancingo

The spatial distribution of Dendroctonus frontalis Zimmermann, 1868, and Dendroctonus mexicanus Hopkins, 1905, was determined from 2020 to 2021 in the Tixtlancingo ejido. The information came from two surveys because, despite the abundant forested areas in this geographical area of the state of Guerrero, Mexico, economic resources for pest biomonitoring are limited. However, it was possible to identify the presence of 76 outbreaks affecting 1117.697 hectares and 95,078 trees, totaling 14,223.8 m3 of standing timber volume. In 2020, 28 outbreaks were reported, with the eastern spatial distribution showing the most damage from bark beetles, particularly in outbreaks 7 and 14 of the surveyed area. The most affected conifers were Pinus maximinoi H. E. Moore (44.71%), Pinus oocarpa Schiede ex Schltdl. (39.93%), and Pinus pseudostrobus Lindl. (15.36%). The affected timber volume was observed in diameter categories of 30 cm for the three pine species, with infestation of 90,549 trees (13,497.6 m3 t.t.v. (total tree volume)) across 1057.64 hectares. In 2021, 48 outbreaks were recorded, with the northeastern and southern parts of the surveyed area showing the most damage from the bark beetle. The trees most affected by the bark beetle were P. oocarpa (59.17%), P. maximinoi (33.94%), and P. pseudostrobus (6.89%). It was observed that the affected volume occurred in trees with diameter categories of 50 cm for the three pine species, affecting 4529 trees (726.214 m3 t.t.v.) distributed over 60.06 hectares. The contribution of this work lies in establishing a baseline for monitoring damage caused by this beetle, which affects forest resources and diminishes the possibility of maintaining carbon capture areas in the medium and long term, thus impacting the Sustainable Development Goals (SDGs) of the 2030 agenda, specifically Goals 11, 13, and 15.

Report of the Nomenclature Committee for Fossils: 16

SummaryThe following five generic names are recommended for conservation: Tetraphyllum Griff. ex C.B. Clarke against Tetraphyllum Hosius & Marck, Steinhauera C. Presl against Steinhauera Göpp., Podozamites against Preissleria, Klukia Racib. against Klukia Andrz. ex Besser, Ficoxylon against Ungerites. The following two species names are recommended for conservation: Pinus pseudostrobus Lindl. against P. pseudostrobus Brongn., Magnolia oblonga (Wall. ex Hook. f. & Thomson) Figlar against M. oblonga M. Chandler. The committee judged the names Notothylacites Němejc & Pacltová and Notothylites Chitaley & Yawale are not sufficiently alike to be confused and should not be treated as homonyms.

Effect of LED lights on the in vitro growth of Pinus pseudostrobus Lindl., plants

Pinus pseudostrobus Lindl. is a species endemic to Mexico and is widely used in reforestation programmes, as it is highly adapted to poor, shallow, limestone soils and has high commercial importance. However, it is necessary to preserve this genetic material since it is in trouble due to high rates of deforestation, land use change, and forest fires, so it is necessary to have effective strategies to obtain good quality seedlings. Due to the properties of LED (light emitting diode) lamps used for illumination in the production of in vitro plants, the effects of two different lighting systems (LED and fluorescent) on an in vitro culture were analysed for the morphological characteristics of the growth and photosynthetic pigment content in P. pseudostrobus seedlings. The length and root size of the seedlings were affected by the type of illumination, where a red LED light was the most effective at 30 days of evaluation. However, a blue LED light was equally effective as a red LED light at 60 days of seedling development. On the other hand, the fluorescent light was better in terms of the number of needles in the first stage, but we found the blue LED light to be better in the second stage. For the photosynthetic pigment content, the highest values were found with the blue LED light. The results showed that the LED lighting system favours the growth, development, and photosynthetic pigment content of the species under study.

CpSSR and High-Resolution Melting Analysis (HRM) for Pinus pseudostrobus Lindl. Variety Genotyping and Discrimination

The unambiguous identification of varieties within the Pseudostrobus complex is a key step to facilitate tree selection and monitoring in the wild as well as in plantations. Molecular tools provide a powerful approach for species delimitation; however, the use of DNA barcodes in this group has met limited success due to widespread haplotype sharing from lineage sorting, hybridization and introgression. Here, we evaluate the utility of real-time PCR coupled with high-resolution melting (HRM) to discriminate among Pinus pseudostrobus Lindl. var. pseudostrobus, apulcensis and oaxacana, from wild populations in central and southern Mexico, using chloroplast DNA sequence variants located within the clpP, ycf2, trnL(UAA)–trnT(UGU) and trnI(CAU)–trnF(GAA) loci. The markers ycf2/trnL(UAA)–trnT(UGU) produced clear melting patterns that separated the varieties pseudostrobus and oaxacana from type var. apulcensis, whereas clpP discriminated over 60% of var. oaxacana individuals. This assay underlines the usefulness of these less-used DNA regions as potential biological markers and exhibits the effect of geography on allele distribution and the likely presence of hybrids among the species and varieties.

Forest Harvesting Impacts on the Structure and Composition of Coniferous Forests in Mexico

The effect of forest harvesting on the composition and structure of a temperate coniferous forest in Mexico was evaluated after three harvesting periods from 2007–2015. In this forest, we identified seven families and eight tree species. The dominant species is Pinus pseudostrobus Lindl. which is also the most important commercial species. Harvesting was oriented towards increasing the abundance of the dominant pine species, resulting in a decrease in forest diversity and favoring a transition to a monospecific forest. The tree canopy structure following harvesting showed a gradual recovery in the number of individuals in each diameter class, but the diameter increment may not necessarily guarantee a sustainable harvest because cutting cycles appear to be too short. The size of harvesting gaps and overall forest cover determine the presence and/or abundance of regeneration (small seedlings, seedlings, saplings, large saplings, and young trees). The establishment of Pinus pseudostrobus and Ilex discolor Hemsl. differed according to their ecological groups.

Daños químico-mecánicos causados por el hongo de pudrición café Gloeophyllum trabeum (Pers.) Murrill en madera de Pinus pseudostrobus Lindl.

Introducción: La madera es propensa a ser utilizada como fuente de carbono por especies de hongos que la dañan. La durabilidad de la madera ha sido categorizada de acuerdo con la pérdida de peso sin considerar la disminución de las propiedades fisicoquímicas y mecánicas inherentes.
 Objetivo: Evaluar cómo afecta la pérdida de peso a las propiedades fisicoquímicas y mecánicas de la madera de Pinus pseudostrobus Lindl. expuesta al hongo de pudrición café Gloeophyllum trabeum (Pers.) Murrill.
 Materiales y métodos: Piezas de madera aserrada de P. pseudostrobus se inocularon con 50 mL de G. trabeum (10 6 UFC∙mL -1 ). Periódicamente (cero, tres, seis y nueve meses), y con la ayuda de una máquina universal de ensayo, se analizó la compresión paralela, la flexión estática (FE) y la compresión perpendicular a la fibra (CPF); además, se cuantificó la holocelulosa, celulosa y lignina.
 Resultados y discusión: Después de nueve meses de interacción con G. trabeum, las piezas de madera fueron resistentes a la degradación, considerando únicamente la pérdida de peso. No obstante, las propiedades químico-mecánicas mostraron que el hongo produjo adelgazamiento y ruptura de las células del tejido ocasionando disminución significativa de FE (100 a 56 N∙mm -2 ) y CPF (42.2 a 20.2 N∙mm -2 ), lo cual redujo su resistencia a los esfuerzos mecánicos.
 Conclusiones: La madera expuesta a la degradación por hongos está afectada significativamente en sus propiedades mecánicas, inhabilitándola para la construcción. Los daños no se reflejan en la estética del material, lo cual es alarmante, ya que el usuario común de la madera de pino no podría notar el problema.

Compatible Taper and Volume Systems Based on Volume Ratio Models for Four Pine Species in Oaxaca Mexico

Estimating tree volume components is an essential element in sustainable forest management. Compatible taper and merchantable outside-bark volume systems based on volume ratio models were globally fitted to four pine species (reduced models) with the aim to select the best reduced model and to fit it with dummy variables and additive effects using Pinus pseudostrobus Lindl as a base species. The study was carried out in the northern mountains of Oaxaca, Mexico. To fit the taper, merchantable volume, stem volume, branch volume, and total tree volume (stem volume and branch volume) equations, a taper dataset of 222, 230, 245, and 333 trees of Pinus douglasiana Martínez (Pd), Pinus oaxacana Mirov (Po), Pinus patula Schltd (Pp), and Pinus pseudostrobus Lindl (Pps), respectively, was used. In general, the compatible systems explained more than 97% in the observed variability for the four studied components: outside-bark diameter (d), merchantable outside-bark volume (Vm), stem outside-bark volume (Vs), and total tree volume (Vt). Alternatively, more than 52% of the observed variability for branch volume (Vb) was also explained. The developed compatible systems based on volume ratio models are a simple and consistent alternative for estimating the outside-bark diameter and variable outside-bark volume, as well as the components of commercial species for uneven-age and mixed-species forests in Oaxaca, Mexico.

Daños químico-mecánicos causados por el hongo de pudrición café Gloeophyllum trabeum (Pers.) Murrill en madera de Pinus pseudostrobus Lindl.

Introduction: Wood is susceptible to be used as a carbon source by fungal species damaging the wood. Its durability has been categorized according to its weight loss, without taking into account the decrease in the inherent physicochemical and mechanical properties. Objective: To evaluate how how weight loss affects the physicochemical and mechanical properties of Pinus pseudostrobus Lindl. wood exposed to brown-rot fungi Gloeophyllum trabeum (Pers.) Murrill. Materials and methods: Sawn timber pieces of P. pseudostrobus were inoculated with 50 mL of G. trabeum (106 UFC∙mL-1). Periodically (zero, three, six and nine months) and with the help of a universal testing machine, parallel compression (PC), static bending (SB) and perpendicular compression to the grain (CPG) were evaluated, and holocellulose, cellulose and lignin were quantified. Results and discussion: After nine months of interaction with G. trabeum, the pieces of wood were resistant to degradation, taking into account only weight loss. However, the chemical-mechanical properties evaluated showed that the fungus produced thinning and rupture of the tissue cells causing significant decrease in SB (100 to 56 N∙mm-2) and CPG (42.2 to 20.2 N∙mm-2), which reduced its resistance to mechanical stress. Conclusions: Wood exposed to fungal degradation is significantly affected in its mechanical properties, disqualifying it for construction. The damage is not reflected in the aesthetics of the material, which is surprising, since the common user of pine wood would not be able to notice the problem.

Estimación de biomasa aérea y carbono, en rodales con y sin manejo forestal en la Reserva de la Biosfera Mariposa Monarca

La estimación de biomasa aérea acumulada en un bosque con manejo para el aprovechamiento forestal maderable es de importancia para evaluar la sustentabilidad por efecto del sistema silvícola, y para entender la dinámica y funcionamiento de los ecosistemas forestales. La acumulación de biomasa aérea refleja la productividad en un sitio determinado. En este trabajo se estimó la biomasa aérea y el carbono, en rodales con y sin manejo forestal, en el Ejido Chincua, Senguio, Michoacán, a través de la generación de ecuaciones alométricas para Abies religiosa (Kunth) Schltdl. & Cham y Pinus pseudostrobus Lindl, mientras que para las latifoliadas se usaron ecuaciones de otros estudios y, además, mediante datos de inventario para todas las especies. El rodal sin manejo tuvo una biomasa de 323.23 Mg ha-1, mientras que el rodal con manejo 287.62 Mg ha-1, los cuales, a pesar de su variabilidad no presentan diferencias significativas (P = 0.96). El contenido de carbono tampoco presentó diferencias significativas (P = 0.97), siendo 155.03 Mg ha-1 y 128.44 Mg ha-1 en los rodales sin y con manejo, respectivamente. Los resultados indican que con el manejo forestal, bajo el sistema silvícola de selección, se conservaron la estructura y composición del rodal con manejo, lo que permitió mantener el almacén de biomasa en una cantidad similar a la de un bosque sin manejo; por lo anterior, los bosques manejados pueden ser sumideros eficientes de carbono, más la cantidad de este elemento en el proceso de cosecha y transformación de la madera a productos forestales de larga duración, como son madera para construcción, muebles, durmientes, postes, entre otros, que permiten su permanencia por periodos relativamente largos.

Priorities for Conservation and Sustainable Use of Forest Genetic Resources in Four Mexican Pines

The strategies for the conservation and sustainable use of forest genetic resources, which are essential for the future adaptation of forest species to changing environments, are also a source of valuable genetic resources for breeding and restoration activities. The first step to define and implement cost-effective strategies is to identify specific priority populations. Mexico, in spite of being characterized by high levels of tree species diversity, mostly lacks a combined strategy for the genetic conservation and use of forest genetic resources. The aims of this work are: (i) to identify areas for gene conservation, and (ii) to propose measures for the conservation and sustainable use of forest genetic resources of four pine species: Pinus greggii Engelm. ex Parl., Pinus oocarpa Schiede ex Schltdl., Pinus patula Schiede ex Schltdl. & Cham. and Pinus pseudostrobus Lindl. To do that, we use the existing information on the distribution, genetic variation and conservation and breeding efforts in Mexico. Overall, 51 areas for establishing genetic conservation units were prioritized and 6 genetic zones for the use of forest genetic resources in breeding and selection of forest reproductive material were identified. The current conservation efforts for the four priority Mexican pines should be improved to satisfy the needs of a national breeding and conservation network.

Estructura, composición y diversidad arbórea y arbustiva en tres condiciones de manejo forestal de Ixtlán de Juárez, Oaxaca.

Las prácticas forestales implican una serie de actividades que pueden generar impactos negativos en la dinámica natural de este ecosistema. El objetivo de este estudio fue evaluar el efecto del manejo forestal en la estructura, composición y diversidad arbórea y arbustiva en Ixtlán de Juárez, Oaxaca. Para ello se establecieron 15 unidades de muestreo distribuidas en tres condiciones de manejo: franjas no aprovechadas (FNA), bordes (B) y franjas aprovechadas (FA) establecidos en bosques con tratamiento de matarrasa. Se describen los cambios en estructura, composicón florística y diversidad de los estratos de árboles y arbustos. Durante el periodo de estudio se identificaron 27 especies vegetales distribuidas en nueve familias. Las especies más frecuentes fueron: Quercus crassifolia Humb & Bonpl., Pinus pseudostrobus Lindl. y Quercus laurina Humb. & Bonpl. Las curvas de acumulación de especies mostraron que las FNA tuvieron un mayor número de especies que las otras dos áreas. La estructura, estimada a partir de los índices de valor de importancia (IVI) y de valor forestal (IVF), estuvo asociada a la presencia de las tres especies previamente mencionadas en las tres condiciones. La categoría fustal fue la dominante en FNA y B; mientras que en FA las categorías dominantes fueron las de latizal y brinzal. Los valores de riqueza fueron bajos en FNA, B, FA, pero con valores altos de equidad. El valor de dominancia fue solamente alto en FA; B y FA fueron los más semejantes entre sí. Se concluye que las prácticas silviculturales promueven la conformación de un bosque coetáneo con dominancia de pinos. Este patrón es menos severo dada la presencia de las FNA, las cuales podrían limitar la pérdida de la diversidad arbórea y arbustiva.

Ecuaciones generalizadas altura-diámetro para bosques de Pinus pseudostrobus Lindl. en Nuevo San Juan Parangaricutiro, Michoacán, México

La estimación precisa de la altura total de los árboles es fundamental para el manejo forestal, pero la medición de todos los individuos en un inventario es prácticamente imposible por los tiempos y costos que genera. El objetivo de este trabajo fue ajustar una ecuación generalizada que estime la altura total como una función del diámetro normal (h-d) para bosques de Pinus pseudostrobus Lindl., en la comunidad indígena de Nuevo San Juan Parangaricutiro, Michoacán. Con datos de 158 sitios de inventario forestal, se ajustaron 12 modelos generalizados de h-d. El modelo de Wang y Tang, que incluye el diámetro normal y la altura media dominante, fue el mejor por presentar parámetros significativos, los mínimos valores del cuadrado medio del error, la raíz del cuadrado medio del error y el coeficiente de determinación ajustado. El análisis de puntos de influencia de los residuales estudentizados varió entre 2.5 y -2.5, mientras que la distancia de Cook no mostró problemas. La distribución de residuales fue homocedástica, el valor en la prueba de Durbin-Watson fue de 1.7 y la prueba de Shapiro-Wilk de 0.97. El índice de curtosis fue de -2.35 y la tendencia en la campana de Gauss fue leptocúrtica. El sesgo fue de 0.004 m y la diferencia agregada fue de -0.017%. El modelo seleccionado resultó confiable al estimar la altura total hasta los 60 cm de diámetro y se puede ser empleado en los inventarios forestales para la especie.

Isolation, characterization and effect of plant-growth-promoting rhizobacteria on pine seedlings (Pinus pseudostrobus Lindl.)

In this study, 10 bacterial strains were isolated from the rhizosphere of coniferous trees on Mount Tlaloc in Mexico. The strains were characterized by their capacity to produce auxins, solubilize phosphates and stimulate mycelial growth of the ectomycorrhizal fungus Suillus sp. All isolates were identified at the molecular level. Moreover, an experiment was established to evaluate the response of Pinus pseudostrobus seedlings to inoculation with the rhizobacteria strains. The isolated strains belonged to the species Cupriavidus basilensis, Rhodococcus qingshengii, R. erythropolis, Pseudomonas spp., P. gessardii, Stenotrophomonas rhizophila and Cohnella sp. All of the strains produced auxins; the best producer was R. erythropolis CPT9 (76.4 µg mL−1). P. gessardii CPT6 solubilized phosphate at a significant level (443 µg mL−1). The strain S. rhizophila CPT8 significantly increased the radial growth of the ectomycorrhizal fungus Suillus sp. by 18.8%. Five strains increased the dry mass of the shoots; R. qingshengii CPT4 and R. erythropolis CPT9 increased growth the most, by more than 20%. Inoculation with plant-growth-promoting rhizobacteria can be a very useful practice in a forest nursery to produce healthy, vigorous plants.

Taper and Volume Systems Based on Ratio Equations for Pinus pseudostrobus Lindl. in Mexico

Studies on functional relationships between relative stem diameter and height to estimate timber yield are useful in the management of commercial forest plantations. With taper analysis data of 42 Pinus pseudostrobus Lindl. trees in the indigenous community of Nuevo San Juan Parangaricutiro , Michoacan, Mexico, six compatible systems for predicting taper (d), merchantable volume (Vm), stem volume (Vs), total tree volume (Vt) and branch volume (Vb) were fitted and evaluated. The compatible taper and merchantable volume equations were based on volume ratio equations. Three Vs equations were tested in each system. In general, the compatible systems presented statistical accuracy in the d, Vm, Vs and Vt components but were less accurate in Vb. Three compatible systems were selected, according to their more efficient goodness-of-fit statistics, and a different total volume equation was incorporated into each system. The compatible systems based on volume ratio equations are simple, reliable tools for estimation of stand timber stocks and product classification of P. pseudostrobus in commercial forest plantations in Mexico.

Pool of Biological Resources for Potential Applications in Solid State Fermentation Obtained from a Forest Plantation of <i>Pinus pseudostrobus</i> Lindl, Mexico

A forest plantation, product of the reforestation of pine trees, represented a pool of biological resources for the implementation of a solid state fermentation process. The trees were identified as Pinus pseudostrobus Lindl from which lignocellulosic material in the form of pine needles was collected. Soil fungi, responsible for plant litter decomposition, were cultured at laboratory conditions and tested for their ability to grow on cellulose and hemicellulose as the sole carbon sources. A fungal strain, belonging to the genus Penicillium, was selected for growing it on pine needles as the substrate in a solid state culture. After following the culture for six days, the newly isolated strain exhibited a much higher capacity for spore production and holocellulose degradation, compared to a purchased strain of Penicillium chrysogenum and two control conditions. This work marks the beginning of future studies focused on commercial applications and represents the first report of a biotechnological process based on pine needles and their degradation by an ascomycetes species belonging to the genus Penicillium.

ALTITUDINAL GENETIC VARIATION AMONG Pinus pseudostrobus POPULATIONS FROM MICHOACÁN, MÉXICO. TWO LOCATION SHADEHOUSE TEST RESULTS

Pinus pseudostrobus Lindl. is the forest species most important economically in the state of Michoacán, at central-west México. We investigated genetic variation among P. pseudostrobus populations along an altitudinal gradient in the native indian community of Nuevo San Juan Parangaricutiro, Michoacán, México. Cones were collected from eight populations at 100 m of altitudinal intervals between 2200 m and 2900 m. Seedlings were grown for approximately two years in two shadehouse environments at Morelia, Michoacán, México and at Moscow, Idaho, USA. Total height was periodically measured during the second growing season to estimate a series of growth indexes for both locations, and dry weights were obtained only for the Morelia test. For the Moscow test there were significant differences (P < 0.05) among populations for cessation of growth, duration of the growth period, and final height. For the Morelia tests there were differences among populations for foliage, shoot and total dry weight (P < 0.025), and significant differences for stem dry weight at P = 0.055 level. There was a strong altitudinal cline for dry weight variables, with seedlings originated from populations from the lowest altitudes having more biomass (r2 = 0.80, P = 0.003). Populations separated altitudinally by about 295 m are likely to be genetically different. We suggest delineation of three altitudinal seed zones (Zone I: 2100 m to 2400 m; Zone II: 2400 m to 2700 m; Zone III: 2700 m to 3000 m), that can be translated into climatic zones delimited according to mean annual temperatures or by degree days > 5 °C. To accommodate climate change we suggest implementing assisted migration programs by transferring populations 300 m upwards to maintain adaptiveness of populations for future climates.

Genetic parameters for seedling growth in Pinus pseudostrobus families under different competitive environments

Pinus pseudostrobus Lindl. is a widely distributed species in Mexico that also occurs in Guatemala, Honduras and El Salvador and has been tested outside its natural range in Brazil, Chile, Colombia, New Zealand, South Africa and Venezuela. Due to its great potential, it is necessary to select genotypes capable of increasing its production in the shortest possible time through genetic improvement strategies, where individuals are subjected to conditions forcing them to express their growth potential in advance. The objectives of the present study were to evaluate the genetic variation among half-sib progenies and to estimate heritability (h 2 ) of stem height (SH) and diameter (SD) for seedlings grown under different competitive conditions in a common garden trial. A split-plot experimental design with four replications and three competitive environments (treatments) was used: (I) low inter-family competition (0.25 × 0.12 m), (II) high inter-family competition (0.12 × 0.06 m), and (III) high intra-family competition; 13 half-sib families were assessed, carrying out monthly evaluations for 10 months. Estimated h 2 at individual and family-means levels for both SH and SD varied among competitive environments. For conditions I and II, a trend towards increasing h 2 with age of seedlings was shown, but for condition III, a reverse trend was observed (values close to zero). High genetic stability in SH performance was found in both I and II, and II and III, pairs of environments, as measured by the type-B genetic correlation (0.70 ≤ r B ≤ 1.0), but it tended to decrease after 9 months, when competition increased; genetic stability in SD was lower (0.20 ≤ r B ≤ 0.80) in both pairs of the environments that were sampled. It was concluded that the competition conditions used in field trials for genotype evaluation may significantly affect the variance components, estimation of genetic parameters and genotype stability.

Experimental determination and modeling of equilibrium moisture content from the sapwood of Mexican pine (Pinus pseudostrobus Lindl.)

A desorption isotherm is a very important basis in the understanding of drying process. In this study, the desorption isotherms from the sapwood of Mexican pine (Pinus pseudostrobus Lindl.) were determined by the gravimetric method (discontinuous control of sample weight) at 30°C and 50°C. The salt method was used in the range of water activities from 0.11 to 0.89. The results show that the desorption ability of Mexican pine sapwood increased with temperature at a given relative humidity. The experimental data was further simulated with the models, i.e., BET, GAB, Oswin and Henderson models. The GAB, Oswin and Henderson models allow the representation of the entire desorption isotherms. The BET model showed a better fit for water activity lower than 0.35, with a mean relative deviation of 0.0286 at 30°C and 0.0167 at 50°C. Simultaneously, the BET model gave a better representation of moisture content in the monolayer saturation region. Overall, the GAB model ensured the best simulation of the entire isotherm, while the Henderson model displayed the worst simulation.

Stemflow variation in Mexico’s northeastern forest communities: Its contribution to soil moisture content and aquifer recharge

► A comprehensive stemflow dataset was collected for two Mexico’s northern plant communities. ► For each species and for each stand, stemflow coefficients and infiltration depths are reported. ► Statistical stemflow differences are found between the species, plant communities and stands. ► Stemflow extrapolated threefold from trees to stands because of overstocked forests. ► Temperate forest stemflow appears to contribute to aquifer recharge because of shallow soils. Stemflow hydro-ecological importance was measured in trees and assessed in Mexico’s northeast forest stands by answering three basic questions: (a) what are the intra and inter-specific stemflow variations; (b) is the stemflow coefficient constant from tree level to stand scales? and (c) what is the stemflow area and wetted soil volume in individual trees and the stemflow volume discharged at the stand scale in two plant communities of northeastern Mexico? Gross rainfall and stemflow flux measurements were conducted on 78 trees of semi-arid, sub-tropical (31 Diospyros texana ; 14 Acacia rigidula ; four Bumelia celastrina ; five Condalia hookeri ; three Cordia bioissieri ; three Pithecellobium pallens ) and temperate forest communities (six Pinus pseudostrobus Lindl. and 12 Quercus spp.). Stemflow was extrapolated from individual trees to the stand scale using 98 inventory plots (1600 m 2 ha −1 each) placed in oak–pine forests and 37 quadrats (5 m × 5 m each) distributed across the Tamaulipan thornscrub forest range. Stemflow infiltration flux and infiltration area measurements assessed the wetted soil volume. Daily measurements were conducted from May of 1997 to November of 1998. Results showed that stemflow coefficients varied between plant communities since they averaged (confidence intervals, α = 0.05) 2.49% (0.57), 0.30% (0.09), and 0.77% (0.27) of the bulk precipitation for Tamaulipan thornscrub, pine, and oak forests, respectively. Intra-specific stemflow variations could not be identified in Tamaulipan although in temperate tree species. Basal diameter explained intra-specific stemflow variation in both plant communities. Stemflow increased threefold since it accounted for by 6.38% and 2.19% of the total bulk rainfall for Tamaulipan thornscrub quadrats and temperate oak–pine inventory plots, respectively. Small shrubs growing underneath large trees, in combination with the presence of small-diameter trees that recorded the largest stemflow coefficients appear to explain the increase of the stemflow coefficient from trees to stands. Stemflow replenishes soil moisture on the average 4.5 (1.4) times larger than does incident rainfall in open soils and appear to contribute to aquifer recharge in temperate forests due to a combination of shallow soils, high infiltration fluxes and the stemflow volume generated during rainfalls with depths >15 mm. Tracing studies should be conducted to test the hypothesis of the stemflow contribution to aquifer recharge in temperate forests of northeastern Mexico.

Response of Pinus pseudostrobus Lindl. to fertile growing medium and tephra-layer depth under greenhouse conditions

Major disturbances that remove vegetation cover create conditions that differ greatly from those in adjacent forests. In volcanic areas, tephra deposition can be a major disturbance that eliminates vegetation cover and creates a barrier for plant establishment. The eruption of the Paricutin volcano, in Michoacan, Mexico, from 1943 to 1952, created large tephra deposits adjacent to forest stands. Many of these deposits still lack native vegetation and understanding of the limiting factors for establishment of native tree species is necessary to restore these areas. Pinus pseudostrobus early growth in response to the amount of fertile growing medium on top of a variable-depth tephra layer was evaluated in a greenhouse experiment. Increasing amounts of fertile growing medium increased height of 28-week-old plants (no growing medium = 5.5 cm tall ±1.8 cm, 3 cm of growing medium = 21.2 ± 4.6 cm and 6 cm of growing medium 24.8 ± 4.4 cm). Other variables showed the same trend (diameter, number of fascicles, belowground biomass and aboveground biomass). Our results suggest that P. pseudostrobus establishment in tephra covered areas will depend on the accumulation of a fertile layer of more than 3 cm in thickness.