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Objective: to construct a dynamic stochastic model with validated biospheric-interaction, estimating allometric equations for the total volumetric increase and cumulative distribution of biomass for Pinus hartwegii Lindl in the states of Mexico and Puebla, considering climate change. Design/Methodology/Approach: the methodology included the use of SiBiFor numerical databases, NASA Power data, Ordinary Least Squares mathematical models, the Random-Forest software, Ridge model with regression, R algorithms and Newton volumetric estimation equations. Results: estimated allometric equations were obtained for the total volume of trees in 2023, highlighting the importance of linear regression models and the validity of the variables used. Newton's mathematical equations and theoretical models for excurrent tree-form types were found to have the best accuracy in estimating the total volume of the barked tree. Limitations of the study/Implications: this study has limitations in terms of generalization to other forest types and the availability of data in Mexico. However, it highlights the importance of understanding forest responses to environmental changes and the need for validated dynamic stochastic models to estimate allometric equations and assess carbon sequestration. Findings/Conclusions: this study highlights the importance of understanding and assessing the carbon storage capacity of forests, especially in the context of climate change. In addition, it underlines the usefulness of linear regression models and variable validation to estimate carbon sequestration in Pinus hartwegii forests. [ABSTRACT FROM AUTHOR]

Climate change has very important effects on high mountain forests (>3500 masl), which face various ecological problems associated with global change including the proliferation of pests and parasitic plants. These sensitive ecological systems cover approximately 39,000 ha of Mexican territory and occur around some of the highest volcanoes in the country. The objective of this research was to determine the spatial distribution and infestation levels of dwarf mistletoe (Arceuthobium spp.) in the main populations of Pinus hartwegii in five mountains of the Trans-Mexican Volcanic System (Pico de Orizaba, Nevado de Toluca, Cofre de Perote, Nevado de Colima and Monte Tláloc) and identify infestation patterns in relation to the structure of the forest. In the study, 2658 sampling sites (1000 m² each) were installed using the contour lines as access transects to the forest, distributed at every 100 of altitude, between 3500 and 4000 masl. Approximately 32 % of the sampled area had some level of attack by dwarf mistletoe, distributed across all diameter categories of the trees. The infestations affected the establishment of natural regeneration and rates of tree mortality.

In this work, we propose that small wood core samples (≤10 cm length), taken from 0.3 m above the soil, represent an accurate means of correlating forest growth with remote sensing data. Short-term correlations between the Normalized Difference Vegetation Index (NDVI) and tree-ring components of the last three to four decades were tested, using 210 Pinus hartwegii wood cores collected at two locations, Tláloc (TLA) and Jocotitlán (JOCO) in central Mexico. The NDVI time series were generated with the Google Earth Engine (GEE) using Landsat 8 images. Also, seasonal trends in NDVI (e.g., spring, summer, autumn, winter) were analyzed through longitudinal analysis. The results showed more statistically significant dendrochronological indices in TLA than in JOCO, but both locations consistently showed an NDVI decrease in 2018 and 2020, indicating a reduction in vegetation vigor. At the two locations, the minimum and maximum NDVI occurred in April and October, respectively. Seasonal NDVI changes for spring were mainly seen at TLA with a decreasing trend, which may be related to a less defined dry season. The significant correlations (p < 0.05) between tree-ring components and the NDVI occurred in the dry season, indicating that the productivity of a given year is defined by the tree vigor shown in April and May, in the case of TLA, and between January and March, for JOCO. Although the NDVI values of JOCO were higher than those of TLA, tree growth, expressed by tree-ring indices, was lower. Our proposed field method to correlate tree-ring information and the NDVI is reliable and can be used in other coniferous forests. [ABSTRACT FROM AUTHOR]

The impact of volcanic eruptions on humans and infrastructure has been significant and widely documented. However, the impact on forests covered by ash or tephra has not been as widely known or documented. This research evaluated the ashfall effects of the 1943–1952 Parícutin eruption on the radial growth of trees located near the top and flanks of the Tancítaro stratovolcano, ca.10 km southwest of the Parícutin volcano. We carried a dendrochronological sampling out in a temperate forest dominated by Pinus hartwegii and Abies religiosa trees. A ring-width chronology was built with 68 increment cores from 47 trees showed two statistically significant suppression events. The first event occurred from 1943 to 1946; it was caused by falling ash of the eruptive columns from Parícutin during the first 6 months of its eruption (February–June 1943). The second event occurred from 1818 to 1823, and it is attributed to the 1818 eruption of Volcán de Colima. The 1943–1946 suppression event observed in the tree rings demonstrates that trees are useful as palaeoenvironmental archives to evaluate the influence of volcanic eruptions in recent centuries in the Trans-Mexican Volcanic Belt. Our results indicate that falling ash immediately impacted the growth of trees in intertropical mountain zones of the Michoacan state located in the Michoacán-Guanajuato Volcanic Field. Such impact means that future eruptions may cause damage to crops and trees at the local and regional levels. Our findings contribute to evaluating volcanic hazards and risks in areas with active volcanoes and monogenetic volcanic fields. [ABSTRACT FROM AUTHOR]

Fire is considered a relevant ecological factor, however, human alterations of fire regime facilitate more destructive wildfires. The aims of this work were to model probability of tree mortality and to identify the factors associated with leader shoot growth in a prescribed burn area and in a nearby wildfire area in a juvenile Pinus hartwegii Lindl. stand in central Mexico. A prescribed burn was carried out in 10-ha stand in March 2012, and compared with a close area affected by a wildfire occurred one week later, as well as with a nearby unburned area taken as control. A logistic model was used to estimate the probability of mortality, and a linear regression model was employed to investigate factors related to leader shoot growth. No tree mortality was recorded in the unburned control. In contrast, mortality was 6% in the prescribed burn and 66.9% in the wildfire area. The probability of mortality was influenced by stem char height (positively, p

Cut stumps are the legacy of forest harvesting and allow for the estimation of carbon loss from the ecosystem. The objective of this study was to estimate aboveground carbon storage and the impact of forest harvesting based on measurements of cut stumps in pine forests within the Área de Protección de Flora y Fauna Nevado de Toluca (APFFNT) in the state of México. A total of 1621 circular 0.1-ha sampling plots were established in a 12,924 ha pine forest (1.25% sampling intensity). Biomass was calculated using conventional volumetric equations incorporating species-specific wood densities. Aboveground carbon storage in the biomass was stratified by forest type including dense forest (≥ 336 trees), semi-dense forest (< 335 and > 150 trees), fragmented forest (< 150 and > 20 trees), and stands with isolated trees (< 20 trees). In the 12, 924 ha of forest dominated by Pinus hartwegii, 1,695,004 MgC was contained in aboveground biomass. Data on forest harvesting obtained by analysis of recent cut stumps allowed for the estimation of the removal of 42,701 MgC. In addition, we accounted for carbon in wind thrown trees of 14,904 MgC, some of which were removed over time in harvests. Total loss of carbon from the forest corresponded to 211,218 MgCO2 per year. In the APFFNT, forests dominated by pine with high biomass (P. hartwegii and P. montezumae) are being replaced by those with lower biomass (Alnus jorullensis). Changes in these communities will result in lower carbon capture in the APFFNT. [ABSTRACT FROM AUTHOR]

Lava flow, pyroclastic flows and ash deposition can impair the vitality and growth of tree growing on or next to volcanoes, and sometimes even remove entire forest stands. In the case that trees are only injured, but not killed, past volcanic process activity can be analyzed through the growth disturbances left in the tree-ring records. We investigated disturbances in growth ring series of Pinus hartwegii trees associated with a pyroclastic flow that covered portions of the northern flank of Popocatépetl volcano on 22 January 2001. In addition, we also documented the post-eruptive colonization of trees on the resulting deposit. The pyroclastic flow burned and killed at least 190 trees and locally shifted the timberline downslope by ~40 m in elevation. A large number of trees were injured to show noticeable fire scars. We analyzed and characterize the damage in flow-surviving trees. Sixteen years after the event, whorl counts on 244 P. hartwegii shoots growing on the surface of the pyroclastic flow deposit showed average ages of 8 yr (this is the age at ~1.4 m height). The ecesis interval or Germination Lag Time (GLT) of trees on the pyroclastic flow deposit was 7 yrs (±2 yr), and the Colonization Time Gap (CTG) was 15 yrs on average (CTG is the sum of GLT and the interval between seedling germination and growth at ~1.4 m height), with local differences related to altitude and/or location on the bare surface. Results obtained at this site can be used to date and to identify the extent of pyroclastic flow deposits on active volcanoes, thereby providing valuable information on the volcanic history (in terms of frequency and runout distances) and therefore also for hazard prevention plans. In addition, it can be useful to calibrate the minimum ages of volcanic landforms. Unlabelled Image • Tree-ring analysis allows characterization of damage caused by a pyroclastic flow to timberline pines. • The pyroclastic flow killed > 190 trees and locally shifted timberline ~40 m downslope. • Spati-temporal patterns of post-eruptive colonization are controlled by altitude, seed sources and geomorphology. [ABSTRACT FROM AUTHOR]

Key message: Under climate warming the presence of key microsite facilitators modify soil moisture levels associated with successful tree recruitment at the treeline ecotone ofPinus hartwegii. Alpine treelines in Mexico are represented by high-elevation forests dominated by P. hartwegii Ldl. To address the degree to which the presence of suitable microsite facilitators are factors for successful recruitment within the treeline ecotone of P. hartwegii and modulate their responses to climate warming, year of natural tree establishment, number of trees recruited, and the presence of shelter elements at different exposures of Monte Tlaloc (in the Trans-Mexican Volcanic System) were recorded. For tree recruitment and microsite facilitation we recorded each tree and the type of potentially protective elements that may improve microsite conditions within a total of 32 circular plots (r = 18 m) in the alpine treeline ecotone (above 4000 m). Temperatures for Monte Tlaloc at 4000 m were estimated using the thermal gradient for the study area, and standard dendrochronological methods and a regression model were used to date tree recruitment. Vector generalized linear models show that maximum growing season temperatures have significantly influenced the temporal pattern of tree recruitment in this system over the past 50 years, but this influence was mediated by the presence (or absence) of specific shelter elements (shrubs, soil depressions, rocks or bare soil) within a specific treeline ecotone exposure, also shaping the spatial pattern of tree recruitment. The response of the treeline ecotone to climate warming at local scales is qualitatively modified by the presence of microscale features, requiring sufficient soil moisture to be available on the site of recruitment. [ABSTRACT FROM AUTHOR]

The wood density of the forest species that form annual growth rings represents a natural archive related with climate variability. The objective of this study was to evaluate if the X-ray computed tomography (XRCT) method is able to detect radial changes in wood density and if it varies according to altitude and exposition of the site; therefore, that method with a medical equipment (XRCT) was used to obtain radial density profiles for Pinus hartwegii Lind. The wood samples came from four contrasting sites at the Tláloc volcano, two altitudinal levels (3500 and 3900 masl), and two exposition levels (NW and SW). A general linear model --including the total ring width as a co-variable-- was used to evaluate the simple and interaction effects of altitude and exposition on wood density. There were statistically significant differences among sites (p≤0.001). The altitude*exposition interaction was significant (p≤0.001), which indicated that changes in wood density are influenced by altitude; however, the degree of change depends on the exposition. In the NW exposition, altitude had a positive effect on wood density, while, in the SW exposition, there was no effect. There was a greater wood density in the site with NW exposition and an altitude of 3500 masl. The ring width --as a transformed variable-- helps to explain a significant part of the variance of the radial density of wood between sites. X-ray computed tomography allowed to study the variation of wood density and, reliably and accurately, to deduce which changes can be attributed to the recent climate variation. [ABSTRACT FROM AUTHOR]

Arthropod communities and epiphytic plants associated with tree canopies have been widely studied and have revealed a great diversity of organisms; however, the community hosted by parasitic plants, such as dwarf mistletoes, remains poorly known. In the coniferous forests of North America, dwarf mistletoe infection (Arceuthobium spp.) significantly damages the health of the forest, causing large financial losses for the forest industry, but it also positively affects diversity, especially of mammals and birds. This study examined the attributes of the arthropod communities associated with two species of dwarf mistletoe [Arceuthobium globosum Hawksw. & Wiens and A. vaginatum (Humb. & Bonpl. ex Willd.) J. Presl] and their host Pinus hartwegii Lindl. In 2010, in five sites located in Zoquiapan (Central Mexico), we collected plant tissue from the three species bimonthly. Arthropods were separated from the plant tissue and identified to the finest level possible. We collected 32,059 individuals, for which 51 morphospecies were identified, belonging to 15 taxonomic orders; the most abundant orders for the three plants were Prostigmata, Thysanoptera and Homoptera. The community associated with P. hartwegii had the highest value of diversity (H′ = 1.47; A. globosum, H′ = 0.64; A. vaginatum, H′ = 0.68) and species richness (S = 40; A. globosum, S = 30; A. vaginatum, S = 35); while abundance was significantly higher for the mistletoes (A. globosum, n = 407 individuals/sample; A. vaginatum, n = 536 individuals/sample; P. hartwegii, n = 134 individuals/sample). Species richness, abundance and diversity were significantly different for the three studied plants, as well for sampling month and the interaction of these two factors (except for diversity). The results suggest that the canopy of P. hartwegii is an important element in the ecosystem, providing a mosaic of resources and conditions to the associated fauna. We also propose that mistletoes are key species within the forest canopy, as they greatly influence the establishment of diverse organisms, particularly arthropods. [ABSTRACT FROM AUTHOR]

Resumen. El bosque de Pinus hartwegii constituye el límite superior arbóreo en las montañas de México. En este estudio se desarrolló una red de cronologías de esta especie, localizadas en volcanes del Eje Neovolcánico Transversal, en el centro del país, y picos elevados de la Sierra Madre Oriental, en el noreste. El Análisis de Componentes Principales integró las cronologías en dos grupos, uno para el centro y otro para el noreste, con los que se desarrollaron dos cronologías regionales de 320 años (1690-2009) y 590 años (1420- 2009), respectivamente. El fenómeno de El Niño Oscilación del Sur (ENSO) en su fase cálida (El Niño) y fría (La Niña), mostró un impacto significativo en el comportamiento de la variabilidad hidroclimática descrita por ambas series. La Niña produjo condiciones climáticas contrastantes, es decir, secas en el noreste y húmedas en el centro, mientras que la fase de El Niño originó sequías en ambas regiones, pero solo durante eventos intensos de ENSO.

Few studies have focused on analyzing the effect of native inoculated ectomycorrhizal (ECM) fungal strains on seedlings under field conditions in temperate forests. However, it is crucial to verify that the positive effects of ECM under nursery conditions also occur in the field, favoring their performance. We evaluated the short-term effect of ECM on three-year-old seedlings of Pinus hartwegii and Abies religiosa in central Mexico by subjecting them to four treatments: inoculation with Inocybe splendens, inoculation with Suillus brevipes (both native strains), inoculation with forest soil, and non-inoculated plants. Percentage of ECM colonization, plant growth (shoot height and stem diameter), and physiological (osmotic potential, stomatal conductance, CO assimilation and water use efficiency) responses were evaluated. We found that these two ECM species were partial ( P. hartwegii) or totally ( A. religiosa) replaced after one and a half years in the field. P. hartwegii seedlings increased their water use efficiency during the dry season, but in A. religiosa seedlings, a clear strategy for avoiding water stress was not detected. This ECM replacement had a negative effect on the physiological performance Of A. religiosa. Our results emphasize the importance of selecting compatible fungal-host species combinations for nursery inoculation and of using sources of inoculum adapted to the environmental conditions of the transplant site, ensuring root colonization prior to field transplanting to minimize seedling mortality due to water stress. [ABSTRACT FROM AUTHOR]

In this study, dendrogeomorphic techniques are employed to analyse the temporal frequency and spatial distribution of rockfalls on a talus slope of La Teta valley, located on the NW slopes of Cofre de Perote volcano at ~ 4000 m above sea level. Based on the interpretation of disturbance signals in growth rings of old-growth Pinus hartwegii Lindl. trees, we identify 100 growth disturbances related with rockfall events dated between 1780 and 2011, with slightly more than half of these events being dated to the last 50 years. The sectors most susceptible to rockfall correspond with the young rock lobes located at the foot of scarps. Roughly three in ten events has been triggered by regional, M > 6 earthquakes, whereas half of the events activity coincides with periods characterized by severe, prolonged summer rainfalls such as the ones occurred in 1995, 1998, 2005 and 2011. [ABSTRACT FROM AUTHOR]

Key message : An increase in winter-spring precipitation appears to have a positive effect on radial growth of P. hartwegii a treeline species in Mexican volcanoes. Abstract: To address the degree to which high-elevation trees reflect climatic variability, a ring-width chronology of 308 years (1705-2012) was developed from a pure stand of Pinus hartwegii forest at the upper treeline of Monte Tlaloc in the Trans-Mexican Volcanic System. A series of variables were used to verify the climatic correlation of the chronology, including climate data, historical archives dealing with agricultural crises and climate anomalies in central Mexico, regional dendroclimatic reconstructions of precipitation, values of the Southern Oscillation Index (SOI), and Tropical Rainfall Index, which are estimators of El Niño/Southern Oscillation phenomena (ENSO). Correlations with local and regional climate data suggested that wet conditions in the winter-spring season had a positive effect on radial growth. Reduced growth was associated with extreme droughts in central Mexico, with some exceptions, such as in 1997, when, due to the massive warming of sea surface temperatures and low precipitation, growth did not begin until May or June and peaked during the cool season. The ring-width chronology indicated an increase in radial growth when SOI values were negative and precipitation was above-mean during the growing season. The lowest recorded growth measurements are associated with extreme droughts and strong warm ENSO events. Given the significant relationship between climate and radial growth of P. hartwegii, this study highlights the potential vulnerability of this high-elevation species to climate change. [ABSTRACT FROM AUTHOR]

The upper timberline in Mexico is expected to be sensitive to climate change. Therefore, Pinus hartwegii recruitment at Monte Tlaloc's tree line ecotone, in the Estado de Mexico, was analyzed, in order to detect a possible progress in the altitude interval of the species, as a result of higher temperatures. To explore the influence of climate in the recruitment pattern, we compared the age frequency of P. hartwegii with temperature and rainfall; additionally, we analyzed this impact on the basis of the year to year change in the thickness of their growth rings and its relationship with the El Niño-Southern Oscillation (ENSO). The age frequency was based on a 269 trees simple; their growth rings were dated a year after they were formed. P. hartwegii recruitment has increased since the late 1970s, which matches the rise in temperature, especially during El Niño events. This situation was made evident by a lower radial increase than the mean of trees found below the upper timberline. The wet periods detected in the years before the greater recruitment years could imply that optimal temperature conditions at greater altitude are not enough to promote a progress in the wider distribution of the species, but that the wetness level must be enough to optimize its development. The lack of synchrony between the recruitment and the radial growth of trees established at lower altitudes suggests an opposite climate impact in the species' growth, which implies a possible long-term withdrawal of the altitude extent. [ABSTRACT FROM AUTHOR]

Se evaluó la supervivencia y crecimiento de tres especies arbóreas bajo diferentes tratamientos de micorrización (Quercus rugosa), y cobertura vegetal (Abies religiosa y Pinus hartwegii) con el objetivo de recomendar los tratamientos para la restauración y manejo del bosque en la cuenca del río Magdalena. La supervivencia, la altura y el diámetro del tallo se evaluaron a lo largo de un año, de agosto de 2006 a agosto de 2007. Los porcentajes de supervivencia más bajos se registraron tanto en Abies religiosa como en Pinus hartwegii en el tratamiento sin vegetación. En el caso Quercus rugosa en el tratamiento con micorrizas fue donde se presentó mayor supervivencia. Asimismo las plantas de Quercus rugosa con micorrizas alcanzaron significativamente un mayor crecimiento en altura que las no inoculadas. Los tratamientos utilizados fueron exitosos para las tres especies arbóreas por lo que se recomienda reforestar adecuadamente con estas especies para un mejor manejo de cada tipo de vegetación dentro de la cuenca del río Magdalena.

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El bosque de Pinus hartwegii constituye el límite superior arbóreo en las montañas de México. En este estudio se desarrolló una red de cronologías de esta especie, localizadas en volcanes del Eje Neovolcánico Transversal, en el centro del país, y picos elevados de la Sierra Madre Oriental, en el Noreste. El Análisis de Componentes Principales integró las cronologías en dos grupos, uno para el centro y otro para el Noreste, con los que se desarrollaron dos cronologías regionales de 320 años (1690-2009) y 590 años (1420-2009), respectivamente. El fenómeno de El Niño Oscilación del Sur (ENSO) en su fase cálida (El Niño) y fría (La Niña), mostró un impacto significativo en el comportamiento de la variabilidad hidroclimática descrita por ambas series. La Niña produjo condiciones climáticas contrastantes, es decir, secas en el Noreste y húmedas en el centro, mientras que la fase de El Niño originó sequías en ambas regiones, pero sólo durante eventos intensos de ENSO.

Dwarf mistletoes are widely studied because of their significant impact on host populations; however, few studies have focused on sympatric species. The understanding of their coexistence is important because it can provide useful knowledge for future management plans. We investigated the incidence, severity, and aggregation patterns of Arceuthobium vaginatum and A. globosum coexisting in Central Mexico. We estimated the correlation between both species incidences ( N = 75 plots), the incidence-severity correlation ( N = 47 plots) for each species, and the effect of biotic (host and non-host species abundance) and abiotic (altitude and slope) factors on the mistletoe incidence. In addition, we compared the hierarchical aggregation among and within plots of the two mistletoe species with a χ test. There is a clear dominance of A. vaginatum in the area, and both species incidences are negatively correlated with each other ( r = − 0.54, P < 0.05) and host abundance ( r = − 0.26, P < 0.05). The remaining factors were non-significant. Both species have a linear relationship between incidence and severity, i.e., they show a uniform increase in severity with incidence, which could help diagnose the degree of tree infection from incidence measurements. The species are aggregated within plots, but only A. globosum shows an aggregation among plots ( χ = 82.25, P < 0.001); aggregation has not been shown previously for two sympatric dwarf mistletoe species. Our results can improve the scientific basis for forest management planning to control dwarf mistletoe and maintain biodiversity. [ABSTRACT FROM AUTHOR]

The objective of this research was to characterize the pattern of spatial structure of a Pinus hartwegii forest in the Sierra Madre Oriental, affected by a fire in 1998. Sampling was stratified by fire severity. Three fire severity classes were defined based on the degree of crown consumption (low, medium and high). Three sample plots of 40m x 40m were established for each severity. The variables obtained for all trees with a diameter at breast height (DBH) ≥ 5 cm in each plot were: DBH to 1.30 m (cm), height (m), spatial location by recording the azimuth (°) and distance (m) from center of the plot to each tree. To describe the stand structure three groups of indices were employed: “contagion†and “distances†(Wi and Di), “dominance†(Ui), and “size differentiation†(TDi and THi) for DBH and height respectively. An analysis of variance was performed to detect differences between dasometrics parameters by fire severity. Statistical analysis shows significant differences (p>0.001) in the parameters such as basal area, diameter, and height, along the low, medium, and high fire severities. The characterization of the Pinus hartwegii spatial structure suggests that, with increasing degree of fire severity, the stands showed an increase on the aggregation index, however, the dimensional differentiation and dominance indices decreases as the fire severity increases.

Hydraulic failure can cause massive die-back of forest trees during drought. With extreme climatic events set to become more frequent and severe due to climatic change, it is essential to study resistance to water stress-induced cavitation. We investigated the genetic differentiation for cavitation resistance among Pinus hartwegii populations, the pine species growing at the treeline in México. Open-pollinated seeds were collected from seven natural populations along an altitudinal gradient (3,150-3,650 masl) from Pico de Tancítaro, Michoacán, western México. Seedlings were raised in a nursery and then established in a randomized complete block design in a common garden experiment. Resistance to cavitation ( P, xylem pressure inducing 50 % loss of hydraulic conductance and S, slope of the vulnerability curve) and specific hydraulic conductivity ( k), were evaluated on branches of 5-year-old seedlings using the Cavitron technique. Mean P was −3.42 ± 0.05 MPa, indicating that Pinus hartwegii is one of the more vulnerable pine species to cavitation. No significant genetic differentiation was detected between populations for cavitation resistance traits ( P and S), but a significant altitudinal cline was found for S. In contrast, k exhibited a significant differentiation among populations and a significant decline with increasing altitude. The lack of genetic differentiation among P. hartwegii populations for cavitation resistance is likely to represent a limitation for adapting to the warmer and drier climates that are expected to occur in México under climatic change. Finally, a worldwide comparison within the Pinus genus showed that pines growing at the treeline were on average more vulnerable to cavitation than those from lowland. This might reflect an adaptation to dry environmental conditions at low elevation. [ABSTRACT FROM AUTHOR]

Human-induced changes in atmospheric composition are expected to affect primary productivity across terrestrial biomes. Recent changes in productivity have been observed in many forest ecosystems, but low-latitude upper tree line forests remain to be investigated. Here, we use dendrochronological methods and isotopic analysis to examine changes in productivity, and their physiological basis, in Abies religiosa (Ar) and Pinus hartwegii (Ph) trees growing in high-elevation forests of central Mexico. Six sites were selected across a longitudinal transect (Transverse Volcanic Axis), from the Pacific Ocean toward the Gulf of Mexico, where mature dominant trees were sampled at altitudes ranging from 3200 to 4000 m asl. A total of 60 Ar and 84 Ph trees were analyzed to describe changes in growth (annual-resolution) and isotopic composition (decadal-resolution) since the early 1900s. Our results show an initial widespread increase in basal area increment ( BAI) during the first half of the past century. However, BAI has decreased significantly since the 1950s with accentuated decline after the 1980s in both species and across sites. We found a consistent reduction in atmosphere to wood 13C discrimination, resulting from increasing water use efficiency (20-60%), coinciding with rising atmospheric CO2. Changes in 13C discrimination were not followed, however, by shifts in tree ring δ18O, indicating site- and species-specific differences in water source or uptake strategy. Our results indicate that CO2 stimulation has not been enough to counteract warming-induced drought stress, but other stressors, such as progressive nutrient limitation, could also have contributed to growth decline. Future studies should explore the distinct role of resource limitation (water vs. nutrients) in modulating the response of high-elevation ecosystems to atmospheric change. [ABSTRACT FROM AUTHOR]

Carbon content of aboveground biomass of six types of vegetation cover in the Magdalena River basin, located in the conservation land in the Mexico City, was estimated. Hence, a map of cover vegetation and land use to the study area was made; a hierarchical stratified sampling design with distribution systematic with a mesh of sampling sites equidistant of 550 meters was used for field work. The method used for field data collection was based on a nested design, with an intensity of sample of 0,64%. There were generated 52 sites of 3000 m². The vegetation cover that showed the highest amount of carbon stored corresponds to the forest of the the Abies religiosa closed with 163 Mg C ha-1 in average; followed by the Abies religiosa - Pinus hartwegii closed with 107 Mg C ha-1, and Abies religiosa opened with 95 Mg C ha-1; about the covers of Pinus sp., Pinus hartwegii closed with 47 Mg C ha-1; Pinus hartwegii - Abies religiosa closed with 39 Mg C ha-1 and Pinus hartwegii opened with 21 Mg C ha-1. [ABSTRACT FROM AUTHOR]

Surface fire has increasingly been regarded as a critical threat to tropical forests, but much of the research documenting degradation of tropical forests by fire comes from the low-elevation humid tropics. Fire in high-elevation tropical forests has received less research attention, but these forests are of high conservation value because they support unique ecosystems, which are often isolated due to their restriction to widely separated peaks., We investigated the frequency and ecological impact of fire on a high-elevation tropical forest of Pinus hartwegii in Pico de Orizaba National Park in central Mexico. This forest was previously thought to have been degraded by excessive human-caused fires. We assessed human-caused changes to the fire regime as well as the impact of climate on fire occurrence, both previously undocumented in this region., We found no increase in fire frequency or evidence of degradation of the forest. We found that the forest was uneven-aged and contained many large and old trees (maximum age 483 years). In the twentieth century, the forest experienced a frequent surface fire regime, with fires scarring trees in 90 of 100 years. However, most fires were small and asynchronous among sites. Inter-annual climatic variability was not an influential driver of fire, and El Niño- Southern Oscillation was not significantly related to the occurrence of widespread fire., Synthesis and applications. Our results show that this high-elevation tropical forest has not been degraded but has existed with frequent fires for at least a century. A trend in the 21st century towards less-frequent fire could be cause for concern, as a decrease in fire frequency could lead to an increase in tree density and a loss of resilience in the face of climate change and other future disturbance. We recommend that managers take into account historical fire regimes in their local areas: frequent surface fires in the case of Pico de Orizaba. It is important to recognize that although fire can be detrimental in many low-elevation tropical forests, it is an integral part of this high-elevation tropical forest ecosystem, and other high-elevation forests may show similar patterns. [ABSTRACT FROM AUTHOR]

Dwarf mistletoes (Arceuthobium spp.) are important plants in temperate forests of Mexico due to their high incidence. At the south side of the Papayo Hill in the "Zoquiapan y Anexas" Natural Protected Area, Mexico State, both, Arceuthobium vaginatum subsp. vaginatum and A. globosum subsp. grandicaule coexist within the same zone and, frequently, on the same host tree of the species Pinus hartwegii. We studied the vertical distribution of both species on the stem, and we registered that A. vaginatum is found more frequently to lower heights of the pines than A. globosum. These results suggest that the nutritional resources are taken in a differential manner, causing a probable competitive relation between the two species. [ABSTRACT FROM AUTHOR]

The El Niño Southern Oscillation (ENSO) is a climate-forcing mechanism that has been shown to affect precipitation and the occurrence of wildfires in many parts of the world. In the southern United States and northern Mexico, warm events (El Niño) are associated with moist winter conditions and fewer fires, while cool events (La Niña) tend to favor dry winters and more fires. We tested this relationship in a region of northeastern Mexico by characterizing the historical fire regime and climatic influences. Fire regimes were reconstructed from fire-scar samples collected from 100 trees in three high-elevation sites on Peña Nevada in southern Nuevo León. The sites were ∼25 ha each, and the site centers were ∼1 km apart. The earliest recorded fire occurred in 1521 and the time period we used for analysis was 1645-1929. The sites were characterized by frequent surface fires before the 1920s. In the three sites, mean fire intervals ranged from 8.6 to 9.6 years (all fires) and 11.9 to 18.6 years (fires that scarred ⩾25% of recording trees). The per-tree mean fire return interval was 17 years, and all three sites burned in the same year seven times between 1774 and 1929. After 1929, fires were nearly eliminated in all sites, likely due to human causes. We found a temporal change in the association between ENSO events and fires; before the 1830s La Niña events were significantly associated with fire years, while after the 1830s this association was not significant. In 1998, when the most severe El Niño event of the past century occurred, the three sites experienced severe, stand-replacing fires that killed many trees that had survived multiple surface fires in the past. Prior to the 1830s, fires tended to occur during dry La Niña years, but since then both La Niña and El Niño have been associated with dry years in this region, especially during the last three decades. This result suggests that ENSO effects have changed over time in this location and that phases of ENSO are not consistent indicators of precipitation, fire occurrence, or fire behavior in this area of northeastern Mexico. [ABSTRACT FROM AUTHOR]

Lahars represent a major threat on the slopes of volcanoes all over the world. In order to realistically assess hazards, knowledge on the occurrence and timing of past lahar activity is of crucial importance. However, archival data on past events is usually scarce or completely missing. Tree-ring records have repeatedly proved to be a reliable data source for the reconstruction of past geomorphic events. However, tree ringshave seldom been applied for the identification of past lahars. Therefore, it was the aim of this study: (i) to identify and describe disturbances in tree growth induced by well-documented lahar events and on this basis; and (ii) to recognise older, unknown lahar events with tree-ring analyses. Based on these goals, we collected 140 tree-ring series from 62 trees (Abies religiosa, Pinus hartwegii and Pinus ayacahuite) standing inside or adjacent to the lahar channel in the Huiloac gorge at Popocatépetl volcano, central Mexico. Most commonly, the known lahar events of 1997 and 2001 resulted in abrupt changes in tree-ring width as well as injuries. The same growth disturbances could be identified in the tree-ring series, indicating that five previously unknown lahar events would have occurred during the 20th century. Popocatépetl is one of the best surveyed volcanoes in the world and past eruptions are precisely noted in archives.As most of these unknown events occurred during periods with no volcanic activity, we believe that they were rainfall-induced rather than related to volcanic activity. In order to assess rainfall intensity threshold values for the triggering of events, the analyses of meteorological data needs to be integrated. In general, the investigated tree species proved to be highly suitable for the reconstruction of mass-movement processes. Therefore, the applied methods can be transferred to other locations where data on past events are missing. [ABSTRACT FROM AUTHOR]

In the period from February through June 2004, the presence of different bird species was studied in two zones located at the Experimental Forest Station Zoquiapan (EFEZ for its Spanish acronym), state of Mexico, one with slightly disturbed pine forest (ZOQ 1) and another with mixed perturbed forest (ZOQ 2). The points recounting method with fixed radio for bird monitoring was used as well as the square embedded method and the quadrant with a central point, the last one to allow sampling the vegetation. The distribution of birds in vertical vegetation strata was characterized and compared using Poisson regression analysis and frequency observation; furthermore, a specific analysis was developed to describe the vegetation structure in both zones. The vertical distribution of birds followed four patterns: low (B), high (A), high-low (AB) and indeterminate (I). The individual's abundance per stratum had a different value within strata and zones; in both sites the upper stratum showed a greater abundance than in the low and medium ones, although the number of individuals per specie registered in each stratum was the greatest in the perturbed mixed forest. The relative importance value (VIR for its Spanish acronym) of vegetation confirmed than ZOQ 1 had Pinus hartwegii as the predominant specie with some shrubs of Penstemon gentianoides and Senecio asteracae. ZOQ 2 was a mixed forest comprised by S. asteracae, P. gentianoides, Lupinus montanus shrubs and Alnus jorullensis, P. hartwegii and Abies religiosa trees. The height histograms determined two and three vertical strata, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The altitudinal pattern of genetic variation in Pinus hartwegii Lindl. populations was explored for seedling height growth, frost damage, grass-stage, and phenological stage of the terminal shoot. A provenance test was conducted with open-pollinated seed from 13 populations collected along an altitudinal transect (3000–3600m) at the National Park Pico de Tancítaro, Michoacán, center-west Mexico. Height growth of seedlings in a nursery was assessed at seven and 18 months of age. Frost damage at −15°C was evaluated in laboratory at 18 months of age; proportion of plants that had left grass-stage and stage of shoot development was assessed at the age of 22 months. Significant differences among provenances (P <0.0001) were detected for all of the evaluated characters. The variation among populations was structured as a moderate altitudinal cline, with populations from lower altitudes showing larger height growth in seedlings, larger proportion of frost damages, fewer seedlings in grass-stage and more seedlings with developed shoot, whereas in populations from higher altitudes, seedlings exhibiting shorter plant height, lower percentages of frost damage, more seedlings with unbroken grass-stage, and fewer seedlings with advanced shoot development were displayed. Options for seed and seedling movement along the altitudinal gradient are discussed under the scope of reforestation, aiming at ecological restoration, conservation of forest genetic resources, and assisted migration considering global warming. We suggest delineation of two altitudinal seed zones (Zone I: 3000–3350m; Zone II: 3350–3700m). [Copyright &y& Elsevier]

Abstract: To study the variation in growth traits, survival, and frost damage between four taxa, Pinus pseudostrobus typical (represented by four provenances) and its variety P. pseudostrobus var. apulcensis (two provenances), Pinus montezumae (two provenances) and Pinus hartwegii (one provenance), seeds of stands of natural distribution were obtained in the States of Michoacán, Puebla, Hidalgo and Veracruz, México. Provenances were evaluated at two field sites located in forests of the Native Indian Community of Nuevo San Juan Parangaricutiro, Michoacán, at contrasting altitudes of 2200 and 2800m. Evaluations made when seedlings were between 15 and 27 months old, indicate that there were large differences in initial growth and in frost damage between the taxa: typical P. pseudostrobus was the species with the largest growth although also the one of the largest percentage of frost damage; P. pseudostrobus var. apulcensis shows both intermediate total height and frost damage with respect to typical variety and to P. montezumae and P. hartwegii. Height growth of P. montezumae and P. hartwegii was lower than the growth of typical P. pseudostrobus and the apulcensis variety, although they presented the lowest percentage of frost damages. In order to reforest sites at Purépecha Plateau in Michoacán, it is suggested to use typical P. pseudostrobus on sites relatively free from frost occurrence, and to use P. montezumae on sites with frost occurrence. It is not recommendable to use P. pseudostrobus var. apulcensis (susceptible to frost occurrence and not having the best growth rate) or P. hartwegii (with the lowest survival rate). P. pseudostrobus var. apulcensis is a distinguishable taxon of P. pseudostrobus, due to its growth characteristics, which support the taxonomic classification according to some authors. [Copyright &y& Elsevier]

Abstract: The first report on oxidant-induced plant damage in the Valley of Mexico was presented over 30 years ago. Ozone is known to occur in the Mexico City Metropolitan Area and elsewhere as the cause of chlorotic mottling on pine needles that are 2 years old or older as observed in 1976 on Pinus hartwegii and Pinus leiophylla. Visible evidences for the negative effects of ozone on the vegetation of central Mexico include foliar injury expressed as chlorotic mottling and premature defoliation on pines, a general decline of sacred fir, visible symptoms on native forest broadleaved species (e.g. Mexican black cherry). Recent investigations have also indicated that indirect effects are occurring such as limited root colonization by symbiotic fungi on ozone-damaged P. hartwegii trees and a negative influence of the pollutant on the natural regeneration of this species. The negative ozone-induced effects on the vegetation will most likely continue to increase. [Copyright &y& Elsevier]

In order to consider the wood specific gravity of Pinus hartwegii in the La Malinche volcano two methods were used: the traditional one of the maximum moisture content {Smith, 1954) and the empirical method proposed recently (Valencia and Vargas, 1997); 22 small pieces wood were extracted with a Pressler drill, to which both methods were applied. The average values, standard deviation, minimum and maximum of the wood density were very similar. It was determined that the specific gravity of the wood was 0,498 g/cm³. It was demonstrated with a simple correlation that the results of both methods were very close to 1,0. The Pinus hartwegii wood is classified as moderately heavy. The specific gravity value obtained in this study can be used for biomass estimations of the wood from this species. INSETS: Densidad de la madera da Pinus hartwegii;MATERIALES Y METODOS;REFERENCIAS;INTODUCCIÓN [ABSTRACT FROM AUTHOR]