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The present study employs petrology, rock magnetics, and paleointensity on four lava flows (seven sites) of the El Jorullo volcano; a historical (1759–1766 AD) cinder cone in the Michoacan-Guanajuato Volcanic Field. El Jorullo lava flows cover an extensive area of ∼10.8 Km2, and a volume ∼0.35 Km3. Rock-magnetic experiments and microscopic observations reveal pseudo-single domain size Ti-poor titanomagnetite as the main carrier of magnetization in all sampled flows. Notably the calculated mean direction from all the sites show a slight westwards bias when compared against the secular variation global models. The mean paleo-direction for the El Jorullo historical eruption is: Dec = 2.5°, Inc = 37.5°, kappa = 214, α95 = 1.8, N = 31; the Virtual Geomagnetic Pole has Plat = 87° N, Plong = 307° E, Kappa = 260, A95 = 1.6; paleointensity data: 45.4 ± 3.6 μT; and Virtual Dipole Moment: 10.3 ± 1 × 1022 Am2. The paleodirections and the paleointensity values from these lava flows are well-constrained and reliable. These results allow to improve the accuracy and reliability of the global and regional secular variation models available for the last centuries.

The lithic in the Cerro Colorado tephra deposits is dominated by clasts from shallow country rocks for a diatreme not well mixed, or, by a combination of material that reflects the relative proportions of country rock in a well-mixed diatreme. The clasts in a tephra ring bed might be ideal to use the paleomagnetic study to determine the emplacement temperature. We report emplacement temperature ranges of pyroclastic lithic fragments from the Cerro Colorado Tuff Ring in the El Pinacate Volcanic Field, Sonora, northwestern Mexico. Paleomagnetic analyses, particularly the thermoremanent magnetization procedure was carried out in 38 small cores, drilled from the 10 to 30 cm in size lithic fragments. It estimates the emplacement temperature ranges of the juvenile basaltic cauliflower bombs and not-juvenile diverse blocks produced in the phreatomagmatic eruption. Titanomagnetite and titanohematite are the main magnetic carriers, along with titanomaghemite. The 22 emplacement temperatures determined in this study are grouped in three temperature ranges, low (310–370 °C), medium (400–460 °C) and high (>500 °C). The low and medium temperature samples show two or more components, while the high temperature samples have, in general, only one component. This wide range of emplacement temperature could be related to the composite thermal history of the pyroclastic material incorporated in the water saturated pyroclastic flow deposit. The comparison of the mean direction of the secondary magnetization component with the secular variation curve of the global model SHA.DIF.14, suggests an age of 3915 ± 59 yr. BP.

Lithological, petromagnetic, paleomagnetic and magnetic fabric studies are employed to determine the flow direction and the location of the source of the, 2.44 to 2.21 Ma, El Castillo ignimbrite in the central-east Mexico. Based on the increasing matrix to pumice ratio and decreasing pumice size, the ignimbrite field is divided into the northwestern, central and south-southeastern sectors. Lithological comparisons among the three sectors reveal that the ignimbrite had flowed from NW to SE, and the source is in the NW part of the study area. Thermomagnetic results concur with the increasing matrix proportions from the proximal to the distal sector. The coercivity and magnetization ratios of the hysteresis parameters are lower in the SE sector than in the NW and central sectors. The dominant flow direction inferred through magnetic fabrics, at most sites, is NW to SE, which coincides with the direction inferred from lithological comparisons. However, at some sites magnetic fabrics demonstrate flow towards ENE or other various directions. The paleomagnetic analysis and field observations reveal that these anomalous directions are a consequence of anticlockwise block rotation and tilting due to normal and lateral faulting in the region.

Cofre de Perote National Park (CPNP) in Veracruz, Mexico is part of the Transmexican Volcanic Belt, and its Pinus hartwegii forests reflect a balance between the various natural factors that represent the region's climatology and hydrology. Like many other areas in this region, the historical fire regimes of these forests and their relationship with climate are unknown, but are needed for sustainable management plans. The main objectives of this study were to reconstruct the historical fire regime in a Pinus hartwegii forest and decipher the influenced of climate. Our investigation focused in two study areas, Valle la Teta (VT) and Barranca Honda (BH). The VT study area was divided into three sites based on humidity and elevation: 1) Humid (VTH), 2) Dry Low (VTDL) and 3) Dry High (VTDH). The approximated area for each site was ​​30, 30, 35 and 50 ha, for VTH, VTDL, VTDH and BH, respectively. We collected 162 fire scarred samples to reconstruct the fire history for the last 550 years (1461−2013). The fire scarred samples contained 1240 fire scars, with most fires occurring in spring (95 %) or summer (5%). Prior to 1973, these sites were characterized by a frequent surface fire regime. In all four sites, the mean fire intervals ranged from 5 to 6 years (for fires that scarred ≥ 10 % of the samples) and 13–23 years (for fires that scarred ≥ 25 % of the samples). Extensive fires (≥ 10 %) coincided with significantly dry conditions based on the Standardized Precipitation Index (SPI), influenced by El Nino Southern Oscillation (ENSO) and the Pacific Decadal Oscillation Index (PDO). We also found a significant relationship between fire occurrence and ENSO, both in its warm phase, El Nino (21 fires ≥ 10 %) and in its cold phase, La Nina (32 fires ≥ 10 %). Synchronization of the cold phase of ENSO (La Nina) with the cold phase of the PDO (negative), facilitated severe drought conditions, resulting in fires with the greatest spatial extent. Since 1973, extensive fires have been absent from the study area most likely due to anthropogenic activities including active fire suppression. These results show a strong climate-fire relationship in these high elevation forests. The lack of fire in the last four decades is concerning and could potentially lead to unnatural stand-replacing fires, unless the historical fire regime is restored to maintain natural processes and increase forest resilience.

Identifying the relative importance of human and environmental drivers on fire occurrence in different regions and scales is critical for a sound fire management. Nevertheless, studies analyzing fire occurrence spatial patterns at multiple scales, covering the regional to national levels at multiple spatial resolutions, both in the fire occurrence drivers and in fire density, are very scarce. Furthermore, there is a scarcity of studies that analyze the spatial stationarity in the relationships of fire occurrence and its drivers at multiple scales. The current study aimed at predicting the spatial patterns of fire occurrence at regional and national levels in Mexico, utilizing geographically weighted regression (GWR) to predict fire density, calculated with two different approaches –regular grid density and kernel density – at spatial resolutions from 5 to 50 km, both in the dependent and in the independent human and environmental candidate variables. A better performance of GWR, both in goodness of fit and residual correlation reduction, was observed for prediction of kernel density as opposed to regular grid density. Our study is, to our best knowledge, the first study utilizing GWR to predict fire kernel density, and the first study to utilize GWR considering multiple scales, both in the dependent and independent variables. GWR models goodness of fit increased with fire kernel density search radius (bandwidths), but saturation in predictive capacity was apparent at 15–20 km for most regions. This suggests that this scale has a good potential for operational use in fire prevention and suppression decision-making as a compromise between predictive capability and spatial detail in fire occurrence predictions. This result might be a consequence of the specific spatial patterns of fire occurrence in Mexico and should be analyzed in future studies replicating this methodology elsewhere.

The Popocatepetl volcano resumed its eruptive activity in 1994 and is still active. The largest eruption recorded during this new stage of activity occurred in December 2000. We traced the volcanic activity signal in tree-rings from Pinus hartwegii trees located in the north slope of the volcano, located at ∼3 km from the volcanic cone. Annually resolved tree-ring widths, elemental and stable δ13C and δ18O isotope composition were measured during the period 1989–2014 to study the effects of the volcanic activity on trees. Our results indicate a high increase in the concentration of metal elements (Co, Cr, Cu, Fe, Li, Mo, Ni, Pb, Rb, Sr, Ti, Zn) in tree rings following the major 2000 volcanic eruption, compared to the pre-eruption period from 1989 to 1993. Other chemical elements such as Al, K and S peaked 2 years later, in the 2003 tree ring, that matched with the formation of a very narrow ring that year. This sharp reduction of growth was probably driven by a combination of harsh climatic conditions (drought) with the lagged negative effects of the 2000 eruption. Carbon isotope discrimination (Δ13C) and δ18O increased from 1995 to 2006, suggesting reduced stomatal conductance, photosynthetic activity and water use efficiency due to the large dust veil covering the study zone. The variation of relevant elements (Ca, Mn) showing significant correlations with tree growth, Δ13C and δ18O can be attributed to the selective availability of elements following the soil acidification caused by the volcanic activity. Our findings suggest that the recent activity of the Popocatepetl might have increased tree vulnerability, as reflected in the sharp reduction of growth following the drought recorded 2 years after the large eruption of December 2000. Our results warn about the cumulative negative effects of volcanic activity and harsh climatic conditions on tree growth and functioning.

The Pinacate Volcanic Field is a Neogene volcanic sequence at the northwestern part of Mexico. This paleomagnetic study (directional and paleointensity) will continue to improve the global paleomagnetic databases. It is the first full vector paleomagnetic analysis within the more than 400 volcanic structures of the Pinacate Volcanic Field, e.g. scoria, cinder cones, large ‘pahoehoe’ and ‘aa’ lava flows. A total of 140 oriented standard paleomagnetic cores from 16 sites of lava flows were collected. Rock magnetic experiments such as thermomagnetic analyses show that Ti-poor titanomagnetite is the main magnetic carrier of the remanence. Microscopy of oxide minerals supports this observation. Parameters from hysteresis and FORC diagrams suggest pseudo-single domain grain sizes or a mixture of single and multidomain particles. The directional analysis of 11/12 volcanic structures provides a mean paleomagnetic direction and corresponding mean paleomagnetic pole (calculated from the site VGPs): Dec = 0.1°, Inc = 54.5°, n = 11, α95 = 6.7°, k = 48, Plat = 86.5°, Plong = 247.8°, A95 = 7.5°, respectively. The mean paleointensity, obtained by using the Thellier-Coe protocol, and estimated from seven volcanic structures is 42.2 ± 3.6 μT, and VDM is 8.1 × 1022Am2. The obtained directions are compatible with the Late Pleistocene paleodirection as expected from the geocentric axial dipole (GAD) field. The virtual geomagnetic pole scatter (Sb) was calculated at 13.5° which is consistent with the paleosecular variation value expected from El Pinacate latitude.

The capacity of A, X and clinoptilolite zeolites to remove Co 2+ or Cs + is compared. The Co 2+ and Cs + exchanged zeolites were thermally and combustion treated until vitrification. Desorption of cobalt and cesium from those treated solids was tested by lixiviation with 1 N NaCl solution. As the calcining temperature increased, the cristallinity of cobalt and cesium exchanged zeolites decreased. The retention of cobalt and cesium in thermally treated exchanged zeolites is slightly higher than in combustion treated zeolites ignited at 1000 °C. The difference is attributed to the compounds (amorphous and crystalline) formed during the treatments. The cobalt and cesium content were determined by neutron activation analyses and the solids were characterized by X-ray diffraction, IR-spectroscopy and scanning electron microscopy (SEM).

Nitrogen fertilization in the nursery, along with altering the configuration of forest gaps, may improve the reforestation success of longleaf pine seedlings. During the very droughty 1998 growing season in Florida and Georgia, survival was higher under the forest canopy than in small (0.10 ha, 36 m diameter) and large (1.6 ha, 144 m diameter) canopy gaps. In the large gaps, survival of containerized seedlings was higher along the edges, particularly the SW edge. Shade from adult trees and the nurse effect of shrubs increased survival, while grass competition reduced survival. During dry years part of the “exclusionary zone” along the edge of canopy gaps (SW sector) may serve as a “survival zone”, at least in the short term. A model using oval-shaped gaps oriented from NW to SE, with an area of 0.25 ha is proposed to maximize the survival and growth of artificially regenerated longleaf pine seedlings.