Marín Pompa-García

Differences in climate–growth relationship indicate diverse drought tolerances among five pine species coexisting in Northwestern Mexico

Key messageWinter and spring wet and cool conditions often linked to El Niño enhance growth in five Mexican pine species which showed different responses to drought.AbstractClimate warming could intensify drought stress in NW México mountains as the Sierra Madre Occidental which are not only centers of pine diversification but also subject to a high hydroclimatic variability. In this region, rainfall and thus forest growth depend on changes in sea-surface temperatures (SST) across the equatorial Pacific related to the El Niño Southern Oscillation (ENSO). Winter moist-cool conditions usually correspond to El Niño episodes characterized by warm SSTs in the equatorial Pacific, whilst dry winters correspond to cold SSTs (La Niña). Consequently, growth responsiveness to dry spells could be used as a proxy of forest vulnerability to increased drought stress. Here, we characterize the growth responsiveness of five coexisting Mexican pine species to hydroclimate, drought, and the ENSO using dendrochronology. Pinus lumholtzii and P. durangensis showed a low responsiveness to maximum temperatures and drought, whereas others as P. arizonica, P. engelmannii, and P. leiophylla were very responsive. Among these drought-sensitive pine species, we found responses to ca. half- (e.g. P. engelmannii) and 1-year long (e.g. P. arizonica) droughts. The most responsive species to drought, P. arizonica and P. leiophylla, were also those showing a higher association between ENSO-related indices and growth. Wet and cool winter and spring conditions, linked to warm SSTs over the equatorial Pacific, were the main hydroclimate factors enhancing growth. Pine species presented different growth responsiveness to drought which suggests that they present diverse tolerances to water shortage. This implies that coexisting pine species will differently face the more arid conditions forecasted for many drought-prone areas.

Tree growth response to ENSO in Durango, Mexico

The dynamics of forest ecosystems worldwide have been driven largely by climatic teleconnections. El Niño-Southern Oscillation (ENSO) is the strongest interannual variation of the Earth’s climate, affecting the regional climatic regime. These teleconnections may impact plant phenology, growth rate, forest extent, and other gradual changes in forest ecosystems. The objective of this study was to investigate how Pinus cooperi populations face the influence of ENSO and regional microclimates in five ecozones in northwestern Mexico. Using standard dendrochronological techniques, tree-ring chronologies (TRI) were generated. TRI, ENSO, and climate relationships were correlated from 1950–2010. Additionally, multiple regressions were conducted in order to detect those ENSO months with direct relations in TRI (p < 0.1). The five chronologies showed similar trends during the period they overlapped, indicating that the P. cooperi populations shared an interannual growth variation. In general, ENSO index showed correspondences with tree-ring growth in synchronous periods. We concluded that ENSO had connectivity with regional climate in northern Mexico and radial growth of P. cooperi populations has been driven largely by positive ENSO values (El Niño episodes).

A system for calculating the merchantable volume of oak trees in the northwest of the state of Chihuahua, Mexico

The taper functions of Kozak (1988), Bi (2000) and Fang et al. (2000) were comparatively analyzed in the present paper to develop a system for calculating the merchantable volume of oaks in the northwestern region of the state of Chihuahua (Mexico). Taper data corresponding to 298 trees were collected in mixed and uneven-aged pine-oak stands located throughout the study area, and covering the existing range of ages, stand densities and sites. Results show that the compatible segmented model developed by Fang et al. (2000) best described the experimental data and is therefore recommended for estimating tree diameter at a specific height, height to a specific diameter, merchantable volume, and total volume for oaks. The equation developed in this study is a fundamental tool for use in forest surveys in the study region and is simple enough to ensure its operational implementation. The results of the statistical analysis show that the equation can be recommended for other regions, although some local adaptations may be needed.

Modeling susceptibility to deforestation of remaining ecosystems in North Central Mexico with logistic regression

Determining underlying factors that foster deforestation and delineating forest areas by levels of susceptibility are of the main challenges when defining policies for forest management and planning at regional scale. The susceptibility to deforestation of remaining forest ecosystems (shrubland, temperate forest and rainforest) was conducted in the state of San Luis Potosi, located in north central Mexico. Spatial analysis techniques were used to detect the deforested areas in the study area during 1993–2007. Logistic regression was used to relate explanatory variables (such as social, investment, forest production, biophysical and proximity factors) with susceptibility to deforestation to construct predictive models with two focuses: general and by biogeographical zone. In all models, deforestation has positive correlation with distance to rainfed agriculture, and negative correlation with slope, distance to roads and distance to towns. Other variables were significant in some cases, but in others they had dual relationships, which varied in each biogeographical zone. The results show that the remaining rainforest of Huasteca region is highly susceptible to deforestation. Both approaches show that more than 70% of the current rainforest area has high and very high levels of susceptibility to deforestation. The values represent a serious concern with global warming whether tree carbon is released to atmosphere. However, after some considerations, encouraging forest environmental services appears to be the best alternative to achieve sustainable forest management.

Viewshed Analysis for Improving the Effectiveness of Watchtowers, in the North of Mexico

The forests in Mexico have been seriously affected by forest fires, and thus detection of fires from watchtowers is essential. The current numbers of watchtowers and effectiveness of their distribution is unknown. The aim of the present study was to determine the current and potential area visible from the watchtowers, and to propose a new network to maximize its effectiveness. Visibility analysis in ArcGis were developed by integrating a digital model of elevation and a vegetation cover map, to determine visibility on a surface from point to point along a given line of sight or across the entire surface in a viewshed. It was found that existing watchtowers provide an overall visibility effectiveness (43%) very low compared with the recommended level. We suggest relocating one of the watchtowers and constructing another, which would increase the overall visibility effectiveness up to 81%.

Temporal Variation of Wood Density and Carbon in Two Elevational Sites of Pinus cooperi in Relation to Climate Response in Northern Mexico

Forest ecosystems play an important role in the global carbon cycle. Therefore, understanding the dynamics of carbon uptake in forest ecosystems is much needed. Pinus cooperi is a widely distributed species in the Sierra Madre Occidental in northern Mexico and future climatic variations could impact these ecosystems. Here, we analyze the variations of trunk carbon in two populations of P. cooperi situated at different elevational gradients, combining dendrochronological techniques and allometry. Carbon sequestration (50% biomass) was estimated from a specific allometric equation for this species based on: (i) variation of intra-annual wood density and (ii) diameter reconstruction. The results show that the population at a higher elevation had greater wood density, basal area, and hence, carbon accumulation. This finding can be explained by an ecological response of trees to adverse weather conditions, which would cause a change in the cellular structure affecting the within-ring wood density profile. The influence of variations in climate on the maximum density of chronologies showed a positive correlation with precipitation and the Multivariate El Niño Southern Oscillation Index during the winter season, and a negative correlation with maximum temperature during the spring season. Monitoring previous conditions to growth is crucial due to the increased vulnerability to extreme climatic variations on higher elevational sites. We concluded that temporal variability of wood density contributes to a better understanding of environmental historical changes and forest carbon dynamics in Northern Mexico, representing a significant improvement over previous studies on carbon sequestration. Assuming a uniform density according to tree age is incorrect, so this method can be used for environmental mitigation strategies, such as for managing P. cooperi, a dominant species of great ecological amplitude and widely used in forest industries.

Reconstructing Evaporation From Pine Tree Rings In Northern Mexico

ABSTRACT Here we reconstructed evaporation using tree-ring width variability. Drought variability and its effects on forest growth have been mainly characterized by changes in precipitation and temperatures, whereas atmospheric drought and evaporation rates have been little investigated. The area of study corresponds to northern Mexico, a region where water resources are increasingly limited. We used correlation analyses to identify the months in which evaporation is most strongly related to tree-ring width series. Then, we built a linear regression model to predict seasonal winter-to-spring evaporation as a function of ring-width indices. Correlation analyses showed that the radial growth of P. cooperi decreased in response to reduced water availability and increased evaporation during the winter prior to the growing season, and also during spring and the early summer of the year of tree-ring formation. Pine growth mainly benefitted from wet and cool conditions from winter to early spring. Linear regression models used in reconstruction were statistically robust and allowed reconstructing January-to-April evaporation for the period 1900–2010. Our study contributes to a better understanding of historical changes in evaporation in northern Mexico and, most importantly, it also emphasizes how atmospheric moisture demand is linked to tree growth.

Sensitivity of pines in Mexico to temperature varies with age

Mexico has an abundance of Pinus species with P. cooperi as a dominant tree species of great ecological importance. In this study, we compared the climate sensitivity of P. cooperi trees of two age classes growing in the Sierra Madre Occidental: younger (< 80 years) and older (≥ 80 years) trees. A regional curve standardization (RCS) of growth ring width was developed for these two age classes. Our statistical analysis showed that annual tree growth was similar between the two age classes in absolute values of tree-ring widths. However, we found that the effects of rising temperatures during the previous winter are age-dependent; that is, maximum and minimum temperatures have opposite effects on the subsequent tree growth. Warming winter maximum temperatures have negative effects on radial growth, which are stronger in younger trees, whilst minimum winter temperatures enhance the growth. However, no difference in radial growth was observed between the two age classes based on precipitation. In climate change scenarios, an increase in temperature would affect younger trees of P. cooperi more than older trees. These effects of increased temperature may lead to a decrease in the growth and subsequent death of the trees. These results could help land managers to develop criteria related to forest management regarding P. cooperi.

ENSO index teleconnection with seasonal precipitation in a temperate ecosystem of northern Mexico

El Nino Southern Oscillation (ENSO) is the most important large-scale circulatory phenomenon that causes climatic variability in northern Mexico. The current challenge is to understand its consequences for both local climate and ecological processes of ecosystems. Within this context, we compared the degree of association of three different ENSO indices with local seasonal precipitation ( P ) in northern Mexico, and used dendrochronological series (tree-ring chronologies [TRI]) of Pinus cooperi to assess the impact of forest growth. The results showed a strong association between ENSO, previous winter precipitation and TRI ( r > 0.5, p = 0.05), indicating a positive relationship between warm ENSO phases and subsequent tree growth. The multivariate ENSO index was slightly better at explaining the connection between P and radial growth than other indices. These results could be used to support further research on the effects of ENSO on local climate and forest ecosystems.

Calidad del bosque de ribera del río El Tunal, Durango, México; mediante la aplicación del índice QBR

La evaluacion de la condicion ecologica de las riberas es un elemento importante en el estudio de los rios alrededor del mundo. El objetivo del presente trabajo fue evaluar la calidad del bosque de ribera, desde un punto de vista estructural y funcional, en un tramo de 21 kilometros del rio El Tunal en Durango, Mexico, mediante la aplicacion del indice QBR. En el tramo estudiado se evaluaron seis sitios seleccionados por su representatividad, accesibilidad y heterogeneidad de su vegetacion. En general, los resultados muestran un rio con indicios importantes de deterioro; se encontraron dos sitios con calidad intermedia, dos sitios presentaron calidad mala y los dos restantes presentaron calidad pesima.