Search Results (6)

The total tree height (h) and diameter at breast height (dbh) relationship is an essential tool in forest management and planning. Nonlinear mixed effect modeling (NLMEM) has been extensively used, and lately the artificial neural network (ANN) and the resilient backpropagation artificial neural network (RBPANN) approach has been a trending topic for modeling this relationship. The objective of this study was to evaluate and contrast the NLMEN and RBPANN approaches for modeling the h-dbh relationship for the Durango pine species (Pinus durangensis Martínez) for both training and testing datasets in a mixed-species forest in Mexico. The knowledge of this relationship is important for forest management and planning in Mexican Forestry. The total dataset considered 1000 plots (each plot 0.10 ha) (11,472 measured trees) randomly selected from 14,390 temporary forest inventory plots and the dataset was randomly divided into two parts: 50% for training and 50% for testing. An unsupervised clustering analysis was used to group the dataset into 10 cluster-groups based on the k-means clustering method. An RBPANN was performed for tangent hyperbolicus (RBPANN-tanh), softplus (RBPANN-softplus), and logistic (RBPANN-logistic) activation functions in the cross product of the covariate or neurons and the weights for the ANN analysis. Also, a different vector of hidden layers was used for training of ANNs. For both training and testing, 10 classical statistics (e.g., RMSE, AIC, BIC, and logLik) were computed for the residual values and to assess the approaches for the h-dbh relationship. For training and testing, the ANN approach outperformed the NLMEM approach, and the RBPANN-tanh had the best performance in both the training and testing of ANNs. Full article

Extreme drought events reduce the productivity of forest ecosystems. One approach for estimating the effects of drought on forests is by assessing their resilience. The objective of this study was to estimate resilience rates at different heights along the tree stem of Pinus durangensis Martínez. The radial growth of 200 cross sections extracted at four heights of tree stems (0.07–0.15, 1.3, 6.3, and 11.0–12.0 m) was analyzed and subsequently transformed into ring-width indices (RWI). These indices were correlated with the Standardized Precipitation-Evapotranspiration Index on a six-month time scale (accumulated drought of six months in the period February–May; SPEI06_FM). Seven extreme drought events were identified (1890, 1902, 1956, 1974, 1999, 2006, 2011), and radial growth before, during, and after each event was determined. Based on ring-width index values, resistance, recovery, and resilience indices were calculated. The results indicated a significant correlation (p ≤ 0.05) between annual radial increment and climate indices along the stem (0.56 to 0.80). Climatic sensitivity was higher in the lower part of the stem, with mean sensitivity (MS) and expressed population signal (EPS) values of 0.38 and 0.97, respectively. Resistance index values ranged from 0.44 to 0.76 and were better expressed in higher sections of the stem. Resilience indices changed over time. Regardless of the height of the tree stem, the latest extreme drought events (1999, 2006, and 2011) have led to a lower resilience of trees, indicating that their recovery capacity has decreased. Therefore, forestry practices in the study area may consider managing tree density as a strategy to regulate the stress in competition and to increase the tolerance of trees to drought. Full article

In recent decades, droughts associated with climate change have increased in frequency and intensity. Given this trend, the understanding of climate variability over time has raised great interest. The main objective of this study was to reconstruct the standardized precipitation-evapotranspiration index (SPEI) from tree rings of Pinus durangensis Martinez at a representative site in the western region of the Durango State, Mexico. To this end, we used radii of 286 cross-sections, which were processed through conventional dendrochronological techniques. In addition, chronologies of total ring and early and latewood were generated, covering 296 years. In parallel, we analyzed the association between the chronologies obtained and the cumulative SPEI for 3, 6, 9, and 12 months. The earlywood residual chronology (EWres) showed the closest association with the six-month cumulative SPEI for February–May (SPEI6_FM). Thus, the SPEI6_FM for the past 296 years was reconstructed through a simple linear regression model. In this reconstruction, 18% of the years were wet, 16% dry, and 66% average. In addition, an increase in the frequency of droughts was observed from 1880 onwards, which might have been related to the rise in temperature due to climate warming. Therefore, the annual rings of P. durangensis are suitable for use as a proxy for the reconstruction of historical climatic events in this region of northern Mexico. Full article

A seed zone or provenance region is an area within which plants can be moved with little risk of maladaptation because of the low environmental variation. Delineation of seed zones is of great importance for commercial plantations and reforestation and restoration programs. In this study, we used AFLP markers associated with environmental variation for locating and delimiting seed zones for two widespread and economically important Mexican pine species (Pinus arizonica Engelm. and P. durangensis Martínez), both based on recent climate conditions and under a predicted climate scenario for 2030 (Representative Concentration Pathway of ~4.5 Wm⁻²). We expected to observe: (i) associations between seed zones and local climate, soil and geographical factors, and (ii) a meaning latitudinal shift of seed zones, along with a contraction of species distributions for the period 1990–2030 in a northward direction. Some AFLP outliers were significantly associated with spring and winter precipitation, and with phosphorus concentration in the soil. According to the scenario for 2030, the estimated species and seed zone distributions will change both in size and position. Our modeling of seed zones could contribute to reducing the probabilities of maladaptation of future reforestations and plantations with the pine species studied. Full article

Species distribution models have become some of the most important tools for the assessment of the impact of climatic change, and human activity, and for the detection of failure in silvicultural or conservation management plans. In this study, we modeled the potential distribution of 13 tree species of temperate forests distributed in the Mexican state Durango in the Sierra Madre Occidental, for three periods of time. Models were constructed for each period of time using 19 climate variables from the MaxEnt (Maximum Entropy algorithm) modelling algorithm. Those constructed for the future used a severe climate change scenario. When comparing the potential areas of the periods, some species such as Pinus durangensis (Martínez), Pinus teocote (Schiede ex Schltdl. & Cham.) and Quercus crassifolia (Bonpl.) showed no drastic changes. Rather, the models projected a slight reduction, displacement or fragmentation in the potential area of Pinus arizonica (Engelm.), P. cembroides (Zucc), P. engelmanni (Carr), P. leiophylla (Schl), Quercus arizonica (Sarg), Q. magnolifolia (Née) and Q. sideroxila (Humb. & Bonpl.) in the future period. Thus, establishing conservation and reforestation strategies in the medium and long term could guarantee a wide distribution of these species in the future. Full article

Drought is a major constraint of forest productivity and tree growth across diverse habitat types. In this study, we investigated the drought responses of four conifer species growing within two locations of differing elevation and climatic conditions in northern Mexico. Two species were selected at a mesic site (Cupressus lusitanica Mill., Abies durangensis Martínez) and the other two species were sampled at a xeric site (Pinus engelmannii Carr., Pinus cembroides Zucc.). Using a dendrochronological approach, we correlated the radial-growth series of each species and the climatic variables. All study species positively responded to wet-cool conditions during winter and spring. Despite the close proximity of species at a mesic site, A. durangensis had high responsiveness to hydroclimatic variability, but C. lusitanica was not responsive. At the xeric site, P. engelmannii and P. cembroides were very responsive to drought severity, differentiated only by the longer time scale of the response to accumulated drought of P. engelmannii. The responsiveness to hydroclimate and drought of these tree species seems to be modulated by site conditions, or by the functional features of each species that are still little explored. These findings indicate that differentiating between mesic and xeric habitats is a too coarse approach in diverse forests with a high topographic heterogeneity. Full article