Revista Mexicana de Ciencias Forestales  Vol. 11 (58)

Marzo – Abril (2020)

Fecha de Recepción/Reception date: 12 de septiembre de 2019

Fecha de Aceptación/Acceptance date: 31 de enero de 2020

_______________________________

1Facultad de Ciencias Forestales, Universidad de Nuevo León. México.

*Autor por correspondencia, correo-e: eduardo.alanisrd@uanl.edu.mx

Abstract

For the characterization of the vertical structure of a Pseudotsuga menziesii forest in the Chinatú ejido, Guadalupe y Calvo municipality, Chihuahua State, eight circular sites of 1 000 m2 dispersed in 80.46 ha were randomly sampled. With the information obtained, the vertical structure of regeneration and standing trees was analyzed using the Pretzsch A Index, abundance (N ha-1), average, minimum, maximum values and coefficient of variation of height and diameter were estimated normal and coverage, as well as diversity based on the Shannon-Wiener Index (H ́) and the Margalef Index (DMg). Eight species were registered for the regenerated plant community, the families with the greatest presence were Pinaceae with five species and Fagaceae with two; the mature plant community recorded 10 species, the most predominant being pinaceae with six species and fagaceae with two. The maximum heights of the forest were 8.0 m and 29.0 m for regeneration and mature woodland, respectively. With the Pretzsch Index A it was determined that the largest number of individuals belongs to stratum III (Low) for both types of trees. The species with the highest regeneration are Abies durangensis, Juniperus deppeana, Quercus tuberculata and Pseudotsuga menziesii, the latter of which is dominant in the tree stratum. The studied forest has a low richness and diversity of species, some of high ecological value for conservation and regeneration of the majority of those present.

Key words: Diversity, vertical structure, Fagaceae, Pretzsch Index, Pinaceae, Western Sierra Madre.

Resumen

Para la caracterización de la estructura vertical de un bosque de Pseudotsuga menziesii en el ejido Chinatú, municipio Guadalupe y Calvo, Chihuahua, se realizó un muestreo aleatorio de ocho sitios circulares de 1 000 m2 dispersos en 80.46 ha. Con la información obtenida se analizó la estructura vertical de la regeneración y del arbolado mediante el Índice A de Pretzsch, se estimó la abundancia (N ha-1), los valores medios, mínimos, máximos y coeficiente de variación de la altura y diámetro normal y cobertura, así como la diversidad con base en el Índice de Shannon-Wiener (H ́) y el Índice de Margalef (DMg). Se registraron ocho especies para la comunidad vegetal regenerada, las familias con mayor presencia fueron Pinaceae con cinco especies y Fagaceae con dos; la comunidad vegetal madura registró 10 especies, las más predominantes fueron pinaceae con seis taxones y fagaceae con dos. Las alturas máximas del bosque fueron 8.0 m y 29.0 m para regeneración y arbolado maduro, respectivamente. Con el Índice A de Pretzsch se precisó que el mayor número de individuos se reúne en el estrato III (Bajo) para ambos tipos de árboles. Las especies con mayor regeneración son Abies durangensis, Juniperus deppeana, Quercus tuberculata y Pseudotsuga menziesii, la última de las cuales es dominante en el estrato arbóreo. El bosque estudiado cuenta con una riqueza y diversidad de especies baja, algunas de alto valor ecológico para conservación y con regeneración de la mayoría de las presentes.

Palabras clave: Diversidad, estructura vertical, Fagaceae, Índice de Pretzsch, Pinaceae, Sierra Madre Occidental.

Introduction

Conifers in Mexico are widely distributed in the national territory and are present in various types of vegetation such as pine forest, thicket, fir forest, Pseudotsuga and Picea forest, Juniperus forest or thicket, Cupressus forest, mesophilic forest of mountain, pine-oak forest, xerophilous scrub and gallery forest (Rzedowski, 1978).

Pseudotsuga menziesii (Mirb.) Franco is one of the most important conifers in the world from its wide distribution, from the area planted in several countries and from its economic value (Owston and Stein, 1974; Hermann and Lavender, 1999). Fowells (1965) indicates that this species is distributed from British Columbia, Canada, to the southern United States. The natural distribution of this species in Mexico is not as abundant, but it includes forests of the states of Chihuahua, Sonora, Coahuila, Durango and Zacatecas in the Sierra Madre Occidental (Western Mountain Chain), as well as in Nuevo León and Tamaulipas states in the Sierra Madre Oriental (Eastern Mountain Chain); generally, the populations are fragmented, with isolated stands or stains, often dominated by other species (Rzedowski, 1978; Dominguez et al., 2004).

Forest biodiversity assessment helps to conserve forest resources effectively and sustainably order their composition, structure and function (Newton and Kapos, 2002; Del Río et al., 2003). For the study of biodiversity, structural indices and dendrometric variables are considered, including diameter, height, basal area, density, among others, in order to achieve a better description (Aguirre et al., 2003).

The structure of a forest mass is related to the habitat and ecological niche of many species of plants and animals, and can be used as an indicator of biodiversity (Murdoch et al., 1972; Degraaf et al., 1998). In order to guarantee a sustainable management of ecosystems, it is necessary to characterize their structural diversity, since it is possible to observe both natural succession processes and those caused by anthropogenic activities, and thus, define the activities that should follow in forest management (Jiménez et al., 2001).

In recent years, in the temperate forests of northwestern Mexico, several studies have been carried out that evaluate the diversity and structure of tree vegetation of timber interest in some specific areas (Návar-Cháidez and González-Elizondo, 2009; Aragón-Piña et al., 2010; Hernández-Salas et al., 2013; Graciano-Ávila et al., 2017). However, these investigations have focused mainly on assessing the composition and horizontal structure, so it is necessary to direct attention to species of high conservation and restricted distribution interest to analyze their regeneration and vertical structure. Therefore, the objective of this study was to determine the richness and diversity of species present in the community, as well as its vertical structure to know the behavior of different tree species and their regeneration in a forest of Pseudotsuga menziesii in Chihuahua State.

Materials and Methods

Study area

Fieldwork was carried out in a mixed forest consisting mainly of Pseudotsuga menziesii, Pinus arizonica Engelm. and Quercus tuberculata Liebm.; in the place known as El Triste, which is located within the Chinatú ejido, Guadalupe and Calvo municipality, southwest of the state of Chihuahua between 40º00'00" - 80º00'00" N and 40º00'00" - 160°00'00" W (Figure 1).

Figure 1. Location of the study area and sampling sites.

The forest extends over 80.46 ha and its altitude varies between 2 530 and 2 830 m. It belongs to the Río Fuerte hydrological region, to the Sierra Tarahumara physiographic province and the Great Plateau and Chihuahuan Canyon subprovince. Litosol is the predominant type of soil in the area and Regosol only covers a minimum part. The region's climate is classified as subhumid temperate, with an average annual temperature of 13.7 °C and an average annual rainfall of 1 126.8 mm (Chávez, 2009).

Field Evaluation

To evaluate the plant community, eight circular sampling sites of 1 000 m2 were established, which were randomly distributed in the study area. In each of them, specimens with normal diameter (d1.30) ≥ 7.5 cm were considered for adult trees, and as regeneration for children under 7.5 cm, but greater than 0.25 m in total height (Conafor, 2012). For each individual the species was recorded, the total height (h) with a Suunto Pm-5 hypsometer; the normal diameter (DAP, for its acronym in Spanish) with a 5 m Forestry Suppliers diameter tape, and the projection diameter of the crosshead crown, with a 100 m TruperTM fiberglass tape measure (north-south and east-west).

Data analysis

To assess the vertical structure of the plant community, the Pretzsch Index (A) was used, with which the vertical structure is divided into three strata. Stratum I (high), which represents the range of 80-100 %, in which the tallest tree constitutes 100 %; from this individual, the following strata are classified: Stratum II (medium), which refers to the 50-80 % range and Stratum III (low), 0-50 % (Aguirre, 2002; Pretzsch, 2009). For a better interpretation of the result, Amax is calculated which corresponds to the maximum value for each of the species in each stratum; this value is reached when all the species occur in the same proportion, both in the stand and in the different strata (Corral et al., 2005) (Table 1).

Table 1. Pretzsch Index (A).

Abundance was determined for each of the strata according to the number of individuals present (N ha-1), the average, minimum, maximum value and coefficient of variation obtained from the height and diameter variables. The diversity of the plant community was assessed using the Shannon-Weiner index (H') (Shannon, 1948), Margalef index (DMg) (Magurran, 2004) and true diversity (D), which allows a better comparison of the richness of species (Jost, 2006) (Table 2).

Table 2. Species richness and diversity indexes.

Results and Discussion

Composition. In the regeneration stage, eight species belonging to six genera of three families were registered (Figure 2). Those with the highest number of species were Pinaceae with five and Fagaceae with two. For the mature plant community (Figure 2), 10 species of seven genera were registered in four families; the families with more species were Pinaceae with six and Fagaceae with two. These results coincide with those of Aragón-Piña et al. (2010), Hernández-Salas et al., (2013) and Graciano (2017), who agreed that these families are widely distributed in the Sierra Madre Occidental, in which the Pinus and Quercus genera stand out. The maximum height of regeneration was 8.0 m and 29 m for mature trees.

Figure 2. Vegetable composition of regeneration and trees.

Vertical distribution. For regeneration (Table 4), the result of the A index was 1.85, with an Amax value of 3.18 and an Arel of 58.21 %, while the mature plant community reflected an A index of 2.58, Amax of 3.40 and Arel of 75.56 %. The above suggests that the tree stratum has a great diversity of species with respect to height.

The above figures are similar to those reported by Méndez et al. (2014) who calculated an A = 2.07 with Amax = 2.70, and by Jiménez et al. (2001) that recorded an A = 2.07 and Amax = 3.50; both in mixed coniferous and broadleaved forests. This vertical distribution analysis showed that as tree height increases, species diversity decreases. Such authors mentioned that the greatest biological heterogeneity was presented as the zone of the strata decreases.

Regeneration in stratum I has 1.01 % of the individuals, II, 4.02 % and III, 94.97 % (Table 3). According to Lamprecht (1990), the species present in all strata are defined as species with continuous vertical distribution (DVC); P. arizonica presented this distribution as it was registered in the three strata (Table 3). The trees behaved in a similar way (Table 3) since stratum I had 2.72 % of the individuals, II with 28.26 % and III with 69.02 %, similar percentages to those reported by Jiménez et al. (2001) who evaluated a multicohortal forest of Pinus - Quercus in northeastern Mexico. The species with DVC in the tree stratum were Q. tuberculata, P. menziesii and Abies durangensis (Table 4).

Table 3. Number and percentage of individuals present in the stages of regeneration and adult trees.

Table 4. Results of abundance (N ha-1), coverage (m2 ha-1) and height (m) of the species in the different strata considered for the Pretzsch index (A), the Shannon index (H´) and the true diversity index (D) of the regeneration strata.

Abundance. Q. tuberculata and P. arizonica shared stratum I of the regeneration with 1 N ha-1 each; in stratum II, Q. tuberculata did not appear, P. menziesii was present with 5 N ha-1, P. arizonica with 4 N ha-1 and Juniperus deppeana Steud. 1 N ha-1. In stratum III, eight species were identified, of which the most abundant were Abies durangensis with 75 N ha-1, J. deppeana with 65 N ha-1, Q. tuberculata with 34 N ha-1 and P. menziesii with 30 N ha-1 (Table 4). The most abundant species in this forest without disturbance are from the Pinaceae family, which coincides with the results of Méndez (2014), which should be treated with reservation because their data comes from a post-fire evaluation. In this type of forest with disturbance, up to 812 N ha-1 (Alanís et al., 2011), and 3 400 N ha-1 (González-Tagle et al., 2008) are recorded with a higher frequency of Fagaceae.

It was observed that all species in regeneration have a presence in the woodland, in addition Arbutus xalapensis Kunth appears with 43 N ha-1 in stratum III. The forest has a greater abundance of P. menziesii than in stratum I of the woodland obtained 8 N ha-1, Q. tuberculata and Abies durangensis 3 N ha-1; stratum II was integrated by nine species of which P. menziesii stand out with 58 N ha-1, P. arizonica with 28 N ha-1 and Q. tuberculata with 13 N ha-1 and in stratum III, 10 species were recorded, the most abundantof which were P. menziesii with 89 N ha-1, P. arizonica with 55 N ha-1, Arbutus xalapensis with 43 N ha-1 and Q. tuberculata with 33 N ha-1 (Table 4). This is consistent with Camacho et al. (2014) who reported greater biological diversity in stratum III, of a pine-oak forest in Nuevo León, Mexico.

Regeneration and tree variables. Regeneration in stratum I showed an average crown diameter (Coverage) of 3.40 m and an average height of 7.5 m; in stratum II, the average cup was 2.27 m, while the height was 4.27 m; and, stratum III averaged a cup diameter of 1.37 m with an average height of 1.32 m. The tallest individuals came from P. arizonica with 1.62 m and Quercus sideroxyla Humb. & Bonpl with 1.60 m (Table 4).

In regard to trees (Table 5), in stratum I, the average diameters measured between 42.92 cm and 53.67 cm, with a maximum of 73.0 cm in the case of Q. tuberculata. The average total height was 25.12 m, with a maximum of 29.0 m for Abies durangensis; in stratum II, average diameters were recorded between 26.43 cm and 53.50 cm, and reached 88.5 cm for Q. tuberculata and 94.0 cm in Pseudotsuga menziesii, which coincides with Dominguez-Calleros et al. (2014) who confirmed that this species registered the largest diameters. Regarding height, the average was 16.58 m with a maximum of 21.60 m for Pinus durangensis and in stratum III in specimens whose diameters measured between 12.50 cm and 18.48 cm, the average height was 8.59 m. Pseudotsuga menziesii obtained similar values to those of Encina-Domínguez et al. (2008), since this species together with Q. tuberculata, P. arizonica and Abies durangensis reached a maximum value of 13.50 m (Table 5).

Table 5. Results of abundance (N ha-1), normal diameter (cm), canopy cover (m) and height (m) of the species in the different strata considered for the Pretzsch index (A) and index of Shannon (H´) and true diversity index (D) of the strata in the mature vegetal community.

Psme = Pseudotsuga menziesii (Mirb.) Franco; Qutu = Quercus tuberculata Liebm; AbDu = Abies durangensis Martínez; Piar = Pinus arizonica Engelm.; PiAy = Pinus ayacahuite Ehrenb. ex Schltdl.; PiDu = Pinus durangensis Martínez; QuSi = Quercus sideroxyla Humb. & Bonpl.; PiCh = Picea chihuahuana Martínez; Jude = Juniperus deppeana Steud; ArXa = Arbutus xalapensis Kunth.

In stratum I, the trees showed an average crown diameter of 11.25 m with a minimum of 4.35 m and a maximum of 18.65 m; in stratum II the average was 6.46 m, with minimums of 1.93 m and maximums of 13.20 m and in stratum III it was 4.53 m, with minimums of 1.60 m and maximums of 15.75 m. The species with outstanding values in this variable were Q. tuberculata with an average of 14.43 m and Abies durangensis with 10.85 m (Table 5).

Diversity and richness of species. The diversity of species in the regeneration plant community through the Shannon Index (H’) was generally low; the highest value was verified in stratum III with 1.63, while for stratum I and II it was 0.05 and 0.16, respectively. Margalef (1972) mentions that the Shannon Index normally ranges from 1 to 5, with values less than 2 being interpreted as low diversity, 2 to 3.5 medium diversity, and greater than 3.5 as high diversity. Therefore, the forestry community studied has a low diversity. The number of effective species or true diversity (D’) for stratum I was 1.05, II 1.17 and III 5.10, meaning that stratum III has 4.3 times more diversity than stratum II and 4.8 than I (Table 4).

With the Margalef Index (DMg) in the plant regeneration community, DMg = 1.52 was determined, similar to the DMg value = 1.32 recorded by Villavicencio et al. (2012) in a temperate pine-oak forest of the Sierra de Quila, Jalisco and far superior to that of Méndez et al. (2014) who calculated a value of DMg = 0.76 in a pine-oak forest of the Sierra de Guerrero, Mexico. However, the wealth is lower than that found in the submontane scrubland by Canizales et al. (2009) who obtained a value of DMg = 6.34; Mora et al. (2013) estimated a DMg of 6.27 and for subdeciduous medium forest, Gutiérrez-Báez et al. (2012) of DMg = 15.23.

The mature plant community as well as the regeneration presented a low diversity based on the Shannon Index (H'), the highest value was presented in stratum III with H' = 1.64 while for stratum I and II it was H'= 0.12 and H' = 0.81, respectively. The number of effective species or true diversity (D') for stratum I was D' = 1.13, for II it was D'= 2.26 and III D' = 5.15, which means that stratum III has 2.2 times more diversity than II and 4.5 than I (Table 5).

The Margalef Index (DMg) resulted in DMg = 1.52 (Table 5), which indicates a species richness similar to that obtained by Graciano et al. (2017) and González et al. (2018), who recorded DMg = 1.53 and DMg = 1.98 in temperate forests of the states of Durango and Nuevo León; otherwise, that of Hernández-Salas et al. (2013), because they calculated DMg = 1.04 and DMg = 0.90 in productive pine and oak forests in the state of Chihuahua.

Conclusions

The studied community has natural regeneration of most of its species despite having large trees that cause a closed canopy; Pinus durangensis and Arbutus xalapensis do not show it, which can be attributed to the shortage of mature individuals. Most of them were presented in stratum III, which suggests that the forest has a high capacity for recovery and replacement of mature trees, which leads to ecosystem conservation.

Based on abundance and defined vertical structure strata, the forest studied is a community dominated mainly by Pseutotsuga menziesii in all woodland strata, stratum I with less presence of Abies durangensis and Quercus tuberculata, while in II and III have associations with P. arizonica, Q. tuberculata and A. xalapensis. Three species with continuous vertical distribution (P. menziesii, A. durangensis and Q. tuberculata) were registered, these being the ones that dominate the upper canopy.

The study of new populations of Pseudotsuga menziesii such as this one, provides quantitative information for decision-making in favor of conservation, especially if it coexists with endemic and protective species (Abies durangensis and Picea chihuahuana).

Acknowledgements

The authors thank the authorities of Chinatú ejido of Guadalupe y Calvo municipality, Chihuahua State, for the facilities provided to accomplish this research study.

Conflict of interests

The authors declare no conflict of interests.

Contribution by author

Samuel Alberto García García: study approach, field data collection, writing and correction of the manuscript; Eduardo Alanís Rodríguez: study approach, organization of work, data analysis, writing and correction of the manuscript; Oscar Alberto Aguirre Calderón and Eduardo Javier Treviño Garza: statistical analysis and correction of the manuscript; Gabriel Graciano Ávila: supervision of field data collection, statistical analysis and correction of the manuscript.

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