Environmental and Soil Variables Affecting the Structure and Floristic Woody Composition of Oak Forests of Northeastern Mexico
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Turkish Journal of Agriculture and Forestry Turk J Agric For (2018) 42: 262-271 http://journals.tubitak.gov.tr/agriculture/ © TÜBİTAK Research Article doi:10.3906/tar-1711-31 Environmental and soil variables affecting the structure and floristic woody composition of oak forests of northeastern Mexico 1, 2 Juan Antonio ENCINA-DOMÍNGUEZ *, José Ramón ARÉVALO SIERRA , 1 3 Eduardo ESTRADA-CASTILLÓN , Miguel MELLADO BOSQUE 1 Faculty of Forestry Sciences, Autonomous University of Nuevo Leon, Linares, Nuevo Leon, Mexico 2 Department of Botany, Ecology, and Plant Physiology, Faculty of Sciences, University of La Laguna, Canary Islands, Spain 3 Department of Animal Nutrition, Antonio Narro Agrarian Autonomous University, Saltillo, Coahuila, Mexico Received: 07.11.2017 Accepted/Published Online: 28.03.2018 Final Version: 07.08.2018 Abstract: The objective of this study was to investigate the influence of environmental and soil factors on the structure and floristic woody composition of oak forests. Oak forests of the Sierra de Zapalinamé in northeastern Mexico (25°N) are distributed in canyons and northwest slopes with higher humidity, surrounded by montane chaparral. We carried out a vegetation inventory across an altitudinal gradient. All trees with diameter at breast height of ≥3 cm were identified and measured. In addition, the cover of understory species was measured in each plot. Using multivariate techniques, we detected two oak forest associations: Quercus greggii - Q. mexicana forest and Q. saltillensis - Q. laeta forest. The forests studied are rich in woody species, including 19 tree and 50 shrub species. The number of tree species decreased at lower elevations, but the shrub species increased. Environmental variables evaluated included elevation, precipitation, temperature, soil pH and electrical conductivity, and soil percentage of sand, clay, and silt. All these variables revealed significant differences for the two oak forest associations. With respect to biotic parameters, significant differences (P < 0.05) in basal area were observed. Multivariate analysis revealed the species distribution along a moisture gradient across elevation. The ecological study of oak forests provides the basis for future research on forest dynamics and can guide conservation efforts to maintain species diversity and endemism in the mountain studied. Key words: Edaphic factors, elevation, forest structure, Quercus, species composition 1. Introduction Santacruz et al., 1996), Chihuahuan desert scrub (Huerta- Altitudinally defined climatic and soil factors are primary Martínez et al., 2004), and boreal forest (Seibert et al., 2007) determinants of differences in species composition and tropical rainforests (Fernandes-Abreu et al., 2012). At and community structure on undisturbed mountains local scales, species richness and the structure of forest (Fischer et al., 2014; Toledo-Garibaldi and Williams- landscapes are strongly influenced by geomorphology Linera, 2014). The occurrence of plant species is and elevation (Behera and Kushwaha, 2007) and also by dependent on various factors acting on different spatial soil physicochemical properties (Estrada-Castillón et al., scales. Elevation represents a complex gradient through 2015) and anthropogenic disturbances (Ramírez-Marcial which environmental variables change simultaneously et al., 2001). (Austin et al., 1996). Most important are temperature Mexico is a center of diversity of the genus Quercus and precipitation (Körner, 2007), both of which influence (Nixon, 1993). This genus forms pure oak or mixed pine - the available humidity, the properties of soils, and their oak stands, one of the most species-rich vegetation types in formation processes (Guerrero-Campo et al., 1999). Mexico and characteristic of temperate mountain ranges Edaphic factors have an important role in the throughout the country (Muller-Using, 1994; Rzedowski, distribution and floristic variations and the abundance 2006; Encina-Domínguez et al., 2011). In northeastern of plants is closely related to soil properties, especially Mexico, the Sierra de Zapalinamé is a mountain range and nutrient availability (Rahayu et al., 2012). Relationships a protected area in the category of ecological conservation, between soil properties and plant species abundance have enacted by the state government of Coahuila (Periódico been described in various grassland habitats (Aguado- Oficial, 1996). Here the oak forest is restricted to canyons * Correspondence: [email protected] 262 This work is licensed under a Creative Commons Attribution 4.0 International License. ENCINA-DOMÍNGUEZ et al. / Turk J Agric For with higher humidity (Encina-Dominguez and Valdés- pinyon pine forest associated with xeric scrubland 9.55% Reyna, 2013). These oak forests contain 259 plant species (UAAAN, 1998). Oak forests are distributed in temperate (Encina-Domínguez et al., 2009), 28% of the flora of sites with more humidity at elevations between 2000 and this mountain range (Encina-Domínguez et al., 2016), 2600 m a.s.l. They are more abundant in the San Lorenzo including Quercus saltillensis Trel., which is endemic to and Boca Negra Canyons, and above Lomas de Lourdes southeastern Coahuila. Moreover, the conservation of (Encina-Domínguez and Valdés-Reyna, 2013). The most these forests is very important because they constitute common tree species in the oak forests are Quercus the main source of drinking water for the city of Saltillo, greggii (A.DC.) Trel., Q. mexicana Bonpl., Q. saltillensis and they offer a habitat for important wildlife such the with scattered Juniperus flaccida Schltdl., Quercus laeta American black bear (Ursus americanus Pallas, 1780). Liebm., and Pinus greggii Engelm. ex Parl. According to Species composition and community structure and Encina-Domínguez et al. (2007), in these forests, the most their relationship with environmental factors are the basis abundant shrub genera are Ageratina, Garrya, and Stevia, for studying forest dynamics. Understanding ecological and the most abundant herbaceous genera are Achillea, processes in forests is one of the most important goals Artemisia, and Polypodium. for proper management and biodiversity conservation 2.2. Vegetation sampling (Arévalo et al., 2012). Little work has been carried out to We estimated vegetation attributes by sampling 66 sites, determine the influence of environmental factors on the located along altitudinal gradients in canyons with a north structure and species composition of the oak forest in the or northwest exposition, where oak species dominate the Sierra de Zapalinamé region. canopy. At each site, we established a circular 500-m2 plot, We will test the following hypotheses: 1) that elevation where all shrubs were recorded and identified, and all is the most important variable in determining the structure trees with diameter at breast height (DBH) of ≥3 cm were and community composition because of its influence on identified, counted, and measured (Olvera-Vargas et al., ambient temperature and precipitation, and 2) that the 1996). Taxonomic identities of collected plant specimens physicochemical properties of the soils are similar through were determined and vouchers deposited at the ANSM oak forests of the study area. herbarium. For species names, we followed the checklist of native vascular plants of Mexico (Villaseñor, 2016). 2. Material and Methods Plot position and elevation were measured using 2.1. Study site a global positioning system (GPS; Etrex, Garmin Ltd., The Sierra de Zapalinamé is located in the southeast of Olathe, KS, USA). Chemical and physical soil factors were the state of Coahuila. It has an area of 45,000 ha, in the based on bulk samples taken from depths of 0–30 cm. municipalities of Saltillo and Arteaga. It is located south The soil samples were mixed, dried, and sifted through a of the city of Saltillo, between 25°15′00″N and 25°25′58″N 2-mm sieve; debris and stones were eliminated. Texture and between 100°47′14″W and 101°05′03″W (Figure (sand, clay, and silt) was determined using a Bouyoucos 1). It belongs to the Gran Sierra Plegada physiographic hydrometer. Organic matter content was determined by subprovince. The elevation ranges from 1590 m in the Walkley and Black method (Nelson and Sommers, the foothills to 3140 m in the Cerro El Penitente, with 1982) and pH was measured in a soil-to-water ratio of intermountain valleys averaging 2200 m. The rocks of 1:5 extract. Soil nitrogen, phosphorus, potassium, and the area are sedimentary, belonging to the Jurassic and electrical conductivity were determined. Qualitative Cretaceous periods; limestone covers 43% of the area, while levels baseline for nutrients obtained such as N, P, K, and 17% is sandstones and conglomerates. Alluvial soils occupy organic matter were according to SEMARNAT (2000) and 30% of the area, with variable depth, mainly found in the Fernández-Linares et al. (2006). plains with alluvial fans at the base of the mountains. Soils in Climatic data were obtained by interpolation from a the valleys are deep. There are also smaller areas of calcium linear regression analysis using records for the last 10 years and phaeozem calcaric xerosols. The dominant climate of from 45 weather stations adjacent to the study area in order the study area is the dry type (BSkw), while the upper parts to have greater variation for the study site (Trewin, 2007). of the mountain have a temperate type (C(w0)). The average Quantitative information was taken from database records annual temperature is 16.9