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Highlights:
The floristic richness of nine sites under study was 597 species (272 genera and 82 families).
At least five species of pinyon pine trees grow in San Luis Potosí, including Pinus nelsonii.
Pinyon pine species are related to Juniperus flaccida, Yucca and Quercus.
Altitude, slope, pH, organic matter and calcium in soil affect floristic similarity.
Introduction
Pinyon pine forests provide a variety of environmental services (Reyes-Carrera, Méndez-González, Nájera-Luna, & Cerano-Paredes, 2013) through the production of pinyon nuts, firewood and other non-timber forest products that are essential to the local economy; however, excessive resource overexploitation, especially intensive pinyon nuts harvesting and overgrazing, have caused the decline of these communities, drastically reducing their extent and diversity (Barrera-Zubiaga, Granados-Sánchez, Granados-Victorino, & Luna-Cavazos, 2018).
The State of San Luis Potosí is home to five species of pinyon pines, all with isolated distribution, confined to the highlands, ravines and intermountain plains, at elevations above 1 700 m (Pérez et al., 2019). One of these species is subject to special protection (Pinus johannis Rob.-Pass.) and two are considered endangered (Pinus nelsonii Shaw. and Pinus pinceana Gordon. & Glend.), due to low population density with restricted distribution, coupled with the high impact of human activities on the habitat (Secretaría de Medio Ambiente y Recursos Naturales [SEMARNAT], 2010), the most important are overgrazing by goats and cattle and the intense mining activity. Under this scenario, it is essential to describe the structure of these semiarid forests, as well as the factors that affect their dynamics, because this will allow the establishment of predictive models, management and sustainable use plans, as well as their conservation (Flake & Weisberg, 2019; Romero, Luna, & García, 2014).
The objective of this study was to describe the floristic-structural attributes of communities dominated by pinyon pine trees in San Luis Potosí and to determine the impact of environmental factors on these species.
Materials and methods
Floristic composition
Floristic composition was derived from floristic listings of the following studies: Hernández and García (1985); Suzán-Azpiri and Galarza (1987); Reyes-Agüero, González-Medrano, and García-Pérez (1996); Granados-Sánchez and Sánchez-González (2003); González, Giménez, García, and Aguirre (2007); Villarreal, Mares, Cornejo, and Capó (2009); Giménez and González (2011); Romero et al. (2014); Torres-Colín et al. (2017), and De-Nova, Castillo-Lara, Gudiño-Cano, and García-Pérez (2018). Species related to pinyon pine forests were selected and seasonal collections were made from September 2019 to March 2021 using the floristic sweep method (Barrera-Zubiaga et al., 2018) which consisted of walks, collection of specimens and herborization, for subsequent identification and deposit in the Herbarium CHAP de la División de Ciencias Forestales and in the Herbarium JES de la Preparatoria Agrícola, both of the Universidad Autónoma Chapingo. The nomenclature used for the species is that suggested by the Missouri Botanical Garden (Tropicos, 2021).
Structural characterization
Figure 1 shows the nine sites with pinyon pine forests in San Luis Potosí. The point-centred quarter method (Cottam & Curtis, 1956) was used at each site and 10 points were randomly selected at a distance of at least 20 m from each other. Individuals with arboreal or shrubby life form with height greater than 1 m were taken as reference. Diameter at breast height (DBH) of the stem of each individual was measured with a diameter tape (Forestry Suppliers, model 283D); in the case of individuals with multiple stems, all were measured and summed. The distance from the center point to the nearest tree was recorded for each quadrat with a measuring tape. The scientific name of the species was recorded, and its height was measured using a Haga hypsometer. With these data, the relative values of frequency, dominance and density of the species were estimated using the following equations:
Basal area was determined with the formula (π * dn2)/ 4 (Romahn & Ramírez, 2006). Density was defined as the total number of individuals of all species in one hectare, using the following formula: area/mean distance2 (Muller-Dombois & Ellenberg, 1974).
The above values were used to obtain the relative importance value (RIV), calculated using the formula proposed by Muller-Dombois and Ellenberg (1974): (relative frequency + relative density + relative dominance) / 3.
With the RIV, the most representative species and floristic associations of each site were defined. The arrangement of the most representative associations was described by physiognomic profiles (Richards, 1952) and Dansereau diagrams (Dansereau, 1957). The symbology used in these diagrams to describe the most representative characteristics by taxon is shown in Figure 2.
Figure 1 Study sites selected in the state of San Luis Potosí corresponding to the municipalities of Guadalcázar (a, e, i), Zaragoza (b and c), Catorce (d), Villa de Reyes (e), Charcas (f), Mexquitic de Carmona (g) and San Luis Potosí (h), based on the distribution of pinyon pine forests in Mexico (Instituto Nacional de Estadística y Geografía [ INEGI], 2021).
Figure 2 Symbols for the structural and phenological description of plant species proposed by Dansereau. Modified from Rosas, Granados, Granados, and Esparza (2017).
Environmental variables
Exposure, slope and altitude were recorded at each site. Samples of soil of nearly 1 kg were collected in paper bags for soil analysis. The samples were obtained from the first 10 cm after removing the leaflitter for subsequent analysis at the Central University Laboratory of the Soils Department of the Universidad Autónoma Chapingo. The following variables were determined in each sample: calcium (Ca), extracted in ammonium acetate at 1 N concentration at pH 7 in a soil-solution ratio 1:20 and determined by atomic absorption spectrophotometry; magnesium (Mg), obtained by atomic absorption spectrophotometry; potassium (K) extracted in ammonium acetate at 1 N concentration at pH 7 in a soil-solution ratio 1:20 and quantified by flame emission spectrophotometry; inorganic nitrogen (N), extracted with potassium chloride at 2 N concentration and determined by vapor entrainment; phosphorus (P), defined by Bray P-1 (Bray & Kurtz, 1945) and Olsen (Olsen & Sommers, 1982) extraction methods; pH, obtained by potentiometer with soil-water ratio 1:2; organic matter (OM), determined by the method of Walkley and Black (1934), and texture by a Bouyoucos hydrometer.
Multivariate statistical analysis
A clustering analysis was performed with binary attributes (presence-absence) of the species composing each locality. The clusters were defined with Jaccard's similarity index as a measure of distance and the Unweighted Pair-Group Method using Arithmetic averages (UPGMA) was used, with a cut-off level of 0.30 of the remaining information. Classification was performed with PAST software version 3.24 (Hammer, Harper, & Ryan, 2001).
The floristic composition was related to the environmental characteristics of the sites by a canonical correspondence analysis (Dhar & Sarker, 2021). The components that were correlated were floristic richness, sites and variables recorded in each site (physical and chemical properties of the soil, altitude and slope). This analysis was performed with CANOCO software version 4.56 (Ter Braak & Smilauer, 1998).
Results and Discussion
Floristic composition and structural characterization
The nine sites under study had a floristic richness of 597 species, grouped in 272 genera and 82 families (Appendix 1). The most representative families are Asteraceae with 45 genera and 81 species (13.6 %), Poaceae with 29/72 (12.1 %), Cactaceae with 18/69 (11.6 %); Fabaceae with 21/38 (6.4 %); Asparagaceae with 6/31 (5.2 %); Fagaceae with 1/24 (4.0 %) and Lamiaceae with 2/21 (3.5 %). The general characteristics and associations of each of the sites are described below.
Guadalcázar
The forest of this locality is located at coordinates 22° 37’ 01.8’’ N and 100° 29’ 20.8’’ W as centroid, at elevations of 1 600 to 1 774 m with northwest exposure; it has calcareous soils with scarce organic matter content. The forest showed the highest density of trees with 902 trees∙ha-1. An association of P. pinceana and Yucca potosina Rzed. was recorded, with the first species having the highest RIV (73.9 %). According to the Mexican Official Standard NOM-059-SEMARNAT-2010 (SEMARNAT, 2010), P. pinceana is in danger of extinction and its location is limited to the lower parts of the canyons, where they form small stands (Martínez-Ávalos et al., 2015). These species together with Rhus virens Lindh. ex A. Gray and Tecoma stans (L.) Juss. ex Kunth form the arboreal stratum with an average height between 1.8 and 3.3 m; in the shrub stratum, the most representative species were Agave striata Zucc., Dermatophyllum secundiflorum (Ortega) Gandhi y Reveal, and Forestiera reticulata Torr., as shown in Figure 3. In addition, this forest had the highest floristic richness with 363 species, 205 genera and 71 families.
Figure 3 Dansereau diagram and physiognomic profile of the pinyon pine forest of Guadalcázar. 11) Brahea decumbens, 2) Agave lechuguilla, 3) Muhlenbergia gracilis, 4) Dermatophyllum secundiflorum, 5) Pinus pinceana, 6) Echinocactus platyacanthus, 7) Tecoma stans, 8) Yucca potosina, 9) Opuntia rastrera, 10) Rhus virens and 11) Agave striata. The symbology for the structural and phenological description of the plant species is described in Figure 2.
Salitrería
The flora includes 213 species, 128 genera and 48 families with a density of 402 trees∙ha-1 with arboreal habit. The predominant association is pinyon pine-oak, in which P. cembroides Zucc. is the species with the highest RIV (65.5 %) with Juniperus flaccida Schltdl. and Quercus spp. as companion species; the canopy has a height between 1.8 and 5.0 m. A similar association was described by Rosas et al. (2017) in Querétaro. The shrub stratum is formed by Arbutus xalapensis Kunth and Sophora secundiflora (Ortega) Lag. ex DC. that do not exceed 3 m. These pinyon pine forests are located at the geographic coordinates 21° 58’ 48.5’’ N and 100° 37’ 09.4’’ W with an altitudinal range of 1 987 to 2 038 m and a southeastern exposure in the municipality of Zaragoza.
El Ranchito
The pinyon pine forests of this locality are located at the coordinates 21° 57’ 27.6’’ N and 100° 37’ 44.4’’ W with elevations between 2 122 and 2 500 m. The tree vegetation is composed of J. flaccida, Quercus rugosa Née and P. cembroides, the latter having the highest RIV (43.3 %). These species form a dense canopy of 6 to 7 m height, while the shrub layer formed by Q. depressipes Trel., Q. deserticola Trel., Agave salmiana Otto ex Salm-Dyck and Dasylirion cedrosanum Trel. does not exceed 3 m height. The northwest exposure of the site favors higher humidity (Romero et al., 2014) and greater amount of organic matter compared to other exposures, due to the presence of larger tree species (Arres, Márquez, & Ramírez-García, 2012). The site is very rocky, where several rupicolous species of the Crassulaceae family, mosses, ferns and lichens develop, as well as abundant hay (Tillandsia spp.), which retains environmental moisture and provides it to the soil (Guevara, Rosales, & Sanoja, 2005). The forest density was low with 440 trees∙ha-1 and its floristic richness was 284 species, 174 genera and 68 families. It is important to mention that the area of the pinyon pine forest is decreasing because of mining activity (Errejón, Flores, Muñoz, & Reyes, 2017).
San José de Coronados
This place is located in the Sierra de Catorce. Its pinyon pine forests are located at coordinates 23° 35’ 20.7’’ N and 100° 54’ 30.5’’ W with an altitudinal range of 1 750 to 2 335 m. They grow on a steep slope with stony soil. A total of 296 plant species divided into 176 genera and 64 families were identified. The density is 394 trees∙ha-1, with P. cembroides being the most relevant species (RIV = 85.5 %) together with Yucca carnerosana (Trel.) McKelvey; this association was also reported Barrera-Zubiaga et al. (2018) in Zacatecas. The average canopy height is between 2.2 and 5.8 m. The shrub stratum is dominated by D. cedrosanum and typical xerophytic scrub species such as Echinocactus platyacanthus Link and Otto and Agave lechuguilla Torr.; the latter occupies a large part of the ground cover throughout the forest. The extent of this forest, as in El Ranchito, is decreasing due to mining activities (Barrera, 2013).
Calderón
It is located in the municipality of Villa de Reyes at coordinates 21° 51’ 27.9’’ N and 101° 02’ 09.4’’ W at an altitude between 2 073 and 2 154 m with eastern exposure, in a stony site with little soil. A total of 197 vascular plant species grouped in 120 genera and 43 families were recorded. The most relevant species is P. cembroides (RIV = 75.5 %), accompanied in the arboreal stratum by Quercus spp. and Y. carnerosana; canopy height varies between 1.5 and 3.6 m. In the shrub layer, the most common species were A. lechuguilla and D. cedrosanum. The community had the lowest tree and shrub density with 327 trees∙ha-1, because the perimeter region of the pine forest is used as a mining area for the extraction of stone material. Soil loss and, in some cases, forest fires caused by the regrowth of vegetation used as food for goat farming are evidence of the anthropogenic impact.
Picacho de Lajas
Located in the municipality of Charcas, pine forests develop on a stony site with scarce soil. This forest has the lowest tree stratum, between 0.8 and 2.7 m, dominated by P. johannis (Figure 4) reported in the area by García-Gómez, Ramírez-Herrera, Flores-López, and López-Upton (2014). The species branches from the base and is accompanied by Yucca decipiens Trel. and Quercus spp. The shrub layer is less dense; D. cedrosanum and A. lechuguilla are the most frequent species. The forest shows the lowest floristic richness with 168 species of 111 genera and 49 families, and a tree and shrub density of 417 trees∙ha-1; they are located at the geographic coordinates 23° 17’ 43’’ N and 101° 07’ 6’’ W, at an altitude of 2 200 to 2 472 m. Land use change was observed in the lower parts of the forest, mainly the establishment of A. lechuguilla plantations (Reyes-Agüero et al., 1996).
Figure 4 Dansereau diagram and physiognomic profile of the pine forest of Picacho de Lajas in the municipality of Charcas, San Luis Potosí. 1) Pinus johannis, 2) Yucca decipiens, 3) Agave lechuguilla, 4) Bouteloua curtipendula, 5) Dasylirion cedrosanum, 6) Stenocactus pentacanthus, 7) Agave schidigera, 8) Quercus depressipes and 9) Quercus cordifolia. The symbology for the structural and phenological description of the plant species is described in Figure 2.
Guadalupe Victoria y la Cruz
Its pinyon pine forests are located at coordinates 22° 06’ 07.8’’ N and 101° 11’ 33.8’’ W at altitudes between 2 300 and 2 400 m in the municipality of Mexquitic de Carmona. The arboreal vegetation is composed of Yucca filifera Chabaud., Q. deserticola, P. cembroides and P. discolor D. K. Bailey & Hawksw.; the latter has the highest RIV (50.5 %) reported in the area by Romero-Manzanares and García-Moya (2002). The forests develop on a stony site with little soil, where the tree species form an open canopy between 1.7 and 5.0 m. The shrub layer is represented by A. salmiana and Dasylirion acrotrichum (Schiede) Zucc. Goat grazing was observed at this site, so the herbaceous stratum and regrowth of tree species are scarce, which may be the reason for the low floristic richness of 196 species, 127 genera and 44 families with a tree density of 511 trees∙ha-1.
La Amapola
The pine populations are located in the San Miguelito mountain range in the municipality of San Luis Potosí, at coordinates 22° 01’ 03’’ N y 10° 07’ 41’’ W, with a southwestern exposure and an altitude of 2 350 to 2 474 m. The topography is mountains with several slopes and a stony substratum of rhyolitic igneous material with little soil. The topography is mountainous and has diverse slopes and a stony substratum of rhyolitic igneous material, with little soil. The floristic richness is 187 species, grouped in 127 genera and 50 families, with a tree density of 775 trees∙ha-1. The tree stratum is dominated by P. johannis (RIV = 39.3 %) accompanied by P. cembroides and Y. decipiens that form an open canopy of between 1.5 and 3.7 m. Pinus johannis was reported in the area by Luna-Cavazos, Romero-Manzanares, and García-Moya (2008) and has a special protection status, according to NOM-059 (SEMARNAT, 2010). The shrub stratum is very poor; it consists of D. acrotrichum and some species of the genera Opuntia and Quercus. The herbaceous stratum is scarce, mainly due to overgrazing by goats, which also affects the regrowth of pinyon pine species.
El Realejo
Located in the municipality of Guadalcázar with a richness of 181 species, divided into 119 genera and 46 families, and a density of 863 trees∙ha-1. In the mountain range located at 22° 41’ 49’’ N and 100° 25’ 43’’ W as centroid, forests dominated by P. nelsonii develop in ravines that range from 2 000 to 2 158 m. This community is important because P. nelsonii is a species endemic to the northern region of the Sierra Madre Oriental of Mexico and is endangered according to NOM-089 (García-Aranda, Méndez-González, & Hernández-Arizmendi, 2018; SEMARNAT, 2010). This pine, together with Y. potosina, Quercus crassifolia Trel. and A. xalapensis form the tree stratum with a height between 1.8 and 5 m (Figure 5). The most representative species of the shrub layer are T. stans and R. virens. In this forest almost no regeneration of P. nelsonii was observed because of the constant disturbances generated by livestock, even though it is located in areas with difficult access.
Figure 5 Dansereau diagram and physiognomic profile of the pine forest of El Realejo, municipality of Guadalcázar, San Luis Potosí. 1) Pinus nelsonii, 2) Tecoma stans, 3) Jatropha dioica, 4) Quercus crassifolia, 5) Arbutus xalapensis, 6) Bouteloua scorpioides, 7) Sophora secundiflora, 8) Yucca potosina, 9) Agave salmiana, 10) Agave striata, 11) Brahea decumbens y and 12) Juniperus montícola. The symbology for the structural and phenological description of the plant species is described in Figure 2.
Classification and management
Figure 6 shows the dendrogram generated from the floristic similarity grouping analysis, with a cut-off line of 0.30 of remaining information, showing three groups. The localities in the first group are dominated by P. cembroides or P. johannis and are found further north in the state, except for the locality of La Amapola, located to the southwest; these localities are distributed at higher altitudes (2 350 m) on slopes of 20 to 30 %, where soils have low Ca concentration, but are rich in K and N (Table 1). These localities have the greatest number of species typical of xerophilous scrub.
The second group consists of forests dominated by P. cembroides or P. pinceana (Figure 6), which grow in soils with slightly acid or neutral pH (6-7) with low concentrations of organic matter and calcium, but rich in K (Table 1). The forests develop in southwest exposure, except for El Ranchito, which is located in northwest exposure, which leads to the existence of P. pinceana pine species as mentioned by Villarreal et al. (2009) and Martínez-Ávalos et al. (2015).
Table 1. Soil physicochemical properties of pine communities in San Luis Potosí.
| Site | Altitude (m) | Slope (%) | pH | N | P | K | Ca | Mg | OM | Sand | Silt | Clay | Texture |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ---------------------mg∙kg-1--------------------- | -----------------%----------------- | ||||||||||||
| G | 1 703 | 20 | 7.95 | 18.42 | 24.17 | 506.5 | 11 582.0 | 451.0 | 14.75 | 57.5 | 21.8 | 20.7 | Loamy |
| ERJ | 2 079 | 30 | 7.11 | 48.13 | 2.34 | 408 | 13 946.2 | 697.1 | 19.83 | 61.0 | 29.0 | 10.0 | Loamy |
| S | 2 000 | 25 | 7.03 | 12.25 | 1.7 | 386.4 | 1 162.7 | 222.3 | 5.91 | 65.4 | 24.9 | 9.7 | Sandy silt |
| ER | 2 151 | 23 | 6.4 | 16.8 | 1.38 | 764.8 | 2 165.8 | 704.4 | 5.1 | 68.6 | 16.5 | 14.9 | Sandy silt |
| SJC | 2 338 | 31 | 8.02 | 16.14 | 17.84 | 256.2 | 8 426.2 | 205.6 | 8.71 | 54.3 | 33.8 | 11.7 | Sandy silt |
| C | 2 103 | 22 | 5.77 | 9.8 | 7.82 | 781.6 | 1 219.4 | 376.4 | 7.66 | 59.4 | 23.7 | 16.9 | Sandy silt |
| PL | 2 409 | 26 | 6.69 | 15.4 | 4.9 | 328.4 | 1 667.7 | 268.4 | 4.6 | 53.7 | 34.6 | 11.0 | Sandy silt |
| GVYC | 2 383 | 23 | 5.36 | 18.2 | 3.94 | 325.2 | 406.8 | 156.2 | 6.87 | 62.7 | 25.7 | 77.7 | Sandy silt |
| LA | 2 412 | 20 | 4.26 | 19.70 | 0.98 | 382.2 | 928.3 | 202.3 | 17.55 | 60.0 | 13.0 | 27.0 | Sandy silt |
OM = organic matter. Sites: G = Guadalcázar, ERJ = El Realejo, S = Salitrería, ER = El Ranchito, SJC = San José de Coronados, C = Calderón, PL = Picacho de Lajas, GVYC = Guadalupe Victoria y la Cruz, LA = La Amapola.
Figure 6 Dendrogram showing the hierarchical relationships of floristic similarity between sampling localities in San Luis Potosí. G = Guadalcázar, ERJ = El Realejo, S = Salitrería, ER = El Ranchito, SJC = San José de Coronados, C = Calderón, PL = Picacho de Lajas, GVYC = Guadalupe Victoria y la Cruz, LA = La Amapola.
The third group is dominated by P. nelsonii, P. discolor and P. cembroides in association with Y. potosina and several oak species; they grow in slightly acidic to neutral soils (pH 5-7) and have a high organic matter content (Table 1). The forests of El Realejo develop in ravines, so it would be assumed that the greatest accumulation of nutrients occurs in the lower parts due to rainfall runoff, with high pH values due to the high concentration of calcium (Osman, 2013), since these forests develop on calcareous soils.
A canonical correspondence analysis was used to manage the pinyon pine forests (Figure 7), which recognizes the correlation between the floristic composition of each site and the environmental variables. Statistical values for the first three axes are shown in Table 2; the results suggest that the difference in floristic composition is mainly due to altitude, calcium, pH, organic matter, slope and texture (Table 2; Figure 7), a product of the physiography at the sites (Granados, Hernández, & López, 2012). These first three axes can explain 53.2 % of the variation among locations.
Table 2. Canonical correspondence analysis for the first three axes indicating the correlation between floristic composition and environmental variables of the sites studied in San Luis Potosí.
| Environmental variables | Axis 1 | Axis 2 | Axis 3 | |
|---|---|---|---|---|
| Altitude (m) | 0.778 | 0.441 | -0.036 | |
| Slope (%) | -0.042 | 0.819 | -0.248 | |
| pH | -0.746 | 0.486 | 0.080 | |
| N (mg∙kg-1) | -0.428 | -0.083 | -0.454 | |
| P (mg∙kg-1) | -0.514 | 0.227 | -0.074 | |
| K (mg∙kg-1) | -0.015 | -0.541 | 0.470 | |
| Ca (mg∙kg-1) | -0.825 | 0.173 | -0.327 | |
| Mg (mg∙kg-1) | -0.514 | -0.327 | 0.351 | |
| OM (%) | -0.527 | -0.235 | -0.636 | |
| Sand (%) | -0.006 | -0.479 | 0.382 | |
| Silt (%) | 0.074 | 0.693 | -0.280 | |
| Clay (%) | 0.449 | -0.362 | -0.146 | |
| Total variance | ||||
| Eigenvalues | 0.332 | 0.255 | 0.208 | Inercia total |
| Correlation species-environmental factors | 1 | 1 | 1 | 1.496 |
| Explained variance (%) | 22.2 | 39.3 | 53.2 | |
Figure 7 Canonical correspondence analysis of the nine sampling sites in the pinyon pine communities of San Luis Potosí. G = Guadalcázar, ERJ = El Realejo, S = Salitrería, ER = El Ranchito, SJC = San José de Coronados, C = Calderón, PL = Picacho de Lajas, GVYC = Guadalupe Victoria y la Cruz, LA = La Amapola.
Soil characteristics are relevant to determine differences in the structure of a plant community (Barrera-Zubiaga et al., 2018; Granados, Granados, & Sánchez-González, 2015; Rosas et al., 2017). Based on the correlation of environmental variables (Table 3), it is highlighted that as altitude increases, the pH value decreases, whereas, at higher pH, Ca and P contents increase. On the other hand, the concentration of silt increases the steeper the slope, because it is not easily eroded by the wind, in addition to showing appreciable cohesion in dry soils.
Table 3 Correlation matrix between environmental variables of nine sampling sites in the pine communities of San Luis Potosí.
| Altitude | Slope | pH | N | P | K | Ca | Mg | OM | Sand | Silt | Clay | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Altitude | 1 | |||||||||||
| Slope | 0.44 | 1 | ||||||||||
| pH | -0.52 | 0.40 | 1 | |||||||||
| N | -0.07 | 0.37 | 0.10 | 1 | ||||||||
| P | -0.54 | -0.08 | 0.71 | -0.15 | 1 | |||||||
| K | -0.37 | -0.52 | -0.22 | -0.19 | -0.16 | 1 | ||||||
| Ca | -0.54 | 0.27 | 0.73 | 0.62 | 0.66 | -0.20 | 1 | |||||
| Mg | -0.43 | -0.08 | 0.16 | 0.50 | -0.11 | 0.66 | 0.37 | 1 | ||||
| OM | -0.36 | -0.07 | 0.10 | 0.70 | 0.29 | -0.17 | 0.71 | 0.23 | 1 | |||
| Sand | -0.09 | -0.28 | -0.39 | 0.02 | -0.63 | 0.54 | -0.41 | 0.46 | -0.26 | 1 | ||
| Silt | 0.30 | 0.78 | 0.49 | 0.12 | 0.22 | -0.63 | 0.26 | -0.37 | -0.17 | -0.65 | 1 | |
| Clay | 0.26 | -0.32 | -0.49 | -0.07 | -0.11 | -0.18 | -0.31 | -0.36 | -0.08 | 0.14 | -0.14 | 1 |
OM: Organic matter
Conclusions
Pinyon pine forests in San Luis Potosí host a floristic richness of 597 species and have three physiognomic-structural variants (pinyon-Yucca spp., pinyon-Quercus spp. and pinyon-Juniperus flaccida) with five pinyon pine species (Pinus cembroides, P. pinceana, P. nelsonii, P. discolor and P. johannis). The associations and floristic composition of each site are determined by altitude, slope, pH, organic matter and soil calcium, so each of the communities must be managed differently, taking into account the particular requirements of the species that develop there. Furthermore, the results of this study can be useful for the design of reforestation strategies, as well as payments for environmental services.
