Coville, MICROPHYLLUS DESERT SCRUB in NORTHEAST MEXICO

STRUCTURE AND DIVERSITY OF Larrea tridentata (DC.) Coville, MICROPHYLLUS DESERT SCRUB IN NORTHEAST MEXICO José Manuel Mata-Balderas, Eduardo Javier Treviño-Garza, Eduardo Alanís-Rodríguez, Alejandro Collantes Chávez-Costa, Ernesto A. Rubio-Camacho, Arturo Mora-Olivo and José Guadalupe Martínez-Ávalos

SUMMARY

Microphyllous desert scrub communities cover about pling sites of 1.0m2 were established in order to evaluate 19.5×10 6ha and are the most common and widely distributed herbaceous vegetation. The plant species were idetified and vegetation in arid areas of Mexico. Larrea tridentata (DC.) the diameters of each individual crown measured. Margalef Coville, an evergreen creosote bush or chaparral that can (DMg) and Shannon-Weiner (H’) indices were calculated to survive in extreme drought conditions, due mainly to its al- determine the richness and diversity of species, respectively. lelopathic substances and secondary metabolites, is typically Forty species, 33 genera and 12 families of vascular plants found as the dominant species in this community. The aim were registered. Families with the most species were Cacta- of this study was to evaluate the structure and diversity of a ceae (13), Fabaceae (8) and Asteraceae (5). The L. tridentata microphyllous scrub community dominated by L. tridentata in microphyllous scrub community has a high species richness Northeastern Mexico. To determine the composition, diversi- compared to other xerophilous scrub communities in North- ty and structure of a community consisting of trees, shrubs eastern Mexico. The distribution of species abundance was and succulents, 10 circular sample sites, each of 500m2, were adjusted to the Pareto model, due to the abundance or rare established. Within each circular site, square-shaped sam- species that characterizes stressful environments.

Introduction cularly, the microphyllous able to survive in extreme tion in Mexico and the threat scrub community covers an drought conditions by making to this community from an- Scrublands are the most area of 19.5×10 6ha in the low- use of other attributes (Ha- thropogenic impacts such as common and widely distribut- er portions of mountain slopes merlynck et al., 2000). The overgrazing, only a few stud- ed vegetation communities in and especially in flatlands presence of allelopathic sub- ies have been generated on arid areas of Mexico (Rze- with alluvial soils (Granado- stances and secondary metabo- communities of L. tridentata dowski, 1978). Despite the Sánchez et al., 2011). Typi- lites has played an important (Mora-Donjuán et al., 2014). unfavorable conditions of the cally, the dominant species in role in helping this bush to The floristic and ecological desert areas, there is a wide this vegetation type is Larrea thrive and occupy large areas studies on xeric scrubs that diversity of succulent species tridentata (DC.) Coville (cre- in scrublands and displace oth- have taken place in recent that hold great ecological rel- osote bush), an aromatic er species that are typical of years in Northern Mexico, evance such as the case of shrub of 1-2 m in height with these ecosystems (Mabry et al., particularly in the state of cacti that are often considered numerous flexuous stems. 1977; Rundel et al., 1994). Nuevo Leon, have focused on endemic or are endangered Unlike other species of shrubs The scrubland distribution the study of Tamaulipan (Hernández et al., 2008). The- that are morphologically and of L. tridentata extends from thornscrub, submontane scrub se plants are distributed in physiologically adapted to the Southwestern United and rosetophilous desert scrub different communities, form- arid conditions, like succu- States to Central Mexico, and (Reid et al., 1990; Pompa- ing mosaics according to the lents, which have spines, in- it is mostly distributed in García et al., 2017; Rascón conditions of the terrain and dumentum or falling leaves, Northern and Central Mexico et al., 2017). L. tridentata mi- the climate (Huerta-Martínez L. tridentata is a defenseless (Granados et al., 2011). Des- crophyllous desert scrub has and García-Moya, 2004). Parti- evergreen species that has been pite its significant representa- been little studied in Northeas-

KEYWORDS / Chihuahuan Desert / Diversity / Index / Larrea tridentata / Margalef Index / Mexico / Shannon / Received: 01/10/2017. Modified: 05/16/2018. Accepted: 05/17/2018.

José Manuel Mata-Balderas. León, México. E-mail: manuel- Alejandro Collantes Chávez- Forestales, Agrícolas y Pecua- (Corresponding author). Forest [email protected] Costa. M.Sc. in Forest Scien- rias, Mexico. Engineer, M.Sc. in Forest Eduardo Javier Treviño-Garza. ces, Universidad Autonoma Arturo Mora-Olivo. Doctor in Sciences and Doctor in Na- Biologist, UANL, Mexico. Ph.D. Chapingo, Mexico. Doctor in Biological Sciences, Universi- tural Resources Management, in Forestry Science, University Sciences and Plant Biotechno- dad Nacional Autónoma de Universidad Autónoma de of Göttingen, Germany. Professor- logy, Centro de Investigación México. Professor-Researcher, Nuevo León (UANL), Mexico. Researcher, UANL, Mexico. Científica de Yucatán, Mexico. Universidad Autónoma de Professor-Researcher, UANL, Eduardo Alanís-Rodríguez. Fo- Professor-Researcher, Univer- Tamaulipas (UAT), Mexico. Mexico. Address: Facultad de rest Engineer, M.Sc. in Forest sidad de Quintana Roo, Mexico. José Guadalupe Martínez-Ávalos. Ciencias Forestales, UANL. Sciences and Doctor in Natural Ernesto A. Rubio-Camacho. Doctor in Natural Resources Carretera Linares - Cd. Victo- Resources Management, UANL, M.Sc. in Forest Sciences, UANL, Management, UANL, Mexi- ria km 145. Apartado Postal Mexico. Professor-Researcher, Mexico. Researcher, Instituto co. Professor-Researcher, UAT, 41. C.P. 67700, Linares, Nuevo UANL, Mexico. Nacional de Investigaciones Mexico.

JUNE 2018 • VOL. 43 Nº 6 0378-1844/14/07/468-08 $ 3.00/0 449 ESTRUCTURA Y DIVERSIDAD DE UN MATORRAL DESÉRTICO MICRÓFILO DE Larrea tridentata (DC.) Coville EN EL NORESTE DE MÉXICO José Manuel Mata-Balderas, Eduardo Javier Treviño-Garza, Eduardo Alanís-Rodríguez, Alejandro Collantes Chávez-Costa, Ernesto A. Rubio-Camacho, Arturo Mora-Olivo y José Guadalupe Martínez-Ávalos RESUMEN

Las comunidades de matorral desértico micrófilo comprenden tio circular se establecieron sitios cuadrangulares de 1m2 para cerca de 19,5’106ha y son la vegetación más común y amplia- evaluar la vegetación herbácea. Las especies vegetales fueron mente distribuida en zonas áridas de México. En estas comu- identificadas y se midió el diámetro de cada corona. Los índices nidades la especie típicamente dominante es Larrea tridentata de Margalef (DMg) y de Shannon-Weiner (H’) fueron calculados (DC.) Coville (‘chaparral’), un arbusto resinoso siempreverde para determinar la riqueza y la diversidad de especies, respec- capaz de sobrevivir en condiciones de extrema sequía debido so- tivamente. Se registraron 40 especies, 33 géneros y 12 familias. bre todo a su contenido de sustancias alelopáticas y metabolitos Las familias con más especies fueron Cactaceae (13), Fabaceae secundarios. El objetivo del estudio fue evaluar la estructura y (8) and Asteraceae (5). La comunidad de matorral micrófilo de diversidad de una comunidad de matorral micrófilo dominado L. tridentata en el noreste de México tiene una riqueza de espe- por L. tridentata en el noreste de México. A fin de determinar la cies alta en comparación a otras comunidades de matorral xeró- composición, diversidad y estructura de una comunidad conten- filo en la región. La distribución de la abundancia de especies tiva de árboles, matorrales y plantas suculentas, se establecieron se ajustó al modelo de Pareto, dada la abundancia de especies 10 sitios de muestreo circulares de 500m2. Dentro de cada si- raras que caracterizan los ambientes extremos.

ESTRUTURA E DIVERSIDADE DE UM MATAGAL DESÉRTICO MICRÓFILO DE Larrea tridentata (DC.) Coville NO NORDESTE DE MÉXICO José Manuel Mata-Balderas, Eduardo Javier Treviño-Garza, Eduardo Alanís-Rodríguez, Alejandro Collantes Chávez-Costa, Ernesto A. Rubio-Camacho, Arturo Mora-Olivo e José Guadalupe Martínez-Ávalos RESUMO

As comunidades de matagal desértico micrófilo compreendem se estabeleceram parcelas quadrangulares de 1m2 para avaliar cerca de 19,5’106ha e são a vegetação mais comum e amplamen- a vegetação herbácea. As espécies vegetais foram identificadas te distribuída em áreas áridas de México. Nestas comunidades a e se mediu o diâmetro de cada corona. Os índices de Margalef espécie tipicamente dominante é Larrea tridentata (DC.) Coville (DMg) e de Shannon-Weiner (H’) foram calculados para determi- (‘chaparral’), um arbusto resinoso sempre verde capaz de sobre- nar a riqueza e a diversidade de espécies, respectivamente. Re- viver em condições de seca extrema devido sobretudo a seu con- gistraram-se 40 espécies, 33 gêneros e 12 famílias. As famílias teúdo de substâncias alelopáticas e metabólitos secundários. O com mais espécies foram Cactaceae (13), Fabaceae (8) e Astera- objetivo do estudo foi avaliar a estrutura e diversidade de uma ceae (5). A comunidade de matagal micrófilo de L. tridentata no comunidade de matagal micrófilo dominado por L. tridentata no nordeste do México tem uma riqueza de espécies alta em com- nordeste do México. Com o fim de determinar a composição, paração a outras comunidades de matagal xerófilo na região. A diversidade e estrutura de uma comunidade contentiva de árvo- distribuição da abundância de espécies se ajustou ao modelo de res, matagais e plantas suculentas, se estabeleceram 10 áreas de Pareto, devido à abundancia de espécies raras que caracterizam amostragem circulares de 500m2. Dentro de cada área circular os ambientes extremos.

tern Mexico, the work of Mora- scrub community located in the Donjuán et al. (2014) being city of Garcia, state of Nuevo one of the few papers pub- Leon, Northeastern Mexico, at lished. In order to contribute to 25º49’01’’North and 100º36’ the knowledge of this commu- 45’’W, at an elevation of 740 nity, the aim of this study was masl (Figure 1). The climate is to determine the composition, dry semiwarm BSh according to diversity and structure of a the Köppen Climate Classi- thicket of the Larrea tridentata fication. The average annual mycrophyllus desert scrub in temperature is 18-22ºC and the one of the most well-preserved hottest months are July and areas of Northeastern Mexico. August. The representative soil type in the study area is Haplic Materials and Methods Xerosol.

Location and site description Vegetation sampling

The study was conducted In September 2014, parame- Figure 1. Location of the study area. a: Northeastern Mexico and within a Larrea tridentara (DC.) ters of the Larrea tridentata micro- Southeastern United States; b: the municipality of Garcia, Nuevo Leon; Coville microphyllous desert phyllus desert scrub commu- c: the spatial location of the sampling sites.

450 JUNE 2018 • VOL. 43 Nº 6 nity were determined at ten 1974) defined by the following Hubel’s metacommunity ze- independent random variables randomly located circular plots equation (Whittaker, 1972): ro-sum multinomial distribu- (Prado and Dantas, 2014). of 500m2. Two levels of strati- tion, with the density approxi- fication were followed: tree, i=1 (AR ,DR ,FR ) mation form Alonso and Results IVI = ∑ i i i shrub and succulent components 3 McKane (2004). In the case of were analyzed in the circular n the Poison lognormal distribu- A total of 40 species belong- area, while the herbaceous veg- The distribution of species tion, the species abundance ing to 33 genera and 12 families etation was studied in a 1m2 abundance is described by us- distributions follow a lognor- of vascular plants were recorded square-shaped site established ing three models: the Pareto mal density function with (Table I). The families with the within each circular plot. model, the Poisson model of Following this experimental normal lognormal series and the TABLE I design, a census of all trees, Neutral Model of Alonso and LIST OF THE SCRUB FLORA COMPRISING THE shrubs, succulents and grasses Mackane (Alonso and McKane, Larrea tridentata SCRUB IN THE MUNICIPALITY was conducted, measuring cov- 2004). The three models were OF GARCÍA, NUEVO LEON, MEXICO erage, height and diameter for fitted according to the maxi- all individuals, except for the mum likelihood method, using Agavaceae diameter in herbaceous and the R software (R Core Team, Agave lechuguilla Torr. succulent vegetation, due to the 2016), via the R Studio inter- Asteraceae lack of a woody stem. The cov- face (R Studio, version 0.99) Acourtia nana (A. Gray) Reveal & R.M. King erage was measured as the area and the Species Abundance Calyptocarpus vialis Less. of ground occupied by plants Distributions (SADs package, Parthenium hysterophorus L. within the circular and quadrat version 0.2.4.). The model selec- Parthenium incanum Kunth Pectis papposa Harv. & A. Gray plots, and was calculated as the tion was conducted by visual Thymophylla pentachaeta (DC.) Small average of the north-south and and statistical methods, via the Viguiera stenoloba S.F. Blake east-west measure of the crown following steps: 1) the predicted Zinnia acerosa (DC.) A. Gray (for trees and shrubs) or of the behavior of the data was evalu- Boraginaceae individual and clump (for suc- ated by graphically observing Cordia boissieri A. DC. culents and herbaceous). the similarity or difference of Tiquilia canescens (A. DC.) A.T. Richardson the distribution of data against Cactaceae Data analysis the theoretical distribution; 2) a Coryphantha neglecta L. Bremer comparison was undertaken of Coryphantha salinensis (Poselger) Dicht & A. Lüthy To estimate the species rich- models selected by the Akaike Infor- Cylindropuntia imbricata (Haw.) F.M. Knuth ness index of Margalef (1958; mation Criterion (AIC), which Cylindropuntia leptocaulis (DC.) F.M. Knuth Echinocactus horizonthalonius Lem. DMg) and the species diversity takes into account the statistical index of Shannon-Weiner (Sha- Echinocactus texensis Hopffer adjustment and complexity. Echinocereus enneacanthus Engelm. nnon y Weaver, 1949), the fol- When two models are com- Echinocereus poselgeri Lem. lowing equations were used: pared with this statistical selec- Mammillaria heyderi Muehlenpf. tion method, the best model is Opuntia engelmannii Salm-Dyck (S−1) chosen based on the lower val- Opuntia microdasys (Lehm.) Pfeiff. DMg = Sclerocactus scheeri (Salm-Dyck) N.P. Taylor In(N) ue in the AIC and the delta AIC (dAIC) in comparing mod- Thelocactus bicolor (Galeotti ex Pfeiff.) Britton & Rose s els based on the outcome of Euphorbiaceae = − × = H’ ∑pi ln(pi ); pi ni / N AIC, minus the minimum AIC. = Jatropha dioica Sessé i 1 If dAIC<2 there is no differ- Fabaceae where S: number of species ence between the models (Kindt present, N: total number of in- and Coe, 2005). Acacia rigidula Benth. dividuals, and n : number of These three models were Dalea lasiathera A. Gray i Mimosa texana (A. Gray) Small individuals of species i. chosen because they can be Prosopis glandulosa Torr. Species abundance (ARi) used to describe the species Senna lindheimeriana (Scheele) H.S. Irwin & Barneby was determined according to abundance distribution, with Rhamnaceae the total number of individuals some differences. The Pareto Karwinskia humboldtiana (Schult.) Zucc. per species, dominance (DRi) distribution follows a power was based on the average law distribution and is com- Koeberliniaceae Koeberlinia spinosa Zucc. crown cover (horizontal ground monly used to make inferences projection from the aerial sec- about the distributions in com- Scrophulariaceae Leucophyllum frutescens (Berland.) I.M. Johnst. tion), and frequency (FRi) was munity assemblages: in plant based on the species presence ecology, for example, this pow- Solanaceae within each sampling site. er law distribution could be Nicotiana glauca Graham Relative values of these vari- used to explain the assumption Nicotiana trigonophylla Dunal ables were used to obtain the of a high presence of pioneer Solanum elaeagnifolium Cav. Importance Value Index (IVI), plants and low presence of late Ulmaceae which represents a weighted successional ones, due to the Celtis pallida Torr. value of the level of taxon rep- implicit ‘costs’ to the ecosys- Ziziphus obtusifolia (Hook. ex Torr. & A. Gray) A. Gray resentativeness expressed as tem of setting the necessary Zygophyllaceae percentage on a scale of 0 to conditions for these plants to Larrea tridentata (DC.) Coville 100 (Müeller and Ellenberg, invade. The neutral model is Porlieria angustifolia (Engelm.) A. Gray

JUNE 2018 • VOL. 43 Nº 6 451 most species were Cactaceae (13), DMg= 4.09, and an H’= 1.75. Parthenium incanum Kunth, ri Muehlenpf., Coryphantha Asteraceae (8) Fabaceae (5) and Also, this stratus has a species Opuntia microdasys (Lehm.) salinensis (Poselger) Dicht & Solanaceae (3); these families richness of 29 species (S), a Pfeiff and Ziziphus obtusifolia A. Lüthy and Coryphantha accounted together for 72% of density of 1,858 individuals/ha (Hook. ex Torr. & A. Gray) A. neglecta L. Bremer recorded the species recorded in the study. and a total crown cover of Gray. Together, these species the lowest IVI values (0.38%). 1622.39m 2·ha-1. The most im- accounted for 75.73% of the The analysis of the distribu- Tree, shrub and succulent stratus portant species (Table II) were IVI of the community. Fur- tion pattern of species abun- Larrea tridentata, Jatropha thermore, 48.27% of the spe- dance showed that the best vi- The tree, shrub and succu- dioica Sessé, Cylindropuntia cies presented values of sual adjustment (Figure 2) and lent components present a leptocaulis (DC.) F.M. Knuth, IVI<1.0%. Mammillaria heyde- statistics (Table III) were ob- tained with the Pareto model, followed by the Poisson model TABLE II of logarithmic series, and fi- STRUCTURAL PARAMETERS OF SPECIES TAKING THE FORM OF TREE, nally by the neutral model. SHRUB AND SUCCULENT GROWTH REGISTERED AT THE SITES OF 500 m2 AREAS Abundance Dominance Frequency Herbaceous stratus Species IVI N/ha % m2/ha % Sites % The herbaceous stratus pres- Larrea tridentata (DC.) Coville 1040 55.97 854.30 52.66 10 9.26 39.30 Jatropha dioica Sessé 204 10.98 201.26 12.41 10 9.26 10.88 ents a DMg= 1.36, and an H’= Cylindropuntia leptocaulis (DC.) F.M. Knuth 144 7.75 182.90 11.27 10 9.26 9.43 1.76. Also, this stratus showed Parthenium incanum Kunth 114 6.14 75.29 4.64 7 6.48 5.75 a species richness (S) of 11, a Opuntia microdasys (Lehm.) Pfeiff. 82 4.41 75.54 4.66 8 7.41 5.49 density of 153,000 individuals/ Ziziphus obtusifolia (Hook. Ex Torr. & A. Gray) 56 3.01 68.46 4.22 8 7.41 4.88 ha, and a total coverage of Prosopis glandulosa Torr. 16 0.86 34.81 2.15 6 5.56 2.85 678.13 m 2 ha-1. Pectis papposa Acacia rigidula Benth. 4 0.22 3.80 0.23 7 6.48 2.31 Harv. & A. Gray, Solanum Koeberlinia spinosa Zucc. 20 1.08 10.39 0.64 5 4.63 2.12 Echinocactus horizonthalonius Lem. 42 2.26 1.71 0.11 4 3.70 2.02 elaeagnifolium Cav., Senna Opuntia engelmannii Salm-Dyck 14 0.75 7.89 0.49 5 4.63 1.96 lindheimeriana (Scheele) H.S. Sclerocactus scheeri (Salm-Dyck) N.P. Taylor 12 0.65 0.04 0.00 5 4.63 1.76 Irwin & Barneby, Dalea lasiat- Echinocereus enneacanthus Engelm. 8 0.43 1.71 0.11 4 3.70 1.41 hera A. Gray, and Tiquilia ca- Agave lechuguilla Torr. 36 1.94 18.10 1.12 1 0.93 1.33 nescens (A. DC.) A.T. Richard- Cylindropuntia imbricata (Haw.) F.M. Knuth 4 0.22 34.21 2.11 1 0.93 1.08 son were the most important Echinocactus texensis Hopffer 14 0.75 0.37 0.02 2 1.85 0.88 Celtis pallida Torr. 4 0.22 19.64 1.21 1 0.93 0.78 species, accounting for 73.37% Echinocereus poselgeri Lem. 6 0.32 0.85 0.05 2 1.85 0.74 of the IVI (Table IV). No IVI Thelocactus bicolor Britton & Rose 6 0.32 0.02 0.00 2 1.85 0.73 for herbaceous species was Nicotiana glauca Graham 2 0.11 7.60 0.47 1 0.93 0.50 <1%, and Parthenium hystero- Karwinskia humboldtiana S. Watson 2 0.11 6.93 0.43 1 0.93 0.49 phorus L. had the lowest re- Mimosa texana Small 2 0.11 6.28 0.39 1 0.93 0.47 corded value of IVI (2.31%). Viguiera stenoloba S.F. Blake 4 0.22 4.52 0.28 1 0.93 0.47 Leucophyllum frutescens I.M. Johnst. 2 0.11 3.30 0.20 1 0.93 0.41 Porlieria angustifolia A. Gray 4 0.22 1.54 0.09 1 0.93 0.41 Discussion Cordia boissieri A. DC. 4 0.22 0.79 0.05 1 0.93 0.40 Coryphantha neglecta L. Bremer 4 0.22 0.08 0.00 1 0.93 0.38 Tree, shrub and succulent Mammillaria heyderi Muehlenpf. 4 0.22 0.06 0.00 1 0.93 0.38 stratus Coryphantha salinensis (Poselg.) Dicht & A. Lüthy 4 0.22 0.01 0.00 1 0.93 0.38 Total 1858 100.00 1.622.39 100.00 100.00 100.00 In the current study, values of 4.09 for the Margalef index A total area of 5000 m2 was evaluated. The abundance (number of individuals N) and coverage (in m2) are expressed per ha. IVI: Importance Value Index. The species are sorted in descending order according to their IVI. (DMg) and of 1.75 for Shannon index (H’) were found. Mora- Donjuán et al. (2014) and Mata et al (2014) reported lower DMg, values, of 2.29 and 2.59, respectively, and similar H’ values, of 1.87 and 1.90, respectively. The tree, shrub, and succulent richness (S) we found in of the Larrea tridentata microphyllus desert scrub (29 species) are higher than those recorded by González- Delgado (2016) and Mora- Donjuán et al. (2014), in 15 species of trees, shrubs and succulents in a microphyllous Figure 2. Rank abundance form for the species abundance distributions. From left to right, the first plot is the desert scrub with a history of Pareto model with best fit to the observed data indicating high abundance for few species and low abundance livestock-use. Alanís et al. for most species; the second is the Poisson lognormal and the third is the neutral model, both are showing a (2015) also registered 15 spe- similar behavior, at the end of the distribution they tend to misfit the data distribution. cies in a microphyllous desert

452 JUNE 2018 • VOL. 43 Nº 6 TABLE III seedlings in these arid environ- viduals/ha and, although the FIT OF THE DISTRIBUTION PATTERNS OF SPECIES ments. The interaction of unpre- total canopy cover reported by ABUNDANCE WITHIN THE STUDY AREA dictable extreme temperatures these authors (2,505m2·ha-1) Model loglik AIC dAIC GL Weight and the prolonged droughts was higher than the ones found have been found by others to be in our study, both are lower Pareto -122 245 0.0 1 0.991 Poisson Lognormal -126 255 10.3 2 0.006 determining factors in the struc- than those reported in other Modelo Neutral -129 260 15.5 1 0.000 ture and function of plant com- studies. The results recorded munities in arid zones (Jordan by Mata et al. (2014), who and Nobel 1979; Rundel and evaluated a microphyllous des- Gibson 1996; PockMan and ert scrubland community in the scrub adjacent to a metropoli- plants, include certain species Sperry, 1997; Hamerlynck Valley of Santa Catarina, West tan area of Monterrey in Nor- of plant families that are closely et al., 2000; Zúñiga-Vásquez of Nuevo Leon, Mexico, are a theast Mexico. These low rich- linked to arid and semi-arid et al., 2017). According to Cha- density of 2,469 individuals/ha ness values reported by Mora- areas of Mexico, where their llenger and Soberón (2008), and canopy cover of 3,439m2· Donjuán et al. (2014) and centers of origin and diversifi- these types of communities, ha-1, which are higher than Alanís et al. (2015), compared cation occur (Rzedowski, 1978). have plant groups with neotrop- those recorded in the present to the results of the present Among the most frequent are ical affinity (37%), are especial- study. It is generally seen that study, were due to both areas the Cactaceae (Guzmán et al., ly rich in endemics, 44% at the this type of community has a having a history of productive 2003), Agavaceae (magueys, genus level growing to 60% at low canopy cover (<40% in all use. This may have altered the izotes and sotoles; Gentry, the species level. These types cases) and it therefore has a structure and composition of 1998), Fouquieriaceae (ocotillo, of vegetation are among the high exposure of the substrate the natural plant communities. Boojum tree, etc.), and Crassu- most important in Mexico be- (without canopy cover). However, because research that laceae families. Crassulaceae is cause of their expanse and con- The Pareto distribution was addresses the study of these a botanical family that, despite tribution to the endemic flora used to model distributions that communities are rare (Pompa- being primarily African, is cos- of the country. The results of follow a power law behaviour García et al. 2017), it is neces- mopolitan; however, in Mexico this research show that the spe- (Newman, 2005). In the case sary to carry out further stud- it has a very important center cies with the highest impor- of plant communities, it could ies to know the ranges of vari- for diversification in the genus tance value is Larrea tridentata explain the trend of the abun- ation in their composition and Echeveria (Meyrán and López, (IVI= 39.09), which is in accor- dance curve when few species diversity. 2003; Thiede and Eggli, 2007; dance with those of other au- have a high abundance that In this study, the Cactaceae Pilbeam, 2008). Furthermore, thors (Granados et al., 2011; decreases with the increase of family has the largest number all these families have extreme- Pompa-García et al., 2017), who number of species (Prado of species (13), coinciding with ly high specific percentages of note that it is a species that et al., 2015). In the presence of the reports by Mora-Donjuán endemism in this region (Rze- dominates the landscape with a large number of rare species, et al. (2014) and Alanís et al. dowski, 1978). respect to its density (individu- the Pareto model has a good fit (2015). These results support The high number of families als/ha) and its canopy cover (Ulrich et al., 2010). The abun- the conclusions of other studies (12) and genera (24) recorded in (m2·ha-1). dant presence of rare species is that recognize the region as one this study can probably be at- The tree, shrub and succu- characteristic of stressful envi- of the most important areas in tributed to the overall structural lent plant components com- ronments with the possible terms of cactus diversity. This complexity of the bushland bined have a density of 1,858 presence of disturbances (Ver- may be due to the high degree (Humphries et al., 1995; Mac- individuals/ha and a total can- berk, 2011), such as the desert, of aridity that occurs in this Gillivray and Grime, 1995). For opy cover of 1622.39m2·ha-1. where a relatively high rate of region of Northeastern Mexico. example, extremes of abiotic The results for density are sim- local extinction and immigra- In general, the xeric scrub, factors such as high and low ilar to those reported by Mora- tion are recorded (Ulrich and which is predominated by suc- temperatures, have strong im- Donjuán et al. (2014), who re- Ollik, 2004). While local ex- culent and semi-succulent pacts on the establishment of corded a density of 1,792 indi- tinction can be random or de- terministic (Harrison, 1991), TABLE IV the fit to the Pareto model sug- STRUCTURAL PARAMETERS OF HERBACEOUS SPECIES gests the latter. This model GROWTH ON 1m2 SAMPLE SITES indicates the presence of pioneer plants and a low presence Abundance Dominance Frequency Species IVI of late successional ones, due N/ha % m2/ha % Sites % to the implicit ‘costs’ to the Pectis papposa Harv. & Gray 76000 49.67 73.12 10.78 9 14.75 25.07 ecosystem on setting the neces- Solanum elaeagnifolium Cav. 9000 5.88 252.29 37.20 6 9.84 17.64 sary conditions for these plants Senna lindheimeriana (Scheele) H.S. Irwin & Barneby 8000 5.23 209.74 30.93 6 9.84 15.33 to invade. Dalea lasiathera A. Gray 19000 12.42 23.88 3.52 6 9.84 8.59 Tiquilia canescens (DC. A.T.Richardson 11000 7.19 10.58 1.56 7 11.48 6.74 Herbaceous vegetation Nicotiana trigonophylla Dunal 6000 3.92 27.37 4.04 6 9.84 5.93 Acourtia nana (A. Gray) Reveal & R.M.King 9000 5l.88 9.66 1.42 6 9.84 5.71 Calyptocarpus vialis Less. 6000 3.92 16.12 2.38 6 9.84 5.38 There is only a small body Thymophylla pentachaeta Small 5000 3.27 8.88 1.31 5 8.20 4.26 of literature that evaluates her- Zinnia acerosa A. Gray 3000 1.96 15.08 2.22 3 4.92 3.03 baceous communities in xeric Parthenium hysterophorus L. 1000 0.65 31.42 4.63 1 1.64 2.31 scrublands. Most studies are 153000 100.00 678.13 100.00 61 100.00 100.00 focused on elements such as The total area evaluated was 100 m2. The abundance (number of individuals N) and coverage (in m2) are expres- trees, shrubs and succulents. sed per ha. IVI: Importance Value Index. The species are sorted in descending order according to their IVI. One of the few studies evalua-

JUNE 2018 • VOL. 43 Nº 6 453 ting the herbaceous communi- Challenger A, Soberón J (2008) Los Synthesis Series Vol. 6. Dow- me tree species of ecological im- ties of Larrea was carried out ecosistemas terrestres. En Capital den, Hutchinson, Ross. Strouds- portance in Mexico: A documen- Natural de México. Vol. I: Cono- burg, PA, USA. 303 pp. tary review. Rev. Chapingo Ser. by Morici et al. (2006), who cimiento Actual de la Biodiversi- Cs. Forest. Amb. 23: 185-219. evaluated the effect of distance MacGillivray CW, Grime JP (1995) dad. CONABIO. Mexico. 28 pp. Testing predictions of the resis- Pilbeam J (2008) The genus Eche- to a water source on the struc- Gentry HS (1998) Agaves of Conti- tance and resilience of vegetation veria. British Cactus and ture of the herbaceous layer nental North America. Univer- subjected to extreme events. Succulent Society. Norwich, RU. when grazed by cattle in arid sity of Arizona Press. Tucson, Funct. Ecol. 9: 640-649. 333 pp. areas of Argentina. Another AZ, USA. 670 pp. Margalef R (1958) Information R Core Team (2016). R: A Language study was undertaken by Pa- Gonzalez Delgado M, Forough- theory in ecology. Int. J. Gen. and Environment for Statistical ssera et al. (1996), who evalu- bakhch Pournavab R, Domin- Syst. 3: 36-71. Computing. R Foundation for guez LR, Guzman Lucio MA, ated the responses of vegeta- Mata JM, Treviño EJ, Valdecantos Statistical Computing. http:// Gonzalez Rodriguez H (2016) A, Jiménez J, Aguirre OA, www.r-project.org tion which was excluded from Composicion floristica y carac- Alanís E, Foroughbackhch R Rascón JM, Marroquín P, Prado EE, terizacion estructural del mato- grazing in a community of La- (2014). Diversidad y composi- García YW, Verdugo EG, Ala- rral desertico microfilo en rrea in the foothills of Mendo- ción vegetal de matorrales en el nís E, Jiménez J (2017) Restau- Galeana, Nuevo Leon. Rev. Valle de Santa Catarina, en el za, Argentina. Evidently, the Mex. Cs. 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