II: Forest Resources Management
Ecological Structure and Wood Volume of Prosopis Species (Mesquite) Communities in Northeast of Mexico
RAHIM FOROUGHBAKHCH1*, MAGINOT NGANGYO HEYA1,
ARTEMIO CARRILLO PARRA2, MARCO ANTONIO GUZMAN LUCIO1, and MARCO ANTONIO ALVARADO VAZQUEZ1
1Facultad de Ciencias Biologicas, Departamento de Botanica,
Universidad Autonoma de Nuevo Leon, Av. Universidad s/n Cd. Universitaria, San Nicolas de los Garza, C.P. 66451, Nuevo Leon, Mexico
institute de Silvicultura e Industria de la Madera, Universidad Juarez del Estado de Durango, Boulevard del Guadiana #501, Ciudad Universitaria, Torre de Investigacion, C.P. 34120, Durango, Dgo. Mexico
The Mexican Gulf coast is characterized by diy regions with high variations in climatic conditions, rich in drought-tolerant or subhumid species, and including multipurpose trees (MPTs) and shrubs, which have more than one substantial contribution such as products or sendee functions to the land-use systems in which they are grown.
This chapter aims to introduce the lecturer with ecological characterization and forest productivity of the mesquite scrub and woodland, their diverse uses as MPTs and shrubs of tropical and subtropical areas of semi- arid zones of northeastern Mexico.
In three physiographic zones, 30 sampling sites were randomly selected, based on cartographic material and digital ortophotos where mesquite was the dominant species.
All mesquite individuals were registered, measuring their height, crown projection, and wood volume. The canopy density, frequency, and importance value (IV) were determined, as well as basal diameter (BD), length of the main stem and in branches with diameters greater than 5 cm, the inferior and superior diameter and corresponding length.
The physiognomy of the studied sites was dominated by shrub and arboreal plants, where the most outstanding vegetation was Prosopis glandulosa. The total floral diversity found were 160 taxa belonging to 59 families, of which Poaceae, Asteraceae, Cactaceae, Fabaceae, and Euphorbiaceae presented the greater number of taxa. The average density of shrubs was of 6575 individuals/ha. The accumulated average cover per site taking in consideration the three layers was 203.20%, being the shrub layer the greatest vegetative cover (85.6%). The shrub and arboreal layers presented greatest IVs (80.31%) of P. glandulosa. The timber volume was significantly greater in arboreal layers (64.675 m3/ha) than shrub layers (26.563 m3/ha). The wood volume had a strong relationship with the variables of BD and crown projection.
The relative values of vegetative cover, frequency, density, and IV of P glandulosa varied significantly by site. In the arboreal layer, P glandulosa reached the greater percentage in all the parameters, dominating completely the stratum. In most of the sites, the mesquite population was integrated by young individuals with short vegetative development, BDs smaller than 20 cm, height average of 4.86 m, cover average of 23.03 m2, and total density of 554.87 individuals/ha in the shrub and arboreal layers.
It has been estimated that there are currently more than 50,000 plant species worldwide. The largest number of native tree species found in a single countiy is 7880 in Brazil. Astonishingly, only about 1000 different tree species are utilized globally (Sutton, 1999; FAO, 2006). Thus, thousands of tree species are either not utilized, underutilized, or used inappropriately. The present human population has wood consumption needs ranging from 0.3 to 0.6 m3/year/habitant (Aktuell, 2007). As a result, the amiual wood and wood-based products consumption have been calculated to be around
3.5 billion m3 approximately, 66% of which are hardwoods used mainly as fuel; the rest are softwoods used principally in industiy (Youngquist and Hamilton, 1999).
In order to satisfy wood needs, the forestry research has been focused on increasing wood production by improving forestry management. Plantations provide another option. In areas of Venezuela and Brazil, 5-90,000 m3/ha/ year of Finns caribea and Eucalyptus grandis are produced, respectively (FAO, 2006); however, the material obtained from these plantations is “different” qualitywise in comparison to wood coming from natural forests (Zamudio et al., 2010).
In a particular case, the Gulf of Mexican coastal plain is vegetated with a woodland shrub community dominated by small trees and shrubs, referred as “Tamaulipas thorny scrub” (Rzedowsky, 1978; INE, 2005). The Tamaulipan shrubland occurs extending from the coastal plain of the Mexican Gulf to the southern rim of Texas State, United States. In these arid and semiarid zones of northeastern Mexico, a great variability in climatic and edaphic conditions causes extremely diverse shrublands in terms of species composition, height, density, and plant associations. The various species occurring in this region can be categorized in several groups based on their ecological adaptations and forestry use, such as the production of timber, posts, firewood, food, medicines, handicrafts, forage, and so on (Bainbridge et al., 1990; Felker, 1996).
One of the tasks of wood and nonwood products must be to concentrate on increasing research to ensure a better utilization of lesser-known tree species from around the world. This should particularly be applied to trees grown on arid and semiarid land which have shown desirable characteristics like genera Prosopis, Helietta, Condalia, and some Acacia species. Prosopis glandulosa (honey mesquite) and P laevigate make a good alternative for a variety of wood and nonwood products (Pasiecznik et al., 2001; Estrada et al., 2004).
For the reasons mentioned above, the present study was made to know the growth characteristics and the population structure of mesquite trees in natural conditions as a contribution to build up the basis for the implementation of a management program of this plant resource with the purpose to guarantee its sustainable exploitation.
5.1.1 DISTRIBUTION AND IMPORTANCE OF PROSOPIS SPP.
Mesquite is widely distributed in the dry regions of America, constituting frequently the only arboreal element of the vegetation. Of the 42 species reported for the American continent, 9 of them are distributed in the arid and semiarid zones of Mexico and south of Texas, United States. Its distribution in Mexico is estimated to take place over 7,000,000 ha, concentrated mainly in the north and center of the country, being P I a ел-igo to and P. glandulosa the species of greater occurrence in the north of Mexico.
P. glandulosa in the northeast of the countiy is reported in the states of Coahuila, Tamaulipas, and Nuevo Leon (Pasiecznik et al., 2001). On the other hand, P lae’igata distributes from the northeast toward the Great Plain and center of the country, occurring in the same areas where P glandulosa and its two varieties are distributed. It is reported that in certain areas of their distribution, the species P. laevigata and P glandulosa coexist with the presence of individuals that present intermediate characters. Rzedowsky (1988) considers that the original distribution of these two species has been modified by human intervention, which caused an intense introgression.
In the vegetal communities of north and northeast of Mexico, the mesquite species are distributed in the Tamaulipan thomscrub (Fig. 5.1) where more than 70% of the species integrating this type of vegetation are thorny deciduous. In this vegetation, mesquite is associated with the species Acacia rigidula, Cercidium macrum, Leucophyllum frutescens, Condalia hookerii, and Castela tortuosa, in the arboreal and shrub layer, whereas the herbaceous layer are represented by Cactaceous like Ferocactus haniatacanthus, Echinocactus texensis, and Echinocereus enneacanthus, as well as species of the Compositae family: Circium texanum, Eupatoriuni coelestinum, and Gynmosverma glutinosum among others (Alanis et al., 1996; INEGI, 2002).
The Prosopis genus comprises about 44 species of trees and shrubs; the number could be as high as 77 since similar species are now included in other genus like Acacia (USDA, 2007). The taxonomy is very complex; the species have been divided into five sections, distributed in North America, Central/ South America, Africa, and Asia (Pasiecznic et al., 2001). The species from the Prosopis section are native to Asia and North Africa; the Anonychium section is composed of a single species P africana, which is found on arid lands of North Africa. The species from the Strombocarpa, Monilicarpa, and Algarobia sections are indigenous to Central and South America where the largest Prosopis forests are also found (Lopez et al., 2006).
Tropical Africa could be where Prosopis originated. As all species are closely related to Adenanthera L. and Pseudoprosopis Harms, all species may have evolved from these two genera. The name Prosopis comes from the ancient Greek word “Prosopis,” which means “bark used for farming sheep skins” (Rodriguez and Maldonado, 1996).
FIGURE 5.1 Tamaulipan scrub modified by disturbance alterations in the semiarid land of northeastern Mexico.
The importance of Prosopis trees have been confirmed in many ecosystems around the world. These species have the capacity to positively influence soils, thus improving the environmental conditions for themselves as well for other plants and animal species. For that reason, they have been grown on plantations in a number of habitats. Even though there are no exact records about the distribution of Prosopis, the common belief is that the first travelers across America used the sweet pods during their journeys. They could have also been spread indirectly by domestic animals consuming the sweet pods. In the last 200 years, the Prosopis species have been introduced or reintroduced in certain areas of Argentina, Chile, Peru, Mexico, and the United States (Pasiecznic et al., 2001), as well as in some regions of Asia, Africa, India, and Australia.
There are contradicting opinions regarding the use of some species in reforestation programs. As a result of their fast colonizing behavior, they have been considered as problematic trees. In fact, some users consider these tree species to be amongst the worst invasive weeds. Prosopis have already infested areas of Africa, Australia, Brazil, and Hawaii, where large amounts of money have been spent on eradication by mechanical, chemical, or biocontrol means (Richardson, 1998; Hughes, 2001). In the United States, an eradication program lasting more than 50 years has been employed to remove Prosopis from grasslands; however, neither herbicides nor mechanical means have proved successful. After a period of tune the Prosopis has always returned (Pasiecznik, 2002).
Natural Prosopis stands have been use as fodder for domestic animals, for example, cows and goats. In 1965, approximately 40,000 metric tons of Prosopis pods were used to feed cattle, sheep, goats, horses, donkeys, and mules (Felker, 1996).
It is also possible to produce flour for human consumption and due to its sugar content even an alcoholic brew. Prosopis flour absorbs 185% of its weight in water, which is quite similar to the results obtained for Phaseolus sp. (Barba de la Rosa et al., 2006).
As Prosopis trees produce an abundance of blossoms, they play an important role in quality honey production (Pasiecznik et al., 2004). Gums are also produced in large amounts from wounds to the bark; which is mainly used as an emulsion stabilizer, colloid protector, and flavor encapsulating agent in the food, cosmetic, pharmaceutical, and petrochemical industries (Beristain et al., 1996; Gerardin et al., 2004).
Mexico’s charcoal exports increased from 2000 to 20,000 mt from 1982 to 1992 (Meraz et al., 1998) with the United States being its main buyer. Five cubic meters of wood are needed to produce a metric ton of charcoal, which means that 100,000 m3 of wood were used in only 1 year. In two traditional Prosopis harvesting municipalities of northwest Mexico, the logging of only approximately 50,000 m3 was authorized from 1990 to 1997 (Leon-Luz et al., 2005; Somoza, 2014). The official statistics regarding nationwide Prosopis harvesting do not reflect the actual harvest, since this wood is grouped together with other species such as Populus sp., Liquidambar sp., Fraxinus sp., and Jnglans sp. Records for these show an overall wood production of 135,563 m3 in 2003 (SEMARNAT, 2007a).