**3. Vegetation**

28 Soil Erosion Studies

Fig. 2. Precipitation histogram for the years 2006, 2007 and 2008 at Cadereyta, Queretaro,

One of the main factors related to the erosion potential of rain is the rainfall frequency and different magnitudes of events in combination with the soil geomorphic thresholds (Bisigato et al., 2009). High intensities of rainfall are the main factor driving the runoff processes

Mean, maximum and maximum intensity in 30 minutes are shown in Figure 3 for the Cadereyta area. Overall, the values of intensities varied from 0.71 to 88.2 mm h-1. Maximum

Fig. 3. Box plot of rainfall intensity by events measured in the semiarid of Mexico.

Mexico.

(Renard et al., 1974).

Vegetation patterns in arid and semiarid ecosystems are characterized by the size and spatial distribution of the higher plant-cover patches. These patches have its main distribution in spots or bands distributed as a mosaic (Aguiar & Sala, 1999). The spots are generally isodiametric or with irregular circular shapes, and the bands range from 1 to less than 100 m (Aguiar & Sala, 1999). Investigators have documented the presence of "islands of fertility" or "resource islands" in arid and semiarid ecosystems at individual plant scale (Moro et al., 1997; Aguiar & Salas 1999; Facelli & Temby, 2002; Rango et al., 2006).

These areas can also be considered as hydrologic islands, and they are observed at the individual plant scale as well as in large area patterns of banded vegetation, where playettes and beaded drainage networks run-on and water infiltration stimulates vegetation growth (Rango et al., 2006).

Fig. 4. Typical distribution of native vegetation in a semiarid environment of Central Mexico.

Soil Erosion Processes in Semiarid Areas: The Importance of Native Vegetation 31

Fig. 5. Canopy and surface LAI dynamics in native plants at a semiarid environment during

*Opuntia imbricata Prosopis laevigata Acacia farnesiana Opuntia* sp

13.00 9.00 8.00 9.00

0.67 2.05 2.57 3.08

0.20 0.69 0.86 0.45

23.60 60.00 53.50 86.70

22.10 35.30 36.60 76.90

Table 1. Characteristics of the vegetation patches studied (Vásquez-Méndez et al., 2010).

the rainfall season in Cadereyta, Queretaro, Mexico.

Plot Area (m2)

Total Height (m)

Trunk height (m)

Canopy cover (%)

Ground cover (%)

Water availability it is a limiting factor in the productivity of arid and semiarid ecosystems. Plants use the necessary water for their metabolic processes. Studies such as those of Fowler (1986) and Nobel (1990) have demonstrated that the species of arid and semiarid regions are characterized by several different patterns of roots distribution. Perennials root zones are wider and deeper than those of annuals. As a matter of fact, phreatophytes are often very deeprooted.

Simpson & Solbring (1977) recognize three major methods of native plant strategies:


The association of annual plants with woody shrubs has been recognized as to have higher organic soil contents, to trap windblown seeds and to protect the seeds or seedlings from predation (Fowler, 1986).

The general vegetation distribution is controlled by precipitation, and at the same time, distribution and amount of precipitation affects the development and distribution of vegetation, which also modifies the atmospheric energy and the storage of water (Xue, 2006; Dekker et al., 2007). Under some circumstances herbaceous layer productivity is lower under tree canopies than in nearby open grasslands, whereas in other instances grassland productivity is higher under tree canopies (Belsky et al., 1989). Studies suggest that tree canopies may improve the water – status of understory species. Native species such as *Prosopis laevigata*, *Acacia farnesiana*, *Opuntia* sp., and even for O*puntia imbricate*, contribute to the development of surface vegetation. The combination of canopy cover and the greatest development of surface vegetation in the rainfall period, when soils are more susceptible to soil erosion, diminish the erosive effect of precipitation at the highest intensities. Therefore some trees of semiarid environments like adult Acacias are considered as nurse plants for understory native species (Yang et al., 2009).

Figure 5 shows the dynamics of vegetation leaf area index (LAI) for four species and their understory. It is clearly observed that once precipitation falls in those areas, ground cover increases significantly. However, canopy cover of O*puntia imbricate* and *Opuntia* sp. does not increased significant in comparison with *Acacia* and *Prosopis*, because the morphology of its rackets.

Some morphometric characteristic of the four main types of vegetation patches in semiarid Cadereyta, are listed in Table 1.

Currently, trees in semi-arid regions are viewed as having the potential to increase crop productivity (agroforestry), to increase the forage production, to improve soil fertility and to reverse or at least stop desertification (Beslky et al., 1989).

On the other hand, plants of *Prosopis* and *Acacia* possess nitrogen-fixing bacteria in their root systems that accumulate nitrogen under the canopy soils. These trees tend to propagate in overgrazing soils (Tapia-Pastrana et al., 1999) and become free of grass competition (Mooney et al., 1977). These trees can be optimal for reforestation and for sustainable use in arid and semiarid zones (El-Keblawy & Ksiksi, 2005; Deans et al., 2003; Álvarez-Yépiz et al., 2008).

Water availability it is a limiting factor in the productivity of arid and semiarid ecosystems. Plants use the necessary water for their metabolic processes. Studies such as those of Fowler (1986) and Nobel (1990) have demonstrated that the species of arid and semiarid regions are characterized by several different patterns of roots distribution. Perennials root zones are wider and deeper than those of annuals. As a matter of fact, phreatophytes are often very




The association of annual plants with woody shrubs has been recognized as to have higher organic soil contents, to trap windblown seeds and to protect the seeds or seedlings from

The general vegetation distribution is controlled by precipitation, and at the same time, distribution and amount of precipitation affects the development and distribution of vegetation, which also modifies the atmospheric energy and the storage of water (Xue, 2006; Dekker et al., 2007). Under some circumstances herbaceous layer productivity is lower under tree canopies than in nearby open grasslands, whereas in other instances grassland productivity is higher under tree canopies (Belsky et al., 1989). Studies suggest that tree canopies may improve the water – status of understory species. Native species such as *Prosopis laevigata*, *Acacia farnesiana*, *Opuntia* sp., and even for O*puntia imbricate*, contribute to the development of surface vegetation. The combination of canopy cover and the greatest development of surface vegetation in the rainfall period, when soils are more susceptible to soil erosion, diminish the erosive effect of precipitation at the highest intensities. Therefore some trees of semiarid environments like adult Acacias are considered as nurse plants for

Figure 5 shows the dynamics of vegetation leaf area index (LAI) for four species and their understory. It is clearly observed that once precipitation falls in those areas, ground cover increases significantly. However, canopy cover of O*puntia imbricate* and *Opuntia* sp. does not increased significant in comparison with *Acacia* and *Prosopis*, because the morphology of its

Some morphometric characteristic of the four main types of vegetation patches in semiarid

Currently, trees in semi-arid regions are viewed as having the potential to increase crop productivity (agroforestry), to increase the forage production, to improve soil fertility and to

On the other hand, plants of *Prosopis* and *Acacia* possess nitrogen-fixing bacteria in their root systems that accumulate nitrogen under the canopy soils. These trees tend to propagate in overgrazing soils (Tapia-Pastrana et al., 1999) and become free of grass competition (Mooney et al., 1977). These trees can be optimal for reforestation and for sustainable use in arid and semiarid zones (El-Keblawy & Ksiksi, 2005; Deans et al., 2003; Álvarez-Yépiz et al., 2008).

Simpson & Solbring (1977) recognize three major methods of native plant strategies:

from almost unattainable zones at very deep phreatic levels.

water by transpiration can be reduced.

and extensive root networks.

understory native species (Yang et al., 2009).

reverse or at least stop desertification (Beslky et al., 1989).

Cadereyta, are listed in Table 1.

predation (Fowler, 1986).

rackets.

deeprooted.

Fig. 5. Canopy and surface LAI dynamics in native plants at a semiarid environment during the rainfall season in Cadereyta, Queretaro, Mexico.


Table 1. Characteristics of the vegetation patches studied (Vásquez-Méndez et al., 2010).

Soil Erosion Processes in Semiarid Areas: The Importance of Native Vegetation 33

Fig. 6. Box plot of runoff by native vegetation in a semiarid environment of Central Mexico

Fig. 7. Typical behavior between runoff and leaf area index of native vegetation in a

Erosion, the detachment of particles of soil and surficial sediments and rocks, occurs by hydrological (fluvial) processes of sheet erosion, rill and gully erosion, and through mass

(Vásquez-Méndez et al., 2010).

semiarid environment of Central Mexico.

**5. Soil erosion** 
