The current status of tropical dry forests in Mexico is very bad!
"Tropical dry forests are among the most threatened ecosystems in the world as a consequence of intensive anthropogenic disturbance" (Portillo-Quintero 144).
The tropical dry forests of Mexico are especially interesting because “tropical dry forests extend for 519,597 km2 across North and South America. Mexico, Brazil and Bolivia” and as of 2009, Mexico had 38% of the total 519, 597km2 of tropical dry forest (Portillo-Quintero, 144). Even though Mexico has the largest extent of tropical dry forest, only 0.2% of those tropical dry forests are protected (Portilo-Quintero, 150).
Why is the current status bad? There was a 64% increase in agricultural lands that replaced original tropical dry forest in Mexico from the year 1977 to 1992. The average deforestation rate at that time was 1.9% per year (Read and Lawrence, 85). This huge increase in the amount of tropical dry forest used for agriculture likely was related to the Mexican government’s support of bulldozing that began in 1970. By 1980, forty-four percent of the original global area of tropical dry forests was destroyed due to human use (Galicia, et al. 38). As of 2009, already 71% of tropical dry forests in Mexico have been converted for human use. Also, still today, only 0.2% of Mexico’s tropical dry forests are protected (Portillo-Quintero 150). The government is still allowing people to use the lands in order to subsist. The tropical dry forests in Mexico today are mostly in fragments due to the timber industry, cattle ranching, and agricultural use such as the growing of maize (Portillo-Quintero 145).
What are the human uses of tropical dry forests that are negatively affecting the ecosystem?
1) Tropical dry forests are subject to heavy human use because most tropical dry forests occur in countries with very high population growth rates. High population growth rates mean that the ecosystem has to support many people with both food and housing. People need to slash and burn the forest in order to grow maize and other crops in order to survive. This creates a very powerful tug of war between the people who need to eat to live and the ecosystem and endemic species which are being decimated in order to support humans. (“The Tropical Seasonal Forest”)
2) Another human use of the tropical dry forests that is negatively impacting the ecosystem is that humans living in the tropical dry forests use land for cattle grazing and therefore, wild animals are being chased out. Fences put up by the inhabitants are preventing certain wildlife from making their seasonal migrations or reaching water holes. (“The Tropical Seasonal Forest”)
3) Lastly, human populations in tropical dry forests perform a lot of wood collecting. The families need wood in order to build, cook, or as fuel. The problem is that the collecting is happening so quickly and extensively that the trees are not able to regenerate fast enough to replace the ones chopped down. (“The Tropical Seasonal Forest”)
Long-term impacts on the ecosystem from human use?
1) Due to the limited amount of precipitation tropical dry forests receive annually, the practices of slash-and-burn agriculture greatly affect the ecosystem’s soil. The composition of the soil is affected and the quality worsens once a tropical dry forest has been used for agriculture and grazing pastures (Aguilar-Fernández, Jaramillo, Varela-Fregoso & Gavito, 179).
2) As we learned in Professor Gillespie’s Geography 5 class, using the Species-Area relationship, if you have the area size and the number of species, the relationship is a curve. As you increase an area, the species increase. For tropical species, when you increase an area ten times, you double the species. Thus, since species richness is positively correlated with area, we know that large continuous forests contain a higher number of species than do smaller, fragmented forests. As forests are being slashed and burned, they are becoming fragmented and the species richness in the area is therefore reduced.
2) As we learned in Professor Gillespie’s Geography 5 class, using the Species-Area relationship, if you have the area size and the number of species, the relationship is a curve. As you increase an area, the species increase. For tropical species, when you increase an area ten times, you double the species. Thus, since species richness is positively correlated with area, we know that large continuous forests contain a higher number of species than do smaller, fragmented forests. As forests are being slashed and burned, they are becoming fragmented and the species richness in the area is therefore reduced.
Bolivia Tropical Dry Forest (1975-1996)
These infrared images, taken by the Landsat satellites 1, 4, and 5, show the conversion from 1975 to 1996 of tropical dry forests into large-scale agriculture in Bolivia, but I speculate that this is also what happened to and is currently happening to Mexico since Mexico also is now used extensively for agriculture.
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