Map of Tropical Dry Forests in Mexico

Map of the distribution of tropical dry forest in Mexico

Source: (Becerra, 10920)

Tropical dry forests can be found in eastern Mexico, but the largest portions are located in western Mexico. Large portions of tropical dry forests span across "southern Sonora to northern and central Chiapas" (Ceballos and Garcia 1349).

As you can see by the green coloring, tropical dry forests occur in Baja California, Sonora, Sinaloa, Tamaulipas, all the way down to Chiapas. There is also a pretty large patch in Yucatan. 

Images of Tropical Dry Forests

Aerial view of tropical dry forest in Bolivia in 1975

This image was taken by NASA Landsat satellites 1, 4, and 5 in 1975. As you can see, there was already a large amount of deforestation and fragmentation taking place in the tropical dry forests of Bolivia by 1975. More recent pictures, which I will present later, will show the transformation of the tropical dry forests in Bolivia into agricultural fields. Even though this is not an image of tropical dry forest in Mexico, I speculate that Mexico's tropical dry forest in 1975 looked similar to this, or maybe even worse due to Mexico's historically low percentages of protected tropical dry forest areas. 

Source: http://terra.nasa.gov/Brochure/Sect_1-2.html

Mature tropical dry forest

This is an image of a mature tropical dry forest in Mexico. This is not a historical image of a tropical dry forest, but from various articles, we can infer that this is what tropical dry forests looked like historically. Notice the fullness of the forest. There is little fragmentation and the forest appears to be large and continuous.


Source: http://tinyurl.com/7hjezod

Tropical dry forest after being slashed for agricultural use

This image is of a tropical dry forest in Mexico that has been slashed for agricultural use. Many areas of tropical dry forest in Mexico are used to grow corn, also known as maize. Today, many areas of tropical dry forest appear like this, with less native vegetation. These forests appear sparse and fragmented when looked at from an aerial view.


Source: http://tinyurl.com/7hjezod

Fragmented tropical dry forest in Mexico

This is an aerial view of a tropical dry forest in Mexico. From this view you can clearly see that the forest is not continuous and has heavy fragmentation. 

Source: http://tinyurl.com/7hjezod

Historical State of Tropical Dry Forests

There is not a lot of information on the historical status of tropical dry forests in Mexico at large, but information about specific areas of tropical dry forest and government policies help us compile a general idea of the status of tropical dry forests in Mexico historically and how that differs from today. Tropical dry forests have historically supported large numbers of humans because its ecosystem characteristics are attractive to people for both settlement and development. Tropical dry forests were once large and continuous before humans began exploiting the lands (Portillo-Quintero and Sánchez-Azofeifa 144). Tropical dry forests on a global scale have been severely affected by “human-induced environmental degradation” or anthropogenic effects. Various reports on the historical status of tropical dry forests suggest that the ecosystem only became heavily endangered and fragmented after human settlement and use of the lands. As more people settled on tropical dry forests, the more the lands were exploited. A large portion of tropical dry forest was lost in the 1970s when the Mexican government supported the clearing of tropical dry forest along the Pacific coast of Jalisco. Bulldozers were used to clear the forest for agriculture, cattle ranching, tourism, and housing uses Romero-Duque, Jaramillo, and Perez-Jimenez 39). By 1980, forty-four percent of the original global area of tropical dry forests was eliminated due to human use. Some of the human uses included converting the forests into grasslands for cattle grazing, use of slash and burn agriculture, and the use of wood as fuel (Galicia, Zarco-Arista, Mendoza-Robles, Palacio-Prieto, and García-Romero 138). So, it seems as though tropical dry forests have been negatively impacted by human use for hundreds of years, but the urgency to preserve them has been relatively recent due to increased environmental awareness and due to the increase in population which has put more stress on tropical dry forests as they are more heavily exploited. 

Source: (Castillo, Magaña, Pujadas, Martínez, and Godínez, 635)

This timeline shows the progression of the Chamela-Cuixmala region in Jalisco, Mexico from the time indigenous people began settlements on the area to 1999. As you can see, from 1492 to 1661, there was very low impact of human activities and the tropical dry forests in this region were still intact. However, once the creation of haciendas began and land started to be distributed to the peasants, the tropical dry forests started to be heavily used for agriculture and cattle grazing. This led to negative impacts on the environment, but they were still relatively low and manageable. From about the 1950s to the 1980s the two main drivers of economic development were tourism and agricultural development and this is about the time researchers began to see major transformations of tropical dry forests. Only more recently, in 1988 were there strong efforts to conserve this area of tropical dry forest. 

Current Human Impacts

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.

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.

Source: http://terra.nasa.gov/Brochure/Sect_1-2.html

Future Prospects for Tropical Dry Forests

The future does not look too bright for the conservation status of tropical dry forests. Already, 71% of tropical dry forests in Mexico have been cultivated and impacted by human use (Portillo-Quintero 150). Studies show that it takes between 55 and 95 years for a forest that has been used for various purposes like agriculture and grazing to recover to its pre-cultivation biomass level (Read and Lawrence, 94). Due to the fact it takes so many decades for tropical dry forests to regenerate, the ecosystem is having a difficult time keeping up with the rate of fragmentation caused by anthropogenic effects. Another issue arises due to the fact that the composition of the soil is being affected (Aguilar-Fernández, Jaramillo, Varela-Fregoso & Gavito, 179). Even if the tropical dry forests were given time to recover from the agricultural damage, native plants destroyed by the slash-and-burn process may have trouble re-sprouting. There may also be a growth of invasive plants that thrive from the new soil composition caused by the slash-and-burn practices. These new invasive plants will make it even more difficult for native plants to regain their original quantities in the tropical dry forests. As we learned in lecture, tropical dry forests are not adapted to fire and invasive plants often grow rapidly and use resources that make the native plants have to compete. Also, the government is in a difficult position of balancing the protection of the ecosystem and the survival of the people subsisting off of the ecosystem. 

Slashed and burned tropical dry forest in Mexico

Source: http://tinyurl.com/7hjezod

As you can see in this image, the slash-and-burn process used in order to farm crops like maize, leaves the tropical dry forest in poor condition. This area may take up to 95 years to recover. 

On a more positive note, we can see slight progress in efforts to conserve tropical dry forests over a span of about 13 years. In 1988, only 0.09% of the forests in the Mesoamerican region had some degree of protection (Miles, Newton, DeFries, Ravilious, May, Blyth, Kapos, and Gordon 492), whereas by 2009, 0.2% of this region was under protection. This increase, though still a small overall percentage of protection, is heading in the right direction (Portillo-Quintero 150).

Success Story: Chamela-Cuixmala Biosphere Reserve

Image of the Chamela-Cuixmala Biosphere Reserve in Jalisco, Mexico

Source: (Romero-Duque, Jaramillo, and Perez-Jimenez, 40)

The Chamela-Cuixmala Biosphere Reserve in Jalisco is an area of protected dry forest in Mexico. The effort to preserve this area was by both National University of Mexico and the Cuixmala Ecological Foundation. This area was originally threatened by a “tourism development scheme promoted by one of the most powerful banks and construction companies in Mexico”, but through legal and public campaigning this area became protected. The Chamela-Cuixmala Biosphere Reserve is made up of 13,200 ha and is owned by the National University of Mexico, nongovernmental organizations, and several private companies (Ceballos and Garcia 1351).

This reserve protects:

            9 major vegetation types

            more than 1100 species of vascular plants

            85 reptiles and amphibians

            265 bird species

            70 mammal species

            81 endemic vertebrate species

            72 species at risk of extinction 
            Source: (Ceballos and Garcia 1351)

What Can Be Done To Improve Human Impacts On Tropical Dry Forests

The best thing to be done is to preserve areas of tropical dry forest in Mexico, but in small quantities at a time. It would be unreasonable to begin to preserve large areas of tropical dry forest and force the inhabitants to leave their homes. Many people are subsisting off of the tropical dry forests in Mexico so we need to find a way to balance their necessities with the necessities of the ecosystem. With 38% of the tropical dry forest area, I believe it would be possible for Mexico’s government to cooperate and protect more than the 0.2% it is currently protecting. According to research conducted by Ceballos and Garcia, currently Mexico has no comprehensive plan to conserve its tropical dry forests. More research and knowledge is needed about how rapidly the tropical dry forests of Mexico are being exploited and whether cultivated tropical dry forest areas will be able to adequately recover without the risk of too many invasive plants and drastic soil composition changes. Rather than moving people out of their homes, I believe more legal campaigning needs to take place as did for the Chamela-Cuixmala Biosphere Reserve. We need to focus on protecting the uninhabited areas of tropical dry forest before they become inhabited and cultivated. I also believe more volunteer groups should be organized to help remove non-native plants so that the tropical dry forests that are trying to recover can do so more quickly. I would not suggest more tourism, although that may be an option to help generate revenue in other ecosystems, due to the fact that tropical dry forest area are sometimes deforested and bulldozed to make space for hotels and tourism. 

Table with data that support my assessment of the current impacts

This bar graph shows the extent (in km2) and percentage of tropical dry forest that occurs in Mexico and other countries where tropical dry forests occur. As you can see, with 38%, Mexico has the greatest percentage of tropical dry forest out of all the countries listed here. This data shows the importance of devising a plan to conserve the tropical dry forests of Mexico. Living within this great expanse of tropical dry forest are many endemic species that need to be protected.  

Source: (Portillo-Quintero and Sánchez-Azofeifa , 149)

This column graph presents the percentage of tropical dry forests under protected areas, as of 2006, within  Mexico and other countries with tropical dry forests. This figure reflects again the importance of preserving the tropical dry forests of Mexico. Mexico has the largest extent of tropical dry forests, yet it is among the countries with the lowest protection. It is imperative that we attempt to protect more area of the topical dry forests of Mexico as much of the ecosystem has already been eliminated. 


Source: (Portillo-Quintero and Sánchez-Azofeifa , 152)

Country	TDF potential extent(based on Olson et al., 2001)	TDF current extent(this analysis)	TDF converted (%)	TDF Protected (km2)	Percentage under protection
(a)
Mexico	625,038	181,461	71	336	0.2
Bolivia	216,031	118,940	45	10,609	8.9
Brazil	168,164	81,046	52	5015	6.2
Venezuela	113,143	29,396	74	302	1.0
Colombia	92,664	30,713	67	1555	5.1
Peru	48,914	2337	95	188	8.1
Nicaragua	32,277	7414	77	–	–
Honduras	26,582	6280	76	–	–
Ecuador	25,275	6443	75	147	2.3
El Salvador	11,291	3344	70	9	0.3
Guatemala	10,431	1463	86	-	-
Costa Rica	7559	1795	76	279	15.6
Panama	6160	2128	65	-	-
Total	1383,529	472,759	66	18,620	3.9
(b)
Subregion
N&C America	719,338	203,884	72	624	0.3
South America	664,191	268,875	60	17,816	6.6
C. Islands	137,130	46,839	66	4797	10.2
Total	1520,659	519,597	66	23,417	4.5
(c)
Country
Cuba	109,879	36,996	66	4023	10.9
Dominican	14,669	6194	58	368	6.0
Haiti	8971	2002	78	0	0
Jamaica	3438	1585	54	400	25
Cayman Islands	173	63	64	3.5	5.6
Total	137,130	46,839	66	4797	10.2

This table displays the current tropical dry forest extent (km²) and the extent of tropical dry forests under protected areas. The table is broken into 3 categories: (a) North, Central and South American countries; (b) countries of the Caribbean islands and (c) a summary of results per subregion. 


From this table we can see that although Mexico has the largest area of tropical dry forest, they have minimal protected area in comparison to many other countries. 


Source: (Portillo-Quintero and Sánchez-Azofeifa , 150)

Works Cited

Aguilar-Fernández, Mónica, Víctor J. Jaramillo, Lucía Varela-Fregoso, and Mayra E. Gavito. "Short-term Consequences of Slash-and-burn Practices on the Arbuscular Mycorrhizal Fungi of a Tropical Dry Forest." Mycorrhiza 19.3 (2009): 179-86.Springer. Web. 29 Nov. 2011.

Becerra, Judith X. "Timing the Origin and Expansion of the Mexican Tropical Dry Forest." Ed. Jose Sarukhan. PNAS 102.31 (2005): 10919-0923. Melvyl. Web. 18 Nov. 2011.

Castillo, Alicia, Antonieta Magaña, Anna Pujadas, Lucía Martínez, and Carmen Godínez. "Understanding the Interaction of Rural People with Ecosystems: A Case Study in a Tropical Dry Forest of Mexico." Ecosystems 8.6 (2005): 630-43. Springer. Web. 28 Nov. 2011.

Ceballos, Gerardo, and Andres Garcia. "Conserving Neotropical Biodiversity: The Role of Dry Forests in Western Mexico." Society for Conservation Biology 9.6 (1995): 1349-353. JSTOR. Web. 29 Nov. 2011.

Galicia, Leopoldo, Alba E. Zarco-Arista, Karla I. Mendoza-Robles, José L. Palacio-Prieto, and Arturo García-Romero. "Land Use/cover, Landforms and Fragmentation Patterns in a Tropical Dry Forest in the Southern Pacific Region of Mexico." Singapore Journal of Tropical Geography 29 (2008): 137-54. Melvyl. Web. 28 Oct. 2011.

Lebrija-Trejos, Edwin. "Dry Forest Secondary Succession in Mexico: Mechanisms and Differential Species Performance." Forest Ecology and Forest Management Group. Wageningen University, 2004. Web. 29 Nov. 2011. <http://www.fem.wur.nl/Wever.Internet/Templates/Standard.aspx?NRMODE=Published&NRNODEGUID=%7b4B57F608-4692-4FDE-969E-4FBB8F4F7C93%7d&NRORIGINALURL=%2fUK%2fResearch%2fTheme%2b1%2ftrejos%2f&NRCACHEHINT=Guest#pictures>.

Miles, Lera, Adrian C. Newton, Ruth S. DeFries, Corinna Ravilious, Ian May, Simon Blyth, Valerie Kapos, and James E. Gordon. "A Global Overview of the Conservation Status of Tropical Dry Forests." Journal of Biogeography 33.3 (2006): 491-505.Melvyl. Web. 29 Nov. 2011.

Portillo-Quintero, C. A., and G. A. Sánchez-Azofeifa. "Extent and Conservation of Tropical Dry Forests in the Americas." Biological Conservation 143.1 (2010): 144-55.Melvyl. Web. 21 Nov. 2011.

Read, Larissa, and Deborah Lawrence. "Recovery of Biomass Following Shifting Cultivation in Dry Tropical Forests of the Yucatan." Ecological Applications 13.1 (2003): 85-97. JSTOR. Web. 29 Nov. 2011.

Romero-Duque, Luz P., Victor J. Jaramillo, and Alfredo Perez-Jimenez. "Structure and Diversity of Secondary Tropical Dry Forests in Mexico, Differing in Their Prior Land-use History." Forest Ecology and Management 253 (2007): 38-47. Melvyl. Web. 28 Nov. 2011.

"Tropical Seasonal Forest." Marietta College. Web. 29 Nov. 2011. <http://www.marietta.edu/~biol/biomes/tropdry.htm>.

"Why Should We Look for Global Change?" NASA's Earth Observing System. Web. 29 Nov. 2011. <http://terra.nasa.gov/Brochure/Sect_1-2.html>.