Tropical dry forests, especially in Western Mexico, are a victim of slash burning deforestation, an unsustainable practice utilized in order to clear the relatively flat land for pasture and crop use. Due in part to their fertile soils and high percentage of nutrients held in the biomass (Gentry), the burning of dry forests imparts a great deal of carbon, nitrogen and phosphorus into ash, yielding a temporary boost in available nitrogen and phosphorus within the soil. Unfortunately, this nutrient increase is short lived, as most of the ash is lost through wind into the atmosphere. Burning of these forests causes intense heat to be radiated into the ground below them, pyro-mineralizing once unavailable nutrients into reactive organic compounds. The excess nitrogen, in the form of ammonia is quickly consumed by nitrifying bacteria which outcompete and reduce availability to vegetation. Although studies have shown that fires have a small immediate effect on the total available soil nutrients, nutrient losses sustained during isolated slash burn plots appear to be long reaching, taking up to a century of fallow to reaccumulate. (Kauffman, 143-145)
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![Picture](/uploads/9/3/8/4/93842968/395260968.jpg?535)
After slash-burning a large region, farmers have two choices: plant fast growing grasses with intention to feed their cattle, or plant seasonal crops with intention of moving when the soil is no longer fertile. This vegetation will quickly consume the nutrients imparted to the soil from the ash of the recently burned forest. The seasonal food crops must be replanted every year and with each harvest remove nutrients from the soil which then must remain fallow before being planted on again. The grasses planted for cattle may be xeromorphic and survive through the severe drought of the dry season, but they will be consumed by the cattle, and the regrowth will quickly consume what nutrients are available to it. Given time, the areas grasses consume most of the nutrients they need for growth from the soil; consequently, are not able to grow at a rate which can sustain the cattle population, and so the farmer clears a new plot of forest and moves his herd there. (Maas, 411-414)
The grasslands which replace the dry forests create gaps between suitable habitats which restricts the movement of endemic canopy species, especially certain birds. This drastic change in biogeographical make up, via fragmentation and elimination of habitat has caused massive loss of species on all trophic levels. Birds which migrate between North America and South America utilize the tropical dry forest as their winter home. (Petit) With migratory species depending on the dry forest biome to survive during the winter, slash and burn has reduced their available habitat and forced them to occupy fragments or less suitable areas. Generalist species are able to move to other types of habitat; however, Mexican dry forests are home to 29% endemic vertebrates and 16% endemic vegetation of which are most are unable to cope with such drastic changes in their environment. These fragments also experience a change in microclimate which alters the vegetation composition of the area. Through this change, vital links are removed from the food chain possibly causing local extinctions of not only flora but fauna as well. (Dinerstein, 37-39)
These slash and burn techniques have been put to use since the Neolithic period in order to increase agricultural production, but weren’t always unsustainable. Although dry forests were productive enough to make up an estimated 42% of tropical forests at one time, humans have been neglecting to account for the environmental impact of their steadily increasing exploitation of diminishing dry forests. With the explosion of the human population in the last thousand years, the impacts felt by these forests have multiplied exponentially. Slash and burn is an unsustainable practice which has helped in the destruction of dry forest; reducing its once vast distribution to less than 2% primary growth in some areas. (Ceiba, Web)
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,Slash and burn not only eliminates habitat and isolates fragments of remaining habitat, but has globally accounted for an increase in CO2 concentration. The release of CO2 from the burning of forests is difficult to quantify, but is without a doubt produced in copious amounts during combustion. The increase in atmospheric CO2 is exacerbated by the loss in forest which would have, through photosynthesis, caused a net reduction of CO2 instead. Weak environmental policies in less developed countries combined with poor public education on the intrinsic value of the ecosystem, have caused this farming method to continue. Westernization and rising human population pressures seem to have the greatest effect on the rate of deforestation, with high variation in forest losses existing between geographic regions which had varying levels of anthropogenic impact. (Laurance,112-114)
Conservation efforts at this point are nearly in vain, as what used to be over 42% of tropical forests, tropical dry forests now make up less than 2% of tropical forests by area. Because these ecosystems require a unique nature grown environment, with semi frequent fire and a consistent dry and rainy season, a simple solution is just not available. Conservation areas which protect wildlife including trees have been created; however, damage is still sustained through illegal harvesting. These conservation areas, although helpful, are not large enough to launch a full recovery of this tattered biome.
Sources:
Figure 1: http://farm4.static.flickr.com/3376/3532537742_5d0ba1375b.jpg
Figure 2: https://commons.wikimedia.org/wiki/File:Beef_Portrait_(5210343960).jpg
Figure 3: http://yournewswire.com/adverse-effects-of-earth-habitat-fragmentation/
Figure 4: http://www2.ucar.edu/atmosnews/just-published/21140/population-trumps-climate-and-carbon-in-shaping-future-of-wildfires
Figure 5: http://www.aptouring.com/destinations/south-america-antarctica/south-america-2017
William F Laurance, Reflections on the tropical deforestation crisis, Biological Conservation, Volume 91, Issues 2–3, December 1999, Pages 109-117, ISSN 0006-3207, http://dx.doi.org/10.1016/S0006-3207(99)00088-9.
Maas, J.M. 1995. Tropical decidous forest conversion to pasture and agriculture. Pages 399-422 in S.H. Bullock, H.A. Mooney, and E. Medina, editors, Seasonally dry tropical forests. Cambridge University Press, Cambridge.
Gentry, Alwyn. 1995. Diversity and floristic composition of neotropical dry forests. S. Bullock, H. Mooney and E. Medina, editors. Seasonally dry tropical forests. Cambridge University Press, Cambridge, U.K.
Daniel R. Petit, James F. Lynch, Richard L. Hutto, John G. Blake, and Robert B. Waide, Management and Conservation Migratory Landbirds Overwintering in the. Neotropics. US Forestry Service. RM-GTR-229 pp. 70-92.
Kauffman, J. B., Sanford, R. L., Cummings, D. L., Salcedo, I. H. and Sampaio, E. V. S. B. (1993), Biomass and Nutrient Dynamics Associated with Slash Fires in Neotropical Dry Forests. Ecology, 74: 140–151. doi: 10.2307/1939509
Dinerstein, E., D.M. Olson, et al. 1995. A Conservation Assessment of the Terrestrial Ecoregions of Latin America and the Caribbean. The World Bank in association with WWF, Washington, D.C.
http://www.ceiba.org/loorecology.htm
Figure 2: https://commons.wikimedia.org/wiki/File:Beef_Portrait_(5210343960).jpg
Figure 3: http://yournewswire.com/adverse-effects-of-earth-habitat-fragmentation/
Figure 4: http://www2.ucar.edu/atmosnews/just-published/21140/population-trumps-climate-and-carbon-in-shaping-future-of-wildfires
Figure 5: http://www.aptouring.com/destinations/south-america-antarctica/south-america-2017
William F Laurance, Reflections on the tropical deforestation crisis, Biological Conservation, Volume 91, Issues 2–3, December 1999, Pages 109-117, ISSN 0006-3207, http://dx.doi.org/10.1016/S0006-3207(99)00088-9.
Maas, J.M. 1995. Tropical decidous forest conversion to pasture and agriculture. Pages 399-422 in S.H. Bullock, H.A. Mooney, and E. Medina, editors, Seasonally dry tropical forests. Cambridge University Press, Cambridge.
Gentry, Alwyn. 1995. Diversity and floristic composition of neotropical dry forests. S. Bullock, H. Mooney and E. Medina, editors. Seasonally dry tropical forests. Cambridge University Press, Cambridge, U.K.
Daniel R. Petit, James F. Lynch, Richard L. Hutto, John G. Blake, and Robert B. Waide, Management and Conservation Migratory Landbirds Overwintering in the. Neotropics. US Forestry Service. RM-GTR-229 pp. 70-92.
Kauffman, J. B., Sanford, R. L., Cummings, D. L., Salcedo, I. H. and Sampaio, E. V. S. B. (1993), Biomass and Nutrient Dynamics Associated with Slash Fires in Neotropical Dry Forests. Ecology, 74: 140–151. doi: 10.2307/1939509
Dinerstein, E., D.M. Olson, et al. 1995. A Conservation Assessment of the Terrestrial Ecoregions of Latin America and the Caribbean. The World Bank in association with WWF, Washington, D.C.
http://www.ceiba.org/loorecology.htm