![Picture](/uploads/9/3/8/4/93842968/1479864652.png)
Tropical dry forests are very diverse in terms of endemism. The endemism of this ecosystem is due to “the spectrum of mechanisms of gene and seed dispersal is distinct: conspicuous flowers and wind-dispersed seeds are relatively more frequent in trees of drier forests” (Bullock et al, pg. 3). Tropical dry forests used to constitute 42% of tropical forests (Gerhardt, pg. 34). Now there are less than 2% of tropical dry forests that remain (Buzzard et al, pg. 1007). The remaining forests are “severely fragmented and disturbed” (Gerhardt, pg.34). The fragmentation of this once vast forest biome is a result of deforestation.
Deforestation has led to only secondary tropical dry forest remaining. Most of the secondary tropical dry forests that do remain are located within various national parks in different countries in an attempt to preserve this biome. Tropical forests generally have a lower biomass than any other forest type which makes it easier to clear the vegetation. The decrease in biomass, compared to other forests, is directly related to the limited growing season (the wet season). Usually the wet season lasts for eight to seven months depending on where the dry forest is located. Tropical dry forests are not composed of one type of tree like most of the northern hemisphere forests. Instead they are composed of both deciduous and semi-evergreen trees.
The bulk of the remaining fragmented forests can be found on the Pacific coast side of Panama, Costa Rica, Nicaragua and Mexico (Griscom and Ashton, pg. 1564). The effects of heavy deforestation are observed, as there are no longer any old-growth forests in the neo-tropics for species comparison. A species comparison between primary and secondary growth allows for evaluation of the local ecosystem species composition. The greatest threat to tropical dry forests is the cattle ranching industry. As the demand for more beef grows exponentially more land is being converted to pasture. These newly formed pastures are then cultivated with exotic African grasses for cattle grazing. The constant land clearing, site preparation for development, and burning were the major contributors to the overall reduction in the forests capacity for recovery (Griscom and Ashton, pg. 1568).
![Picture](/uploads/9/3/8/4/93842968/landscape.jpg?1479864804)
Most of the remaining dry forests in Costa Rica can be found in the Area de Conservación. Most of the current research being conducted on reforestation is taking place at this conservation park. Current research aims to figure potential outcomes for reforesting a deforested site as well as the successional patterns that the tropical dry forests undergo. One study done in the Santa Rosa sector within the Area de Conservación yielded conclusions “[a]lthough [tropical dry forest] tree species are highly drought tolerant, abiotic conditions in early successional forests are key limiting factors for recruitment and assembly” (Buzzard et al, pg. 1011). Buzzard et al not only discerned that early successional tropical dry forests seem to regenerate within 60-90 years, that the tree species are dominated by slow growth, and exhibit conservative traits when abiotic factors for plant growth are limited.
The majority of exploitation of tropical dry forests is due to logging or conversion of land to pasture for cattle ranching. The evidence for the continual land conversion for human use is evident in Panama. The region was first cleared for selective logging in the 1800s. The land was then sold to prospective cattle ranchers in the early 1900s. Due to the significant tree loss most of the fertile soil has been lost to erosion. The soil containing the seed bank has also been subject to constant fire to keep the land clear of natural vegetation. The fires and soil erosion has degraded the soil quality which leads to a reduction in the natural endemic tree species growth. The landowners now sell this undesirable nutrient deficient land to real estate companies. This is due to the area rising in tourism popularity (Griscom et al, pg. 757-759).
The studies that were examined showed that tropical dry forests can recover from even their limited numbers. Tropical dry forests recover at a slower rate than other forest types due to the limited amount of rainfall and annual droughts. However, “[t]he ability of the abandoned land to regenerate will depend on past management and disturbance history” (Griscom and Ashton, pg. 1568). Degradation of land due to human impact can be less severe changes in the ecosystem composition; as in the loss of the seed bank. However, degradation can also be extremely severe by directly affecting the soil fertility which in turn affect the natural seedlings survival and ability to adapt to the altered soil.
![Picture](/uploads/9/3/8/4/93842968/planting-trees-1-1000x662.jpg?316)
Currently there are five different techniques for reforestation of tropical dry forests. The first kind of restoration technique is passive restoration which involves letting the land regenerate on its own and monitoring logging and cattle grazing on these regenerating dry forests. Protection from fire and selective cattle grazing is the second restoration technique. This technique is being tested in Costa Rica where cattle are selectively grazing to reduce fire outbreaks on conserved land. Fires were found to be more frequent when cattle were removed completely from conserved pasture in Guanacaste. The third type of restoration technique is enrichment planting of native tree species in cleared areas. This restoration technique is better suited for land that is unable to regenerate on its own. Removing exotic grass species is another restoration technique due to the exotic grass species encouraging more fires than the native grasses. Once the exotic grasses have been removed the native grasses are then planted. The last type of restoration technique is changing the soil composition of the area and then starting a tree plantation. This is not only the most expensive but is also the most extreme and should be used in areas where the soil has been severely degraded. The tree plantations provide shade to the newly planted native seedlings which increases their survival (Griscom and Ashton, pg. 1573-1575).
Sources:
- Gerhardt, Karin. “Effects Of Root Competition And Canopy Openness On Survival And Growth Of Tree Seedlings In A Tropical Dry Seasonal Dry Forest.” Forest Ecology and Management 82 (1996): 33-48. Web. 16 Nov. 2016
- Bullock, Stephen H. et al. Seasonally Dry Tropical Forests. Cambridge University Press, 1995.
- Griscom, H. P., et al. “The Structure And Composition Of A Tropical Dry Forest Landscape After Land Clearance; Azuero Peninsula, Panama.” Journal Of Sustainable Forestry 30.8 (2011): 756-774. GreenFile. Web. 4 Oct. 2016
- Buzzard, Vanessa, et al. “Re-Growing A Tropical Dry Forest: Functional Plant Trait Composition And Community Assembly During Succession.” Functional Ecology 6 (2016): 1006. Academic OneFile. Web. 4 Oct. 2016
- Griscom, Heather P., and Mark S. Ashton. “Restoration Of Dry Tropical Forests In Central America: A Review Of Pattern and Process.” Forest Ecology And Management 261. The Ecology and Ecosystem Services of Native Trees: Implications for Reforestation and Land Restoration in Mesoamerica (2011): 1564-1579. ScienceDirect. Web. 18 Nov. 2016
- Figure 1: http://partners-rcn.org/tree-islands-tropical-forest-restoration-outlook-rosy-10-years/