The tropical rainforest is a hot and moist biome that is found near the equator of the Earth. Rainforests receive more than 200cm of evenly distributed rainfall per year. (“Earth Floor: Biomes,” 2005n.d.)They also have little variation in temperature, averaging more than 20 degrees Celsius. (Schwarz, 2019) These conditions allow rainforests to be very biodiverse, having the greatest biodiversity in the world.
The Amazon rainforest is a moist tropical rainforest in the Amazon biome that covers most of the Amazon basin of South America. The Amazon rainforest spans across nine countries. The majority of the rainforest is located in Brazil (60%), Peru (13%), Colombia (10%) and minor amounts in Ecuador, Bolivia, Venezuela, Guyana, Suriname and French Guiana. (Amazon Tours, 2017n.d.). The Amazon rainforest is also highly productive with fast-growing plants competing for light. It is an important global source of oxygen as it collects carbon dioxide, reducing the pollutant effects on the atmosphere. It is extremely diverse, accounting for 10% of known species on earth. This paper will focus on how the plant community maintain species richness within the rainforest.
There are many different species of plants and animals that exist in the Amazon Rainforest due to its high productivity. Species richness can be viewed on a spatial and temporal scale. How diverse an environment is depends on the time of the year (seasons) and the range of landmass when it comes to a rainforest. Through these lenses, a rainforest’s diversity depends on genetic differentiation, environmental change, habitat diversification and biotic interactions.(Hill & Hill, 2001)
Genetic differentiation is the accumulation of differences of allele frequencies of all species and how they vary from one location to another. (Verity & Nichols, 2014) The Amazon rainforest is rather hot from being close to the equator and experiences rain all year round. This allows the rainforest to have a low extinction rate since it is not being affected by seasonal changes for example disruption in winter and deviation of glaciation, contributing to species richness.
A forest is a biproduct of the out-competition of confers due to rapid evolution and adaptive radiation,(Hill & Hill, 2001) this means that flowering plants has been present in the tropics for a long time due to environmental factors. The climate is an optimal condition for plant growth, in fact the best rate of reproduction exists in rainforests. The rate of reproduction is higher than the rate of extinction. However, productivity is not enough to explain why the Amazon is species rich.
The Amazon rainforest extends throughout nine different countries due to fragmentation of other existing environments. The Amazon tropical rainforest experiences both dry and wet periods. During dry periods, forests became fragmented into small patches at high elevation divided by lowland savanna. During wet periods, tropical forests gain more surface area.(Hill & Hill, 2001) The rainforest experiences more wet periods than dry and in this period these fragmented blocks from other existing environments merges with the rainforest, introducing species that are distinct to the fragments and in turn increasing the diversity of the rainforest. In this way, repeated fragmentation of existing environments contributed to the species richness of the Amazon rainforest.
Even though the Amazon Rainforest has benefitted from fragmentation, it does suffer from it. Major sources of fruit, flowers and animal populations are the large canopy and emerging trees. Large trees make up 1.8 percent of all trees but 23 percent of above-ground forest biomass. These trees influences the forest structure, composition, and carbon storage and also are reproductively dominant. Loss of these tree severely impacts the rainforest ecosystem. Large trees mortality is almost three times faster near the forest edge when compared to trees in the interior (Almeida et al., 2019). It is suggested that large trees may be vulnerable in fragmented rainforest due to being prone to uprooting and breakage near forest edges, structural parasites reducing survival and being sensitive to drought, reducing the fecundity of the trees (Laurance, Delamonica, Laurance, Vasconcelos, & Lovejoy, 2000). A higher mortality rate results in decreased fecundity and lessens the spread of the trees which also decreases the ability of being a carbon sink and reducing greenhouse gases.
The fragmentation effects on the structure and dynamics of the rainforest changes with time ,revealing the impact to be both persistent and non-persistent of forest fragmentation more than 20 years after fragment isolation(Almeida et al., 2019). During post fragmentation, fragments results in increased regeneration of trees limiting the effects of the fragmentation.
With the increase effects of climate change one can expect climate changes in the Amazon rainforest. In the Amazon, plant population depends on the ever-frequent rainfall that occurs. If the amount of rainfall changes in the Amazon, one can expect dieback depending on the stabilizing effect of long-term rainfall variability (Hedin, Brookshire, Menge, & Barron, 2009). Climate change can lead to longer periods of drought. In the event that there is increased drought periods, the Amazon would suffer from an increased tree mortality and risk of fire. This could cause a severe reduction in the uptake of carbon dioxide, accelerating the effects of global warming. However, these changes can lead to the forest turning into a savannah. Also, rainfall variability which will be increased over a period of time. This can act as a strong environmental filter among plant community properties, influencing a higher resilience to these changes. In addition, seedlings are dominant in drier regions of the tropics making them more drought resistant.
Plant trait diversity is also a factor in the maintenance of species diversity in the Amazon rainforest. It can acts an insurance across large spatio-temporal scales against climate change (Hedin et al., 2009). The plant population can adjust to new conditions, giving species more functional role than they had before. The functional role of a species is defined by its functional characteristics and the presence of different roles indicates the heterogeneity of those characteristics in the population. Such operational heterogeneity, as one element of biodiversity, is assumed to enhance the reaction variability of the environment and the resilience of the community (Hedin et al., 2009). Tropical forests should be highly resistant because they have a large variety of plant traits making them highly resilient. Since the Amazon is very species rich, it is more resilient even without plant trait diversity.
Species richness is the number of different species represented in an ecological community, landscape or region. When it comes the Amazon rainforest, it is very rich, housing ten percent of the world’s known species. This is maintained by many different factors whether spatial or temporal, high productivity, plant trait diversity and environmental changes. There isn’t any specific thing that determines how species rich the rainforest is, rather due to all these factors working together the rainforest is able to maintain species richness.
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- Amazon Tours. (2017). Where is the Amazon Rainforest Located? | Rainforest Cruises. Retrieved November 2, 2019, from Rainforest Cruises website: https://www.rainforestcruises.com/jungle-blog/where-is-the-amazon-rainforest-located
- Earth Floor: Biomes. (n.d.). Retrieved November 2, 2019, from http://www.cotf.edu/ete/modules/msese/earthsysflr/rforest.html
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- Verity, R., & Nichols, R. A. (2014). What is genetic differentiation, and how should we measure it - G ST, D, neither or both? Molecular Ecology, 23(17), 4216–4225. https://doi.org/10.1111/mec.12856