Introduction
You wake up on a sunny and perfectly adequate Saturday morning ready to watch Grey's Anatomy on the couch
for the next 7 hours, when you open the fridge to see that it is
devastatingly empty. With unwashed hair and just enough money for pita
chips and hummus, your growling insides lead you to hop in the car and head towards the market which is only 3 miles away. You
are just about to turn into the parking lot of the market when you see
that there is a giant wall separating the parking lot from the market –
as I see it, a giant wall separating your growling stomach from being
satisfied by hummus and pita. This phenomenon is called habitat fragmentation. Now, in the peatlands and forests and tundras and mountains, being separated from nutrients, light, and water affect the growth and survivability of plants (just as being separated from Mediterranean nutrients greatly affects the survivability of the human).
The formal or ecological definition of habitat fragmentation is: the breaking apart of an area of land that was previously a continuous landscape. It is a barrier separating the same species' from the same habitat. Now, one might ask how the environment is affected with the separating of habitats. To put it short, habitat fragmentation causes "populations become more isolated and are reduced in size … and may also change the abiotic conditions of the surrounding landscape, which influences biotic interactions" (Lienert, J. 2004).
"Plants
and animals may live in naturally fragmented habitats and can be well
capable of coping with the special conditions associated with habitat
fragmentation. However the extent of anthropogenic fragmentation during
the last decades and centuries far exceeds natural fragmentation rates
and is operating at a much faster time scale than many populations can
adapt to" (Lienert, J. 2004).
Throughout
this paper I will discuss habitat fragmentation versus drought, and how
the lack of access to water can affect plant species especially in
combination with fragment size. After reviewing all of my collected sources, the consensus across the board is that drought and habitat fragmentation affect the resilience of the land for future stressors (Asbjornsen et al. 2004). It is important to study natural and man-made habitat fragmentation as we approach an increasingly warmer future and the increased probability of droughts in many environments across the globe.
Body
Habitat
fragmentation can influence the mobility, species diversity, and
biomass of plant species, and edge effects of these fragments show the
greatest variability. The
mobility of a plant's seeds are crucial to the survivability of that
plant in the fragmented area. Some seeds can travel by wind, by animal
or insect, and some seeds can even lay dormant in the ground during
unfavorable times and rejuvenate when it is favorable. For the seeds
that travel by wind, it is imperative that those seeds land in soil that
will be conducive for propagating more plant life in the are. However,
in the season of a drought and limited soil
resources it is not likely that the seed will fruit and survive.
According to 1 of the 9 studies, some problems with testing for plant
dispersal are the uncertainty of dispersal mechanisms in specific areas
and how far those seeds will spread (Pearson, R. G., and T. P. Dawson. 2005).
But it was determined in that study that long-distance seed dispersal
"has the potential to greatly increase the ability of species to migrate
rapidly through fragmented landscapes" (Pearson, R. G., and T. P. Dawson. 2005).
When
it comes to species diversity, land isolation and lack of water to
plants do not make for ideal circumstances. Drought in fragmented landscapes may lead to a decrease in biodiversity as drought resistant species begin to take over the land. "As the frequency of extreme droughts increase, plant mortality is likely to occur in rapid pulses than on a gradual decline" (Gitlin et al. 2006). And
in addition to being isolated this could decrease the plants'
plasticity and prevent them from recovering or spreading into new land
areas (Gitlin et al. 2006).
Loss
of biomass is another symptom of drought and landscape fragmentation.
Many plants have adaptations to water loss, but that is because they
have been previously exposed to drought. However in areas where plants
have not been previously introduced to extreme drought and cannot adapt,
plants often drop their leaves. And in dropping their leaves they
decrease canopy cover and The decrease in biomass could contribute to atmospheric carbon levels as the plants and trees decompose (Laurance et al. 2001). According to one study biomass loss was highest
on smaller plots of land at the edge of the fragmented area, and two
other studies state that the environmental effects at the edge of these
forests there is just a greater variability.
The small, isolated plots that arise from habitat fragmentation at the edges of the plots often show the most variability and "are the dominate drivers of ecological change" (Laurance et al. 2007). These negative effects
are especially high in the beginning because the edges are more expose
to the elements; they are "permeable to penetration of heat light and
wind" and they are not yet adapted to that exposure (Guerrero, P. C., and R. O. Bustamante. 2009). It would be ideal, though for a plant intolerant to shade and tolerant to drought to live in an isolated plot to better adapt to the change in habitat; they would have a better shot at surviving and reproducing (Guerrero, P. C., and R. O. Bustamante. 2009). These plots, especially if located at the edge of a larger piece of land have higher mortality rate of trees (Laurance et al. 2007).
Plants at the edge on these smaller plots are also at risk for a
greater chance of invasive species inhabiting and draining what
nutrients and life is left.
The
plots below show the difference in plant mortality as you move inland
from the fragmented Amazonian forest edge. It can be seen here that the
drought had a strong effect on the percentage of dead trees in the
forest, although there was more resilience post-drought. It
can also be seen that from this study, that the percentage of dead
trees fluctuated more at the edges post-drought most likely due to the
"dynamic vegetation of the exterior edges versus the interior plots" (Laurance et al. 2001).
(Lienert, J. 2004)
Conclusion
"The effects of simultaneous spatio-temporal environmental variation will continue to pose problems for establishing general principles of the effects of habitat patchiness on population dynamics" (Hertzberg et al. 2000). According to 5 of the 9 papers collected for this topic address that the effects from fragmentation and drought will continue to effect the landscapes of the world as climate change increases, because it will increase extreme weather patterns.
However, not all plants are subject to these severe drought effects and land isolation. Some plant species are drought resistant and very mobile which lead to the probability that these species would survive and dominate the landscape (Hertzberg et al. 2000). And I say 'probability' because it cannot be known for sure what favorable habitat requirements are needed for a plant to endure. Additionally, if land near fragmented landscapes is young and growing, that young land will provide shade and it will act as a buffer from harsh amounts of light and wind during severe droughts.
Perhaps you are now thinking about what can be done to help mitigate the issues discussed in this paper. Well, we can "protect forest edges and the adjoining matrixes," (Laurance et al. 2007). We can maintain resilient populations of keystone species in areas through conservation efforts as well.
Works Cited
Asbjornsen, H., M. S. Ashton, D. J. Vogt, and S. Palacios. 2004. Effects of habitat fragmentation on the buffering capacity of edge environments in a seasonally dry tropical oak forest ecosystem in Oaxaca, Mexico. Agriculture, Ecosystems & Environment 103:481–495.
Gitlin, A. R., C. M. Sthultz, M. A. Bowker, S. Stumpf, K. L. Paxton, K. Kennedy, A. Muñoz, J. K. Bailey, and T. G. Whitham. 2006. Mortality Gradients within and among Dominant Plant Populations as Barometers of Ecosystem Change During Extreme Drought. Conservation Biology 20:1477–1486.
Guerrero, P. C., and R. O. Bustamante. 2009. Abiotic alterations caused by forest fragmentation affect tree regeneration: a shade and drought tolerance gradient in the remnants of Coastal Maulino Forest. Revista chilena de historia natural 82.
Hertzberg, K., N. G. Yoccoz, R. A. Ims, and H. P. Leinaas. 2000. The effects of spatial habitat configuration on recruitment, growth and population structure in arctic Collembola. Oecologia 124:381–390.
Laurance, W. F., H. E. M. Nascimento, S. G. Laurance, A. Andrade, R. M. Ewers, K. E. Harms, R. C. C. Luizão, and J. E. Ribeiro. 2007. Habitat Fragmentation, Variable Edge Effects, and the Landscape-Divergence Hypothesis. PLoS ONE 2.
Laurance, W. F., G. B. Williamson, P. Delamônica, A. Oliveira, T. E. Lovejoy, C. Gascon, and L. Pohl. 2001. Effects of a strong drought on Amazonian forest fragments and edges. Journal of Tropical Ecology 17:771–785.
Lienert, J. 2004. Habitat fragmentation effects on fitness of plant populations – a review. Journal for Nature Conservation 12:53–72.
