The Effects of Climate Change on the Ecosystem of the Desert

Introduction

The term climate change has been around for a while, but is becoming a greater topic of concern, as the issue gets worse. Climate change typically tends to be thought of as global warming or the melting of artic ice, but it is a much bigger issue that has created numerous problems throughout all ecosystems. Species have declined throughout the world due to habitat destruction, overexploitation, invasive species, and pollution. However, climate change has become another major factor for species decline and the problem continues to worsen (Barrows and Murphy-Mariscal 2012). Climate change is best described as the change in global or regional climate patterns, such as the rising global average temperature and the increased levels of atmospheric carbon dioxide. In addition, climate change encompasses the effects of these changes on the planet such as extreme temperatures, drought, heatwaves, the loss of sea ice, and rising sea levels.

One of the most susceptible ecosystems of climate change is for hot and dry deserts. With the extreme temperatures, droughts, and loss of habitats, the species that live there are struggling to overcome these obstacles. The effects of climate change are pushing many desert species to their physiological limits and are causing many to lose their habitats as well. In particular, hot deserts are expected to increase in temperature at faster rates than other regions (Bachelet et al. 2015). Desert ecosystems are becoming threatened due to the changes of the climate and desert species are facing higher mortality rates as these conditions worsen. Through the impacts that climate change has had on the environment, species are dealing with extreme states that threaten the health and functionality of desert ecosystems.

Climate Change on the Desert Environment

Deserts of the Southwestern United States are already characterized by high environmental temperatures and scarce water resources. Across the globe, deserts have warmed and dried more rapidly over the last fifty years than other ecoregions and these shifts are expected to continue (Bai et al. 2016). Because of this, deserts are important when looking at the effects of climate change. The first major environmental change in desert ecosystems is the temperature. Based on a journal from 2016, the Mojave Desert had a mean July maximum temperature of 117 degrees Fahrenheit. In comparison, the Sonoran Desert has a lower elevation and, because of this, is even hotter than the Mojave. These temperatures are predicted to rise and in the Sonoran Desert, maximum rates of change are predicted to exceed what native plants and animals have ever experienced in the recent past (Bachelet et al. 2015). The temperature for the Mojave Desert has risen by approximately 2°C in the last century and hot and dry deserts are predicted to continue these trends, resulting in many other environmental issues in desert ecosystems. As the temperature of the environment rises, the soil temperature of deserts will rise and dry out as well. The soil temperature for the Mojave Desert region tends to be 4.24°C higher than the air temperature, but the two are highly correlated. During a 19-year study, the soil of the Mojave Desert increased at an average rate of 0.79°C per decade (Bai et al. 2016).

Another large change in desert environments is the amount of available water. Precipitation in hot and dry deserts is low, making the amount of available water in the area sparse. The Mojave Desert, for example, has an annual rainfall that is usually less than 150 mm, with a great portion of the region having less than 100 mm. Additionally, the precipitation varies temporally, and mostly occurs in the winter (Bai et al. 2016). With climate change impacting the desert environment, precipitation is expected to become more variable and droughts more extreme. The aridity of this region makes even small changes in the water supply likely to have large ecological consequences (Bachelet et al. 2015).

The impacts climate change has on the precipitation and the soil are both changing the growth of many plant species and resulting in a shift of distribution of life. With the soil becoming warmer, plant growth will be affected through the changes in chemical and pedogenic processes within the soil (Bai et al. 2016). Plant species will also respond to major drought events, by shifting to a higher climate and increasing in mortality events. There is evidence that climate change has already caused this to happen and there is concern with a decrease in herbaceous cover and vegetation in desert ecosystems (Bachelet et al. 2015). In addition to these factors, fires can also play a role in the loss of habitats in desert ecosystems. Although fires are not directly created by it, climate change has still played a role on increasing the severity of habitat loss from fires. In these desert regions, fires are caused by the interaction of increased nitrogen deposition, which increases the productivity for invasive grasses. These grasses will make fires be able to spread and start easier (Barrows and Murphy-Mariscal 2012). With the environmental extremes and loss of many habitats and resources, climate change is having a major impact of desert species.

Direct Impacts on Desert Species

Through the changes of hot and dry desert environments, desert species are struggling to adapt to the harsh conditions and ecosystems are being impacted because of it. The changes in climate are affecting desert species directly through thermal and hydric stress and indirectly through the loss of resources and habitats (Iknayan and Bessinger 2018). The change in environmental factors are not only affecting the behavior of many of these species, but are also putting many in danger of going extinct. Desert plants and animals have evolved in the environmental extremes of North American desert ecosystems; however, effects of climate change are causing many species to approach their physiological tolerances (Bachelet et al. 2015).

The increased temperatures of this already arid environment are causing reptiles, as well as other animals, to change their behavior as an attempt to adapt. To escape the lethal temperatures, species shift their activity periods to earlier in the day or season and seek shelter in shaded areas such as shrubs or burrows (Barrows 2010). Along with the temperature rising, the soil is also rising along with it, making the desert a very dry and arid environment that many species cannot handle. These changes in soil can have a big impact on organisms by affecting plant growth and natural processes within the soil (Bai et al. 2016). In addition to rising temperatures, there have also been an increase in heat waves that are causing catastrophic mortality rates for many desert beings. For desert birds, heat waves have occasionally led to significant mortality events and as the climate keeps getting hotter, these mortality occurrences will only become more frequent. Due to rising temperatures, birds will require more water to stay hydrated and will face the conflict of conserving their water to avoid dehydration or evaporating the water to maintain their body temperature below lethal limits (McKechnie and Wolf 2009).

Another factor that is having a great tole on desert species is lack of a sufficient amount of water and moisture in the environment. Climate change is expected to increase the variability of precipitation by affecting the frequency and intensity of rain and drought events. With these changes, desert species are having a difficult time finding enough drinkable water in order to hydrate themselves and with the temperatures becoming more extreme, these water requirements are only increasing. Small birds, in particular, will be affected by this because they experience higher rates of evaporative water loss, reaching up to five percent of their body mass every hour. These higher rates will make small birds rapidly reach the limits of their dehydration tolerance (McKechnie and Wolf 2009).

Additionally, as the environment obtains less water there will be a decrease in herbaceous cover, plant species, and vegetation (Barrows 2010). Desert plants require soil moisture for germination and establishment and will be greatly affected by the decrease in precipitation (St. Clair and Hoines 2018). Extended droughts, in particular, are making food resources largely unavailable and are decreasing the area of suitable habitats. In an experiment looking at climate change effects in the Mojave-Sonoran Desert interface for Agassiz’s Desert Tortoise and the common chuckwalla, the suitable habitat was reduced by 88% for the tortoises and 92% for the chuckwallas (Barrows 2010). Additionally, at the Mojave-Sonoran Desert region, die-offs of six species of perennial shrubs were documented ranging from 55% to 100% for adults and 81% to 100% for juvenile plants. Only one of the species showed no mortality as a result of drought (Barrows and Murphy-Mariscal 2012). Many species rely on these resources for food and shelter. For desert tortoises, their diet relies on annual plants, perennial grasses, and cactus that are becoming largely unavailable due to extended droughts (Barrows 2010). This is then affecting their presence in habitats where they once thrived because the ecosystem can no longer support the amount of species with its decreased resources (Barrows et al. 2016). Many habitats are also being lost due to fires. Climate change has affected the productivity of invasive grasses and has made the landscape very dry (Barrows and Murphy-Mariscal 2012). This has caused it to be easier for fires to wipe out a larger area of habitats.

In order to avoid these problems, many species are moving to higher elevations to shift toward cooler and wetter climate regimes. From the correlations between climate and species distributions, it is likely that species who are more sensitive to a decrease in precipitation, have already been migrating to higher elevations (Barrows 2010). Unfortunately, not all organisms can shift themselves either due to low mobility or just because they can’t take the stress of increased activity without a sufficient supply of water. Agassiz’s desert tortoise, for example, has limited mobility to travel long distances, therefore creating a disadvantage for this species to shift to a more suitable climate (Barrows et al. 2016). In addition, the shifting of species to higher regions is only a temporary solution because the cooler and wetter climate of higher elevations will eventually be dominated by the effects of climate change.

However, because desert species have adapted in this tough environment for many years, they have evolved many techniques and strategies that enable them to outstand the extreme events. As stated previously, a shift in activity periods or taking shelter can help many species avoid these high temperatures. Taking this a bit further, the lizard species L. kintorei uses a burrow system as a buffer to the temperature extremes and low humidity. This not only creates protection from the environment, but is creating more moisture that many reptiles need (Moore et al. 2018). Species can also evolve biologically to help combat these conditions. Desert tortoises have evolved a large urine bladder that enables them to consume and store large quantities of water for periods of time when water is not available.

However, the effects of climate change might still be too extreme for many adapted species, causing them to overpass their physiological limits. For example, the Desert tortoise in the Mojave Desert is listed as threatened under the U.S. Endangered Species Act and a large body of the research toward conservation has addressed how desert tortoises deal with drought conditions (Barrows 2010). Additionally, many species are going be affected through their ability to produce offspring. For example, the sex of tortoise eggs is determined by temperature as well as the health of the hatchlings (Bachelet et al. 2015). Black-throated sparrows will also lay more eggs in their clutch if they are provided with drinkable water. Laying eggs increases the amount of water required for these sparrows, because of the large water composition of the eggs (Coe and Rotenberry 2003). Many of these species in danger are keystone species and are necessary to have the ecosystem function. This will lead to climate change having great impacts on the wellbeing of ecosystems, that will indirectly put highly evolved and resilient species at risk.

Potential Consequences and Future Solutions

Like all ecosystems, the desert is dependent on many species in order to make the system operate successfully. In particular, keystone species are especially important and without them the system will lose its functionality. Keystone species play a critical role in regulating ecosystems and can drastically impact the system when their population is decreased or eliminated. With the impact of climate change on desert environments, many species are becoming threatened, including some that are required to keep the ecosystem working. In desert ecosystems, birds are very important for all the services that they provide. Birds have many essential roles in desert ecosystems such as predators, scavengers and seed dispersers (Iknayan and Bessinger 2018). Many plants depend on this seed dispersal for reproduction (St. Clair and Hoines 2018). Over the last century, birds in the Mojave Desert have been experiencing occupancy decline and erosion of site-level species richness, demonstrating a collapse of the Mojave avifauna community. In addition, the effects of climate change are affecting the fitness of desert birds (Iknayan and Bessinger 2018). Unfortunately, without a sufficient amount of desert birds, many ecosystems will collapse or be dominated by an individual species.

Climate change has also had an effect on plant populations through the rising temperatures, change in soils and excessive droughts. As climate change worsens, terrestrial ecological processes will gradually change to reflect the impacted environmental conditions (Bai et al. 2016). If these changes continue to become more extreme, many keystone plant species could disappear. Joshua trees are an example of a keystone species that are important in the deserts of southern California. They are utilized by many species and provide a habitat to many birds, mammals, and insects. In a study of Joshua tree forests in the Mojave Desert, it was determined that temperature was negatively correlated with Joshua tree stand density. This correlation may result from the impact that higher temperatures have on seed germination, recruitment, and drought mortality of Joshua trees (St. Clair and Hoines 2018). This will then consequently affect the habitat of many species that utilize these trees.

With the decrease of many species, desert ecosystems will lose much of their biodiversity and species richness. As an ecosystem, deserts are already on the low scale for biodiversity because of the harshness of the environment. This makes desert ecosystems even more vulnerable to losing their species because there will not be substitutes to fulfill previous and essential roles. Desert birds, however, do comprise a species-rich community in this unwelcoming region. However, there has been a nearly uniform decrease in site-level richness across the Mojave Desert, along with a decrease in occupancy for desert birds, indicating the community is in the process of collapse (Iknayan and Bessinger 2018). Lower biodiversity also increases the chance for a whole ecosystem to be wiped out during a single major climate event.

Desert ecosystems are relevant to look at when studying climate change because they experience the effects in a much more extreme way. Looking at deserts and the consequences of climate change will provide an outlook of potential consequences the environmental changes are not reversed or seriously delayed. Deserts will feel the effects of rising temperatures and decreases in available water to the fullest extremes, because they already are such as extreme environment. That is why it is important to put more research into these regions on the devastating consequences of climate change and how to combat this problem.

Looking into the future, further research must be done to help preserve desert species and maintain biodiversity. Primarily action must be taken upon global warming and decreases in precipitation, through the reduction of human impacts. This must be done by creating new global policies that work toward reducing greenhouse gas emissions, stopping the use the use of fossil fuels, and creating an effort to conserve biodiversity (Iknayan and Bessinger 2018). Ecosystem-specific research is also necessary due to the heterogenous effects on different areas of the Earth. Looking at the direct impacts of extreme events on desert species as well as linking predicted climates to survival and reproduction will help gain a better understanding of the risks this ecosystem faces (McKechnie and Wolf 2009). Possible solutions such as reintroduction of species and an installation of artificial water sources have been attempted, however no significant solutions have been found. In fact, these attempts can actually do more harm than good. For example, the artificial water sources can pose a drowning hazard to reptiles such as desert tortoises and have been found to have the remains of tortoises within them (Andrew et al. 2001). Further conservation research is necessary to discover ethical and permanent solutions within desert ecosystems.

Conclusion

The issue of climate change continues to create many serious issues for ecosystems throughout the world. The environmental changes are only becoming more extreme and are creating many problems for natural ecosystems. Largely due to the actions of humans, species of the desert are especially being affected as they gradually lose many necessary resources, such as food, water, and habitats. Climate models continue to predict an increasingly dry and hot future, causing these resources to become scarcer (Iknayan and Bessinger 2018). The desert is a very important region to observe when looking at the effects of climate change. Deserts already have a harsh environment, which makes their ecosystems more susceptible to becoming unsuitable for life. Because of this, the desert can show a glimpse into the future if climate conditions continue to escalate. It offers a prescient warning to the future with less biodiversity and species being pushed toward physiological extremes (Iknayan and Bessinger 2018). Because of this, there needs to be more research on the impact’s climate change has had to desert ecosystems, including physiological modeling of these direct impacts on the animals that live there.