The Frequency and Canopy Cover of species in the desert vs. the gully of the Borrego Valley.

Transcription

1 The Frequency and Canopy Cover of species in the desert vs. the gully of the Borrego Valley. Sarah K. Byce 1 North Campus Drive Allendale, MI BIO March 2013

2 Byce 2 Introduction When one thinks of a desert, they would probably envision rolling sand and radiating heat. But in actuality, only about 10% of deserts actually have sand dunes (National Geographic). Deserts are anything but a barren wasteland, they are rich in a diversity of plants and animals that have adapted to the harsh conditions (National Geographic). They are defined as, a place that receives less than 10 inches of rain per year (National Geographic). So, this statement means, it doesn t have to be a hot desert, there can be cold dry deserts too. Deserts are a part of a broader category called dry lands; these dry lands have what is known as a water deficit, they frequently lose more moisture through evaporation than they can receive from annual precipitation (National Geographic). Sometimes plants that live in a desert go years without seeing a drop of fresh rainfall; they have adapted also by growing incredibly long roots to reach water beneath the surface (National Geographic). The driest deserts only get about one centimeter of water each year, and that comes from condensed fog rather than rain (National Geographic). There are four major types of deserts: hot and dry, semiarid, costal, and cold (UCMP). Both hot and cold deserts cover about one-fifth of Earth s land surface (Desert), (UCMP). More than one billion people, one-sixth of Earth s population, actually live in desert regions (National Geographic). Global warming could affect the increasing amount of deserts; higher temperatures may produce and increasing number of wildfires that alter desert landscapes by eliminating slow-growing trees and shrubs and replacing them with fast-growing grasses (National Geographic).

3 Byce 3 One kind of desert is hot and dry. These tend to occur at low latitudes, such as the Sahara and deserts in Mexico or Australia (UCMP). In North America the four major deserts are Chihuahuan, Sonoran, Mojave, and Great Basin (UCMP). Hot and dry deserts are mostly located around the Tropic of Cancer and/or Tropic of Capricorn (Desert). Northern Africa s Sahara desert reaches temperatures of up to 122 F during the day (National Geographic). Temperatures generally range from about 68 to 77 F; the maximum temperature range is 110 to 120 F (Desert), (UCMP). The atmosphere above these deserts areas contains a small amount of humidity, this results in daily extremes (UCMP). These types of deserts are extremely hot and lack a regular amount of rain fall (Desert). The rainfall that does occur is in concentrated short periods between long rainless ones; an average [ ] under 15 cm a year (Desert). Sometimes rain starts falling and evaporates before reaching the ground (UCMP). Due to the rain fall, or lack thereof in this type of desert, the soil is different than most. The soil here is course-textured, shallow, rocky, or gravely with good drainage (UCMP). The plants in these locations are unique due to location, rainfall, and soil. There are very few plants in these deserts; the plants that are located there lie close to the ground, and consist mostly of shrubs and short woody trees (Desert), (UCMP). Some examples are, turpentine bush, prickly pears, and brittlebush (Desert), (UCMP). All of these plants have adaptations to be able to survive in the extreme weather; their greatest acclimatization is being able to conserve water for long periods of time (Desert). A few species of plants will open their stoma during night hours to reduce the amount of evaporation (UCMP). The only animals that live in these parts of the world, must be burrowing animals to keep away from the sun and heat during the day; they will often come out at night however (Desert)( National Geographic). The most common animals of

4 Byce 4 habitats like this are nonmammalian vertebrates, such as reptiles (UCMP). Some examples of these nocturnal carnivores would be borrowers, mourning wheatears, horned vipers (Desert), (UCMP). There are relatively few large mammals in deserts because most are not capable of storing sufficient water and withstanding the heat (UCMP). The camel, however, is capable of going days without food or water, this is because they have adapted to the climate they live in and have learned to conserve the water they have (National Geographic). Semiarid is another type of desert. These deserts are increasing at a surprising rate; this process known as desertification is not caused by drought but usually arises from the demands of human population that settle on the semiarid lands to grow crops and graze animals (National Geographic). Semiarid deserts of this kind include the sagebrush of Utah, Montana, and [the] Great Basin (UCMP). During the summer months the days tend to be long and quite dry, but the winter offers some concentrated rainfall (UCMP). The temperature rarely goes above 100 F and the condensation of dew caused by night cooling may equal or exceed the rainfall received by some deserts (UCMP). The average rainfall for the year spans from 2 to 4 cm (UCMP). The soil in semiarid deserts can range from sandy and fine-textured to loose rock fragments, grave or sand (UCMP). The plants in this area have a spiny nature to protect from threatening surroundings (UCMP). These spines reduce the amount of transpiration (UCMP). Some examples include: creosote bush, white thorn, cat claw, and brittle bush (UCMP). The animals in this region, such as kangaroo rats, rabbits, skunks, and lizards tend to live in the shadow; they follow the shadow of the plant to stay out of direct heat (UCMP). The third kind of desert is Coastal. These deserts occur in moderately cool to warm areas [ ] a good example is the Atacama [desert] of Chile (UCMP). The maximum temperature for a

5 Byce 5 costal desert is about 95 F and 25 F is the minimum (UCMP). Average rainfall reaches between 8 and 13 centimeters (UCMP). The soil is fine-textured [ and has] good drainage (UCMP). All of the plants with thick and fleshy leaves or stems can take in large quantities of water when it is available and store it for future use (UCMP). Like many of the other hot deserts, the animals that live here have also adapted to the conditions. For example, some toads seal themselves in burrows with gelatinous secretions and remain inactive for eight to nine months until heavy rain occurs (UCMP). Other animals in coastal deserts include, insects, coyote, bald eagle, and snakes (UCMP). The final desert type is cold deserts. Cold deserts are found more closely to the Arctic areas of the globe (Desert). They generally occur in the basin and range [ ] of Utah, Nevada, and some parts of western Asia (UCMP). During the winter time cold deserts range from 29 to 40 F and 70 to 79 F during the summer months (Desert). Cold deserts having a covering of snow in the winter instead of dropping a few degrees in temperature like the hot and dry deserts do (Desert). The combination of snow and rain in cold deserts averages out to about centimeters each year (Desert). The heaviest rainfall of the spring is usually in April or May (UCMP). The soil is heavy, silty, and salty [ ] relatively porous and drainage is good (UCMP). There might be a few grasses or mosses covering a cold desert, but it never becomes warm enough to grow other plants (Desert). The height of scrub varies from 15 to 122 cm (Desert), (UCMP). All cold desert plants are either deciduous and more or less contain spiny leaves (Desert), (UCMP). Animals in these deserts also burrow, trying to keep warm; this is why [one] might find some of the same animals [as] in hot and dry deserts (Desert). Some

6 Byce 6 examples include, antelope, ground squirrels, jack rabbits, and kangaroo rats (Desert), (UCMP). The Mojave Desert specifically, is rich in life and nutrients. It is the smallest of the deserts in North America, located in the south eastern part of California, between the Great Basin and the Sonoran (Mojave Desert). It lies in the rain shadow of the Sierra Nevada Mountains due to the orographic effect (Mojave Desert). The Mojave includes, Death Valley, Pahrump Valley, Amargosa Valley, and the Las Vegas Valley (Rausch). This desert covers about 25,000 square miles and is at an elevation of about 3,000 feet (Mojave Desert). Some of the land is getting destroyed however because of the encroaching surrounding cities, military bases, and farms around the Colorado River (Mojave Desert). There is evidence the Mojave, about 10,000 years ago, was once home too many lakes and rivers, but since has dried up (Rausch). Temperature wise, the Mojave can reach 120 F in just one day (Rausch). During the winter however the temperature often stays below freezing at night but warms up to a [ ] comfortable temperature in the day; because of these extremes, it is full of organisms with adaptions (Rausch). Much of the rain occurs between October and March, but it only gets about 2.5 inches a year (Mojave Desert). The Mojave is home to scrub such as, brittlebush, creosote bush, and sagebrush (Mojave Desert). Animals in the Mojave have light colored feathers and fur to reflect the light of the sun (Mojave Desert). The plants also have short root systems to absorb the surface water (Mojave Desert). The specific Bajada used for research was located in the Borrego Valley in San Diego, California. The map used was a plot of land 4,800 square meters that gives the exact location of seventeen different species of shrub and cacti. Each circle on the map represented the

7 Byce 7 individual plant and diameter of that plant in meters. There was a large gully located to one side, but the rest was a barren desert (Department of Biology). Based on the information researched about deserts, and looking at the plot of land being used in lab, two hypotheses were created. The first hypothesis states: based on increased circle size, the gully has more canopy cover; the second states: there is more Creosote Bush in the gully than desert, based on initial glance. Materials & Methods To begin researching these hypotheses, a set of steps needs to be carried out. The first thing to be done is determine the quadrat location, meaning the plot of land in the Bajada sampled. Using a table of random numbers, a dice is rolled to establish the number to count over and down on the table of random numbers. The number landed on is used to decide the x and y-axis. The first two numbers in the three digit number given are multiplied together for the x-axis; the next two are multiplied for the y-axis. For example, if the random number is 934, the x-axis dimension would be 27 (9x3) and 12 (3x4) would be the y-axis. After concluding which numbers will represent the x and y-axis, two strings were cut and tied around the board: one vertically and the other horizontally. These strings will serve as guides when determining quadrats. The two strings were placed on the corresponding numbers, as determined by the random table. Where the strings cross, making four sections, a 6x6 centimeter quadrat stencil was placed in one of the corners; be consistent for all nine samples. After deciding which quadrant to use, for example the northwest corners, as was used in this exercise; trace the stencil with a dry erase marker. The circles beneath the traced square are the species to be observed and recorded in a data table. The following steps are quite complicated. After

8 Byce 8 drawing a quadrat, record the species letter and diameter of the circle into a table (Appendix A: Table 1). Once all observations have been done in all nine quadrats, a calculation to determine frequency (Appendix B: Formula 1) and canopy cover (Appendix B: Formula 2) should be done. Results After all calculations, tables, and graphs were completed there were a few clear results that emerged. The first thing that emerged was, many plants said to be located in the Bajada plot, were not found in our nine quadrat samples (Appendix A: Figure 1). The two most frequent species in the gully and desert are Bur Sage and Teddy Bear Cholla. Although these two species are quite frequent, they do not have very big canopy cover (Appendix A: Table 2). Lastly, from the graph (Appendix A: Figure 1), it can be seen many species were only found in the desert, for example: Brittlebush, Barrel Cactus, and Pencil Cholla. Based on the quadrats sampled and data collected, neither hypothesis can be confirmed. As seen in the table (Appendix A: Table 2), showing canopy cover for each species in the desert and the gully, the amount of canopy cover is far larger than in the gulley, which is not what was hypothesized. It is also unsupported that there is more Creosote Bush in the gully than the desert; based on the table (Appendix A: Table 1), depicting Creosote Bush s frequency independently calculated, and the graph (Appendix A: Figure 1), representing each species frequency based on location, it is clear to see, from the data collected Creosote Bush is more abundant in the desert than the gully. Discussion Measuring quadrats from a plot of land in the Borrego Valley and determining the species that live in nine specific samples was done to see if: based on increased circle size, the gully has

9 Byce 9 more canopy cover; and based on initial glace, there is more Creosote Bush in the gully than the desert. Based on graphs and tables (Appendix A) it cannot be confirmed either hypothesis is true. The data collected shows, the desert has more canopy cover and there is more Creosote Bush in the desert. So, in this case, with this data, initial glance did not help to conclude these hypotheses. Some reasons this could be is because of the random sampling. Although it is a very good way to sample, it may not have been the best in this situation. Taking these random samples did not seem to get a good mixture of species. For example, when working in the gully area, quadrats did not surround many species, the quadrat would be located just on the edge of the gully where no plants were located. Although neither hypothesis can be confirmed, Creosote Bush has a higher frequency in the desert. It can also been seen (Appendix A: Table 2) Creosote Bush has a greatest canopy cover in both the desert and the gully. So although Creosote Bush may not be large in number, it is quite large in diameter, covering lots of ground.

10 Byce 10 References Department of Biology. (2013, Winter). Biology 121-General Biology II: Laboratory Experiments and Exercises. Allendale: Grand Valley State University. National Geographic. (n.d.). Deserts: Arid But Full of Life. In Environment. Retrieved March 15, 2013 Rausch, C., & Utz, J. (2005). Mojave Desert. In Desert Survivors. Retrieved March 17, 2013 University of California Museum of Paleontology (UCMP). (n.d.). The Desert Biome. Retrieved March 13, 2013 West Tisbury Elementary School. (2010, September 23). Desert. In Blue Planet Biomes. Retrieved March 9, (2010, September 23). Mojave Desert. In Blue Planet Biomes. Retrieved March 17, 2013

11 Byce 11 Table 1: Raw Data Collected in Borrego Valley Appendix A: Tables, Graphs, Charts Table 2: Canopy Cover Gully vs. Desert

12 Byce 12 Table 3: Frequency of Creosote Bush compared in the Gully to the Desert Figure 1: Depiction of amount each species was found in the desert vs. the gully

13 Byce 13 Appendix B: Calculation Formulas Formula 1: Frequency Frequency = Total number of seperate quadrats in which species occurs Total number of quadrats sampled Formula 2: Canopy Cover Canopy Cover = (Number of species in a specific size diameter of species)