UCLA Department of Geography
tmccleery@ucla.edu
Puerto Rico has seen significant changes in flora species in its 40 million years of evolutionary history. In its original state, Puerto Rico had nearly 100% forest cover with 547 native species. However, as with many other regions, European discovery of the island and subsequent development has led to invasive plant species and land use practices that decrease forests, so that 6% of Puerto Rican forest cover remains, and only 1% is mature forest with all native species. Including exotic species, a total of 750 species can now be found on the island (Lugo 2004). Stopping the spread of invasive species into tropical rain forests is essential for the protection of biological communities and the conservation of native tropical forests.
tmccleery@ucla.edu
Introduction
Puerto Rico has seen significant changes in flora species in its 40 million years of evolutionary history. In its original state, Puerto Rico had nearly 100% forest cover with 547 native species. However, as with many other regions, European discovery of the island and subsequent development has led to invasive plant species and land use practices that decrease forests, so that 6% of Puerto Rican forest cover remains, and only 1% is mature forest with all native species. Including exotic species, a total of 750 species can now be found on the island (Lugo 2004). Stopping the spread of invasive species into tropical rain forests is essential for the protection of biological communities and the conservation of native tropical forests.
The genes, species, and ecosystems that make up the earth's biological diversity are important because their loss and degradation diminishes nature. Evidence suggests that the biosphere acts as a self-regulating whole and that diverse systems may be more resilient (Lowe, Borowne et al. 2000). Safeguarding the earth's diversity is one of the best ways to ensure human and ecosystem health. Invasive species drastically alter the makeup of plant communities and challenge the success of native production. If global climate change and species introduction rates continue at today's unprecedented rate, projections estimate that more than half of the current species could become extinct. Exotic plant invasions have been reported to decrease biodiversity, reduce productivity, degrade wildlife habitats, displace native plants, and alter ecosystem functions. Exotic species are changing the rules of the game under which all organisms exist. It is important that humans develop a plan to rid forests of destructive invasive plants. This project aims at taking the first step, pinpointing exact locations in the forest where exotic species are located.
Due to increased numbers of invasive species, 400 of the 958 species that are listed as threatened or endangered are considered to be at risk primarily because of competition with or predation by non-indigenous species (Pimentel et. al 2004). Invasive species are causing large costs to the United States due to things such as disease. The challenge in controlling the problem is not only the cost, but in preventing further damage of the environment. President Clinton gave $28 million for the defense against alien species invasions over an 18 month period (Pimentel et. al 2004). Additionally, he created the Interagency Invasive Species Council to mobilize the increase of invasive species (Pimentel et. al 2004). Furthermore, a Federal Interagency Weed Committee was formed to prevent non-indigenous species invasions (Pimentel et. al 2004). In the entire research process, no evidence was found to suggest that any prevention plans have been created specifically to prevent exotic species invasion in Puerto Rico. Remote sensing will be used to help distinguish these invasive species and to show their spread throughout local environments. Education plans and biological research surrounding non-native plants must be made to stop the altercation of the environment that invasive species are causing.
The author hypothesizes that urban expansion and land use change will drive understory woody regeneration of Puerto Rican forests to be dominated by exotic legumes, because these species have a competitive advantage over non-legume native trees in sites with compacted and acidified soils. Additionally, forest canopies experiencing high invasive legume rates due to urban expansion and land use change will have lower Normalized Difference Vegetation Index (NDVI) values. Futhermore, reserves near roadsides and urban areas will have more red color in Google Earth images due to the flowering invasive African Tulip.
During the summer of 2011, with the help of another student and UCLA Assistant Professor, Daniela Cusack, soil and tree leaves were taken from four different watersheds throughout Puerto Rican forests, as well as conducting surveys of seedling and sapling species diversity. The four watersheds represent a gradient of urbanization, with one in a strongly urban watershed, one in a rural watershed that is dominated by secondary forests and pastures, and two remote watersheds in protected rain forests. Professor Cusack already had sites set up in all of these watersheds with canopy species diversity information. The collection of soil carbon and nitrogen data provided this project with additional background information.
Following field work, remote sensing acted as an aid for this project. Satellite imagery of Puerto Rico was obtained from Maryland Land Cover Facility. The images were downloaded from the Landsat 7 ETM+ satellite and the ETM+ tiles were dated January of 2007 . The attention of this project focused mainly in the San Juan region because that was where the urbanization gradient was most prevalent. Therefore, ETM+ images were subsetted to show only the Rio Piedras watershed using ENVI 4.8. This watershed is outlined in black in the image provided above. For the analysis process, it was essential a shapefile containing all 9 study sites was inserted into ENVI. This shapefile was created by Lori Cornell, an environmental studies PhD student at SUNY. The shapefile was inserted into ENVI by inserting a Vector file and specifying shapefile. An NDVI was then performed which showed the greenness of each study site examined. An NDVI works using this formula:
In Google Earth, the African Tulip Invasive legume can be seen by its distinct red flowers that bloom in the summer. Imagery from Google Earth was collected in October of 2006, so the imagery revealed this distinct red color. To identify these legumes in specific study sites, imagery from Google Earth was used, saved to the desktop, and then uploaded onto ENVI. In ENVI, a density slice was generated. However, the density slice was unable to detect the exact values of the red color change. As a result, the author resorted to identifying legumes in the canopy via Google Earth based on the red color and results from field work.
NDVI
NDVI Spectral Signatures
#1
#2
#3
#4
#5
#6
#7
#8
Correlating NDVI values with Distances to Urban Center and Major Roads
When evaluating NDVI values next to distances to major roads and the urban center, the higher NDVI values correlated with farther distances from the urban center and lower values correlated with shorter distances. Distance to the roadside did not seem to make as much as an impact. The distance from the urban center played a greater role than the distance to a major road, in determining NDVI values, as evidenced by NDVI values for locations 1 and 2. Once forests were within 6,500 meters from the urban center, NDVI values became positive and then roadside distances accounted for small increases and decreases in NDVI values.
Spectral signatures are used in ENVI to reveal the values in and surrounding the area one is looking at. The spectral signature was further proof of the theory that more invasive species are located in the areas near roadsides and the urban center. Image 1, an area 3553 meters from the urban center and 632 meters from a major road, has an overall lower spectral signature than all the others. The values surrounding the study area are lower, meaning more invasive species. Image 3 and 4, located in native forests, reveal high values in the study area. Once the image continues nearer to the roadside, which is distanced at 2113 and 1435 meters respectively, the values tend to become lower. This demonstrates that the farther one continues out of the protected reserve to the roadside, the lower the values become, therefore more exotic legumes! Image 7 is a great example of this phenomenon. Being located only 208 meters from a major road located on the left, the values at the study area are positive and moderate. At the left end of the spectral signature however, one can see the values tailing off at very low numbers. This is due to the presence of the roadside affecting the spread of invasive species.
Google Earth Images
Based on this study, a conclusion was made that canopies are more often driven to exotic invasion when they are located near areas of urban expansion. NDVI values rendered lower, therefore more invasive exotic species, when study areas were nearer to the urban center. Based on the results, it seemed that distance to the urban center was a bigger factor for legume presence than major roads. However, the distance to major roads differentiated between about .1 NDVI in the positive valued results. The spectral signatures revealed that at a localized view, the distance to the roadside does have an affect on surrounding areas of the study sites and are aiding the spread of invasive species.
In a study analyzing invasive species in a tropical rain forest, satellite images available online for download were often not clear enough at the canopy level to see species diversity. Therefore, it was necessary to use Google Earth to investigate where invasive species occurred since Google Earth had much higher resolution imagery. However, to do more advanced techniques such as an NDVI and change detections, satellite imagery was necessary because it allows you to investigate other more advanced problems. Since downloadable imagery has more available bands, researchers can view different aspects of a study site. The major problem faced in this project was trying to do a density slice of images from Google Earth to identify invasive species. ENVI was unable to detect the slight change of color that the red invasives were showing. Even when attempting to do a supervised classification, ENVI was still not detecting the legumes. The only really successful part of studying legume invasions at this localized level was creating an NDVI and viewing the legumes in Google Earth.
Other studies have also analyzed the presence of invasive species in the tropics. In dry forests of Hawaii, remote sensing was also used to analyze biological invasions. Here, Kellner, et al. found that invasive species were able to succeed because they had no natural enemies such as generalists and ungulates (Kellner, Asner et al. 2011). Another remote sensing study in Hawaii, revealed that invasive species invaded sites with increased nutrient availability (Asner and Vitousek 2005). In the end, it seems invasive species are finding a way into native tropical forests and dominating whatever niches they can, using whatever resources available.
Invasive species contribute to global climate change by modifying the composition and function of ecosystems, but many studies have documented only local-scale spread of invasive plants into forests. At a global level, invasive species are not being studied as a whole, avoiding the effects of invasive species on ecosystems and habitat destruction. The next step in ecosystem ecology is studying global effects of invasive species and how it is altering the world around us.
Asner, G.P. and P.M. Vitousek (2005). "Remote analysis of biological invasion and biogeochemical change." Proceedings of the National Academy of Sciences of the United States of America 102(12): 4383-4386.
Kellner, J.R., G.P. Asner, et al. (2011). "Remote analysis of biological invasion and the impact of enemy release." Ecological Applications 21(6): 2094-2104.
Due to increased numbers of invasive species, 400 of the 958 species that are listed as threatened or endangered are considered to be at risk primarily because of competition with or predation by non-indigenous species (Pimentel et. al 2004). Invasive species are causing large costs to the United States due to things such as disease. The challenge in controlling the problem is not only the cost, but in preventing further damage of the environment. President Clinton gave $28 million for the defense against alien species invasions over an 18 month period (Pimentel et. al 2004). Additionally, he created the Interagency Invasive Species Council to mobilize the increase of invasive species (Pimentel et. al 2004). Furthermore, a Federal Interagency Weed Committee was formed to prevent non-indigenous species invasions (Pimentel et. al 2004). In the entire research process, no evidence was found to suggest that any prevention plans have been created specifically to prevent exotic species invasion in Puerto Rico. Remote sensing will be used to help distinguish these invasive species and to show their spread throughout local environments. Education plans and biological research surrounding non-native plants must be made to stop the altercation of the environment that invasive species are causing.
The author hypothesizes that urban expansion and land use change will drive understory woody regeneration of Puerto Rican forests to be dominated by exotic legumes, because these species have a competitive advantage over non-legume native trees in sites with compacted and acidified soils. Additionally, forest canopies experiencing high invasive legume rates due to urban expansion and land use change will have lower Normalized Difference Vegetation Index (NDVI) values. Futhermore, reserves near roadsides and urban areas will have more red color in Google Earth images due to the flowering invasive African Tulip.
Study Area
During the summer of 2011, with the help of another student and UCLA Assistant Professor, Daniela Cusack, soil and tree leaves were taken from four different watersheds throughout Puerto Rican forests, as well as conducting surveys of seedling and sapling species diversity. The four watersheds represent a gradient of urbanization, with one in a strongly urban watershed, one in a rural watershed that is dominated by secondary forests and pastures, and two remote watersheds in protected rain forests. Professor Cusack already had sites set up in all of these watersheds with canopy species diversity information. The collection of soil carbon and nitrogen data provided this project with additional background information.
ArcGIS 10 was used to map the distances from each study area to the urban center and major roadsides and to map species compositions and soil characteristics. This project will analyze invasive species in 9 different sites from space located in the urbanization gradient described above. These sites are located at:
The distances to the urban center and major roads were measured using ArcGIS 10. These distances were recorded in order of appearance on the previous graph as follows.
Shortest Distance to Urban Center in Meters
- 3,553
- 4,791
- 6,805
- 7,381
- 8,312
- 10,527
- 10,269
- 10,908
- 12,127
Shortest Distance to Major Road in Meters
- 632
- 745
- 2113
- 1435
- 1610
- 2625
- 208
- 1271
- 1188
Materials and Methods
Following field work, remote sensing acted as an aid for this project. Satellite imagery of Puerto Rico was obtained from Maryland Land Cover Facility. The images were downloaded from the Landsat 7 ETM+ satellite and the ETM+ tiles were dated January of 2007 . The attention of this project focused mainly in the San Juan region because that was where the urbanization gradient was most prevalent. Therefore, ETM+ images were subsetted to show only the Rio Piedras watershed using ENVI 4.8. This watershed is outlined in black in the image provided above. For the analysis process, it was essential a shapefile containing all 9 study sites was inserted into ENVI. This shapefile was created by Lori Cornell, an environmental studies PhD student at SUNY. The shapefile was inserted into ENVI by inserting a Vector file and specifying shapefile. An NDVI was then performed which showed the greenness of each study site examined. An NDVI works using this formula:
where NIR= Near Infrared and VIS= Visual spectrums. The bands were arranged in a 4-3-4 array to perform the NDVI. The NDVI values were then recorded to show how the greenness correlated with legume regeneration in the canopies of Puerto Rican forests. Spectral signatures were generated to see NDVI values of the area surrounding the study site to provide additional information.
9 study areas marked in red circles in San Juan Puerto Rico
Imagery from Landsat 7 ETM+
Resolution: 30m x 30m
In Google Earth, the African Tulip Invasive legume can be seen by its distinct red flowers that bloom in the summer. Imagery from Google Earth was collected in October of 2006, so the imagery revealed this distinct red color. To identify these legumes in specific study sites, imagery from Google Earth was used, saved to the desktop, and then uploaded onto ENVI. In ENVI, a density slice was generated. However, the density slice was unable to detect the exact values of the red color change. As a result, the author resorted to identifying legumes in the canopy via Google Earth based on the red color and results from field work.
San Juan, Puerto Rico
Google Earth Image
October 2006
Results
Google Earth Image
October 2006
Results
NDVI
NDVI Spectral Signatures
#1
#2
#3
#4
#5
#6
#7
#8
#9
Correlating NDVI values with Distances to Urban Center and Major Roads
Spectral signatures are used in ENVI to reveal the values in and surrounding the area one is looking at. The spectral signature was further proof of the theory that more invasive species are located in the areas near roadsides and the urban center. Image 1, an area 3553 meters from the urban center and 632 meters from a major road, has an overall lower spectral signature than all the others. The values surrounding the study area are lower, meaning more invasive species. Image 3 and 4, located in native forests, reveal high values in the study area. Once the image continues nearer to the roadside, which is distanced at 2113 and 1435 meters respectively, the values tend to become lower. This demonstrates that the farther one continues out of the protected reserve to the roadside, the lower the values become, therefore more exotic legumes! Image 7 is a great example of this phenomenon. Being located only 208 meters from a major road located on the left, the values at the study area are positive and moderate. At the left end of the spectral signature however, one can see the values tailing off at very low numbers. This is due to the presence of the roadside affecting the spread of invasive species.
Google Earth Images
1. All Invasive
2. All Invasive
3. All Native
4. All Native
5. Mostly Invasive
6. Half Invasive, Half Native
7. Mostly Native
8. Half Invasive, Half Native
9. Mostly Invasive
The categories given to each Google Earth image were based on the values obtained from the NDVI values. In the native forests, which are located far from the urban center and major roads, it is evident that the canopy is filled with green trees containing a lot of different canopy layers and a closed canopy, as evidence by images 3 and 4. In the invasive images nearer roadsides and the urban center, the red from the invasive African Tulip in bloom can be viewed. The best representation of the African Tulip is provided in image 1, where red spots dot the image. Image 1 is located closest to the urban center and major roads. Its forests are therefore more affected by the pressure of urbanization. Again images 3 and 4, located in a protected reserve, best represent healthy native forests.
Discussion
Based on this study, a conclusion was made that canopies are more often driven to exotic invasion when they are located near areas of urban expansion. NDVI values rendered lower, therefore more invasive exotic species, when study areas were nearer to the urban center. Based on the results, it seemed that distance to the urban center was a bigger factor for legume presence than major roads. However, the distance to major roads differentiated between about .1 NDVI in the positive valued results. The spectral signatures revealed that at a localized view, the distance to the roadside does have an affect on surrounding areas of the study sites and are aiding the spread of invasive species.
In a study analyzing invasive species in a tropical rain forest, satellite images available online for download were often not clear enough at the canopy level to see species diversity. Therefore, it was necessary to use Google Earth to investigate where invasive species occurred since Google Earth had much higher resolution imagery. However, to do more advanced techniques such as an NDVI and change detections, satellite imagery was necessary because it allows you to investigate other more advanced problems. Since downloadable imagery has more available bands, researchers can view different aspects of a study site. The major problem faced in this project was trying to do a density slice of images from Google Earth to identify invasive species. ENVI was unable to detect the slight change of color that the red invasives were showing. Even when attempting to do a supervised classification, ENVI was still not detecting the legumes. The only really successful part of studying legume invasions at this localized level was creating an NDVI and viewing the legumes in Google Earth.
Other studies have also analyzed the presence of invasive species in the tropics. In dry forests of Hawaii, remote sensing was also used to analyze biological invasions. Here, Kellner, et al. found that invasive species were able to succeed because they had no natural enemies such as generalists and ungulates (Kellner, Asner et al. 2011). Another remote sensing study in Hawaii, revealed that invasive species invaded sites with increased nutrient availability (Asner and Vitousek 2005). In the end, it seems invasive species are finding a way into native tropical forests and dominating whatever niches they can, using whatever resources available.
Invasive species contribute to global climate change by modifying the composition and function of ecosystems, but many studies have documented only local-scale spread of invasive plants into forests. At a global level, invasive species are not being studied as a whole, avoiding the effects of invasive species on ecosystems and habitat destruction. The next step in ecosystem ecology is studying global effects of invasive species and how it is altering the world around us.
References
Asner, G.P. and P.M. Vitousek (2005). "Remote analysis of biological invasion and biogeochemical change." Proceedings of the National Academy of Sciences of the United States of America 102(12): 4383-4386.
Kellner, J.R., G.P. Asner, et al. (2011). "Remote analysis of biological invasion and the impact of enemy release." Ecological Applications 21(6): 2094-2104.
Lowe, S., M. Borowne, et al. (2000). 100 of the World's Worst Invasive Alien Species. The Invasive Species Specialist Group. S.S. Commission, World Conservation Unit.
Lugo, Ariel E. "The outcome of alien tree invasions in Puerto Rico." Front Ecol Environ 2.5 (2004): 265-273
Pimentel, David, Rodolfo Zuniga, and Doug Morrison. "Update on the environmental and economic costs associated with alien-invasive species in the United States". Ecological Economics 52 (2004): 273-288.
Lugo, Ariel E. "The outcome of alien tree invasions in Puerto Rico." Front Ecol Environ 2.5 (2004): 265-273
Pimentel, David, Rodolfo Zuniga, and Doug Morrison. "Update on the environmental and economic costs associated with alien-invasive species in the United States". Ecological Economics 52 (2004): 273-288.
