Kevin EckhardtGEOG 49111/17/2008
Lab 5 – Plant Invasion and Land Use in the Galápagos Islands
Guava in the Agricultural Zone
Relationship to Farm Characteristics
Farms
The following information has been gathered for each of the sixteen farms in the agricultural zone: area of the farm; number of cattle on the farm; percentage of the farm used for crop agriculture; percentage of the farm used as pasture for cattle grazing; and whether or not the farm residents participate in tourism or fishing. Each of these variables was compared with the percentage of the farm containing guava to see if any possible relationships exist.
There does not appear to be a linear relationship between the size of a farm and the percentage of the farm’s land containing guava. A binomial regression, however, fits the data much better than the linear regression. This could indicate that as a farm increases in size it is likely to have higher percentage of guava, possibly because it is more difficult to keep the guava under control. After a certain point though, increasing a farms size leads to a lower percentage of guava. This could be due to a larger famer having more “remote” area which is not in a close proximity to contributing factors.
The percentage of guava on a farm appears to decrease as the number of cattle on the farm increases. This seems contrary to the hypothesis that pigs and cattle play a large role in the spread of guava. However, it does not take into account feral animals or the impact of the animals on areas outside of the farm.
The percentage of guava on a farm also decreases as the percentage of the farm used for either crop agriculture or pasture increases. This could indicate that larger the area of the farm that is in use, the smaller the area of the farm that contains guava.
Average Pasture / Average Crops / Average GuavaOther Activities / None / 62.5% / 22.5% / 30.2%
Fishing / 25.0% / 5.0% / 65.0%
Tourism / 25.0% / 12.5% / 50.0%
Farms which participate in other activities show much less pasture and crop land and much more guava, on average, than farms which do not.
Fields
The sixteen farms in the study have been subdivided into 49 fields. The following information has been gathered for each field: the area of the field, the year the field was last cleared of guava, whether the field is used for pasture, and whether the field is used for crops.
The area of a field does not appear to be an indicator of the percentage of the field that contains guava.
As one would guess, fields which were cleared more recently tend to have less guava.
Pasture / Crops / Average Guavano / no / 59.0%
yes / no / 27.1%
yes / yes or no / 24.7%
no / yes / 40.8%
yes or no / yes / 31.3%
yes / yes / 19.6%
Fields used for either pasture or crops have, on average, a much lower percentage of guava than fields which are not. Fields used for both pasture and crops showed the smallest average percentage of guava.
Relationship to Proximity of Roads and Buildings
Fields were classified as having low, medium, or high proximity to buildings and roads based on their distance from those features. A field was considered to have “high” proximity to a feature if any part of the field was within 100 meters of the feature; “medium” proximity if the entire field was more than 100 meters from the feature, but any part was within 500 meters of the feature; and “low” proximity if the entire field was more than 500 meters away from the feature.
Field proximity to buildings can be seen in figure kevineck_1.
Proximity to a BuildingField Count / Average Guava
High / 27 / 34.01%
Medium / 14 / 38.25%
Low / 8 / 34.55%
Field proximity to roads can be seen in figure kevineck_2.
Proximity to a RoadField Count / Average Guava
High / 24 / 34.65%
Medium / 13 / 39.96%
Low / 12 / 31.58%
Field proximity to either a road or a building can be seen in figure kevineck_3.
Proximity to Either a Road or a BuildingField Count / Average Guava
High / 34 / 35.28%
Medium / 10 / 37.65%
Low / 5 / 30.82%
Field proximity to both a road and a building can be seen in figure kevineck_4.
Proximity to Both a Road and a BuildingField Count / Average Guava
High / 15 / 30.54%
Medium / 19 / 40.56%
Low / 15 / 33.42%
Fields that have a medium proximity to roads or buildings have a higher average amount of guava than fields with either a high or low proximity to roads or buildings. The highest average guava amounts are seen on fields in medium proximity to a road (slightly higher if it is a medium proximity to both a road and a building). The lowest guava amounts are seen on fields with a high proximity to both a road and a building, followed closely by field with a low proximity to either a road or a building.
Relationship to Activity Level
Farms were classified as “active”, “partially abandoned”, or “abandoned” based on how the farm’s fields were being used. To be considered “active”, 75% of a farm’s fields needed to be in use (for pasture and/or crops) and have been cleared of guava since the beginning of 1999. Farms with less than 25% of their fields in use were considered “abandoned”. All other farms were classified as “partially abandoned”.
Count / Average Cattle / Average Pasture / Average Crops / Average GuavaActivity / Active / 9 / 25 / 63.3% / 20.0% / 27.4%
Partially Abandoned / 5 / 13 / 26.0% / 12.0% / 62.5%
Abandoned / 2 / 00 / 00.0% / 05.0% / 71.4%
Abandoned and partially abandoned farms have, on average, a much higher amount of guava than farms which are active.
Spatial Clustering
Visual examination of fields for guava yields the following patterns:
/ Fields with large clusters or groves of guava are often not in use./ Fields with large guava free areas are often used for pasture or near buildings.
/ Fields used for crops often have thin rows of guava but the rest has been cleared.
Guava in the Park Zone
Relationship to Distance from Agricultural Zone
Areas in the Park Zone closer to the Agricultural Zone are likely to contain more guava than areas further away from the Agricultural Zone.
Relationship to Bordering Fields
Areas in the Park Zone that border the Agricultural Zone do appear to have more guava when they are adjacent to a field with a high percentage of guava, but the correlation is not very tight.
The highest guava levels in the Park Zone along the border area were seen when adjacent to fields that had not been recently cleared, but again the correlation is not very tight.
Pasture / Crops / Average Guavano / no / 28,783
yes / no / 30,908
yes / yes or no / 26,802
no / yes / 11,393
yes or no / yes / 17,558
yes / yes / 22,696
When looking at how fields are used, the lowest amount of guava in the Park Zone border area is seen adjacent to fields which are used for crops. Areas adjacent to unused fields or fields which are used partly or entirely for pasture tend to have higher amounts of guava than fields which are used solely for crops.
Relationship to Characteristics of Bordering Farms
Areas in the Park Zone which border the Agricultural zone tend to have more guava when they are adjacent to a farm with a high percentage of guava.
A larger number of cattle on a farm seem to indicate a higher amount of guava in adjacent areas of the Park Zone, but the correlation is not tight.
Neither the percentage of a farm used for crops nor the percentage of a farm used for pasture seems to correlate to the amount of guava in adjacent areas of the Park Zone.
Farm Activity Level / Park Zone Guava CountActive / 26,698
Partially Abandoned / 82,616
Abandoned / 16,144
The guava count of Park Zone areas which are adjacent to partially abandoned farms is much higher than in areas adjacent to active or abandoned farms.
Summary
Inside the agricultural zone the activity level on farm, regardless of what that activity is, seems to be an indicator of the amount of guava that is found on the farm. At the farm level, increasing quantities of cattle, pasture land, and crop land all seem to correlate to lower percentages of guava on the farm. Fields which are used for either pasture or crops tend to have a much lower amount of guava than fields which are not in use. Close proximity to buildings also seems to correlate with a lower amount of guava. These are not surprising findings, as making room for planting crops or grazing cattle would require the clearing of guava.
In the border area of the park zone the specific activities of the adjacent farms and fields have an impact. Larger numbers of cattle on a bordering farm tend to indicate a higher amount of guava in the adjacent areas of the park zone. Park zone areas adjacent to fields which are used for crops tended to have a much lower quantity of guava than either abandoned fields or fields used for pasture.
Distance appears to play a part in both the agricultural zone and the park zone. Areas inside the park zone tend to have a much larger amount of guava the closer you get to the agricultural zone. Inside the agricultural zone the largest farms, by area, tended to have less guava than the medium sized farms. Areas with low proximity to roads or building also tended to have less guava than areas with medium proximity. The amount of guava increases as you move away from areas of high activity, but eventually begins to decrease again as you get farther away.
Additional information about farming practices on the island would be useful for further study. Do farmers rotate fields at all, changing from crop land to pasture or letting fields “rest”? What types of fencing or border controls are used? Are cattle corralled in pasture land or allowed to roam freely? Are crops fenced in or protected from cattle or other animals? The lower amounts of guava in areas of the park adjacent to crops versus those areas adjacent to pasture seems to lend credence to the theory that animals are contributing to the spread of guava. More information about how these animals are controlled would be very useful in further exploration of this hypothesis and possible suggestions for better control of guava in the future.
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