LOOKING BACK OVER 13 YEARS OF LAND USE AND COVER

Soil is seen to change and so are we. In fact, our needs over time determine how we use the land and how this influences its current state. This storymap analyzes vegetation cover and land use in areas of human use, which are not under the protection of the Galapagos National Park (GNP) and which are used for the development of the second most important economic activity of the Galapagos archipelago, agriculture (CGREG, 2020).

The Galapagos Islands Archipelago consists of almost 800,000 ha, spread over 18 large islands and islets. Ninety-seven percent of the land area is protected, the rest is urban and rural areas totaling about 26,000 ha on five populated islands (Isabela, Floreana, Santa Cruz, Baltra, and San Cristóbal). And the uses that the human population settled on the islands has given to the soil has been varied.

For decades, human communities settled in rural areas have been the main sources of soil change in these areas. Therefore, mapping the vegetation cover of these areas is crucial for better understanding, management and administration of protected areas. In the case of Galapagos, being a World Natural Heritage Site, it is essential not only to demonstrate change, but also to evaluate and monitor the state of the land surface, which becomes an important requirement for the proper use of the "soil" resource.

Soil mapping requires a series of steps that include, among others, classifying and mapping vegetation, field verifications, identification of key sites, etc. These are considered key activities for the characterization of an area, based on the vegetation cover of the area, and for the governance and management of natural resources (NRNR), since the structure and composition identified are the basis for all living beings and the infrastructures where they occur (Xie et al., 2008).

For years, the vegetation of Galapagos has been of interest to researchers who have sought to describe and understand its diversity and distribution. The most recent published vegetation mapping studies of the islands have also sought to integrate species diversity with land use. The most recent are the following:

• Cartografía de Galápagos. The Nature Conservancy (TNC): Se completó en junio 2006 usando información satelital con una escala geográfica final de 1:50000, con imágenes SPOT de un tamaño de pixel de 20 metros. (https://docplayer.es/13498293-Cartografia-galapagos-2006-conservacion-en-otra-dimension.html)
• Rivas-Torres et al., 2018:   Estudio que combinó tecnologías de sensoramiento remoto para la extracción de la cobertura vegetal de las Áreas Protegidas de Galápagos (Rivas-Torres et al., 2018).
• Laso et al., 2019: Estudio similar  al anterior, complementado con clasificación supervisada en las zonas rurales de  Galápagos (Laso et al., 2019).

This storymap aims to tell about land use change in the agricultural zone of the four populated islands of the archipelago for the years between 2006 and 2019 using inputs generated by previous studies that provide cartographic information on this topic. The first map shows the distribution of agricultural activity on the four populated islands, with the exception of Baltra. Using as inputs the thematic maps of vegetation cover and land use of these agricultural areas made by TNC in 2006 and Laso et al. in 2019, the changes in vegetation cover and land use during 12 years were spatially analyzed according to the availability of the information, its interoperability, quality and last update.

To accomplish this analysis, Geographic Information Systems (GIS) was used, specifically ArcGIS Pro software where, with the support of the Change Detection tool, vegetation cover change between 2006 and 2019 can be automated. This tool provides a guided workflow to perform change detection which is a process that serves as a key requirement of remote sensing and raster processing (digital image analysis). It consists of the process of comparing several raster maps or images of a specific location at multiple times to identify pixels (spaces or places) that have been transformed by climatic, abrupt or long-term changes.

Although the methodologies of the TNC and Laso et al. studies are different, as are the sources from which they obtained their data, the principles of remote sensing (identifying, observing and measuring properties of an object or event without making direct contact with it) and classification of land cover and land use are the same. In order to make both layers compatible, it is necessary to standardize their thematic categories, which are detailed in Table 1. It is important to note that the attributes of these different maps were standardized through the CGLS Copernicus Global Land Service Product Manual (Page 20, Figure 5. Buchhorn et al., 2020), which details the possible coverages of the geographic features to be compared between 2006 and 2019.

In addition to the thematic standardization between both layers, a geometric standardization called the Minimum Mapping Unit (MMU) is also applied. For this, the scales of both layers were analyzed and the one with the smallest detail was selected and with that scale (or pixel size) to make both maps compatible. In this case the pixel size is 100 meters, corresponding to the TNC 2006 layer. By means of this standardization, plots identified at different times that coincide spatially are obtained, thus being able to automate the analysis of these changes in the GIS.

Agricultural areas in Galapagos are approximately 25,000 ha. The current spatial analysis shows that 31.6% has not changed; the remaining (68.4%) has shown some type of change in land cover or land use.

The information generated can be used to answer key questions about the management of the agricultural areas of the Archipelago.

1. What percentage of the agricultural area was gained by introduced vegetation?

2. What percentage of the agricultural area was reclaimed for native vegetation?

3. What percentage of the agricultural area was cattle raised for crops* (*crops and pasture)?

The land cover changes analyzed in this study were grouped into 6 major categories: native vegetation, introduced or invasive vegetation, crops, pastures, buildings and water bodies. These are indicators of the type of management and use of agricultural land. In other words, during the years analyzed, what was the farmers' preference for land use in their environments. 

Figure 3. shows a visual sample of native vegetation recovered in agricultural areas. Proportionally, Floreana Island has been the island where there has been the least recovery of native vegetation, while San Cristóbal has had a significant recovery. The analysis shows that native vegetation is gaining space in all the agricultural zones in the four islands explored, mainly in the peripheries or limits of the islands.

The analysis of the detection of changes in land use between 2006 and 2019 shows that, in agricultural areas, native vegetation has recovered to a lesser extent, while the dominant land use has migrated towards the use of land for crops or abandoned spaces that provide favorable conditions for occupation by introduced species. This last change confirms something that is a worldwide trend, where agricultural activities are losing labor (either due to industrialization or preference for higher income/comfort activities) and farms or plots are being forgotten (Laso et al., 2019), causing the spread of introduced or invasive vegetation to be more feasible.

It is important to highlight that, during this time of analysis, certain farms have changed their agricultural activity to tourism-agriculture, especially on Santa Cruz Island, taking advantage of the giant tortoise migration zones. These farms do not appear at first glance in the categories analyzed in this work (see Table 5), but this could be an important factor for the recovery of native vegetation in agricultural areas between 2006 and 2019.

In addition, detecting changes in agricultural zones allows us to identify the socioeconomic or environmental factors that have led to the growth of invasive vegetation in an agricultural zone surrounded by a protected area, while the areas of native vegetation have diminished considerably.

References:

Buchhorn, M., Smets, B., Bertels, L., Roo, B. D., Lesiv, M., Tsendbazar, N.-E., Li, L., & Tarko, A. (2020). Copernicus Global Land Service: Land Cover 100m: version 3 Globe 2015-2019: Product User Manual (Dataset v3.0, doc issue 3.3). Zenodo. https://doi.org/10.5281/ZENODO.3938963

Laso, F. J., Benítez, F. L., Rivas-Torres, G., Sampedro, C., & Arce-Nazario, J. (2019). Land Cover Classification of Complex Agroecosystems in the Non-Protected Highlands of the Galapagos Islands. Remote Sensing, 12(1), 65. https://doi.org/10.3390/rs12010065

Rivas-Torres, G. F., Benítez, F. L., Rueda, D., Sevilla, C., & Mena, C. F. (2018). A methodology for mapping native and invasive vegetation coverage in archipelagos: An example from the Galápagos Islands. Progress in Physical Geography: Earth and Environment, 42(1), 83-111. https://doi.org/10.1177/0309133317752278

Xie, Y., Sha, Z., & Yu, M. (2008). Remote sensing imagery in vegetation mapping: A review. Journal of Plant Ecology, 1(1), 9-23. https://doi.org/10.1093/jpe/rtm005