Islands are particularly vulnerable to the effects of land cover change due to their limited size and remoteness. This study analyzes vegetation cover change in the agricultural area of Santa Cruz (Galapagos Archipelago) between 1961 and 2018. To reconstruct multitemporal land cover change from existing land cover products, a multisource data integration procedure was followed to reduce imprecision and inconsistencies that may result from the comparison of heterogeneous datasets. The conversion of native forests and grasslands into agricultural land was the principal land cover change in the non-protected area. In 1961, about 94% of the non-protected area was still covered by native vegetation, whereas this had decreased to only 7% in 2018. Most of the agricultural expansion took place in the 1960s and 1970s, and it created an anthropogenic landscape where 67% of the area is covered by agricultural land and 26% by invasive species. Early clearance of native vegetation took place in the more accessible—less rugged—areas with deeper-than-average and well-drained soils. The first wave of settlement consisted of large and isolated farmsteads, with 19% of the farms being larger than 100 ha and specializing in diary and meat production. Over the period of 1961–1987, the number of farms doubled from less than 100 to more than 200, while the average farm size decreased from 90 to 60 ha/farmstead. Due to labor constraints in the agricultural sector, these farms opted for less labor-intensive activities such as livestock farming. New farms (popping up in the 1990s and 2000s) are generally small in size, with <5 ha per farmstead, and settled in areas with less favorable biophysical conditions and lower accessibility to markets. From the 1990s onwards, the surge of alternative income opportunities in the tourism and travel-related sector reduced pressure on the natural resources in the non-protected area.
<p>Understanding the complex interactions between climate, vegetation and soils is important for the sustainable management of soil ecosystems in the context of climate and land use change. Few benchmark data exist on soil-landscape and vegetation interactions, as most soil ecosystems have a legacy of past land use and management.</p> <p>By working in the Galapagos Islands, a UNESCO World Heritage Site, we have the opportunity to better constrain the coevolution of soils and vegetation over millennial timescales for pristine soil ecosystems. Five monitoring sites are located on the Pacific Island of Santa Cruz, and they cover a ~10 km long NW-SE stretch. Along this gradient with a 10-fold increase in mean annual precipitation, the climate effects on the coevolution of soils and vegetation were quantified. Soil weathering extent was assessed through geochemical proxies, and these data were then related to time-series of precipitation, air and soil temperature, and humidity to explore the relationships between soil and vegetation development, and climate. Then, by contrasting the data from five pristine soil ecosystems with data from agricultural soils, new information was obtained on the anthropogenic effects on soil ecosystems.</p> <p>Soil weathering indices and elemental mass balances were used as a measure of soil development and were derived from the soil's physical and chemical properties measured at soil profiles. For the pristine sites, there is a nonlinear relationship between the degree of soil and vegetation development and (hydro)climatic data. Forest conversion into agricultural land leads to measurable effects on soil ecosystem services and functions.</p>
<p>Understanding the spatial variation of rock-derived weathering products across heterogeneous landscapes is important to constrain ecosystem processes. Few quantitative data exist on soil-landscape development in pristine volcanic ecosystems, as most of these ecosystems are prone to intensive land use and management. By working in the Galapagos Islands, a UNESCO World Heritage Site, we aim to constrain physical erosion and weathering over millennial timescales from empirical data in pristine ecosystems. Our monitoring sites on the island of Santa Cruz cover a ~10 km long NW-SE stretch with a 10-fold increase in precipitation rates and associated changes in vegetation cover. In five ecosystems, we monitor two sites: one that is developed on basaltic lava flows and a second one on basaltic scoriae. By controlling for the age and composition of the basaltic parent material, we focused on the unique natural soil landscapes that developed along the sharp hydroclimatic gradient. We determined weathering extent, and rates of physical erosion based on geochemical proxies and meteoric <sup>10</sup>Be isotopes (<sup>10</sup>Be<sub>m</sub>). These data were then related to time-series of precipitation, air, and soil temperature to explore the relationship between soil development, climate, and parent material. Along the hydroclimatic gradient, the empirical data on chemical weathering and physical erosion show a nonlinear relationship with the precipitation rate.</p>
<p>In the Galapagos archipelago, about 96% of the land area has been declared a Protected National Park in 1959. Of the four inhabited islands, Santa Cruz is the most populated, with 15,393 inhabitants in 2010. The non-protected area in Santa Cruz corresponds to the south-central part of the island and the bay area around Puerto Ayora. Over the period 1961-2018, the agricultural land expanded from 6% to 67% of the non-protected land area. In a field-based study around the settlement of Santa Rosa, we monitored hydrometeorological and soil physical and hydrological properties over the period July 2019-December 2021. Six sites were monitored including two replicates per land cover type: (i) native <em>Miconia</em> forest, (ii) agricultural land, and (iii) abandoned farmland with invasive species. The spatiotemporal distribution of rainfall and air temperature over the sites is recorded via one weather station, four rain gauges, air temperature and relative humidity sensors; and the atmospheric input and rainfall were sampled at biweekly basis. After pedological characterization of the six profiles, soil and rock samples were taken per horizon for analysis of elemental chemistry, mineralogy, texture, C/N ratio, and organic matter content. Upslope of the soil profiles, TDR probes measured volumetric soil moisture content, soil electrical conductivity and temperature; and soil water samples were taken using suction lysimeters.&#160;</p><p>&#160;</p><p>Over the monitoring period, the highest rainfall amounts were measured in January (226 to 265 mm), and the lowest in May (20 to 25 mm). Most of the year, the relative air humidity is close to 100% with values dropping to 60% in March. The lowest air temperatures (15 &#176;C) are measured in August, and the highest (29 &#176;C) in March and April. Solar radiation strongly fluctuates from 80 W/m<sup>2</sup> during the rainiest month to 220 W/m<sup>2</sup> in March. Deeply weathered soils are developed on basaltic parent material and have a depth up to 50 cm. Soils are loose and lack macro-structure. The dry bulk density varies as a function of land cover, with the highest bulk densities of 0.9 g.cm<sup>-</sup>&#179; in abandoned farmlands, intermediate values of 0.7 g.cm<sup>-</sup>&#179; in agricultural land and lowest values of 0.5 g.cm<sup>-</sup>&#179; in forests. Although the air temperature is similar amongst all six sites, there are clear differences in the soil temperature between agricultural and abandoned farmland, and forest sites. Our data show that soil moisture is systematically higher in the two forest sites compared to the agricultural and abandoned sites. &#160;</p><p>&#160;</p><p>As such, the field data provide evidence of the impact of forest clearing on soil physical properties and soil-water balance.</p><p>&#160;</p><p>Keywords</p><p>Soil weathering, soil water balance, Galapagos, basaltic soils, Agricultural expansion</p><p>&#160;</p>
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