Agriculture changes soil properties on the Galápagos Islands – two case studies

Soil Research ◽  
2019 ◽  
Vol 57 (3) ◽  
pp. 201 ◽  
Author(s):  
Martin H. Gerzabek ◽  
Armin Bajraktarevic ◽  
Katharina Keiblinger ◽  
Axel Mentler ◽  
Maria Rechberger ◽  
...  

The Galápagos Islands have faced a huge rise in the number of inhabitants and tourists over recent decades. As a consequence, natural forest vegetation has been converted to arable land to meet the increasing demand for agricultural produce. However, studies on soils and soil use change in the Galápagos Islands are scarce. In this study, we assessed the impacts of agricultural land-use on the islands of Santa Cruz and San Cristóbal. The site on Santa Cruz was called El Cascajo (EC, Leptosol, 5 years after conversion to intensive agriculture) and that on the oldest island of the Galápagos archipelago, San Cristóbal, Cerro Verde (CV, Ferralsol, 15 years after conversion). At both sites, we compared arable soils to soils under forests within the adjacent Galápagos National Park, which had formed on the same parent materials. Several soil properties showed a significant impact of the arable use. Soil organic carbon (Corg) stocks were relatively high at both sites (between 94 ± 28 and 142 ± 10 Mg ha–1). At CV, the stocks were 25% lower in arable plots compared with natural forest, but the observed decrease at EC was non-significant. Many other parameters like total nitrogen and several Mehlich-III extractable nutrients were closely correlated with the changes in Corg. Microbial biomass carbon (Cmic) and dissolved organic carbon were significantly lower in arable plots compared with forest at both sites. At EC, Cmic/Corg dropped by a factor of 1.9. Changes in pH and the use of agrochemicals, evidenced by pesticide residues detected in the soil, might be a possible explanation. Ammonium-N decreased and nitrate-N increased tremendously in the arable plots on both islands. Our research shows that present agricultural practices have potential for improvements towards a more sustainable agricultural use of soil resources on the Galápagos Islands.

2016 ◽  
Vol 13 (1) ◽  
pp. 59-68
Author(s):  
Roshan M. Bajracharya ◽  
Him Lal Shrestha ◽  
Ramesh Shakya ◽  
Bishal K. Sitaula

Land management regimes and forest types play an important role in the productivity and accumulation of terrestrial carbon pools. While it is commonly accepted that forests enhance carbon sequestration and conventional agriculture causes carbon depletion, the effects of agro-forestry are not well documented. This study investigated the carbon stocks in biomass and soil, along with the selected soil properties in agro-forestry plots compared to community forests (CF) and upland farms in Chitwan, Gorkha and Rasuwa districts of Central Nepal during the year 2012-2013. We determined the total above ground biomass carbon, soil organic carbon (SOC) stocks and soil properties (bulk density, organic carbon per cent, pH, total nitrogen (TN), available phosphorus (P), exchangeable potassium (K), and cation exchange capacity (CEC)) on samples taken from four replicates of 500 m2 plots each in community forests, agro-forestry systems and agricultural land. The soil was sampled in two increments at 0-15 cm and 15-30 cm depths and intact cores removed for bulk density and SOC determination, while loose samples were separately collected for the laboratory analysis of other soil properties. The mean SOC percent and corresponding soil carbon stocks to 30 cm depth were generally highest in CF (3.71 and 3.69 per cent, and 74.98 and 76.24 t ha-1, respectively), followed by leasehold forest (LHF) (2.26 and 1.13 per cent and 40.72 and 21.34 t ha-1, respectively) and least in the agricultural land (3.05 and 1.09 per cent, and 63.54 and 19.42 t ha-1, respectively). This trend was not, however, observed in Chitwan, where agriculture (AG) had the highest SOC content (1.98 per cent) and soil carbon stocks (42.5 t ha-1), followed by CF (1.8 per cent and 41.2 t ha-1) and leasehold forests (1.56 per cent and 35.3 t ha-1) although the differences were not statistically significant. Other soil properties were not significantly different among land use types with the exceptions of pH, total N, available P and CEC in the Chitwan plots. Typically, SOC and soil carbon stocks (to 30cm depth) were positively correlated with each other and with TN and CEC. The AGB-C was expectantly highest in Rasuwa district CF (ranging from 107.3 to 260.3 t ha-1) due to dense growth and cool climate, followed by Gorkha (3.1 to 118.4 t ha-1), and least in Chitwan (17.6 to 95.2 t ha-1). The highest C stocks for agro-forestry systems in both above ground and soil were observed in Rasuwa, followed by Chitwan district. Besides forests, agro-forestry systems also hold good potential to store and accumulate carbon, hence they have scope for contributing to climate change mitigation and adaptation with co-benefits.Journal of Forest and Livelihood 13(1) May, 2015, page: 56-68


1970 ◽  
Vol 19 (1) ◽  
pp. 63-72 ◽  
Author(s):  
Mohammad Zabed Hossain ◽  
Mihir Lal Saha ◽  
Chaman Binta Aziz ◽  
Sirajul Hoque

This study examined the effect of deforestation on the soil properties (physico-chemical and bacterial) of the Sal (Shorea robusta Roxb. Ex Gaertn.) forests in Bangladesh. Physico-chemical properties and the bacterial colony counts of soil were studied by comparing a natural Sal forest site with deforested and planted with Menjium site, deforested and planted with Mahogoni site, as well as deforested but not planted but covered with profuse growth of Axonopus compressus grass species site. Moisture content was significantly lower in the deforested and planted with Menjium site and deforested and planted with Mahogoni site than the natural forest site and the deforested but not planted site. Total organic carbon, total nitrogen and available nitrogen contents were significantly lower in the natural forest site. Significantly higher number of bacterial colony and higher organic carbon and moisture contents were found in the deforested but not planted site indicating that both organic carbon and moisture content were important for microbial growth. The present study clearly showed that deforestation significantly altered the soil physico-chemical and bacterial communities of the Sal forests. It was also revealed that plantation with different exotic plants were found to be different in influencing soil properties. Key words: Bacterial colony; Deforestation effects; Sal forest; Soil physico-chemical properties DOI: http://dx.doi.org/10.3329/dujbs.v19i1.8945 DUJBS 2010; 19(1): 63-72


2020 ◽  
Author(s):  
Aleksey Prays ◽  
Sonia Banze ◽  
Friedrich Jalowy ◽  
Klaus Kaiser ◽  
Robert Mikutta

<p>The decline in organic carbon (OC) stocks after conversion from grassland to cropland under conventional soil tillage practices was 24-32% for American prairie soils. The respective decreases in OC stocks ranged from 27% to more than 40% for steppe soils of the European part of Russia and was about 31% in semi-arid steppe soils of South Siberia. Here, we present results on the soil OC stocks in steppe soils of Northern Kazakhstan, which partly were converted to arable land over the last 60 to 90 years. We sampled soils by genetic horizons along a north-south transect, where precipitation increased towards north but negligible variation in temperature. Soil samples were analyzed for organic and inorganic carbon as well as bulk density.</p><p>Surprisingly, we found along the transect on average only 3.5% smaller OC stocks at 0-10 cm depth in arable than in natural soils. Even more astonishing, all arable soils tested had larger OC stocks in the layers beneath 10 cm depth than the natural steppe soils. On average, the OC stocks in 10-100 cm depth were 34% larger in soils under arable management than in natural steppe soils. We credit the enhanced deep soil accumulation of OC in arable soils of Northern Kazakhstan to colloidal translocation of OC-rich particles along vertical pores. The cause of the increased in colloidal transport under arable management is still under evaluation but appears connected to the clayey soil texture and the large abundance of expandable clay minerals. We conclude that despite of the intense land use and severe climatic conditions accumulation of subsoil carbon is possible even after many decades of cultivation history. Our findings stress the importance of considering whole soil profiles for analyzing the consequences of land use change on the net carbon balance of soils.</p>


Zootaxa ◽  
2017 ◽  
Vol 4244 (1) ◽  
pp. 39 ◽  
Author(s):  
TOBIAS PFINGSTL ◽  
HEINRICH SCHATZ

Two species of Fortuyniidae, found on the Galápagos Islands (Ecuador) are described and illustrated based on the adult and juvenile instars. Alismobates galapagoensis sp. nov. was found on six islands of the archipelago, in littoral and supralittoral habitats. It is morphologically similar to A. inexpectatus Pfingstl & Schuster, 2012 from Bermuda, but differs from that species and all other known congeners by a prominent cuticular ridge on epimeron III among other unique character combinations. Litoribates caelestis gen. and sp. nov. was found on the islands Santa Cruz and Bartolomé in the littoral zone under Maytenus and mangroves. Notes on distribution and ecological preferences of both species are included. 


2016 ◽  
Vol 62 (1) ◽  
pp. 10-18 ◽  
Author(s):  
Gabriela Barančíková ◽  
Jarmila Makovníková ◽  
Ján Halas

Abstract The direction of changes and conversion of soil organic carbon (SOC) is in most current ecosystems influenced by human activity. Soil Science and Conservation Research Institute is responsible for monitoring the agricultural soils in a five-year cycle. One part of the soil monitoring involves the determination of the soil organic carbon (SOC) storage. Further, we followed the conversion of arable land on grassland during more than 20 years of monitoring period at some locations where changes in land use occurred. Ten places on basic network and 2 places on key monitoring localities in which arable land have been converted into grassland were identified. About 50 percent of studied soils converted into permanent grassland were Cambisols. The other converted soil types were Luvic Stagnosol, Stagnic Regosol, Mollic Fluvisol, and Stagnic Luvisol. The results showed that after the third monitoring cycle (2002), increase of SOC was observed in all the localities, with the change in land use. Statistical parameter (t-test) confirmed significant differences between the set of average SOC values before and after the land use conversion. The chemical structure of humic acids (HA) isolated from arable soil and permanent grassland indicated increasing of aliphatic carbon content in grassland HA. More aromatic and stabile were HA isolated from arable soils.


1982 ◽  
Vol 60 (11) ◽  
pp. 2325-2333 ◽  
Author(s):  
Harry C. Evans ◽  
Robert A. Samson

Twenty-one species of entomogenous fungi, collected during a mycological survey of the island of Santa Cruz, are listed. Several coccid-associated species are described in detail, including Hirsutella sphaerospora sp. nov. on Eriococcid larvae; Hirsutella besseyi Fisher; and Torrubiella confragosa Mains, putative teleomorph of Verticillium lecanii (Zimm.) Viégas. In addition, Hirsutella darwinii on a spider host is described as new. The entomogenous mycoflora is similar to that of mainland Ecuador and the ecological implications are discussed particularly in relation to coccid populations.


Oryx ◽  
2007 ◽  
Vol 41 (3) ◽  
pp. 337-342 ◽  
Author(s):  
Cruz Márquez ◽  
David A. Wiedenfeld ◽  
Sandra Landázuri ◽  
Juan Chávez

AbstractAlthough the killing of giant tortoises in the Galapagos Islands has been prohibited since 1933, poaching of tortoises still occurs. Personnel of the Galapagos National Park Service and the Charles Darwin Research Station regularly survey populations of tortoises throughout the archipelago and report all dead tortoises found. For the 10-year period 1995–2004 the field personnel reported evidence of 190 giant tortoises killed, primarily on the southern portion of Isabela Island. For the first 6 years the number of tortoises found killed was <15 per year, but since 2001 the number killed has increased dramatically, with 49 tortoises poached in 2004. During the same 10 years the number of tortoises found dead from natural causes was 131. Many of these deaths can be attributed to events associated with the 1997–1998 El Niño or with outbreaks of disease on Santa Cruz Island in 1996 and 1999. The results indicate that poaching exceeds natural mortality, and is a significant factor affecting these long-lived and slow-reproducing animals. Environmental education efforts in the human population of southern Isabela appear to have had little effect. Because tortoise poaching takes place at a small number of sites, effective enforcement at those sites could reduce killing of tortoises.


1987 ◽  
Vol 119 (10) ◽  
pp. 881-885 ◽  
Author(s):  
Stewart B. Peck ◽  
William A. Shear

AbstractTheridion strepitus sp. nov. is described from lava tube caves from Isla Santa Cruz, Galápagos, Ecuador. It is the only species known in this worldwide genus that is eyeless and it is the only Galápagos species that has stridulatory picks on the male abdomen. The stridulatory apparatus demonstrates that the species is not a descendant from the other Theridion species known in the Galápagos, but is probably a relict of a lineage now extinct there in epigean habitats.


2019 ◽  
Vol 28 (1) ◽  
Author(s):  
Asta Kazlauskaite-Jadzevice ◽  
Liudmila Tripolskaja ◽  
Jonas Volungevicius ◽  
Eugenija Baksiene

Conversion of arable soils into other land uses can stabilize and increase accumulation of soil organic carbon (SOC) and in addition prevent deterioration in its properties. The data has shown changes in SOC sequestration in Ap horizon after arable land conversion (1995–2015) into managed grassland, abandoned and pine afforested. SOC in Arenosol topsoil was positively affected by long term fallow and conversion into grassland. Abandoned land and fertilised managed grassland accumulated significantly more SOC, 48% and 38% respectively compared with arable land. In unfertilised managed grassland SOC stocks decreased 2.3% during 21 years, but losses were lower than in fertilised arable land. Pine afforestation of loamy sand helped to reduce the intensity of SOM mineralization compared to arable land. The Ap horizon thickness in pine forest soil increased from 28 to 31 cm during 21 years period. However, SOC stock decreased by 1% due to reduction in carbon concentration.


2018 ◽  
Author(s):  
Diego Urquía ◽  
Bernardo Gutiérrez ◽  
Gabriela Pozo ◽  
María José Pozo ◽  
Analía Espín ◽  
...  

AbstractThe threat of invasive plant species in island populations prompts the need to better understand their population genetics and dynamics. In the Galapagos islands, this is exemplified by the introduced guava (Psidium guajava), considered one of the greatest threats to the local biodiversity due to its effective spread in the archipelago and its ability to outcompete endemic species. To better understand its history and genetics, we analyzed individuals from three inhabited islands in the Galapagos archipelago with 11 SSR markers. Our results reveal similar genetic diversity between islands, suggestive of gene flow between them. Populations appear to be distinct between the islands of San Cristobal and Isabela, with the population of Santa Cruz being composed as a mixture from both. Additional evidence for genetic bottlenecks and the inference of introduction events suggests an original introduction of the species in San Cristobal, from where it was later introduced to Isabela, and finally into Santa Cruz. Alternatively, an independent introduction event for Isabela is also possible. These results are contrasted with the historical record, providing a first overview of the history of P. guajava in the Galapagos islands and its current population dynamics.


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