Research articleEffects of vegetation management on plant diversity in traditional irrigation systems
Introduction
Agriculture is undoubtedly the main transforming agent of the landscape (Medley et al., 1995). Over the past 50 years, patterns of agricultural expansion have led to the loss of biological diversity and ecosystem services, undermining the long-term sustainability of agricultural production. Therefore, the conservation of biodiversity should become a fundamental part of agricultural landscapes to reach global conservation goals (SCDB, 2008; Martin et al., 2014). A case in point involves the traditional vegas of Spain, historical agricultural areas based on smallholdings irrigated through traditional channels (acequias), which inoculate biodiversity and its services inside the agroecosystem (vega), making agricultural production more sustainable and compatible with wildlife conservation. These types of agricultural systems might be considered High Nature Value Farming (EEA, 2004), which constitute the equivalent of hotspots of biological biodiversity in rural areas, and it is often characteristic of areas dominated by extensive agriculture, as in the case of traditional vegas, with polyculture where different species grow together in small properties (EEA, 2004).
The irrigation is vital in many places to ensure agricultural yield and, in fact, agriculture absorbs 92% of water resources consumed by mankind (Hoekstra and Mekonnen, 2012). Among the many types of irrigation systems, the traditional acequias are common-property irrigation ditches with the function to carry water from the source (e.g. mountains) to the agriculture areas (floodplains or valleys), simply by gravity. They are usually constituted by a principal channel (acequia principal or canal principal), secondary branches (ramales), and tertiary branches (hijuelas), arranged like a net. They are spatially organized separating farm properties and have associated right of way, usually 1 m at both sides from the center of the channel, which cannot be invaded, plowed, built, fenced, etc., for private use. Acequia, a word recognized by the Royal Academy of Spanish Language, derives from the Arabic (as-sāqiya) and means water-bearer, irrigation canal, or conduit. Spanish settlers inherited this Roman and mainly Islamic irrigation system in southern Spain, coming from North Africa and Middle East, and later brought that technology to the Southwest of the United Stated as well as some semidry areas in Meso- and South America (Butzer et al., 2010; López, 1995; Mata and Fernández Muñoz, 2010; Raheem et al., 2015).
Acequias promote the development of riparian vegetation, which depends on the ecological conditions where the irrigation system is located and the disturbances caused by human management (Espín et al., 2010;Plaza and Guzmán, 2010). Moreover, they provide a series of ecosystem services frequently difficult to quantify (Fleming et al., 2014), the main ones being: landscape creation, food security through extensive agriculture, involvement in nutrient cycles, soil formation, and greater temporal extension of the irrigation season (Rivera, 2011). They also have hydrological, riparian, and agroecosystemic attributes similar to those provided by rivers (Fernald et al., 2007). In addition, they help prevent damage such as flooding, regulate return flows to rivers, and even recharge aquifers (Espín et al., 2010). Furthermore, they act as ecological corridors and provide a suitable place for nesting and breeding for bird species (Peña, 1999; López-Pomares et al., 2015). They are also important in preserving the traditional knowledge about agricultural practices and agrobiodiversity in the vegas (Chan et al., 2012). Therefore, acequias are not simple ditches that carry water but have many more implications, being currently a key element for biodiversity conservation (wild and cultivated) in these agroecosystems. Despite its importance, this agroecosystems are in danger of disappearing because of elements such as wastewater discharges, modernization of irrigation systems, waterproofing, and the loss of traditional vegas by urbanization. To gain the multiple benefits from this irrigation system, farmers must keep them free of excessive vegetation, which would impede the water flow (Ayllón Valle et al., 2010). For this, farmers traditionally use two methods:
- 1
Clearing banks (C): This treatment requires labor, more commonly practiced in former times when the debris cleared could be used to feed livestock. Traditionally, sickles were used, now replaced by weeding machines.
- 2
Burning banks (B):This is the predominant treatment in most of the vegas in SE Spain in order to save time and effort. Traditionally this is done in winter to minimize the risk of the firesspreading.
In the present work, we hypothesize that traditional management of vegetation in the acequias (clearing and burning), both considered a disturbance, increase floristic biodiversity. We base our hypothesis on Connell's intermediate perturbation theory (Connell, 1978), which states that intermediate levels of disturbance result in the highest biodiversity values. Biodiversity analyses in traditional acequias have been the target of several studies. However, these studies have been based almost exclusively on the biological (less), economic, historical, or social importance of the system, whereas the management perspective has not yet been analyzed. Therefore, our objective is to show the effects of traditional management of vegetation in the acequias on plant diversity and soil.
Section snippets
Study area
This study was conducted in the south of the vega of Granada (Spain). The vega (as called by local population) is located in the heart of the Granada province (SE Iberian Peninsula), occupying the depression formed by the river Genil and its tributaries, and bordered by mountains ranges belonging to the Betic systems (García Leal, 2014). This traditional farmland is partly defined by the presence of thousands of kilometers of acequias which bring water mostly from Sierra Nevada mountain to the
Soil results
The soil analyzed showed significant differences in two out of 11variables studied. These variables were pH and CaCO3 equivalent. Both variables increased significantly in the burning treatment (B) with respect to control (0). In addition, differences were significantly higher in the clearing treatment (C) than in control (0) only for pH (Fig. 2). For all other response variables, no significant differences were detected with the application of any kind of traditional management (Table 1).
Plant-diversity results
In
Discussion
The soil variables remained quiet stable after treatments. We found significant differences only in pH and CaCO3 equivalent. The weak rise in pH is commonly found in the literature for burnt treatments (Úbeda, 2001). This higher pH is due to the increase of hydroxyl groups in the clays and the formation of oxides derived from the carbonate dissociation (Giovannini, 1994); however, this increase proved minimum, although still significant, due to the low intensity of the burning (Díaz-Fierros et
Conclusions
Both traditional management approaches (burning and clearing) increase floristic biodiversity, this effect being much more evident in the burnt treatment. The changes detected in biodiversity community are intrinsic to the community itself, due to reduced competition levels. It also shows that the treatments have little or no influence on the successional dynamics, which depend on a wide variety of factors.
The burnt treatment promotes the establishment of new species, as well as increases in
Acknowledgments
We thank to the landowner Fernando Reyes Jorquera, for the access to the Acequia and the application of the traditional treatments on vegetation. Also, we thank to David Nesbitt for the English revision and Javier Ruiz for his support during fieldwork.
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