Elsevier

Science of The Total Environment

Volume 661, 15 April 2019, Pages 504-513
Science of The Total Environment

Soil erosion on the “El Portalet” mountain trails in the Eastern Iberian Peninsula

https://doi.org/10.1016/j.scitotenv.2019.01.192Get rights and content

Highlights

  • Mountain trail erosion is a problem due to increased recreational activities.

  • An easy-to-apply and low-cost methodology was developed to survey mountain trail erosion.

  • Trail erosion ranged from 24.39 to 40.40 Mg ha−1 y−1 at “El Portalet” study site.

  • Measuring trail width and depth in the centre of the trail give 91% accuracy.

  • Erosion rates on trails are non-sustainable.

Abstract

Leisure activities in natural areas have experienced a large increase in popularity. In Mediterranean ecosystems, research on soil erosion in agriculture and forest fire affected land has been well developed but trail erosion has not been widely studied. In this work we evaluated two trails in the eastern Iberian Peninsula to assess soil erosion rates and provide new data. The study area is located in a semi-arid Mediterranean climate (around 400 mm y−1) and in limestone terrain with scarce soil development. The average erosion rates were 24.39 Mg ha−1 y−1 and 40.40 Mg ha−1 y−1 for the “Barranc de la Cova de la Hedra” and “Casa del Racó” study trails, respectively. These are non-sustainable rates due to the shallow soils and slow soil development in Mediterranean ecosystems. We found that the depth at the centre of the trail and the maximum depth measured could quickly and easily assess soil erosion rates in the mountain trails. Measuring the width and depth in the centre of the trail can assess 91% of the total erosion and reduces the time of the survey by 80%.

Introduction

Rangelands offer ecosystem services from which humankind derives benefits (Havstad et al., 2007; Yahdjian et al., 2015). They supply food, freshwater, wood and fibers, regulate climate and floods, support nutrient cycling and soil formation, and finally, provide cultural services like aesthetic, educational and recreational services (Braat and De Groot, 2012). One of these recreational services is the use of trails for sports, social interaction, and travel (Monz et al., 2010a). Trails can be understood as veins and arteries that allow humans to visit natural lands, but trails can also damage nature (Bryan, 1977; McQuaid-Cook, 1978; Whinam and Chilcott, 1999).

A continuous increase in mountain leisure activities such as hiking and more recently mountain biking has been recorded since the 1960s (Fish et al., 1981; Mihai et al., 2009). Bratton et al. (1979) showed a 63% increase in visitors to Great Smoky Mountains National Park, USA between 1963 and 1976. Goeft and Alder (2001) found that this type of tourism in the natural areas of eastern Australia increased by 25–30% yearly since 1997. Other examples showed >600,000 visitors annually in a national park in the Spanish Pyrenees (Bodoque et al., 2017), >500 people daily at peak visitation in Aconcagua Provincial Park (Barros et al., 2013) and 3.5 million tourists annually in Tatra National Park in Poland (Ćwiąkała et al., 2017). A growing pressure on nature exists in these areas due to the rise in recreational activities. Ng et al. (2018) found that recreation increased more than six-fold in just seven years in Hong Kong. This is a general trend in the mountains of developed regions (Chakraborty, 2018; Kuščer et al., 2017; Schamel and Job, 2017). Moreover, biking on mountain trails is more and more popular and little is known about the effects this new sport activity has on soil sustainability (Goeft and Alder, 2001; Lei, 2004; Törn et al., 2009; White et al., 2006).

The continuous and increasing use causes these trails to degrade and lose a non-renewable resource of high value, the soil. This is especially true if these trails are poorly designed (Marion and Leung, 2004; Tomczyk et al., 2016) or used in an inappropriate manner such as the use of mountain bikes in sensitive areas, large running or biking competition events, motorized vehicles, or general overuse by visitors. There are several impacts associated with recreational activities on trails such as soil compaction, soil erosion, loss of vegetation cover, damage to roots, introduction of exotic species, displacement of wildlife, and increase of water turbidity (Leung and Marion, 2000; Brevik and Fenton, 2012). Managers are under pressure to improve and extend the trail network and to try to concentrate user traffic. Likewise, the intensity of use often leads to hikers creating new trails (informal trails) as they search for easier and/or shorter sections (Newsome and Davies, 2009). On the other hand, and in the case of mountain bikers or off-road vehicles (ORV), users seek bigger drops, turns or the establishment of technical trails which, more often than not, cause even more damage to the traditional trails (Goeft and Alder, 2001).

Despite the effects of the recreational trails cited previously, there is very little information about soil erosion on mountain trails and most of the research has been concentrated in the USA (Deluca et al., 1998; Leung and Marion, 1999; Monz et al., 2010b; Pickering et al., 2010). Other regions in the world are much less researched even though they are also prone to soil degradation due to mountain trail activities.

Some information is available for tropical areas (Wallin and Harden, 1996). The Mediterranean mountains are affected by intense soil erosion due to rugged terrain, the climatic conditions (drought and intense thunderstorms), and the millennia old use of the mountains for crops, grazing and timber production (McNeill, 2003; Poesen and Hooke, 1997). Most of the research in Mediterranean environments has been devoted to the impact of grazing (Pulido, 2018), agriculture (Rodrigo-Comino et al., 2017, Rodrigo-Comino et al., 2018a) and forest fires (Lucas-Borja et al., 2016) on soil erosion. These key topics to understanding soil erosion processes and rates in the Mediterranean belt have been deeply researched, but the impact of trails has not been adequately investigated.

Only two countries in the Mediterranean have a research record on trails and soil erosion: Spain and Italy. The pioneering research has occurred in the central and northern parts of the Iberian Peninsula (Bodoque et al., 2005; Lopez-Vicente et al., 2013). Bodoque et al. (2005) found that soil loss ranged between 102 and 170 Mg ha−1 y−1 on trails in the Sierra de Guadarrama over a 10-year period, while Lopez-Vicente et al. (2013) found a current erosion rate of 6.1 Mg ha−1 y−1. Bodoque et al. (2017) determined soil erosion rates between 52.7 and 151.3 Mg ha−1 y−1 on trails in the Pyrenees, and López-Vicente and Navas (2009) reported that trails contributed 14% of the total erosion while occupying only 2% of the total area of the studied basin. Pelfini and Santilli (2006) measured soil erosion rates of up to 7.1 mm y−1 in the alpine trails of Italy due to trekking, and another study in the Dolomites (Tarolli et al., 2013) found that recreational trail use caused soil erosion but did not give numerical values.

Most of the research about soil erosion on Mediterranean mountain trails has been focused in Central Spain, the Pyrenees and the Alps, where rainfall is high (1000 mm y−1) due to the altitude and vegetation cover is dense. Meanwhile the semiarid Mediterranean climatic zone is not represented in this assessment. In fact, current research only focuses on mountainous terrains where vegetation is very dense due to natural forest recovery and afforestation applied by national and regional administrations. In general, the research about soil erosion on Mediterranean trails is limited and does not exist in the Mediterranean semiarid areas at all. Moreover, to enable to assess trail erosion over larger areas, we need to develop easy-to-apply and low-cost assessment methodology to obtain data for large areas of the world. Therefore, the aims of this work were: i) to assess the soil erosion rates along a recreational trail in Eastern Mediterranean Mountain terrains; and ii) update an easy-to-apply and low-cost methodology to assess long-term soil erosion rates on mountain trails.

Section snippets

Study area

The study area was selected in a representative range in the eastern Iberian Peninsula (Fig. 1). The Portalet trail is a 20-year old trail located in the municipality of Canals, in the Serra Grossa range, and it is used by hikers and mountain bikers. Within the study area we selected two study trail sections representing different environmental conditions based on the aspect and slope, and then, vegetation cover and soil characteristics. Study site A (called “Casa del Racó”) trail is located on

Results

Table 1 shows the general characteristics of the two study sites. The age of both trails was 20 years and the trail A study site was 10 m longer than B but narrower (0.67 m vs. 0.81 m respectively). Trail A covered a larger area (23.45 m2 vs. 20.25 m2). With the Mann-Whitney test we did not find clear differences between the two trails in rock fragment cover but did regarding slope angle (p < 0.01) with a results in average slope angles of 10.93° for A and 2.04° for B.

Trail A had a higher

Discussion

We measured the rates of soil erosion on two trails in a semiarid Mediterranean mountainous terrain. Initially we reviewed the literature for methodologies to assess trail erosion, we found photogrammetry and GIS methodologies (Warner and Kværner, 1998; Tomczyk, 2011; Tomczyk and Ewertowski, 2013), and field techniques based on cross sectional surveys (Garland, 1990; Sack and Da Luz, 2003; Cao et al., 2014). We developed an easy to apply and low-cost methodology that favours an efficient survey

Conclusions

The El Portalet trail study area in Eastern Spain is representative of Mediterranean trails that are affected by increasing traffic from hikers, runners and bikers. We assessed the state of the trail at two sites and found that the average lowering after 20 years ranged between 4.33 and 6.91 cm, which provides erosion rates ranging from 24.39 to 40.40 Mg ha−1 y−1. These soil erosion rates are much higher than sustainable levels found in the literature. In addition, we found a clear relationship

Acknowledgements

This research is one of the results of the RECARE-FP7 project (ENV.2013.6.2-4, http://recare-project.eu). Professor Eric C Brevik from Dickinson University improved the draft manuscript with key comments and suggestions. Mauro Ponsoda, Antonio Minervino, Antonio Giménez Morera, Farhat Bayat and Kıvanç Yuksul contributed to the field and laboratory work. Saskia Keesstra contributed to the writing of the draft manuscript and improved the last version.

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