GEO-ECOLOGY IN THE ANTHROPOCENE

Human activities have left signatures on the Earth for millennials, and these impacts are growing in the last decades. As a consequence, recent global change suggests that Earth may have entered a new human-dominated geological epoch. In the last years, much scientific debate has focused on the definition, stratigraphic signatures and timing of the Anthropocene. However, there is no a geological evidence, because these changes must be recorded in geologic stratigraphic material. Consequently, the definition of Anthropocene is controversial and the International Union of Geological Sciences (IUGS) has not provided a formal and official definition. Regardless of whether one is concerned with the proposed new Anthropogenic geologic epoch, it is evident that humans have significantly altered vegetation patterns and land cover (i.e. agriculture and subsequent land abandonment, conversion of forest to grasslands for pastoral use), water dynamics and distribution of fresh water (i.e. construction of dams), biogeochemical cycles (such as the carbon cycle), soil formation and soil erosion processes. Likewise, human have created and modified new landscapes (defined as anthropogenic

ABSTRACT.Human activities have left signatures on the Earth for millennials, and these impacts are growing in the last decades.As a consequence, recent global change suggests that Earth may have entered a new human-dominated geological epoch.In the last years, much scientific debate has focused on the definition, stratigraphic signatures and timing of the Anthropocene.However, there is no a geological evidence, because these changes must be recorded in geologic stratigraphic material.Consequently, the definition of Anthropocene is controversial and the International Union of Geological Sciences (IUGS) has not provided a formal and official definition.
Regardless of whether one is concerned with the proposed new Anthropogenic geologic epoch, it is evident that humans have significantly altered vegetation patterns and land cover (i.e.agriculture and subsequent land abandonment, conversion of forest to grasslands for pastoral use), water dynamics and distribution of fresh water (i.e.construction of dams), biogeochemical cycles (such as the carbon cycle), soil formation and soil erosion processes.Likewise, human have created and modified new landscapes (defined as anthropogenic landscapes).This special issue includes 11 contributions concerning studies about the definition and timing of the Anthropocene as a new geological era, and showing some of the most important human impacts on the Earth.

Introduction
The concept of Anthropocene is widely accepted by the scientific community, although the definition as a new era is still pending on a formal definition by the International Union of Geological Sciences (IUGS).Many authors have discussed the formalization of the Anthropocene over the last decade (i.e.Finney and Edward, 2006;Brown et al., 2013;Zalasiewicz et al., 2017).Two influential papers were published at the beginning of the 21 st century; Crutzen and Stoemer (2000) and Crutzen (2002) proposed that we live in the Anthropocene, a time, in which "humans have replaced nature as the dominant environmental force on Earth" proposing the term "Anthropocene".Nevertheless, other authors as Lewis and Macklin (2014) and McGregor and Houston (2018) only recognized the value of the Anthropocene as an informal and useful concept to stimulate political, social and public awareness 7 Cuadernos de Investigación Geográfica 45 (1), 2019, pp.5-18 of past and present human impacts, indicating that "a formal definition presents some disadvantages".Likewise, other authors suggest that there was a previous and significant influence of man on the Earth (with less relevance and local impacts) (Peña-Monné and Sampietro, 2019).It is called the Early Anthropogenic Era and some authors use the term PaleoAnthropocene (Foley et al., 2005;Ruddiman and Thomson, 2001).González-Álvarez (2019) indicated that anthropogenic impacts with different intensities on landscapes occur since prehistory.This author analyzes the long-term anthropization of alpine and subalpine areas in the northwestern area of the Iberian Peninsula and highlights the potential of landscape archaeology (cultural and environmental traits of landscapes) to analyze the Anthropocene.Nevertheless, according to the International Union of Geological Sciences (IUGS) (announcement made on July 2018) the Holocene has been subdivided in three ages, and we are now living in the "Meghalayan Age", but the Anthropocene remains undefined (Valladares et al., 2019).The Meghalayan Age defines the "late Holocene" and the present day, but makes no mention of the human impact on the environment.
Despite, the refusal of the IUGS to define the Anthropocene, a second issue that should be addressed, in the case of the official definition of a new era, is its beginning: When did the Anthropocene start?There is some controversy about the start of Anthropocene and a large number of possible dates, varying from early in the Holocene (Smith and Zeder, 2013), to the rise of Anthropocene methane from rice and livestock production (5000 years ago) (Ruddiman, 2013), to the Columbian Exchange (Crosby, 1972), the Industrial Revolution (Crutzen, 2002), to the World War II (Zalasiewicz et al., 2010), or to the radionuclide events in 1960.Most of the authors recognize that the second half of the 20 th century is a time of major anthropogenic global environmental changes.In that sense, Zalasiewicz et al. (2015Zalasiewicz et al. ( , 2017) ) proposed to use radionuclide deposits from atomic bombs as a potential Anthropocene Global Boundary Stratotype Sections and Points (GSSPs).Some geologists argued against its establishment as a formal period of geologic time (Ruddiman et al., 2015).Others, as the subdivision of Quaternary Stratigraphy of the Geological Society of London, (preliminary) dated in 16 July 1945 (the first atomic bomb) the beginning of the Anthropocene.To sum up, there is not a consensus yet about definition and time.
Even though the Anthropocene concept is still unapproved and controversial, in the last decade scientific research related to the Anthropocene is increasing.The term Anthropocene has already produced thousands of publications.At the end of October 2018, Scopus includes 2,850 sources containing the term Anthropocene (showing an exponential trend) with about 30,500 citations (h-index 71) (Fig. 1).
Moreover, scientific journals focusing on the topic have appeared in the last decades: e.g.The Anthropocene, The Anthropocene Review, Elementa-Science of the Anthropocene.Furthermore, the increasing scientific interest in the Anthropocene is reflected in the many reviews, special issues, meetings and monographs devoted to the Anthropocene research during the last two decades.For example, special issues were 8 Cuadernos de Investigación Geográfica 45 (1), 2019, pp. 5

Human impacts on the Earth
Human activities have left signatures on the Earth for millennia and the impacts are growing in the last decades (Tarolli, 2016).Human activity is now global and induced changes to the lithosphere, hydrosphere, cryosphere, pedosphere, biosphere and atmosphere.Here we list some of the impacts associated with a high variety of anthropogenic processes: (i) land use changes and vegetation distribution, (ii) changes in biodiversity (both on land and in the sea) as a result of habitat change/ Cuadernos de Investigación Geográfica 45 (1), 2019, pp.5-18 loss, predation and invasive species, (iii) changes in number, magnitude and intensity of fires, (iv) changes in the hydrological cycle, and (v) changes in soil dynamics, geomorphological and erosion processes and sediment transport dynamics.However, as stated by Lewis and Maslin (2015) these changes are spatially heterogeneous and diachronous, and probably this is one of the difficulties to officially define the Anthropocene era.
In the following paragraphs we will discuss some of the main anthropogenic changes mainly focused in 5 interrelated topics, integrating different temporal and spatial scales.
(i) Land use changes from natural vegetation to agricultural land (i.e.forest cutting and grassland conversion; deforestation and expansion of cropland) are the two largest spatial transformation of Earth's surface in human history.Montserrat and Gómez-García (2019-in this issue) discussed the variations on the forest and herbaceous domains in the landscape of the Iberian Peninsula in the last 20,000 years and questioned the importance of the effect of large herbivores (mega-herbivores) on vegetation patterns.They hypothesized that (i) mega-herbivores help structuring the landscape maintaining a high biodiversity, and (ii) the disappearance of these herbivores probably caused different ecological effects.Nevertheless, they did not find clear evidences to support or reject these hypotheses.On the other hand, González-Sampériz et al. (2019-current issue) indicated that the Anthropocene is the origin of current landscape transformation and presented evidences of deforestation processes in the subalpine belt in the Central Pyrenees with a high temporal and spatial variability, suggesting that during the Middle and Modern ages deforestation of the subalpine belt and the expansion of grasslands were common, coinciding with the increasing prevalence of transhumance (suggesting the onset of the Anthropocene).During the 17 th century the montane belt was also deforested as a consequence of demographic growth and the expansion of cultivation.These data, which were obtained in the Pyrenees are similar to the ones obtained in other Mediterranean mountain areas (i.e.Colombaroli et al., 2010;Roepke and Krause, 2013;García-Ruiz et al., 2016).These are only two examples of scientific discussions about anthropogenic land use change and vegetation pattern dynamics.During the 20 th century many land use changes occurred worldwide.Foley et al. (2005) suggested that land use change is one of the main factors involved in environmental change, nowadays being cropland abandonment (in mountain areas worldwide) and intensification of agriculture.Mediterranean mountain areas are a good example of cropland abandonment and revegetation processes (Molinillo et al., 1997), with consequences for quality and quantity of water resources, soil resources and other ecosystem functions and services (García-Ruiz and Lana-Renault, 2011).Furthermore, the intensification of agriculture, occurring in a high diversity of areas, also affects soil quality, geomorphological processes and the quality and quantity of water (i.e.Cerdà et al., 2012).
(ii) The anthropogenic transformation of ecosystems has serious impacts on biodiversity and has serious consequences for natural resources and land management (Hobbs et al., 2006).Dirzo et al. (2014) suggested that in the last 10 Cuadernos de Investigación Geográfica 45 (1), 2019, pp.5-18 centuries an "anthropogenic" biodiversity loss has been observed (referred to as the Anthropocene defaunation).For example: 322 species of terrestrial vertebrates have become extinct since 1,500 and a 25% decline in abundance.Similar values have been observed related to invertebrates.As well, deforestation and clear cutting activities negatively affected biodiversity.However, results of studies show a high variability.García et al. (2019-in this issue) analyzed land cover and landscape changes in the Ordesa and Monte Perdido National Park (OMPNP) and the effects of these changes on some endemic plants.This study concluded that: (i) the reduction of traditional land use is not threatening narrow-distributed plants, and it might even improve the situation of some plants and trees, and that (ii) landscape diversity is getting lower in the OMPNP (landscape simplification), leading to a plant diversity reduction.On the other hand, the role of biological invasions, that have recently challenged the traditional concept of biogeography in the Anthropocene, should also be highlighted.Gallardo and Vila (2019-in this issue) indicate that the geographical distribution of invasive species is dependent on human activities that promote their expansion.These authors highlight the need to apply modelling techniques in order to anticipate the potential distribution of invasive species, including climate but also human variables.The application of these models in the Iberian Peninsula indicates that minimum annual temperature was the most important variable, together with other human variables as distance to port or accessibility, underpinning the need to include anthropogenic predictors.
(iii) The first major human impact on the environment (although at local scale) was probable the use of fire, linked to land use changes and vegetation dynamics.Fire has been one of the main causes of disturbance of vegetation over time (i.e.Carracedo et al., 2018).Although fire is not anymore part of our traditional activities, its frequency and intensity are related to human activities (Leone et al., 2009;Rodrigues et al., 2016).What is clear is that wildfires are a common phenomenon worldwide, increasing in frequency and magnitude as a result of environmental and climatic changes, impacting natural resources, infrastructures and millions of people every year (Bowman et al., 2009).
(iv) The hydrological cycle is also increasingly affected by anthropogenic changes disturbing water dynamics, atmosphere, groundwater, lakes, rivers and oceans.These changes also modify some other Earth system components and cycles as sedimentation, nutrient and carbon balances, greenhouse emissions and aquatic biodiversity.Human activity can influence fluvial processes and water resources: indirectly through land use change or directly through river management.Some major changes are inter-basin transfers, transformations of the stream network (dams, reservoirs) (Fig. 2), deforestation and afforestation, changes in flood and drought cycles and changes in water quality regimes (i.e.Ehret et al., 2014;Savenije et al., 2014;Arthington et al., 2018).For examples, since medieval times, floodplains were transformed (Brown et al., 2018), introducing weir and mill-based systems, and during the last century the "industrialization of channels" occurred through hard-engineering.Sediment fluxes, floodplains and delta-plains are also affected by the sediment load reduction due to natural revegetation and afforestation of mountain abandoned areas (Syvitski and Kettner, 2011;Sanjuán et al., 2016).
Cuadernos de Investigación Geográfica 45 (1), 2019, pp.5-18 (v) Human activity also influences soil formation, soil erosion processes and sediment transport.An old example is the development of agriculture that generated an anthropogenic impact replacing natural vegetation and soils.Vanwalleghem et al. (2017) indicated that many of the soil features are of anthropogenic origin and concluded that there are strong links between historical land uses and soil management changes, soil erosion and agriculture sustainability.Recently, it has been demonstrated that organic farming agriculture can improve soil quality and ecosystems, and transform the soils into a sink of carbon as a way to reduce global warming (i.e.Skinner et al., 2014).Novara et al. (2019-in this issue) highlighted the use or organic farming with cover crops as a significant strategy for soil organic matter restoration and climate change mitigation in long-term cultivation areas.Likewise, the European Commission (see European Commission, 2006) identified several soil threats that are a consequence of human activities such as urbanization, intensive agriculture or deforestation (Ferreira et al., 2018).Halifa-Marín et al. (2019-in this issue) investigated the effects of anthropic changes (afforestation, check-dam building, land abandonment) on erosion processes, fluvial morphology, sediment sources, and soil carbon pools.The study, carried out in SE Spain, demonstrated that fluvial morphology has changed during the last decades increasing bank erosion and gully development, and affecting inner fluvial plains or alluvial fans, and their vegetation cover.All these changes affected also the soil organic 12 Cuadernos de Investigación Geográfica 45 (1), 2019, pp.5-18 carbon reservoir stored in the fluvial sediments and soils in the catchment.Many studies have also suggested that major land use changes in the Anthropocene has increased soil erosion rates worldwide (i.e.García-Ruiz et al., 2017) and that agricultural activities show the highest erosion rates (Montgomery, 2007) (see Fig. 3).In that sense, Pijl et al. (2019-in this issue) indicated that vineyard terraces showed the highest erosion rates of all Mediterranean landscape types.Their study demonstrated that vineyard mechanization shows higher erosion rates than non-mechanization fields, concluding that anthropic mechanization and related compaction and transformation of agricultural landscapes (terraces and infrastructures) increase soil loss risk in an already erosion prone landscape type.Finally, Poesen published in 2017 the review paper titled "Soil erosion in the Anthropocene: Research needs" concluding that soil erosion in the Anthropocene mainly occurs as a consequence of a combination of natural and human-induced soil erosion processes, although an increasing number of studies indicates that anthropogenic soil erosion processes have become dominant.Finally, human activities have modified more than half of the Earth's land area (forms and landscapes) (Hooke et al., 2012), the Mediterranean region probably being the best-known man-made landscape (García-Ruiz et al., 2017).To conclude, some anthropogenic landforms should be highlighted.One of the best examples of human Cuadernos de Investigación Geográfica 45 (1), 2019, pp.5-18 landscapes is the creation of agricultural terraces (Tarolli et al., 2014(Tarolli et al., , 2018)).Terracing of hillslopes and mountain sides for agricultural use is certainly one of the largest anthropogenic geomorphic processes in many mountain worldwide areas (Arnáez et al., 2017;Camera et al., 2018;Calsamiglia et al., 2018) (Fig. 4).Tarolli (2016) highlighted other examples as urban development, urban growth, embankments for railways, roads, canals, irrigation networks, open mining or below ground mining, land levelling and soil quarrying.In that sense, the paper written by Raczkowska (2019-in this issue) presents a good example of human impacts in the Tatra Mountains including mining and metallurgy, wood exploitation and oil extraction, as well as tourism activities.Nonetheless, at present, the human population becomes more urban and for this reason it is necessary to promote social involvement and proactive behavior towards nature and environment.Puigdefábregas and Pérez-García (2019-in this issue) discussed about the psychological processes involved in the interaction between human and their environment highlighting the need to recover empathy with the natural environment and to draw guidelines to improve people´s concern to care for the environment.

Final Remarks
The articles of this special issue cover a broad range of topics related to the Anthropocene and demonstrate that many research topics related to the Anthropocene are 14 Cuadernos de Investigación Geográfica 45 (1), 2019, pp.5-18 still open for debate.The discussion to establish a formal definition of the Anthropocene is still an open question that has not been yet solved by the working group of the ICS Subcomission on Quaternary Stratigraphy or by the International Union of Geological Sciences (IUGS).A second debate is about where to place the Anthropocene's chronological boundaries, although the mid-twentieth or late eighteenth centuries are the most commonly proposed dates.
Regardless of whether one is concerned with the proposed new Anthropogenic geologic epoch or the general concept of accelerating human influences on Earth, it is evident that human activity affects lithosphere, hydrosphere, cryosphere, pedosphere, biosphere and atmosphere, modifying all major biogeochemical cycles of the Earth and creating new landscapes and landforms.

Figure 2 .
Figure 2. Dam construction in the Central Pyrenees (Yesa reservoir).Dams and reservoirs have been constructed worldwide modifying the hydrological dynamics and transforming the stream network.Photo: Estela Nadal-Romero.

Figure 3 .
Figure 3. Soil erosion in young vineyard fields in La Rioja (Spain).Agricultural activities modified the soil and intensified soil erosion processes.Many authors suggest that soil erosion invineyards are the highest soil erosion rates worldwide.Photo: Luis Ortigosa.

Figure 4 .
Figure 4. Terraces around Bestué (Pyrenees, Spain).Terraced slopes were built to cultivate steep slopes in mountain areas, creating complex anthropogenic landscapes.Nowadays, most of the terraced systems are abandoned and revegetation processes occur.Photo: Estela Nadal-Romero.