Elsevier

Agriculture, Ecosystems & Environment

Volume 207, 1 September 2015, Pages 126-140
Agriculture, Ecosystems & Environment

Changes in landscape fire-hazard during the second half of the 20th century: Agriculture abandonment and the changing role of driving factors

https://doi.org/10.1016/j.agee.2015.04.011Get rights and content

Highlights

  • Agriculture abandonment played a major and changing role through time in increasing landscape fire-hazard, but this role changed through time.

  • Factors driving agricultural abandonment also changed through time.

  • Increases in landscape fire-hazard first occurred in remote areas, while more recently these took place in areas closer to urban settlements and towns.

  • Structural factors, like abundance of wildland area, low mechanization and aged farmers, always promoted abandonment and increased landscape fire-hazard.

Abstract

Past the middle of the 20th century, forest fires started to increase markedly in the Mediterranean countries of southern Europe. Hazardous land-use and land-cover (LULC) changes are considered major drivers of increased fire-hazard and fire risk. However, the contribution of various LULC changes to increased fire-hazard, as well as the role of environmental or socioeconomic factors in driving them, including its changing role over time, are poorly known. Understanding how changes in socio-economics in interaction with other factors modify landscape fire-hazard and risk is a major priority in fire-prone areas. Here we determined changes in fire-hazard through time, focusing on the contribution of agriculture abandonment to it, and on the changing role of its driving factors, in a large (56,000 km2) rural area in West-Central Spain. The study period covers from 1950s to 2000. LULC maps at different time steps (1950s, 1978, 1986 and 2000) were available, as well as environmental and socioeconomic information at various scales. We analyzed trends in LULC change, focusing on those altering fire-hazard, and used general linear models (GLM) with generalized linear mixed models (GLMM) to account for the effects of variables at different spatial scales in determining changes leading to shifts in fire-hazard. We found that the proportion of hazardous LULC types increased twofold (26–42%) from 1950s to 2000. Until 1986, agriculture abandonment was the dominant LULC change leading to increased fire-hazard. Post-1986, LULC changes were mainly driven by deforestation due to fires and densification caused by natural vegetation dynamics. Models showed that the first abandoned lands were driven by local environmental and socioeconomic constraints (small farms, in distant locations, in municipalities with low population), whereas later abandonments were driven by non-local ones (large farms, in more productive soils, closer to towns, populations with high unemployment, and higher employment in the services sector). Throughout the entire period, high proportion of wildland vegetation, low mechanization level, and large number of land-holders older than 55 years favored abandonment. This implies that as the population ages, larger, more accessible and productive areas are abandoned, fire-hazard will increase closer to human settlements, increasing the wild-land urban interface and fire risk.

Introduction

Fire activity has increased markedly during the second half of the last century in many parts of the world (FAO, 2001, Bowman et al., 2009). Fires are mainly driven by climate, fuels, availability of ignitions and, in some countries, firefighting capacity. While changes in climate (Westerling et al., 2006, Koutsias et al., 2012) and urban encroachment (Syphard et al., 2007, Syphard et al., 2012, Lampin-Maillet et al., 2011) have been proposed as major drivers of change in fire regime in some areas, changes in fuels and landscape-level fire-hazard might have also played a dominant role (Fernandez-Ales et al., 1992, Lepart and Debussche, 1992, Moreira et al., 2001, Kalabokidis et al., 2007, Carmel et al., 2009). In the case of Mediterranean countries of southern Europe, fires started to increase during the early 1970’s, but not so much in Northern Africa, indicating that socioeconomic factors were a major driver of change. More so, trends in fire activity in various countries was decoupled from changes in climate (San-Miguel-Ayanz et al., 2012), which further supports that socioeconomic changes, including changes in fuels and landscapes (Moreno et al., 1998, Rego, 1992), and also firefighting capacity in recent times (Brotons et al., 2013), were behind it, although additional effects of changes in climate cannot be excluded (Koutsias et al., 2013, Bedia et al., 2014). Recent studies indicate that trends in fire activity in some of the southern European countries have discontinuities that suggest a role for various factors, including land-use and land-cover (LULC) changes (Moreno et al., 2014).

In spite of LULC changes being widely recognized as driving factors of changes in fire, a quantification of this process, including the factors driving them, is yet poorly known. Moreover, considering the ever dynamic nature of the factors affecting fires, an assessment of the variable role that the different factors play through time in affecting landscape fire-hazard is lacking. Nowadays, the validity of the stationary role of environmental and socioeconomic factors in explaining LULC changes, mainly agriculture abandonment, has been questioned (Hatna and Bakker, 2011, Bakker and Veldkamp, 2012); suggesting that relationships between croplands and environmental conditions (Bakker and Veldkamp, 2012) as well as the role of socio-economic factors (Kuemmerle et al., 2008, Müller and Munroe, 2008, Baumann et al., 2011) have changed during last decades. This is important because socioeconomics and their effects on the landscape continue changing. Anticipating how these factors vary through time to affect landscape level fire-hazard is important to project future changes in fire regime, notably in a context of changing climate, land-use patterns and life styles.

Moreover, establishing cause–effect relationships between explanatory factors and LULC changes have also proven difficult (Irwin and Geoghegan, 2001, Nelson, 2001) mainly due to: (i) the patterns of LULC changes are spatially heterogeneous and location specific (vary spatially from one region to another, being anisotropic), (ii) LULC changes have a clear hierarchical spatial structure being scale-sensitive (i.e., the probability of LULC change depends on factors operating at different scales), and (iii) the role of driving factors are spatially heterogeneous (Koutsias et al., 2010) and temporally non-stationary (Bakker and Veldkamp, 2012). In spite of these limitations, the most common statistical approach for explaining LULC changes has been based on general linear model (GLM), such as logistic or multinomial regression, which assume independence of observations and relate LULC changes with explanatory factors acting at different scales obscuring patterns and processes across scales (e.g., Serneels and Lambin, 2001, Bakker et al., 2005, Améztegui et al., 2010). Multilevel modeling or general linear mixed models (GLMM) can include explicitly spatial structures as municipalities or other spatial divisions, thus allowing studying the effects of different spatial scales on a particular response variable, while providing a robust estimation of error (Snijders and Bosker, 1999, Diez-Roux, 2000). Apart from providing better statistical inference by modeling excess heterogeneity present in the data, GLMM address spatially misaligned explanatory variables and spatial structure in the ecological pattern. Recently, several works have used GLMMs to develop explanatory models on land-use patterns and changes around the world (Pan et al., 2004, Neumann et al., 2011, López-Carr et al., 2012). In the case of models of agriculture abandonment in Mediterranean rural areas the standard GLMs (logistic and/or multinomial) have been used (Van Doorn and Bakker, 2007, Millington et al., 2008); or only descriptive analyses about the relationship between agricultural abandonment and driving factors have been carried out (Moreira et al., 2001, Romero-Calcerrada and Perry, 2004). No study has approached agriculture abandonment in this region of the world based on robust approaches such as GLMMs. This is important for understanding causal factors in the modification of a landscape highly reactive to fire.

Here we studied that the main LULC changes occurred from 1950s to 2000 by three distinctive periods (1950s–1978; 1978–1986 and 1986–2000), in a large rural area in Central-Western Spain, focusing on changes leading to shifts in fire-hazard. For this purpose, we focused on the contribution of agriculture abandonment to such changes. Furthermore, we modeled agriculture abandonment using GLMMs based on environmental and socio-economic factors at each time-step to detect possible changes in drivers through time. Finally, we developed spatially-explicit maps of agriculture abandonment from GLMMs and tested their predictive capacity. The hypotheses to be tested were: (a) early abandonments were driven by local constraints due to low economic development, but late abandonments would be driven by non-local factors due to the effects of globalization process; consequently, (b) drivers of land abandonment leading to change in fire-hazard were not constant over time, varying in their relative role with time.

Section snippets

Study area

The study area is in Central-Western Spain; UTM coordinates 4369–4551 and 201–394 in the zone 30 North, covering 56,000–km2 (Fig. 1A). The area is characterized by the mountainous landscapes of Sierra de Gredos, running across the northern half of the area, flanked by relatively flat areas towards the North and South (Fig. 1B–C). The climate is mild and relatively wet in the flat areas and cold and very wet in upper mountains (Fig. 1D). Soils in the mountain areas are shallow, with high

General LULC trends

From 1950s to 2000 there was a continuous decrease of the non-hazardous LULC types (Fig. 3A). Croplands were the ones that lost a larger extension (−13%), followed, at a distance, by deciduous forests (−4%) and agroforestry areas (c.a. −2%) (Fig. 3A). In relation to non-hazardous LULC changes, agriculture conversion was maximum during the first period and decreased sharply in the latter period; afforestation with non-hazardous species and densification to deciduous forests was reduced (<5%) and

LULC and socio-economic changes from 1950s to 2000: implications for fire-hazard

We have shown that landscape fire-hazard continuously increased from 1950s to 2000 due to hazardous LULC changes and stability of hazardous LULCs, both of which tended to occupy greater extension over time. The most important hazardous LULC changes during the entire period were agriculture abandonment and deforestation, the former being dominant until 1986 (pre-1990 period) and the latter thereafter. The intense agriculture abandonment of marginal areas and the concentration of agriculture in

Conclusions

We have shown that the main LULC changes occurred from 1950s to 2000 globally increased fire-hazard in the study area. During the pre-1990 period, agriculture abandonment occurred in mosaic mountain rural areas, with high proportion of wildland vegetation, that were also affected by other hazardous changes (deforestation, afforestation and densification), increasing sharply the landscape fire-hazard. During the post-1990 period, deforestation by forest fires dominated over agriculture

Acknowledgements

The research leading to these results has received funding from the European Union’s Seventh Framework Programme (FP7/2007–2013), Project FUME, grant agreement no. 243888. We acknowledge the estimated help of Carmen Arroyo in digitizing old LULC maps and I.R. Urbieta for her fruitful comments.

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