Landscape Dynamics as a Function of Land Use

Pressure and Land Use/Cover Change in the Izta-

Popo Park, Mexico*

Lenom Cajuste Jr., Ángel Bustamante, Manuel J.

Mora, Enrique Ojeda, and Edgar V. Gutiérrez

Colegio de Postgraduados,

Montecillos, México, 56230, MEXICO

lenomcb1@colpos.mx

Valentino Sorani

Dept. Ecología Evolutiva

Universidad Autónoma Estado de Morelos

Cuernavaca, Morelos, 62209, MEXICO

vsorani@yahoo.com.mx

Abstract— The Izta-Popo national park serves as an air and

water purifying-recharging system for several central valleys,

including the Valley of Mexico. Its ecosystem services have been

under high land use pressure because of its vicinity to the Capital

city and main cities surrounding it. The effects of such pressure

however, are still being under study, since the complexity of land

use patterns and ecosystem functions supported by the vast

network of rural and periurban communities varies within short

term periods and small geographical extents. The objective of

this study was to determine the changes in landscape patterns in

the area using landscape analysis methods, within a period of 40

years (1973-2013). Five Landsat subset images (three from the

NALC dataset and two LandsSat ETM+ from the 2000’s) were

analyzed through land cover identification and land change

detection. Results showed an increase in land cover classes and a

general reduction of forestland mass in the study area. As a

result, water retention and infiltration to the aquifers in the area

have sensitively decreased through time. The intricate patterns in

land cover elucidate complex human-environment interactions

and intense land use dynamics, both in the national park as well

in the physical geography of the surrounding communities.

Keywords—landscape dynamics, land use/cover change, land

use pressure, GIS, Mexico

I. INTRODUCTION

The Izta-Popo ecosystem is a protected national park that comprises 13 municipalities, covering an extension of 90,284 ha, according to CONANP [1, 2]. The park was established in 1935 with an initial surface of 39,819 ha that contained a portion of forestland; its main purpose was to preserve the area as a recharge zone for water resources to the Capital City aquifers. Nowadays, the park bears three altitudinal sub-ecosystems: an alpine grassland, a pine forest, and a fir-pine forestland. Within these sub-ecosystems 18 endemic species occur with certain risk of danger, along with another 17 non-endemic species sharing the same dangerous condition [3]. In addition, its biodiversity count is greater than 470 registered species [3, 4], which among other characteristics granted the park the category of Biosphere Reserve in 2010 by UNESCO.

The Izta-Popo Park provides a variety of environmental services (air-purification, water filtration and provision, food and wood supply, inter-biome corridor, and scenic views, among others) which are consumed by locals and inhabitants living in main urban centers. Because of the increasing population living in the Valley of Mexico and other surrounding valleys [5, 6], and their growing demands for water, food, and related goods, these services face considerable degradation risk, as pressure for intense land use increases.

Despite the amount of studies carried out by several researches in the area, the dynamics of land use and land patterns, as the ecological functions in the park are still not well understood [7, 8], prompting to shift the methods used so far, in new ways to analyze these issues with the aid of remote sensing and landscape dynamics techniques, being such, the goals of this research.

II. MATERIALS AND METHODS

A. Area of Study

The study area is located about 60 Km southeast of Mexico City (Fig. 1). Its altitudinal range goes from 2850 to 5400 m above sea level. Climate varies from a temperate weather with cumulative yearly rainfall of 700 mm, to cold weather with summer rains and fog amounting 1200 mm in a year [3]. As mentioned in the previous section, vegetation within the park consists of grasslands and forestlands, with bare soil and ice in the vicinity of craters and peaks. Soils are of volcanic origin, with varying textures and depth, rich in organic matter and amorphous silica. Timber and mushroom harvesting are the main activities, followed by agriculture.

B. Procedure

Five subsets of Landsat images were obtained to study the changes in land cover during the last 40 years. Three subsets belong to the NALC triplicates (Landsat MSS), covering the last three decades of the previous century (1970, 1980, and 1990); whereas the fourth and fifth subsets belong to a 2000

Partial funds provided by CONACyT project grant #38294, and the Research Initiative #9 “Applied Geomatics” at COLPOS.

Fig. 1. Location of the study area.

and a 2010 (Landsat ETM) scenes, respectively. Land cover classes were identified using an object-oriented classification technique, based on segmentation routines using support vector machines (SVM) [9-11]. Furthermore, patch dynamics and landscape analysis were carried out using spatial statistical metrics, such as compactness and fragmentation indices [12-15]. In addition, correlation-regression analysis was performed to identify trends within space and time between the different landscape parameters.

III. RESULTS AND DISCUSSION

A. Land Cover Classification

In terms of land cover classes, the classification process revealed an increase in number of classes through time, as seen in Fig. 2. In addition, the land cover classification detected a growing number of patches as the average size of patches decreased continually along the decades. Regarding forestland mass, this cover also decreased in extension throughout time at an average rate close to 5% per decade (Fig 3.).

Fig. 2. Number of land cover classes detected through time.

Spatial statistics confirmed a decrease in compactness and an increase in fragmentation indices (Fig. 4). Although there has been in general more land cover classes with time, these corresponded in particular, to fewer land major cover classes,

Fig. 3. Decrease of forestland extension through time.

suggesting the people in communities surrounding the park is trying to diversify their portfolio of rural activities, in order to maintain and preserve their income level. This seems evident when taking into account the “ecosystem services payment” and the “carbon sequestration payment” programs the Federal Government has issued during the last ten years [8]. These programs have reduced the impact of logging and clear-cutting practices, which were carried out for agricultural expansion purposes within the park.

B. Landscape Dynamics and Spatial Metrics

The fact of a decrement in compactness with an increment in fragmentation within the patches of the park landscape, as observed in Fig. 4, confirms the theory of a higher magnitude of land use pressure and therefore, a higher intensity of land use occurring within the Izta-Popo Park. This finding explains well the increasing number of patches, from 227 clusters identified in the 1970 scene, to 813 units detected in the 2010 scene. As a result, the average size of patches decreased from 3,310 ha in the 70’s, to 343 ha during the last decade.

When observing the distribution of patches among the main land cover classes (Table 1), the increasing number of forest patches differs from the increasing numbers of other main land cover classes. While the number of forest patches was slightly double-folded in forty years, the numbers of agricultural patches was multiplied twenty times, and other main land cover classes increased 60 to 70 times, within the same period of time. This finding shows again the positive effects of federal programs to protect in to some extent the forestland in the park.

Fig. 4. Distribution of compactness and fragmentation indices through time.

TABLE I. DISTRIBUTION OF PATCHES AMONG MAIN LAND COVER

CLASSES AND THROUGH TIME.

Land cover

class

Year

1970 1980 1990 2000 2010

forest 218 349 394 394 463

grassland 7 19 48 96 154

agriculture 2 4 14 56 123

other 0 3 24 17 73

C. Correlation – Regression Analysiis

Significant correlation coefficients were obtained between land cover variables and landscape metrics. High correlations were found between land cover classes with forestland extension (-0.9498) and number of total patches (0.9474); whereas a low correlation was found between the number of land cover classes and the number of forest patches (0.4358). These pieces of information confirm what was already mentioned in the previous section: the increase in land use pressure caused an increase in land cover classes, which is reflected in the number of total patches, on one hand; and on the other hand, the federal programs helped to reduce increased fragmentation within forestland patches.

In addition, with data about poverty indices collected from the communities surrounding the park during the last two decades, a regression analysis prove significant the fact that poverty was alleviated with the increase in land cover classes (r²= 0.8973) and at the expense of forestland extension (r²=0.6789). Therefore, we assume land use pressure has significant effects on land cover and landscape patterns within the park; although no significant relationships were detected between land use pressure and landscape metrics, such as compactness ratio or fragmentation index for individual land cover types.

The pressure for land use however is having its effects in agricultural areas surrounding the park, The major turnovers regarding land use and cover have been detected in these rural fields, as a continuing in-migration from marginal farmlands in neighboring states have sparked growth of population in the valleys of Mexico and Puebla. In addition, farmers from agricultural lands in the area have adopted new strategies to increase grain and dairy production, intensifying use of water, fertilizers and other inputs. Therefore, more attention should be paid in terms of protecting the park resources, in order to maintain sustainable levels of land use.

IV. CONCLUSIONS

Within the last 40 years of existence, the number of land cover classes has increased in the Izta-Popo National Park and surrounding areas, increasing the fragmentation of landscape patches. The Federal Government has issued programs however, to reduce the impact of rural activities on the park resources, including water and forestlands extractions. More analysis is needed to understand better the human-environment

interactions within the national park and its surrounding, to ensure long term sustainable land use.

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