Landscapes Forest and Global Change - ESA - Escola Superior ...

T. Höbinger et al. 2010. Impact of changing cultivation systems on the landscape structure of La Gamba
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To investigate the landscape pattern of the area and to uncover differences among the eight
landscape sections, we used the software FRAGSTATS 3.3 (McGarigal and Marks 1995) to
compute the landscape metrics Patch Density (PD), Patch Area (AREA), Fractal Dimension
(PAFRAC), Similarity Index (SIMI), Contagion Index (CONTAG) and Patch Richness Density
(PRD). The different patch types were characterized by the class level metrics Patch Area
(AREA), Fractal Dimension (PAFRAC), Euclidean Nearest Neighbor Distance (ENN) and
Edge Contrast (ECON). We applied the eight neighbor rule to guarantee that linear landscape
elements were identified as single patches (McGarigal and Marks 1995; Schindler et al. 2008).
As the landscape sections differed in size, we used only metrics standardized for area (e.g. Patch
Density instead of the absolute number of patches).
3 Results
Primary vegetation covered 29% of the study area, secondary vegetation 35%, anthropogenic
ecosystems 34% and water (rivers and ponds) 2% (see Figure 1). The most area consuming land
use types of the agricultural land mosaics were pastures (61 %) and oil palm plantations (31 %).
Other land use types (e.g. rice, cacao, bananas) covered only small areas (< 4%). All landscape
metrics clearly separated forests from rural sections. Generally, forest areas showed lower
values of PD, PAFRAC and PRD and higher values of SIMI and CONTAG compared to rural
areas (see Figure 2a). The differences between forests and rural areas were most evident for
traditional pasture-dominated landscapes, which typically consisted of many small patches of
different type and included many linear landscape elements such as live fences, streets or
drainage ditches. Rural sections including few linear landscape elements and big plantations or
undivided pastures were characterized by metric values more similar to those of forest sections.
Most rural sections of the study area had much higher fractal dimensions than forests. Patch
types including lines showed the smallest patch areas and the highest fractal dimensions (see
Figure 2b). Patches of primary forest had the biggest AREA and the lowest fractal dimensions.
Secondary forests were smaller and had higher fractal dimensions. All other natural patch types
such as riparian vegetation were of very small extent and more complex shaped. The
comparison of AREA and PD showed that oil palm plantations consisted of bigger, but less
numerous patches compared to pastures (see Figure 3). Primary forests had the biggest AREA,
but the lowest PD. Secondary forests were characterized by a much smaller AREA and clearly
higher PD. Riparian vegetation covered only smaller areas, but showed a relatively high PD.
Categories including linear landscape elements showed the smallest AREA and highest PD.
4 Discussion
For this study eight landscape metrics were chosen with regard to the suggestions of other
authors (Botequilha Leitão et al. 2006, Cushman et al. 2008, Schindler et al. 2008). The chosen
metrics clearly distinguished forest and rural sections. Forest sections consisted of relatively
few, big and compact shaped patches. Conversely, rural areas included more, smaller patches
and were more diverse. Fractal dimensions were considerable high for rural areas. This can be
caused by very high values of PAFRAC for the categories “settlement and road”, “drainage
ditch and river” and “live fence and timber plantation” that included linear elements. This
clearly demonstrates the importance of considering linear elements when assessing patch shape
complexity.
The inclusion of linear landscape elements also has a strong influence on the values of
landscape metrics and demands a careful interpretation of the results. For example, the results of
this study are not consistent with other studies that show that agriculture causes simple and
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.