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

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J.L. Hernández-Stefanoni et al. 2010. Effects of l<strong>and</strong>scape structure <strong>and</strong> st<strong>and</strong> age on species richness <strong>and</strong> biomass<br />

642<br />

configuration affects the structure <strong>and</strong> composition of plant communities depends on processes<br />

occurring at different spatial scales (Cushman <strong>and</strong> McGarigal, 2004). In order to assess the<br />

relationship between community attributes <strong>and</strong> l<strong>and</strong>scape structure across different scales it is<br />

necessary to consider scale-dependent ecological processes (Bellier et al, 2007). Thus, the goal<br />

of this study was to relate plant species density <strong>and</strong> biomass with l<strong>and</strong>scape structure, st<strong>and</strong> age<br />

<strong>and</strong> spatial variation of ecological structure at different spatial scales.<br />

2. Methods<br />

2.1 Study Area<br />

The study was conducted in a l<strong>and</strong>scape mosaic of 22 x 16 km 2 in Yucatán, México.<br />

The climate is tropical, warm, with summer rain <strong>and</strong> a dry season from November to April.<br />

Mean annual temperature is ca 26ºC, <strong>and</strong> mean annual precipitation between 1000 <strong>and</strong> 1200<br />

mm, concentrated between June <strong>and</strong> October. The l<strong>and</strong>scape consists of Cenozoic limestone<br />

hills with moderate slope (10-25°) alternating with flat areas, <strong>and</strong> the elevation ranges from 60<br />

to 160 m.a.s.l (Flores <strong>and</strong> Espejel 1994). The l<strong>and</strong>scape is dominated by seasonally dry<br />

semideciduous tropical forests of different ages of ab<strong>and</strong>onment after traditional slash-<strong>and</strong>-burn<br />

agriculture (Figure 1).<br />

2.2 Remotely sensed data <strong>and</strong> imagery processing<br />

A Spot 5 satellite image acquired on January 2005 was geo-referenced to Universal<br />

Transverse Mercator Projection (WGS 84) <strong>and</strong> radiometrically corrected to minimize the effect<br />

of atmospheric scattering. A false color composite image was created from b<strong>and</strong>s 2 (red), 3<br />

(near infrared), <strong>and</strong> 4 (mid infrared). This composite image was used as a spatial reference<br />

framework for selecting suitable training sites. At least three training sites were selected for<br />

each of the following l<strong>and</strong>-cover types: 1) 3-8 y-old secondary forest; 2) 9-15 y-old secondary<br />

forest; 3) >15 y-old secondary forest on flat areas; 4) >15 y-old secondary forest on hills; 5)<br />

agricultural fields; 6) urban areas <strong>and</strong> roads. The training areas <strong>and</strong> the false color image were<br />

used to perform a st<strong>and</strong>ard supervised classification of the Spot 5 b<strong>and</strong>s using the maximum<br />

likelihood algorithm (Idrisi Kilimanjaro V14.1, 2004). The overall accuracy <strong>and</strong> Cohen’s Kappa<br />

statistic were used to assess the accuracy of the map (Campbell, 1987).<br />

2.3 Calculation of l<strong>and</strong>scape pattern metrics<br />

We selected the following metrics that have been found relevant in l<strong>and</strong>scape studies<br />

(Mazerolle & Villard, 1999): patch density (PD), edge density (ED), mean area weighted shape<br />

index (SHAPE_AM), mean area weighted proximity index (PROX_AM), mean area weighted<br />

Euclidean nearest neighbor distance (ENN_AM) <strong>and</strong> total edge contrast index (TECI; see<br />

McGarigal et al. 2002 for a description of each metric). To calculate the proximity index, a<br />

search radius of 10 pixels (300 m) was used, which coincides with empirically derived evidence<br />

about the average size of a patch type. The weighted edge contrast between vegetation cover<br />

classes, required to compute the total edge contrast index, was calculated as the inverse of the<br />

Morisita-Horn similarity index between each pair of vegetation cover classes.<br />

2.4 Species density <strong>and</strong> biomass data<br />

Field data were recorded from a hierarchical plant survey conducted during the rainy<br />

season of 2009. First, 23 l<strong>and</strong>scapes of 1 km 2 were selected encompassing the whole range of<br />

forest fragmentation; within each l<strong>and</strong>scape, 12 sample sites were located following a stratified<br />

r<strong>and</strong>om design considering each of the four secondary forest cover classes (276 sampling sites<br />

in total). Each sampling site consisted of two concentric circular plots: all woody plants > 5 cm<br />

<strong>Forest</strong> <strong>L<strong>and</strong>scapes</strong> <strong>and</strong> <strong>Global</strong> <strong>Change</strong>-New Frontiers in Management, Conservation <strong>and</strong> Restoration. Proceedings of the IUFRO L<strong>and</strong>scape Ecology<br />

Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)<br />

2010, Instituto Politécnico de Bragança, Bragança, Portugal.

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