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

J.O. López-Martínez et al. 2010. Ecological factors influencing beta diversity at two spatial scales in a tropical dry forest
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Variation in community composition among sites was partitioned using the method of
Borcard et al (1992). Four sets of explanatory variables were considered at the local level:
environmental variables (soil attributes, % stoniness), landscape structure (TECI, SIEI, LPI),
spatial dependence (PCNMs), and stand age; whereas only two sets of variables were used at
the landscape level: landscape structure and spatial dependence. To determine the amount of
variation explained independently by each set of predictor variables, we performed partial
constrained ordination separately for each set of variables at both levels. Due to the length of
gradients, CCA was used at the local level (3.99 SD), while RDA was used at the landscape
scale (2 SD).
3. Results
The land cover thematic map of the study area is shown in Figure 1. The total area
occupied by this landscape was 37,243 ha, 94.8% corresponded to tropical sub-deciduous forest
in any of the four vegetation classes, whereas 5.2% corresponded to agriculture and urban areas.
We obtained an overall accuracy in the supervised classification of 73.3% and the Kappa index
was of 0.7.
Figure 1: Location and land cover map of the study area obtained from a supervised classification.
A total of 22,262 woody individuals belonging to 204 species and 52 families were
recorded in 276 sites in 23 landscapes. Of total of sites sampled, 51 belonged at class 1, 77 to
class 2, 83 to class 3 and 62 to class 4. The most abundance species was Neomillspaughia
emarginata with 3,421 individuals, whereas 29 species were represented only by a single
individual.
3.1 Local scale.
Detrended correspondence analysis at the local scale showed a large length gradient of species
composition (3.99 sd; Fig. 2a). Vegetation class 4 differed significantly from the other classes.
Canonical correlation analysis showed that total variation explained was 13.79%. Variation
partitioning showed that space is the most important variable explaining 5.95% of species
composition, followed of the soil variables with 5.83% (Table 1). Vegetation class 1 was
negatively associated with organic matter (SOM), stoniness, stand age and TECI whereas
vegetation class 4 showed the opposite pattern (Fig. 2b).
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.