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E. Tetetla-Rangel et al. 2010. Relationships among landscape structure, climate and rare woody species richness
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On the other hand, variation partitioning revealed that spatial dependence was the variable most
strongly associated with rare species richness; the amount of variation explained by this variable
ranged from 13 to 17% for the different levels of rarity (Figure 2). Environmental variables
explained a higher percentage of variation for the low and medium levels of rarity, compared to
the high level and to all rare species.
Table 2: Regression standardized coefficients and partial multiple correlations for predicting rare woody
species richness from environmental attributes.
CLIMATE AND
Level of rarity
LANDSCAPE STRUCTURE All rare spp. Low Medium High
(R 2 = 0.05)* (R 2 = 0.08)* (R 2 = 0.16)* (R 2 = 0.03)*
MEAN PRECIPITATION -0.22 (0.05) 0.17 (0.03) 0.17 (0.03)
MEAN TEMPERATURE MAXIMUM -0.17 (0.03) -0.20 (0.03)
SD ALTITUDE -0.17 (0.03)
TECI 0.25 (0.03) -0.27 (0.02)
LSI -0.20 (0.02) -0.46 (0.03)
ED 0.58 (0.03)
NP 0.24 (0.03)
* Coefficient of determination for the model.
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Environmental Space Shared Total
Environmental Space Shared Total
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Environmental Space Shared Total
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Components
Figure 2: Partitioning of the variation of rare species richness by environmental and space components.
All species (a), low level of rarity (b), medium level of rarity (c), and high level of rarity (d).
4. Discussion
The most important variable explaining variation in rare woody species richness was spatial
dependence (Figure 2). This result suggests that the distribution of these species is strongly
affected by dispersal limitation (Hubbell 2001). Alternatively, rare species distribution may be
influenced by other environmental variables operating at local scales, such as physical and
chemical soil properties, and microclimate (Jones et al. 2008; Lindo and Winchester 2009).
However, the relative contribution of spatial and environmental components varied among the
different levels of rarity. We found that as the level of rarity increases, the amount of variation
explained by environmental variables decreases. This suggests that dispersal limitation or local
environmental factors may be most important for species with the highest level of rarity, that is,
those with low frequency, high levels of habitat specificity, and restricted distribution. Since the
majority of rare species studied belonged to the highest level of rarity, the patterns shown by all
rare species were very similar to those of species with the highest level of rarity.
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.