Illegal logging, landscape structure and the variation of tree species richness across North Andean forest remnants

We explored the influence of a common practice in tropical countries, namely illegal logging for household consumption (ILHC), as well as that of characteristics of habitat structure on the variation of tree species richness across 10 cloud forest remnants of a Colombian Andean landscape. We estimated species richness for total, early and late successional tree species for each forest fragment. We also generated a binomial ILHC variable and six quantitative habitat descriptors related to patch size, shape and isolation. The data were analyzed with generalized linear models (GLMs) and model selection techniques based on Information Theory, complemented with partial regression analyses. We found that the presence of ILHC decreased the number of species for all tree groups, being this variable the major driver of richness variation across forest remnants. Our analyses also indicated that landscape characteristics played secondary roles in determining tree richness in all cases. Additionally, stronger negative impacts of ILHC on late successional tree species suggest that these logging activities are likely to move back ecological succession towards earlier stages of this process. As far as we know, this is the first study documenting the relative importance of ILHC practices against landscape structure for tree species richness. Our results strongly emphasize the need to consider ILHC in investigations and conservation initiatives involving tree species richness in fragmented tropical landscapes.