The Effect of Selective Loggin on Bird Population - Essay Example

Robinson and Robinson examined the effect of selective logging within a southern Illinois forest in the United States. In their study, the authors compared the abundance of birds within uncut areas of the forest compared to areas where cutting had occurred recently (1 to 5 years before the experiment) or historically (10 to 15 years prior). The prevalence of birds was determined using a count system, where researchers spent six minutes at each post and recorded the number of birds that were observed or heard.

Observation points were allocated along a transect line at 150 metre intervals. The authors determined that for most species, there was no significant difference of bird abundance between cut and non-cut areas. Only two species were significantly less common in cut areas than in non-cut areas. These were the Red-eyed Vireo and the Ovenbird. However, the nest predator, the Blue Jay, had a significantly higher prevalence in cut areas than in non-cut areas. The study was well designed, and the authors took into account a number of potentially confounding effects, such as observer bias and overlapping observations between the different posts.

The authors also examined the power of their statistical tests, and were able to test whether there were significant differences between a large number of different bird species. One limitation of this study was that both control and experiment aspects of the study occurred within the same forest, with the authors using unlogged parts of the forest as the control. This makes it difficult to determine whether the trends that were observed are specific to the forest studied, or they occur widely.

A study also published in 1999 also examined how selective logging affected the bird community. This study took place in a Brazilian Atlantic forest. The author chose two nearby sites, one had experienced selective logging and the other had not. The areas were tested for a number of factors including vegetation structure and measures of the diversity and richness of the bird species that were present, as well as the composition of species. The author determined that diversity and richness of the bird species did not vary between sites, however, which species were present and which were absent, differed considerably.

Like the first study, the author made use of spot-counts to determine the abundance of bird species. This study was not powerful, as only two areas of forest were examined, one control (no logging) and one experimental (selective logging). Consequently, there was no replication, and it is difficult to extrapolate from the results of this study to general conclusions. Additionally, the lack of replication made it difficult to test whether the observed results differed significantly between the two areas.

Thus, although the study shows that selective logging is having a negative effect on some species, there is not enough information to determine whether this is because of selective logging, or because of the particular sites chosen for the study. A final study on selective logging examined this in an Indonesian forest. Observations were taken from a number of stations, each of which was classified as having been logged in the previous six years, or as not having been logged. There was a significantly higher number of birds at the non-logged site than at the logged site, suggesting that logging decreased the abundance of species .