Name

Instructor

Subject

Date

Introduction

Different bird species inhabit different areas ranging from plains to forests. The mature forests can be replaced by a new environment in case of fire and woodcutting. During forest regeneration, it passes through the stage where many shrubs are found. Certain bird species utilize the new environment as their habitat.

Birds living in disturbed forests are often called shrubland birds. In the last 50 years, the population of shrubland birds has decreased in their habitats. Fire control, human land development, and reduced shrub area due to the recolonization by mature forests decrease the habitats for these birds. Currently, the remaining sections after woodcutting are the main settlement areas for these bird species. Shrubland birds occupy the place of clearcutting a year or two after the harvest, and their population peaks after 4-8 years. The recent demand to stop clearcutting in the USA has lead to the development of the different harvest methods which offer new habitats for shrubland birds, beside the clearcut areas.

The authors Perry and Thill have addressed the problem of the impact of logging on the shrubland birds. They hypothesized that extensive clearcutting is a method of creating habitats for particular birds without fire. The authors have included twelve different bird species in their study. Eight of the species were early shrubland birds, and three other species were associated with the less intense disturbance of the forest during clearcutting. The last species included the brown-headed cowbird (Molothrus ater), which is a significant nest parasite of shrub-nesting birds.

Material and Methods

The study was performed in the Ouachita Mountains of west-central Arkansas, east-central Oklahoma National Forest, and the Ozark-St. Francis National Forests in Magazine District. The population of the bird species was followed in 20 areas, which were divided into five groups. Each area contained over 70 year-old forests with similar pine and hardwood trees in abundance. Each group in the different areas was later treated with one of the harvest methods, which include modified clearcutting, single-tree selection, group selection, and shelterwood. One group consisting of four areas was untreated. The areas were compared two years before the treatment, and in next 16 years after treatment, with the year 1993 being Year 0. The bird surveys were performed between May 3 June 12 during the breeding period. Five stands were picked in each plot in a manner that they were more than 150 meters apart and at least 90 meters from boundaries.

Results

The density of the vegetation in the areas has increased. The overstory trees were constantly increasing in all sampled plots while the midstory vegetation has increased significantly in clearcuts and shelterwoods. During the first year, the woody shrub layer was the biggest in the controls. However, the clearcuts, shelterwoods, and single-tree selection have developed more dense shrub layer over the period of 5-16 years.

American Goldfinch population peaked after 3-5 years, except for clearcuts (1-3 years). Blue grosbeak detections peaked in shelterwoods (3 y), single-tree (5 y), and in clearcuts (8 y). Common Yellowthroat peaked after 3 years, except for clearcuts (5 y). Field sparrows were only detected in clearcuts, shelterwoods, and single-tree selection (3-5 y). Indigo bunting species has peaked in all stands after 3-5 years. Northern bobwhite was detected mainly in clearcuts after 5-8 years. Praire warbler detections peaked in shelterwoods, single-tree (3 y), and clearcuts (5 y). White-eyed vireous peaked after 8 years while Yellow-breated chat peaked after 5 years only in harvested areas. Hooded warbler’s peak was detected after 12 years. Kentucky warbler peaked after 8 years in harvested areas only. Northern cardinal was detected mainly in shelterwoods and clearcuts with the peak being after 12-16 years. Brown-headed cowbird, which is parasitic to shrubland birds was detected in harvested areas with a peak after 3 years (Perry and Thill Web).

Discussion

The bird population, in general, have changed as expected. In the first years after the harvest, together with the increase of midstory and shrub levels of vegetation, the significant increase in population of shrubland birds was observed. Depending on the type of harvest, the peak was observed between 3 and 8 years after the harvest. On the contrary, the species that inhabit the areas with less disturbed forests have reached the peak population after 12-16 years. This shows that the shrubland birds prefer woody shrubs while the latter prefer forests with a developed midstory level. The parasitic cowbird arrived together with shrubland birds on the harvested areas. Its population peak is related to the peak of the shrubland birds population, confirming that it relies on their population.

The decline of the populations starts as early as 5 years after the harvest for field sparrow while the other species’ decline start 10 years after the harvest. This is a result of incremental changes in the forest level densities found after each year, showing clearly how different habitats influence the biodiversity of the forests.

A comparison performed between different areas shows several correlation, and there were no species found in control areas, in the majority. This is not a surprise because they have low shrub and midstory level densities. In fact, only four species were observed, and the total mean detection was 9-30 times lower than in harvested areas. Although there were many differences in the various species in harvested areas, the mean values show that the clearcuts offer the best habitat for shrubland birds, followed by shelterwoods, single and group selection, in that order. The shrubland bird species preferred slightly disturbed forests like Kentucky, and hooded warblers preferred shelterwoods and single-selection woods over the clearcuts, which were inhabited by the shrubland birds. This was probably the outcome of reduced nesting places for this species.

Clearcuts have generally reported the highest detection rates, especially after 5-12 years. At this period, the other harvested areas will have already regenerated. The species, which prefer slightly disturbed forests like Kentucky and hooded warblers remained in the clearcuts even 12-16 years after the harvest. The next most profitable, in terms of detection increase area, was shelterwood. This can be attributed to the removal of the overstory since they can quickly develop shrubs and midstory. In addition, it was found that a few of the bird species have preferred this area.

Conclusion

From the work of Perry and Thill, one can conclude that if humankind is willing to maintain the biodiversity and the population of certain birds, clearcutting of the forests is one of the best options. This method, which is substituting natural fires, generates the habitat for various birds, which can live only in these areas. Unfortunately, the public opinion does not allow for the extensive clearcutting that can sustain the population of the shrubland birds.

Perry and Thill have studied different methods of harvesting and their influence on the bird population. In that study, we find that the shelterwood forest harvesting method can be a preferable alternative to cleacutting, which will sustain the population of shrubland birds and be acceptable for public opinion (Perry and Thill Web).

I chose the article because it shows that destruction is sometimes a source of life in nature. Unfortunately, the ecological movement, which tries to preserve certain areas, can lead to accidental extinction of the other species.

Work Cited

Perry, R.W. and R.E. Thill. Long-term responses of disturbance-associated birds after different timber harvests.” Forest Ecology and Management, 307: 274–283. Web. 4 Oct. 2013.