Masters Theses

Allison Mains

Date of Award

8-2000

Degree Type

Thesis

Degree Name

Master of Science

Major

Ecology and Evolutionary Biology

Major Professor

David A. Buehler, Thomas G. Hallam

Committee Members

Arnold M Saxton, A. C. Echternacht

Abstract

Tropical forests are disappearing at an accelerated rate due to increasing human development. In Costa Rica, reforestation of agricultural areas is occurring with plantations of an exotic, fast-growing hardwood tree, Gmelina arborea. Research on tropical plantations and their effect on local avifauna is severely lacking. Information is critically needed concerning whether or not these plantations can play a role in sustaining tropical avian communities. To help fill this need, we conducted 50-m point counts in May-July, 1998 and 1999 within stands of Gmelina, as well as within pastures and native forests. Avian community patterns were assessed according to different age classes and landscape contexts of Gmelina stands. In addition, community patterns of the plantations were compared with avian communities in stands of native forest and pastures. Habitat analyses within the plantations were conducted to identify stand features related to avian use. Mean abundance (A) per point differed across community types (Gmelina, pastures and native forest) but not amongst Gmelina age classes. In 1998, A was greater in pastures and native stands (13.4, 9.6 individuals per point, respectively) than in young (1 year; 5.6), intermediate (2-5 years; 3.6), or old (6-9 years; 4.1) Gmelina stands. In 1999, pastures (23.9) contained the greatest A above that found in any of the other forested areas, followed most closely by native stands (119). Both richness (R, number of species), and diversity (D, Shannon-Weaver) per point differed among the age classes of Gmelina and among the community types. Young stands contained a greater R (3.9) and D (1.0) than did the intermediate age class (1.06, 0.4) or the old age class (1.9,0.5) R and D in all Gmelina stands were less than R and D in pastures (7.2, 1.6) R and D in intermediate and old stands were less than R and D in native stands (4.7,1.3). In 1998, community similarity was strongest between young stands and pastures (42%) and Gmelina stands compared amongst themselves (37%-56%). Similarity of old Gmelina stands compared with native stands was weak (23%). Again in 1999, young stands and pastures showed the strongest similarity (50%). Similarity amongst Gmelina stand age classes was weaker than that in 1998 (26% - 48%). Similarity between old stands and native stands was slightly stronger (29%). In 1998 and 1999, abundance (A) in Gmelina stands adjacent to native forests (ADJ; 7.3, 9.3) did not differ from native stands (9.6, 11.9) in either year. In both years, pastures contained a greater A (13.4, 24.0) than any Gmelina stands (4.0 - 9.3). R was greatest in pastures (7.3) and lowest in Gmelina stands surrounded by other Gmelina (GMEL; 1.8) and Gmelina stands isolated from other forested areas (ISOL; 1.7). R in ADJ stands (3.4) did not differ from native stands (4.8). Mean D was greatest in pastures (1.6) and native stands (1.4) and lower in ADJ stands (1.0). GMEL (0.5) and ISOL (0.5) stands contained the lowest D. In 1998, community similarity was greatest between ADJ and native stands (55%) and amongst Gmelina stands (39% - 44%). In 1999, similarity was greatest between ADJ and native stands (42%), ISOL and native stands (41%) and amongst Gmelina stands (40% - 50%). Insectivorous birds predominated in all community types. Frugivorous species and individuals were more prevalent in forested sites and especially so in native forest stands. Granivorous and omnivorous species were more prevalent in the pastures than they were in the wooded sites. Habitat features were measured and correlated with the avian distribution patterns observed. Differences in vegetative structure amongst Gmelina stands and community types were variable within and across years. Stands where understory structure was greater tended to be more diverse. Implications for the role of plantations in avian conservation, such as stand vegetative features and landscape context, are discussed. Maintaining heterogeneity and vegetative structure within and around stands may help increase bird diversity. Establishing plantations in cleared areas with close proximity to native forests will provide additional forest cover, which may in turn enhance local bird diversity. The use of plantations in ecological restoration and regeneration of native forests is also presented.

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