Effects of forest fragmentation on Heliconia acuminata seedling recruitment in central Amazonia

Abstract

I present the results of a 2-year experiment comparing seed predation, seed germination, and seedling survivorship patterns of the Amazonian understory herb Heliconia acuminata in forest fragments and continuous forest. These empirical results were compared with natural patterns of recruitment in permanent 5,000 m 2 demographic plots adjacent to experimental areas. The number of naturally occurring seedlings established in demographic plots was 1.5-6 times greater in continuous forest than it was in 1-ha or 10-ha fragments. This result mirrors the pattern of seedling establishment in experimental transects, in which seeds in fragments were 3-7 times less likely to become established than those in continuous forest. Predation of experimentally sown seeds was extremely low at all sites, and is therefore not responsible for the observed pattern. Instead, reductions in seedling abundance in forest fragments are probably due to lower levels of seed germination. Forest fragments have higher air and soil temperatures, lower relative humidity, and increased leaf-litter accumulation, all of which can alter the cues used to initiate germination. While the growth of seedlings was similar in forest fragments and continuous forest, seedling survivorship in fragments was highly variable. These results suggest that altered environmental conditions may exacerbate reductions in plant recruitment resulting from modified plant-animal interactions. Strategies aimed at reducing the intensity of abiotic edge effects should therefore be incorporated into plant conservation efforts.

Consequências ecológicas da fragmentação florestal na amazônia

“…Por exemplo, plantas do gênero Heliconia apresentaram menor taxa de germinação nos fragmentos (Figura 7), provavelmente devido às mudanças microclimáticas próximo às bordas e o aumento na deposição de serapilheira (Bruna 1999(Bruna , 2002. além disto, a perda diferencial dos dispersores de sementes pode ter efeitos distintos sobre a taxa de dispersão de espécies com sementes grandes ou pequenas.…”

Produção e espessura da serapilheira na borda e interior de fragmentos florestais de Mata Atlântica de diferentes tamanhos

“…Outra mudança importante que acaba por acentuar as mudanças no microclima é o aumento da intensidade luminosa no interior dos fragmentos devido ao aumento da abertura do dossel (Kapos 1989). Essas alterações microclimáticas geram diversas mudanças na comunidade vegetal dos remanescentes, tais como o aumento das taxas de mortalidade de árvores na proximidade da borda (Laurance et al 2001), baixa taxa de germinação em fragmentos florestais (Bruna 2002), diminuição da riqueza e abundância de espécies lenhosas e herbáceas na proximidade da borda (Fontoura et al 2006), diminuição da densidade de plântulas em fragmentos (Benítez-Malvido & Martinez-Ramos 2003) e alterações na produção de serapilheira (Scariot 2000, Sizer et al 2000, Vasconcelos & Luizão 2004. De acordo com Scariot (2000) e Sizer et al (2000), após 10 a 15 anos de isolamento, fragmentos isolados na Amazônia Central tendem a apresentar queda de serapilheira semelhante àquela observada em áreas de floresta contínua, provavelmente devido à redução dos efeitos de borda, à regeneração da matriz e ao crescimento de lianas e arbustos na borda.…”

Heliconia acuminata reproductive success is independent of local floral density

“…As part of a long-term study of H. acuminata population dynamics, a network of permanent 5000m 2 demographic plots has been established in six of the continuous forest reserves administered by the Biological Dynamics of Forest Fragments Project (BDFFP), located 70 km north of Manaus, Brazil (2°30'S, 60°W). Each of these plots consists of fifty 10x10 m subplots (see Bruna, 2002;Bruna and Kress, 2002 for details), in which the number of flowering plants ranges from 1-7 (Fig. 1).…”