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   Falcataria moluccana (tree) français     
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         Interim profile, incomplete information
         General Impact

    The exotic nitrogen-fixing tree Falcataria moluccana dramatically alters forest structure and litter inputs in forests it invades. In rare wet lowland forest on young lava flows in Hawaii, F. moluccana is a particular problem as it grows rapidly, reducing light-levels and outcompeting native slow-growing Metrosideros polymorpha. Enhanced leaf litter quality and quantity of F. molucccana compared to native species causes increases in soil nutrient levels, decomposition rates, microorganism community composition and soil invertebrates. Ecosystem processes are altered in both terrestrial and aquatic environments where F. moluccana invaded riparian areas (Hughes & Denslow, 2005; Allison et al., 2006; Atwood et al., 2010).

    For a detailed account of the impacts of F. moluccana please read Impacts of Falcataria moluccana.

         Location Specific Impacts:
    Palau English 
    Reduction in native biodiversity: F. moluccana has invaded extensive portions of Palau’s wetland-mangrove forest, and poses a critical threat to this forest type in Palau (T. Togia, unpublished report).
    Babeldaob Is. (Palau) English 
    Reduction in native biodiversity: F. moluccana has invaded extensive portions of Palau’s wetland-mangrove forest, and poses a critical threat to this forest type in Palau (T. Togia, unpublished report).
    Koror Is. (Palau) English 
    Reduction in native biodiversity: F. moluccana has invaded extensive portions of Palau’s wetland-mangrove forest, and poses a critical threat to this forest type in Palau (T. Togia, unpublished report).
    Seychelles English 
    Modification of nutrient regime: Most of the soils in the Seychelles tend to be phosphorous-limited. In such soils F. moluccana only negligibly increased soil nitrogen (Kueffer et al., 2008; Kueffer, 2010), compared to massive increases in nitrogen-limited sites such as in Hawaii (Hughes & Denslow, 2005). Nitrogen-fixation by F. moluccana may be restricted by phosphorous deficiency (Kueffer et al. 2008; Kueffer, 2010).

    Modification of successional patterns: On Silhouette Island, Seychelles F. moluccana (Paraserianthes falcataria) shows a patchy distribution indicative of wide seeding and maturation only in forest clearings which are in keeping with its wind-dispersed seeds and extreme fast growth. This species creates gaps when trees fall, and is one of the main species involved in gap creation on the island. The combination of being a major gap-creator and a gap-requirer results in a tendency for same-species creation of large forest trees (Gerlach, 2004).
    Hawaii (United States (USA)) English 
    Competition: In Hawaii Falcataria moluccana is currently invading the few remaining stands of native-dominated wet lowland forest on early-successional lava flows. These flows tend to have minimal soil development and are dominated by native Metrosideros polymorpha during initial stages of primary succession (30-200 year old flows). Less common, older flows (> 300 years of age) support a greater variety of native tree species including M. polymorpha (Allison et al. 2006; Hughes & Denslow, 2005). F. moluccana grows very rapidly, outcompeting M. polymorpha and creating a canopy over top of this slow-growing native. Where this occurs, M. polymorpha often dies from lack of light under the canopy of Falcataria trees (Mueller-Dombois, 2008; Mascaro et al., 2009). Other factors such as increased competition for water may also contribute to the decline of this native species. The loss of Metrosideros represents a profound compositional and structural change to native Hawaiian forests (Hughes & Denslow, 2005).

    Ecosystem change: Changes in litter resources caused by nitrogen-fixing F. moluccana exert bottom-up control on litter-based food chains in Hawaii. Leaf litter of F. moluccana was found to create an invertebrate community that greatly differed from that found in native Metrosideros polymorpha litter. In particular, F. moluccana litter had 400% more non-native fragmenters (Amphipoda and Isopoda) and 200% more non-native predaceous ants (Tuttle et al., 2009). This is attributed to greater N and P concentrations, lower CN ratio and greater leaf surface area of F. moluccana litter compared to M. polymorpha (Hughes & Uowolo, 2006).

    Nitrogen-rich leaves of F. moluccana also have the potential to alter ecosystem processes in aquatic environments. Decomposition of leaves may lead to increases in nitrogen concentration of streams with riparian margins invaded by F. moluccana. This may stimulate algal production and further alter the stream food web and community composition through increased densities of herbivorous organisms, and cause the food web to change from autochthonous-based to allochthonous-based. This may make streams with F. moluccana-invaded riparian zone more susceptible to future invasions by aquatic species (Atwood et al., 2010).
    Interaction with other invasive species: In addition to altering ecosystem processes, F. moluccana changes the composition and structure of wet lowland forests in Hawaii from native-dominated to strongly alien-dominated. In particular F. moluccana may facilitate invasion of other exotic species such as Psidium cattleianum, possibly due in part to increased N and P supply (Hughes & Denslow, 2005).

    While litter resources were found not to improve the diet, growth or survivorship of the invasive frog Eleutherodactylus coqui, other characteristics of F. moluccana may have positive impacts for the frog. Additional habitat structure (e.g. larger boles, more vines on boles, and greater tree height) for foraging and calling, and more shade, might support more E. coqui on a landscape-scale. Further research is necessary to determine whether this occurs (Tuttle et al., 2009).
    Modification of nutrient regime: Invasion by F. moluccana significantly increases litterfall rates (1.3 to 8.6 fold) (Hughes & Denslow, 2005) and litter quality and increases decomposition rates in Hawaii (Allison et al., 2006; Hughes & Uowolo, 2006). Due to its nitrogen-fixing biology, invasion by this tree in Hawaii dramatically alters the nutrient regime. The litter quality of F. moluccana is greater than its native counterparts, having lower C: N and C: P ratios and higher N: P ratios. Litter N may be 4–55 times greater (Hughes & Denslow, 2005).

    Changes in litter inputs provide C and N substrates that can support increased microbial growth and enzyme production. Microbes synthesise enzymes required for degradation of Falcataria litter, which further accelerates litter decomposition and nutrient mineralization. Thus F. moluccana creates a positive feedback to nutrient cycling through its litter production (Allison et al., 2006). Allison et al. (2006) found Falcataria invasion to increase the activity of soil acid phosphatase dramatically. They also found large shifts in microbial community composition under Falcataria. Although mycorrhizal abundance and total microbial biomass did not change, fungal: bacterial ratios declined dramatically in younger sites under Falcataria, which may correspond to dominance to bacteria adapted to nutrient-rich soil conditions. The effect of Falcataria invasion on soil microbes and enzymes diminished with substrate age (Allison et al., 2006).

    Where F. moluccana invades riparian zones, leaf litter inputs into streams are altered with up to 13 times more bioavailable dissolved organic carbon (BDOC) than from native M. polymorpha. While the amount of dissolved organic carbon was found to be similar between invaded and non-invaded streams, sustained increases in the amount of BDOC entering riverine systems in Hawaii has the potential to affect nutrient and organic matter dynamics and food webs that depend on riparian vegetation (Wiegner & Tubal, 2010).

ISSG Landcare Research NBII IUCN University of Auckland