Traits data of naturalized and non-naturalized alien species of four Indonesian Botanic Gardens

The establishment of new botanic gardens in tropical regions highlights a
need for weed risk assessment tools suitable for tropical ecosystems. The
relevance of plant traits for invasion into tropical rainforests has not
been well studied.  Working in and around four botanic gardens in
Indonesia where 590 alien species have been planted, we estimated the
effect of four plant traits, plus time since species introduction, on: a)
the naturalization probability and b) abundance (density) of
naturalized species in adjacent native tropical rainforests; and
c) the distance that naturalized alien plants have
spread from the botanic gardens.   We found that
specific leaf area (SLA) strongly differentiated 23 naturalized from 78
non-naturalized alien species (randomly selected from
577 non-naturalized species) in our study. These trends may
indicate that exotics with high SLA benefit from at least two factors when
establishing in tropical forests: high growth rates and occupation of
forest gaps. We also found that height was unrelated to
naturalization probability, but naturalized aliens were having high SLA
and were short.  Exotic species that
were present in the gardens for over 30 years and those
with small seeds also had higher probabilities of becoming
naturalized, indicating that garden plants can invade the understorey of
closed canopy tropical rainforests, especially when invading species are
shade-tolerant and have sufficient time to establish. On average, exotic
species that were not animal dispersed spread 78 m further into the
forests than animal-dispersed species. We did not detect relationships
between the measured traits and estimated density
of naturalized exotics in the adjacent forests. Synthesis: Traits
were able to differentiate exotic species from botanic gardens that
naturalized in native forest from those that did not; this is promising
for developing trait-based risk assessment in the tropics. To limit the
risk of invasion and spread into adjacent native forests, we
suggest tropical botanic gardens avoid planting exotic species
with fast carbon capture strategies and those that are shade tolerant.