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We use identical methods to monitor the production of flowers and seeds and the recruitment, growth and mortality of seedlings in four Neotropical forests. Each study takes place in a large (6 to 50 ha) Forest Dynamics Plot (FDP). All free-standing woody stems larger than 1 cm in diameter at breast height are mapped, identified and measured at five year intervals by collaborators from the Center for Tropical Forest Science and the Smithsonian Institution Global Earth Observatories in each FDP. Together, our studies of seed production and seedling, sapling and adult performance document the complete life cycles of more than 1,000 Neotropical tree species. The flower, seed and seedling data address a wide range of basic research questions and global change issues. Four examples follow.

Environmental control of the timing of flowering and fruiting

In temperate and boreal latitudes, an inhospitable winter and seasonal changes in temperature and photoperiod control the timing of flowering and fruiting or reproductive phenology of most plants. In contrast, the growing season never ends in the wet tropics, seasonal temperature variation is usually less than diurnal variation and, at the equator, photoperiod is constant. Current understanding of the environmental controls of phenology of wet tropical forest plants consists of hypotheses. Our data provides weekly (to twice monthly) temporal resolution for up to 23 years for more than 1,000 tropical forest plant species to test these hypotheses. Our analyses have provided numerous insights into environmental controls of seasonal and inter-annual variation in flower and seed production.

Seed dispersal

Seed dispersal controls the ability of plants to reach regeneration sites and to colonize new habitats. We are able to estimate seed dispersal distances using the locations of our seed traps and all potential seed-bearing trees within the large Forest Dynamics Plot. Our analyses have provided insights into species attributes that influence seed dispersal and the consequences for seed limitation and species coexistence.

Plant demography and species coexistence

Our data on seed production, seedling recruitment and seedling growth and survival combined with CTFS/SIGEO data on sapling and adult growth and survival provide the only complete life cycle information for any tropical tree species. Our analyses of these spatially explicit data have established widespread negative density dependence, in which individual performance declines as the local abundance of conspecifics increases. A new generation of studies will integrate all life stages from seed to adult to evaluate the life time strength of density dependence for populations and the potential to maintain hundreds to thousands of co-existing species.

Long term trends and global change

Human activities are increasing atmospheric concentrations of carbon dioxide and other trace gasses, increasing deposition of nitrogen and other pollutants, and changing the global climate. Allocation to reproduction is a potentially sensitive indicator of plant responses to global atmospheric and climate change. Our analyses have detected long-term changes in flower production and in production by different life forms that appear to be responses to these anthropogenic drivers.

We initiated seed and seedling studies at Barro Colorado Island, Panamá in 1987; Luquillo, Puerto Rico in 1992; Parque Nacional San Lorenzo, Panamá in 1997; and Estacion Cientifica Yasuni, Ecuador in 2000. Funding is from the Smithsonian Institution (Panamá) and the National Science Foundation of the United States (Ecuador and Puerto Rico).
 

Table 1.

The four long-term studies of flower and seed production and seedling recruitment, growth and survival as of 1 January 2011.

 

Barro Colorado Island, Panamá

Estación Biológica Yasuni, Ecuador

Luquillo, Puerto Rico

Seed and flower production

First census
Jan 1987
Feb 2000
X 1992

Number of censuses each year

52
24
26

Number of 0.5-m2 seed traps

250*
200
120
Number of species recorded
527** >800** 136
Number of data records
601,372
166,857
201,686
Seedlings
First annual census
1994
200X
2006

Number of 1-m2 seedling plots

800
600
360
Number of species recorded
295* 729 -
Number of seedlings recorded
54,400**
23,539
-

* 200 traps were located in a stratified random manner in 1987. Fifty additional traps were randomly located in natural tree fall gaps between 2002 and 2004.
** approximate