Compositional Shifts in Undisturbed Neotropical Forests: Effects of Climate Change? William F. Laurance 1,2 & Richard Condit 1 William F. Laurance 1,2 & Richard Condit 1 1 Smithsonian Tropical Research Institute, Panama 2 Biological Dynamics of Forest Fragments Project, Manaus, Brazil 2 Biological Dynamics of Forest Fragments Project, Manaus, Brazil

Atmospheric CO 2 Pre-industrial level was 280 ppm Pre-industrial level was 280 ppm Current level (378 ppm) is highest in last 20 million years Current level (378 ppm) is highest in last 20 million years In experiments, elevated CO 2 increases photosynthesis, growth, and water-use efficiency for most plants (for tropical trees, only seedlings assessed) In experiments, elevated CO 2 increases photosynthesis, growth, and water-use efficiency for most plants (for tropical trees, only seedlings assessed) Data from Mauna Loa, Hawaii

Evidence for pervasive changes in Amazonian tree communities W. F. Laurance et al. (2004) Pervasive alteration of tree communities in undisturbed Amazonian forests. Nature 428:

18 1-ha plots in forest interiors 18 1-ha plots in forest interiors Monitored years Monitored years 115 most abundant genera 115 most abundant genera Study Design:

Changes in Central Amazonia 1)Concerted shifts in species composition (14 times more than expected by chance), with fast-growing canopy and emergent trees evidently gaining a competitive advantage over smaller, slower-growing trees 2)Accelerating forest dynamics 3)Accelerating growth for most genera

Barro Colorado Island  ha in area -isolated in 1914

50-hectare plot 

BCI 50-ha Plot Established in 1982, recensused in 1985, 1990, 1995, 2000 Established in 1982, recensused in 1985, 1990, 1995, 2000 Subdivided into 50 1-ha plots Subdivided into 50 1-ha plots Included only species present in >10 1-ha plots and >10 cm dbh (142 species) Included only species present in >10 1-ha plots and >10 cm dbh (142 species) Bootstrapping used (at 1% alpha level) to assess changes in density and basal area for each species between Bootstrapping used (at 1% alpha level) to assess changes in density and basal area for each species between

BCI: Changes in Tree Density and Basal Area Tree Density: -19 increased (13%) -23 decreased (16%) Tree Basal-Area: -22 increased (15%) -20 decreased (14%) Overall: -Nearly 30 times more significant changes than expected by chance

Amazonia: Differences in Growth Form

BCI: No Differences in Growth Form species

Amazonia: Larger Trees are Winning IIII

BCI: No Effect of Tree Size

Amazonia: Winners Grow Faster

BCI: No Difference in Growth Rate species

Amazonia: Accelerating Forest Dynamics

BCI: Decelerating Forest Dynamics Mortality: is higher than the other intervals is higher than Recruitment: and are higher than both and is higher than

Amazonia: Accelerating Growth Rates Growth accelerated more for winners than losers –Winners: 57% –Losers: 22% –Other genera: 40%

BCI: Decelerating Growth Rates -Growth was higher in than in all other intervals (P<0.0001) -Growth was also higher in than in the final two intervals (P<0.0003)

What is Driving the Tree- Community Changes on BCI? 1)BCI is a forest fragment

2)Parts of BCI are recovering from past disturbances – year-old regrowth near the plot: previous source of successional-plant propagules –Successional species are now declining on the plot

3) BCI has experienced a long-term drying trend and recent severe droughts

Population Trends vs. Drought Tolerance

Conclusions Tree-community changes in central Amazonia are consistent with elevated productivity, possibly from rising CO 2 levels Tree-community changes in central Amazonia are consistent with elevated productivity, possibly from rising CO 2 levels Changes are BCI seem to be driven by recent droughts and possibly nonequilibrium conditions on the plot Changes are BCI seem to be driven by recent droughts and possibly nonequilibrium conditions on the plot The drivers of change may differ among different forests. Thus, there is a dire need for more long-term studies of tree-community dynamics that explicitly test global-change hypotheses The drivers of change may differ among different forests. Thus, there is a dire need for more long-term studies of tree-community dynamics that explicitly test global-change hypotheses

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