Importance of Natural Resources

Xiaojuan Liu – Growth-trait relationships depend on species richness in subtropical forest

Hi everyone, my name is Xiaojuan Liu, I am
from Institute of Botany Chinese Academy of Sciences. I would like to introduce you about our recent
paper on Journal of Ecology about growth-trait relationships in subtropical forest are stronger
at higher diversity Over the past decades research has shown that
forests with more species have a higher growth and productivity than forests with a few to
single species. When considering relative young developing
forests, the effect of increased number of species on productivity has shown to increase
with time. Understanding how and why these forests with
more species have higher productivity is an important question in ecology. In this research we focused on the individual
trees, because community forest depends on the sum of individual trees. Trees have different characteristics, called
functional traits, that can be linked to growth rate and growth strategies. Variation in these traits can be linked to
differences in growth. So to determine the role of traits on growth,
and to determine if the role of traits for growth also depends on species richness,
here we asked 3 questions in our study: The first one is do traits change with species
richness? The second is how are individual traits related
to individual growth? Is this also depending on species richness? The third is do trait-growth relationships
change with tree age and forest development With these questions, we did experiment in
the world largest forest biodiversity-ecosystem functioning experiment that was located in
the South China, called BEF-China. The tree in BEF-China is planted in 2009
and 2010 which was designed with tree species richness with 6 levels 1, 2, 4, 8, 16 or 24
different species. In total there are 566 plots, with each plot
planted with 400 trees. Because forests consists of individual trees
that can live for many years, and over years trees change in size, so trees from different
species have typically different characteristics we call traits, while trees also can change
their traits due to the local environment. The values for the different traits can determine
individual growth, but the surrounding on the individuals, like neighbor trees, also
influence growth, for example because of competition for resources. So with this background, we selected 547 individuals
from 31 species and measured 9 leaf traits, 2 stem traits and 2 root traits across 5 years
in 5 richness levels. Here come the main results. The first results is we analyzed if trait
values would change with species richness. What we found is if we consider all species
together, the number of branches, leaf chlorophyll and leaf phosphorus can slightly change with
species richness at plot level. But at the species level we found different
effect and directly of trait changes with species richness. All together these results indicate that tree
characteristics can change with changes in local and community level biotic conditions. The second result is we found that growth-trait
relationships become stronger with higher richness. From the 12 traits we measured there were
5 traits that had an over significant relationship with growth. However, more interestingly, there were 6
traits that showed a significant changing relationship between trait and growth with
species richness. For example, we found that in plots with only
a single species in leaf area did not result in variation in growth among the individual
trees, but at higher species level we observed that individuals with bigger leaf area also
had higher growth. So in general we observed that differences
among individuals at higher species richness plots was related to bigger differences in
growth rates. Beside we also found that these richness effects
on the relationships between traits and growth were observed at the plot level, but also
at the neighborhood level. The third result, we found growth-trait relationships
are changing over year. We found that if growth-trait relationship
changes with years and if this was different for plots with a single species or with different
species, we observed that per year the number of branches had the strongest relationships
with growth, and the relationship changed slightly between the years. In addition, the relationship of growth and
leaf chlorophyll also changed with years. In addition, we observed that these yearly
relationships were different in species monoculture and higher species richness level. So with these 3 results, we give the main
conclusions that traits can change with plant species richness and growth-trait relationship
becomes stronger at higher species richness level. And growth-trait relationship can change over
time. So in summary, our study made an initial step
to show that trait effects on growth are more pronounced at higher richness levels, indicating
that to elucidate how functional traits shape biodiversity–ecosystem functioning relationships,
an important step is to consider the biotic context of individual trees within a community Thank you very much

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