Long-term effects of intercropping on multi-trophic structure and bio-thermodynamic health of mixed Eucalyptus-native tree plantations

1. The intercropping approach of Eucalyptus and native trees has
been widely recommended, as an ideal replacement for
monoculture Eucalyptus plantations (EUs), to ameliorate global
biodiversity loss and mitigate environmental change. However, both
suitable native tree species and the best intercropping ratio
between Eucalyptus and native trees have not been determined.
2. To fill this gap, a four-level intercropping gradient of
Eucalyptus urophylla planted with eight native tree species was set up
(i.e., 20%NS, 30%NS, 40%NS, 50%NS), monitored and compared to a
monoculture E. urophylla plantation (EU) and a randomly mixed plantation
of nine native tree species (NS) in southern China. 3. The
results showed that the intercropping ratio of Eucalyptus and native trees
had a long-term effect on tree layer structure and health status and a
cascading effect on the thermodynamic health state of soil microbes.
Shade-tolerant woody species are more suitable for intercropping with
Eucalyptus. Intercropping plantations with not less than 30% native trees
were more favorable for long-term survival and growth of both planted
Eucalyptus and native trees and provided much more favorable conditions
for the natural immigration of other native trees, which leads to a
healthy plant community with significantly higher eco-exergy compared to
EU. The initial mixing ratio between Eucalyptus and high diversity native
trees affected soil fertility through its long-term effects on the
biodiversity and bio-thermodynamic state of trees and soil microbes. 4.
Synthesis and applications. Our results highlight the long-term positive
effect of the intercropping ratio of Eucalyptus and high diversity native
trees on multi-trophic biodiversity conservation, bio-thermodynamic health
development, and soil fertility conservation. In the conversion of
monoculture Eucalyptus plantations (EU) to multi-species plantations, it
is recommended to mix more than 30% native tree species that have
different ecological niches with Eucalyptus.