Abstract
Understanding the shade-tolerance ability of a species is crucial for the successful tending of
young seedlings and selecting forestation species. Yet, no systematic investigations about the
shade tolerance of native tree species have been carried out so far by foresters in Taiwan. In
this study, we cultivated numerous seedlings of native broadleaf tree species in a nursery at
National Pingtung University of Science and Technology. We measured the photosynthetic
capacity (Amax) of 180 species during the rainy seasons of 2009~2014. The quantified data
were applied as a physiological index for determining the shade-tolerance ability of a species
and thereby classifying the species into 5 different shade-tolerance levels. To validate the
suitability of this application, 6 experts of dendrology with years of field experience were asked
to fill out a questionnaire for the tested species. The questionnaire inquired about the most likely
light environment for natural recruits of each species. Then we compared the Amax results with
the experts’ opinions. Results showed that Amax of the 180 species ranged 35.8~9.1 μmol
CO2 m-2 s-1; the first 5 species with the highest Amax values included Hibiscus taiwanensis,
Melia azedarach, Mallotus japonicus, Hibiscus tiliaceus, and Broussonetia papyrifera, while
Garcinia subelliptica showed the lowest. With reference to the experts’ opinions, we divided
Amax into 5 levels: ≧ 26.0, 25.9~21.0, 20.9~15.0, 14.9~12.5, and < 12.5 μmol CO2 m-2 s-1, corresponding to shade-tolerance levels 1, 2, 3, 4, and 5 (namely very intolerant, intolerant, moderately tolerant, tolerant, and very tolerant). By the Amax classification, numbers of
species belonging to levels 1 to 5 were 18, 37, 70, 33, and 22; while according to the experts’ opinions, respective numbers were 21, 52, 63, 40, and 4. Few species were considered to be
very tolerant by the experts. The 2 sets of results showed a significant positive relationship
with a Pearson’s correlation coefficient of 0.92. Out of the 180 species, 131 (73%) species
were classified into the same level by the 2 methods, and 49 species showed only 1 rank
difference. Thus, employing Amax to classify the shade tolerance of subtropical broadleaf
tree species is objective and practical. With these physiological data, we have established
a database of shade-tolerance levels of subtropical broadleaf tree species of Taiwan. It
provides references for forestation, ecological restoration, and ornamental applications.