The reintroduced Formosan Sika deer has caused severe impacts to the regeneration of forest
vegetation in the Kenting Karst Forest. The impacts of deer herbivory were studied by comparing
the dynamics in species richness and natural regeneration of seedling communities in an exclosure
plot (890 m2) vs. an unfenced control plot (850 m2) in the vicinity. We also planted seedlings of
12 tree species prone to deer damage in both plots. During the 2-yr investigation period, the species
richness and abundance of large-sized (height ≥ 10 cm), middle-sized (height < 10 cm), and
emerging seedlings in the exclosure plot all increased. On the other hand, large- and middle-sized
seedlings in the control plot decreased, with only emerging seedlings increasing. In the control
plot, the abundance of large- and middle-sized seedlings that were highly preferred by Formosan
Sika deer were more greatly reduced compared to lower-preference seedlings. However, in the
exclosure plot, amounts of higher-preference seedlings of all size classes increased. Values of the
Shannon-Wiener index (H’) and Simpson’s index of species diversity of large-sized seedlings increased in the exclosure plot, but both indices decreased in the control plot. This study found that
the browsing pressure of Formosan Sika deer on seedling communities had lowered to individuals
of < 10 cm in height. The browsing preferences of various tree species in the karst forest were significantly
related to the preferences obtained in previous artificial feeding tests. Planted seedlings
in the control plot were severely browsed within a short time, and only 2 species had 3 seedlings
survive. While in the exclosure plot, 120 seedlings of 11 species survived. Therefore, the value of H’
of large-sized seedlings increased from 2.51 to 2.90 in the exclosure plot. In conclusion, exclosure
treatment increased the species richness of the seedling community and promoted natural recruits.
Natural regeneration of tree species that are highly preferred by Formosan Sika deer will be hampered
if there are no fences for protection. Abundances of these 3 sizes of seedlings had increased
3.4-times 2 yr after establishing the exclosure plot. This showed that the recovery rate of the seedling
community was relatively fast.