Regeneration of woody plants along topographic gradient in subtropical evergreen broadleaved forests in Taiwan

We developed a seedling index (SI), which measures the number of seedlings in proportion to total regeneration individuals (seedlings and sprouts), to test whether the regeneration patterns of woody plants in evergreen broadleaved forests varied across topographic gradient. Our hypothesis was that sprouting in woody plants would be higher in highly-disturbed areas such as ridges and valleys, whereas seedlings would prevail on the less-disturbed slopes. A total of 131 sample plots in evergreen broadleaved forests were sampled from 400 to 2,600 m above sea level in Hsueshan mountain, northern Taiwan. Results show that seedling is the more dominant regeneration type, with the mean number of seedlings across all sample plots three times that of sprouts. The mean values of seedling index (SI) were all higher than 0.5 in valley-, slope-, and ridge-sites, suggesting that the regeneration of woody species is more dependent on seedlings regardless of topographic location. Of the 70 woody species analyzed, 59 species were more dependent on seedlings (SIs higher than 0.5). We classified the 70 species by their SI values into three groups: seedling dependent (37 species), intermediate (22 species), and sprout dependent (11 species). The majority of species were consistent in their reproductive modes across sites, with only 17% of the species changing their seedling-sprout-dependence across the topographic gradient. This suggests that the regeneration methods of woody plants should be mostly intrinsically determined, with only a few species relying on different major reproductive methods across topographies.