Abstract
BackgroundThe ability of overstory tree species to regenerate successfully is important for the preservation of tree species diversity and its associated flora and fauna. This study investigated forest regeneration dynamics in the Cat Ba National Park, a biodiversity hotspot in Vietnam. Data was collected from 90 sample plots (500 m2) and 450 sub-sample plots (25 m2) in regional limestone forests. We evaluated the regeneration status of tree species by developing five ratios relating overstory and regeneration richness and diversity. By examining the effect of environmental factors on these ratios, we aimed to identify the main drivers for maintaining tree species diversity or for potential diversity gaps between the regeneration and the overstory layer. Our results can help to increase the understanding of regeneration patterns in tropical forests of Southeast Asia and to develop successful conservation strategies.ResultsWe found 97 tree species in the regeneration layer compared to 136 species in the overstory layer. The average regeneration density was 3764 ± 1601 per ha. Around 70% of the overstory tree species generated offspring. According to the International Union for Conservation of Nature’s Red List, only 36% of threatened tree species were found in the regeneration layer. A principal component analysis provided evidence that the regeneration of tree species was slightly negatively correlated to terrain factors (percentage of rock surface, slope) and soil properties (cation exchange capacity, pH, humus content, soil moisture, soil depth). Contrary to our expectations, traces of human impact and the prevailing light conditions (total site factor, gap fraction, openness, indirect site factor, direct site factor) had no influence on regeneration density and composition, probably due to the small gradient in light availability.ConclusionWe conclude that the tree species richness in Cat Ba National Park appears to be declining at present. We suggest similar investigations in other biodiversity hotspots to learn whether the observed trend is a global phenomenon. In any case, a conservation strategy for the threatened tree species in the Cat Ba National Park needs to be developed if tree species diversity is to be maintained.
Highlights
The ability of overstory tree species to regenerate successfully is important for the preservation of tree species diversity and its associated flora and fauna
Species diversity status of the overstory vs. the regeneration layer In 90 sample plots, we found a total of 97 tree species in the regeneration layer compared to 136 species in the overstory tree layer, indicating that species richness
Many previous studies have found that a single environmental factor fails to explain forest regeneration characteristics [1, 3, 4, 6, 7, 9, 11, 15,16,17, 19, 24, 51, 59, 67,68,69,70,71]. These results are confirmed by our study since we found that PC2, which represented a combined fertility, rough terrain, and moisture gradient, explained the pattern of tree species regeneration better than single environmental variables
Summary
The ability of overstory tree species to regenerate successfully is important for the preservation of tree species diversity and its associated flora and fauna. Southeast Asia harbors approximately 15% of the world’s tropical forests [29] located in countries such as Cambodia, Indonesia, Malaysia, Myanmar, the Philippines, Thailand, and Vietnam This part of the world can be regarded as a biodiversity hotspot where the greatest number of endemic and threatened species in the world can presumably be found [26, 30]. These forests are important for environmental protection, socio-economics, and the living conditions of forestdependent populations [31] To maintain these tropical forests and their diversity, we need to understand the degree to which tree regeneration patterns depend on abiotic and biotic factors and how they change due to natural or human disturbances [32]. Research on natural regeneration under potential limiting factors other than light are, still rare especially in Southeast Asia
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