Tree Regeneration Characteristics in Limestone Forests of the Cat Ba National Park, Vietnam

Abstract

Background: Forest regeneration is decisive for future forest development and therefore of major concern to forest ecologists. The 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 hotpot in Vietnam. Data was collected from 90 sample plots and 450 sub-sample plots in the regional limestone forests. We compared species richness between the regeneration and overstory tree layers and examined the effect of environmental factors on the occurrence of regeneration. We developed five ratios to relate overstory and regeneration richness and diversity. Results: We found 97 tree species in the regeneration layer compared to 136 species in the overstory layer. Average regeneration density was 3,764 ± 1,601 per ha. Around 70% of the overstory tree species generated offspring. Of the tree species threatened according to The International Union for Conservation of Nature’s Red List of Threatened Species, only 36% were found in the regeneration layer. A principal component analysis provided evidence that the regeneration of tree species was linked 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, 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. Conclusion: We conclude that 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.

Vegetation structure of forests over limestone and its influencing environmental factors in Samar Island Natural Park, Philippines

“…The distribution of tree species in tropical mountain ecosystems is the result of the interaction of multiple environmental factors that limit species distribution simultaneously (Mandle and Ticktin 2012;Diez et al 2014;He et al 2022). The literature has repeatedly emphasized that factors causing landscape heterogeneity are either natural or anthropogenic in nature or a combination of both (Keane 2017;Pham et al 2021). Natural factors that have been identified as causing variation in species composition, including light conditions, temperature, and relative humidity, amount of rainfall (Buot and Okitsu 1999;Miao and Jianmeng 2015;Urban 2015;Winter et al 2015;Trindade et al 2018;Dong et al 2019;Iturrate-Garcia et al 2016;Diaci et al 2020;Fan et al 2020;Nepali et al 2021), soil conditions, soil type, soil texture, soil moisture (Suzuki et al 2002;Heryati et al 2011;Davis et al 2018;Toro et al 2019), floristic composition and structure and abundance of microclimates (Richards 1996;Duchicela et al 2021), microbial composition and natural disturbances particularly, typhoons, erosion, and landslides, as well as anthropogenic disturbance history (Hong et al 1995;Muniandy et al 2009;Buot and Osumi 2011;Cardinale et al 2012;Jiang et al 2016;Tran et al 2016;Boukili et al 2017), can greatly influence the species diversity in SINP.…”

Forests over limestone in Guiuan, Eastern Samar, the Philippines: Species composition and influencing environmental factors

“…However, the remaining proportion of unexplained variations could be caused by other environmental factors that were not sampled or considered and could potentially explain the variation but were not included in the analysis. In general, the distribution of tree species in tropical ecosystems is the result of the interaction of multiple environmental factors that limit species distribution simultaneously (Diez et al 2014;Keane 2017;Pham et al 2021;He et al 2022). This study provides an overview of the factors influencing vegetation in the forests over limestone of GMRPLS using the canonical correspondence analysis, and to some extent depth investigation on temperature, elevation and particularly, disturbance.…”