Interactive Effects of Intertidal Elevation and Light Level on Early Growth of Five Mangrove Species under Sonneratia apetala Buch. Hamplantation Canopy: Turning Monocultures to Mixed Forests

• Main Authors: Zhongmao Jiang, Wei Guan, Yanmei Xiong, Mei Li, Yujun Chen, Baowen Liao
• Format: Article
• Language: English
• Published: MDPI AG 2019-01-01
• Series: Forests
• Subjects: intertidal elevation; light level; mangrove; restoration; survival
• Online Access: https://www.mdpi.com/1999-4907/10/2/83

The introduced Sonneratia apetala Buch. Hamplantation plantations have occupied more than 3800 ha in China. The prevalence, fast growth rate, and high seed production of <i>S. </i><i>apetala</i> have raised concerns about the risks to native mangrove habitats. Efforts are required to convert these introduced monocultures to mixed or native forests. In this study, we examined native mangrove colonization in the introduced <i>S. </i><i>apetala</i> plantations at the Qi’ao Island, Zhuhai, China. A 12-month field study was conducted to evaluate the effects of intertidal elevation and light level on the survival and early growth of five native mangrove species, viz., <i>Bruguiera</i><i> </i><i>gymnorrhiza</i><i> </i>(L.) Savigny, <i>Kandelia</i><i> </i><i>obovata</i><i> </i>Sheue, Liu &amp; Yong, <i>Aegiceras</i><i> </i><i>corniculatum</i><i> </i>(L.) Blanco, <i>Avicennia</i><i> </i><i>marina</i><i> </i>(Forssk.) Vierh., and <i>Rhizophora </i><i>stylosa</i><i> </i>Griff.. Across intertidal elevations and light levels, the survival of <i>B.</i><i>gymnorrhiza</i><i> </i>was the highest<b>. </b>All the species had relatively higher survival rates under 30% canopy closure. Although the seedlings<b> </b>survived best at high intertidal elevation, the relative growth rate (RGR) was the highest at low intertidal elevation, and it was promoted by high light level. The stem height at low intertidal elevation was higher than that at high intertidal elevation, and it was the highest under 30% canopy closure. <i>B. </i><i>gymnorrhiza</i> and <i>R. </i><i>stylosa</i> at high intertidal elevation had relatively high leaf numbers, whereas <i>K. </i><i>obovata</i> and <i>A. marina</i> showed a reverse tendency. The growth of stem diameter showed a decreasing trend initially and then increased with better performance at low intertidal elevations, and <i>B. </i><i>gymnorrhiza</i> presented the best value under 30% canopy closure. <i>B</i><i>ruguiera</i><i> </i><i>gymnorrhiza</i> showed the highest growth rate under similar conditions. Overall, intensive canopy thinning is an effective measure to promote native mangrove growth in <i>S. </i><i>apetala</i> plantations. Additionally, increasing planting density especially at low intertidal elevations may improve native mangrove establishment and growth. Furthermore, <i>B</i><i>ruguiera</i><i> </i><i>gymnorrhiza</i> is the best choice in the effort to plant native species in <i>S. </i><i>apetala</i> plantations in the study area.