Abstract
Planting high-quality seedlings with desirable growth attributes are associated with successful survival and growth performance following outplanting. Considering that most tree species from the Dipterocarpaceae family are on the IUCN Red List of Threatened Species, proper conservation of such species is necessary. Very little is known with no clear consensus regarding whether increasing the seedling production period enhances outplanting survival and growth potential of tropical dipterocarp species planted under enrichment planting in Malaysia. In this study, one potential Bornean tropical indigenous species, Shorea macrophylla (de Vriese) P.S. Ashton, was produced in the Universiti Malaysia Sarawak nursery and outplanted at Sampadi Forest Reserve, Sarawak. Different nursery production periods (3, 6, 9, and 24 months) were tested for the species at the time of planting as well as for the subsequent growth performance after 12, 24, and 42 months of outplanting. The findings revealed that older (9- and 24-month-old) S. macrophylla seedlings were morphologically larger from younger (3- and 6-month-old) seedlings. Nonetheless, the overall pooled mean survival rates declined from 61.7 to 44.6% after 12, 24, and 42 months of outplanting. For the 42-month period, the survival rate for the 9-month-old seedlings was significantly higher than that for the 3-, 6-, and 24-month-old seedlings. Notwithstanding, the relative growth rate of the stem diameter was higher for the 3- and 9-month-old seedlings than for the 6- and 24-month-old seedlings after 42 months of outplanting. Thus, maintaining plant material from the seedlings produced at 3, 6, and 9 months of age would be beneficial for the initiation of transplantation in restoration programmes in Sarawak. The 24-month-old seedlings will also be useful, especially during irregular flowering and unpredictable fruiting intervals. A further experimental study on other environmental factors that could influence the outplanting performance of the seedlings in the tropical forest restoration area of Sarawak, Malaysia, is necessary.
Highlights
Seedling quality is a critical component in the successful implementation of forest restoration programmes [1]
After 42 months of outplanting, the field survival rate of the 9-month-old seedlings was significantly higher (7.3–20.0%) than that of the other seedlings. ere was a significant month × age interaction effect observed for the survival rates of S. macrophylla seedlings after 12, 24, and 42 months of outplanting (Table 3)
Notwithstanding, higher survival is usually reported in seedlings planted under secondary and logged forests; for example, 37.5% to 70.0% of Shorea parvifolia seedlings were alive after 24 months in Indonesian secondary forests where line planting techniques have been used [45], and more than 94% of Dryobalanops aromatica and S. parvifolia seedlings survived after 22 months in a secondary forest of Sampadi Forest Reserve and Balai Ringin Protected Forest in Sarawak [36]
Summary
Seedling quality is a critical component in the successful implementation of forest restoration programmes [1]. Various previous studies have shown that age and size are two reliable, easy-to-use seedling quality indicators for field early performance [2]. According to Li et al [3], by prolonging the cultivation period of seedlings in a nursery, i.e., by increasing the age of seedlings at the time of planting, larger seedlings may be produced. Larger seedlings usually perform better than smaller seedlings after planting [4, 5], especially under conditions of weed competition [6] and herbivorous vertebrate browsing [2]; decreasing survival with increasing seedling size has been detected at extremely harsh sites [7]. Grossnickle [8] specified that greater foliar mass of larger stocks allows increased photosynthetic efficiency, facilitating rapid growth and use of site resources during establishment.
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