Loke Thian Yew (2023) The establishment, survival, and growth of dipterocarp seedlings within lowland dipterocarp forest, Sabah, Malaysia. Doctoral thesis, Universiti Malaysia Sabah.
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Abstract
Tropical forests loss is unprecedented. Efforts had been taken to restore forest loss worldwide, however, the loss is faster than the recovery. The objectives of this study is to 1) estimate the potential of natural regeneration in remnant forests using aboveground carbon density as a surrogate of forest quality, 2) examine biotic and abiotic factors affecting survival and growth of seedlings following a masting event and gain insight into how this contributes to the recovery process. To address the first objective, a total of 446 circular plots were established at seven sites across Sabah. Line transects were used at 5 of the sites, with the other two sites sampled using a cluster plot sampling design. Circular plots measuring 2 m radius were established and the coordinates were marked using Garmin GPSMAP® 64s along the transect line with a minimum of 75 m between each plot. All dipterocarp seedlings within the plots were enumerated. The plot coordinates were overlaid over the Carnegie’s Airborne Observatory 30 m resolution carbon map in QGIS and the average aboveground carbon (ACD) determined by averaging the 9 pixel cells surrounding the seedling plot. A generalized linear mixed effect was used to investigate the relationship between ACD and dipterocarp seedling density. For the second objective, eight 16 ha plots were established within Sungai Tiagau Forest Reserve and all trees greater than 25 cm dbh enumerated. Thirty six 2 m radius circular plots were established within each of the 16 ha plots, and all seedlings enumerated. The seedlings were censused four times at irregular interval over a 37 month period and the growth and survival of the seedlings recorded. Kaplan-Meier analysis was used to compare the survival of seedling for community and the 11 most abundant species while generalized linear mixed effects model was used to analyze the effect of biotic and abiotic factors on seedling survival. The biotic factors includes seedling initial height, conspecific and heterospecific seedling and adult tree basal area and seedling diversity while abiotic factors includes canopy openness and organic litter layer thickness. Five models were fitted to the data using different combinations of the explanatory variables including height model, abiotic factor model, conspecific model, interaction of abiotic and conspecific model, and lastly the full model. Relative growth rates of 5 most abundant species were calculated. Factors affecting the RGRs were then analyzed using generalized linear models and the same biotic and abiotic factors from the survival study. There was a significant relationship between the density of the dipterocarp seedlings and ACD (z = 4.120, p<0.05). Natural regeneration is suppressed below 125 Mg C ha-1, with ACD lower than 40 Mg C ha-1 having no seedling. Seedling survival decreased rapidly in the first 2 censuses. Shorea pauciflora seedlings had the highest survival (75%) after 37 months and Shorea parvifolia the lowest (27%). The initial seedling height significantly affected seedling survival for all species, with taller seedlings having a higher probability of survival. Conspecific seedling and adult tree basal areas only affect Shorea fallax survival. Parashorea smythiesii had the highest relative growth rates, almost twice that of Dryobalanops lanceolata, 0.00051 cm cm-1 day-1 and 0.00026 cm cm-1 day-1 respectively. Initial seedling height significantly affected RGR, with taller seedlings having slower RGRs for all studied species. Canopy openness significantly affected all species except Parashorea smythiesii. This study demonstrates that natural regeneration occurred only at sites above 125 Mg C ha-1 whereas sites below this have to go through either assisted natural regeneration or active restoration. The survival and growth of seedling were highly affected by seedling initial height. This study suggests the use of ACD for forest restoration prescription to increase the effectiveness of forest restoration.
| Item Type: | Thesis (Doctoral) |
|---|---|
| Keyword: | Tropical forests loss, Tropical forest restoration, Biodiversity, Seedlings |
| Subjects: | S Agriculture > SD Forestry > SD1-669.5 Forestry |
| Department: | FACULTY > Faculty of Tropical Forestry |
| Depositing User: | DG MASNIAH AHMAD - |
| Date Deposited: | 10 Jul 2024 11:01 |
| Last Modified: | 10 Jul 2024 11:01 |
| URI: | https://eprints.ums.edu.my/id/eprint/39054 |
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