Seedling survival and growth in nursery and outplanting in Sebangau National Park, Central Kalimantan, Indonesia, 2009-2016

Data were collected from the Natural Laboratory of Peat-swamp Forest special research zone in Sebangau National Park, Central Kalimantan, Indonesia. This is an ombrogenous, non-masting peat-swamp forest, which experienced selective logging over a ~40 year period by timber concessions until 1997 and illegal hand-loggers until 2004. This past illegal logging was associated with creation of numerous small canals, causing peat drainage and making the peatland vulnerable to fire during the dry season. Tree planting has thus been trialled to accelerate reforestation, involving both growing seedlings in nursery conditions and subsequent outplanting, to test the performance (survival and growth) of different native tree species under different outplanting conditions (treatments).

Regarding the nursery datasets, seeds and wildlings were sourced from adjacent relatively undisturbed forest. Seeds were collected from the ground, with damaged seeds discarded, and were germinated in the nursery. After reaching 0.5-1 cm in height, seedlings were transferred to plastic, peat-filled polybags and given a unique numbered tag to facilitate monitoring. Watering and weeding were conducted when necessary. Seedlings were generally grouped into species cohorts on entry into the nursery. Fertiliser was added for some seedling batches (typically 6-9 g of Dekastar Plus: 13% N, 13% P2O5 and 13% K2O, plus micro-elements B, Cu, Mn, Mo and Zn), with seedlings thus categorised as non-fertilised, fertilised or unknown. Nursery data were collected between December 2009 and February 2014 for 40 native tropical peat-swamp forest species from 29 genera. Monitoring involved recording whether a seeding was alive and measuring the height in cm from the main stem base to the top of the highest leaf/branch. Nursery data cohorts were defined as groups of the same species, seedling source (seedling or wildling) and treatment (fertilised, non-fertilised or unknown) entering the nursery in a given month, with the resulting dataset consisting of a total 97 seedling cohorts.

Regarding the outplanting datasets, six distinct small-scale trials were implemented, producing a combination of species mixes (total 24 species; mean 7, range 2-11 species per trial), use of seedlings vs. wildlings, treatments and site conditions. See the Supplementary Information file for full details of planting trials. All species used were native to tropical peat-swamp forests in the region, with outplanted seedlings sourced mainly from the above seedling nursery. No root pruning was conducted. Where plastic polybags were used to grow seedlings in the nursery, these were removed upon outplanting, taking care to minimize root disturbance. Two trials included planting in weaved organic baskets (referred to by the local name “bakul” herein), typically measuring 20 cm height and 15 cm diameter, which were not removed prior to outplanting. Outplanted seedling monitoring involved recording whether a seeding was alive and measuring height in cm from the main stem base to the top of the highest leaf/branch. Seedling cohorts were defined as the same species, site condition, treatment, and plot or transect, resulting in a total 156 outplanted seedling cohorts.