Closing the life cycle of forest trees: The difficult dynamics of seedling-to-sapling transitions in a subtropical rain forest

1. Experimental and observational studies on seedling dynamics posit mechanisms that can influence forest diversity, structure, and function. However, high mortality and slow growth of seedlings make it difficult to evaluate the importance of this life-history filter to total tree life history. Quantifying the duration and transition of the seedling phase would help us understand this 'black box' in tree population biology. 2. We used a 16-year dataset of comprehensive seedling-to-sapling demography from a subtropical rain forest to construct population models that capture temporal demographic fluctuations for eight major tree species. We used data-driven demographic models and simulations to estimate the transition ratios from newly recruited seedlings to saplings of 2 m height and the time taken to attain 2 m height for a newly recruited seedling conditional on its survival. 3. Projections among species estimated that as few as 57 to more than 40,000 seedlings (with a median of 2,087) were required to make a single 2 m high sapling. Furthermore, it would take 22 to 200 years (with a median of 47) for a newly recruited seedling to become a 2 m high sapling. We found that temporal variation in demographic rates could greatly reduce the number of seedlings per established sapling, but not passage times. We also identified the importance of consistently fast growth rates for seedlings to escape the high mortality of early stages. 4. Synthesis. Our findings demonstrate that high mortality in the very early seedling stage severely limits the probability that a newly recruited seedling will transition to the sapling stage. Although the passage times vary, we found this to be true across species with a range of life-history strategies. Only seedlings with consistently fast growth rates are expected to pass through this life-history filter. Findings from seedling studies should consider how short term studies of seedling demography might capture the rare exceptional individuals and exceptional conditions that might define the dynamics of this seedling bottleneck.Seedling survival data (file name: fs_seedling_surv_data.txt) This file contains the annual seedling survival data of the eight major tree species in the Fushan Forest Dynamics Plot from February 2003 to February 2019. There are ten columns in this file: 'census' for the seedling census number 'year' for census year 'date' for census date 'tag' for the tag number of each seedling 'sp' for species code 'ht' for seedling height 'status' for seedling survival status in the current census 'surv' for seedling survival in the following census (1: alive, 0: dead) 'growth' for seedling growth increment in the following census (in cm) 'interval' for time interval between seedling censuses (in years) Seedling growth data (file name: fs_seedling_growth_data.txt) This file contains the seedling growth data of the eight major tree species in the Fushan Forest Dynamics Plot from February 2003 to February 2019. There are 11 columns in this file: 'census' for the seedling census number 'year' for census year 'date' for census date 'tag' for the tag number of each seedling 'sp' for species code 'sprout' for sprout identifier 'ht' for seedling height 'status' for seedling survival status in the current census 'surv' for seedling survival in the following census (1: alive, 0: dead) 'growth' for seedling growth increment in the following census (in cm) 'interval' for time interval between seedling censuses (in years) Sapling survival data (file name: fs_sapling_surv_data.txt) This file contains the sapling survival data of the eight major tree species in the Fushan Forest Dynamics Plot from 2004 to 2009. There are 8 columns in this file: 'tag' for the tag number of each sapling 'sp' for species code 'date1' for date of the first census 'status1' for sapling survival status in the first census 'size1' for dbh in the first census (in mm) date2' for date of the second census 'status2' for sapling survival status in the second census 'time1' for census interval between the first and second census (in years) Funding provided by: Ministry of Science and Technology, TaiwanCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100004663Award Number: MOST 104-2621-B-259-001Funding provided by: Taiwan Forestry Research InstituteCrossref Funder Registry ID: http://dx.doi.org/10.13039/100013035Award Number: 94AS-11.1.2-FI-G1(01)-1Funding provided by: Taiwan Forestry Research InstituteCrossref Funder Registry ID: http://dx.doi.org/10.13039/100013035Award Number: 93AS-2.4.2-FI-G1(2)Funding provided by: Ministry of Science and Technology, TaiwanCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100004663Award Number: MOST 104-2917-I-564-019Funding provided by: Taiwan Forestry Bureau*Crossref Funder Registry ID: Award Number: 95-00-2-05Funding provided by: Taiwan Forestry Bureau*Crossref Funder Registry ID: Award Number: 96-00-2-02Funding provided by: Taiwan Forestry Bureau*Crossref Funder Registry ID: Award Number: 97-00-2-01Funding provided by: Taiwan Forestry Bureau*Crossref Funder Registry ID: Award Number: tfbk-990207Funding provided by: Taiwan Forestry Bureau*Crossref Funder Registry ID: Award Number: 104AS-13.7.5-FB-e4Funding provided by: Taiwan Forestry Bureau*Crossref Funder Registry ID: Award Number: 105AS-12.7.4-FB-e3Funding provided by: Taiwan Forestry Bureau*Crossref Funder Registry ID: Award Number: tfbc-1070219Funding provided by: Taiwan Forestry Bureau*Crossref Funder Registry ID: Award Number: 92-00-2-06Funding provided by: Taiwan Forestry BureauCrossref Funder Registry ID: Award Number: 95-00-2-05This dataset contains a 16-yr seedling demographic data and a 5-yr sapling survival data of eight major tree species in the Fushan Forest Dynamics Plot (FDP), Taiwan. The seedling data span from February 2003 to February 2019, while the sapling data span from 2004 to 2009. In November 2002, 318 1-m2 seedling plots were established along four 400 m trails within the Fushan FDP. All seedlings of the eight study species