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Survival and growth of Symphonia seedlings in a reciprocal transplantation experiment

Citation

Tysklind, Niklas et al. (2021), Survival and growth of Symphonia seedlings in a reciprocal transplantation experiment, Dryad, Dataset, https://doi.org/10.5061/dryad.stqjq2c1q

Abstract

Trees are characterised by the large number of seeds they produce. Although most of those seeds will never germinate, plenty will. Of those which germinate, many die young, and eventually only a minute fraction will grow to adult stage and reproduce. Is this just a random process? Do variations in germination and survival at very young stages rely on variations in adaptations to microgeographic heterogeneity? and do these processes matter at all in determining tree species distribution and abundance?

We have studied these questions with the Neotropical Symphonia tree species. In the Guiana shield, Symphonia are represented by at least two sympatric taxa or ecotypes, Symphonia globulifera found almost exclusively in bottomlands, and a yet undescribed more generalist taxon/ecotype, Symphonia sp1.  A reciprocal transplantation experiment (510 seeds, 16 conditions) was set up and followed over the course of 6 years to evaluate the survival and performance of individuals from different ecotypes and provenances.

Germination, survival, growth, and herbivory showed signs of local adaptation, with some combinations of ecotypes and provenances growing faster and surviving better in their own habitat or provenance region. S. globulifera was strongly penalised when planted outside its home habitat but showed the fastest growth rates when planted in its home habitat, suggesting it’s a specialist of a high-risk high-gain strategy. Conversely, S. sp1 behaved as a generalist, performing well in a variety of environments. 

The differential performance of seeds and seedlings in the different habitats matches the known distribution of both ecotypes, indicating that environmental filtering at the very early stages can be a key determinant of tree species distributions, even at the microgeographic level and among very closely related taxa. Furthermore, such differential performance also contributes to explain, in part, the maintenance of the different Symphonia ecotypes living in intimate sympatry despite occasional gene flow.

Methods

The experimental design aimed to collect seeds from mother trees from two contrasting habitats and the associated ecotypes: SF-S. globulifera and HT-S. sp1;  and from two broad regions with markedly different rainfall patterns: 'east', with the highest rainfall in French Guiana, and 'west', the driest part of French Guiana (Fig. 2). Seeds were transplanted onto experimental gardens installed on HT and SF habitats at two field sites in the 'east' and 'west' regions, respectively, which were not among the sampled sites for the seeds.

Seeds were collected between September 2008 and April 2009, due to large differences in flowering times, from nine mother trees belonging to both ecotypes in the 'western' region and from five mother trees in the 'eastern' region, composing the variables “Provenance region” and “Ecotype” (Table 1). From each mother tree, 35-39 seeds were collected and sown in polypropylene germination plates with soil in a common shadehouse at the Kourou Agronomic Campus prior to transplantation into field sites between May and July 2009. This meant that seeds spent between 27 and 315 days in the shadehouse, depending on the seed collection and transplant dates.

Whether seeds had germinated at the moment of transplant or not was stored in the variable “transplant status”.

To avoid confusion, we hereafter refer to “seed” when discussing aspects regarding the phase prior to germination, “seedling” for those aspects regarding the phase after germination, and “individual” for those aspects regarding both seed and seedling phases.

Individuals (i.e. seed or seedling) were transplanted to gardens established at each field site (i.e. east vs. west) and habitat: three in SF and three in HT conditions in each site, totalling 12 gardens (see Brousseau et al. 2020, under revision at Molecular ecology, for the description of sites).

Notice that, because S. globulifera and S. sp1 are late-succession, shade-tolerant trees, the gardens were established under canopy cover. Field site plantation and habitat compose the variables “Plantation region” and “Habitat”, respectively (Table 2; Fig. 2). Each garden was fenced from large herbivores with chicken wire. Prior to transplanting, all understory vegetation (i.e. up to 5 cm D.B.H.) was removed; the canopy was left undisturbed. Regeneration other than the transplanted seedlings was removed yearly by hand. Individuals were distributed over the twelve gardens as follows: each garden was arranged in 44 ten-seedling slots. In each garden, six slots were randomly attributed to Symphonia (the remaining slots were used for other experiments), and then three individuals per mother plant were assigned to random positions within those slots in each garden. Individuals were allocated to different gardens depending on their provenance, ecotype, plantation region, and habitat without differentiating between those that had germinated in the shadehouse and transplanted as germinated seedlings or those transplanted as ungerminated seed (Table 2). Data for each individual (i.e. germination status at transplantation, germination year, survival, growth-associated traits, and herbivory) were collected at transplant date and then yearly in September from 2009 until 2014, except for 2012 (Suppl. Table 1). Individual survival was recorded as follows: 1 for seedlings found alive and 0 for ungerminated seeds transplanted to field sites and yet to germinate, and for seedlings previously living but found dead. Seedling height was measured in centimetres between the apical bud and the collar. Stem diameter was measured in millimetres at the collar in two orthogonal directions and estimated as the mean of the two measures. As an architectural trait, we selected “total number of leaves”, an indicator of seedling leafiness. Herbivory was determined as follows: each leaf was assigned one of five classes of percentage of damaged area (0-20%; 20-40%; 40-60%; 60-80%; 80-100%) and then seedling herbivory attack level was estimated as the average of the percentage of damaged area of all its leaves

Usage Notes

This contains raw data on the survival and growth of a reciprocal transplantation experiment of Symphonia in French Guiana. 

Two different ecotypes/species, S. globulifera and S. sp1, exists in sympatry. The former is a seasonally floded specialists, whereas the latter prefers hilltops and slopes. Seeds from both ecotypes and from two regions (east and west) were collected from mother trees and grown in a reciprocal transplantation experiment. 
The experiment was established in 2009, and measurement were taken annualy except for 2012. 
Year 0 = 2009
Year 1 = 2010
Year 2 = 2011
Year 4 = 2013
Year 5 = 2014


The traits measured were height (cm), diameter (mm), and total number of leaves, as well as the relative growth rates (difference between years)  in these three variables. 

We also calculated predation as an average percentage of damaged in all leaves. Germination and survival were recorded as 0 (ungerminated or dead) and 1 (alive). Trait data for individuals that were ungerminated or dead are recorded as NA. 

Contact scientist: Niklas Tysklind (niklas.tysklind@ecofog.gf), Ivan Scotti (ivan.scotti@inrae.fr), Caroline Scotti-Saintagne (caroline.scotti-saintagne@inrate.fr). 

Fields description available in ReadMe_Symphonia_RTE.txt 

Funding

Agence Nationale de la Recherche, Award: ANR-10-LABX-25-01

Feder

European Union, Award: PO-FEDER ENERGIRAVI

Feder

European Union, Award: PO-FEDER ENERGIRAVI