DOI: 10.5061/dryad.wdbrv15pd
title: Demographic differentiation among pioneer tree species during old-field succession of a Neotropical rainforest

description: Early pioneer species share life histories enabling them to colonize
 disturbed sites, but how much they differ demographically and how such
 differentiation determines pioneer species turnover during succession are
 still open questions. Here, we approached these issues by comparing the
 demography of dominant pioneer tree species during the old-field
 succession of tropical rainforest in Southeast Mexico. We assessed changes
 in population density, population structure, vital rates, and intrinsic
 population growth rate (r) of the pioneer species Trema micrantha,
 Cecropia peltata, and Trichospermum mexicanum during the first 35 years of
 succession. For this, we combined chronosequence and long-term (from 2000
 to 2018) data from 14 old-fields with 0.5-35 years fallow age. Trema
 colonized and disappeared first during succession (&lt; 15 years),
 followed by Cecropia (&lt; 28) and Trichospermum (&gt; 31). All
 species exhibited hump-shaped successional trajectories of population
 density and biomass with Trema reaching a peak first, followed by Cecropia
 and later Trichospermum. Species exhibited a fast reduction in r with
 fallow age, with Trema reaching negative growth rates (r &lt; 0) in
 the third, Cecropia in the fourth, and Trichospermum in the seventh year
 of succession. Recruitment, growth, and mortality rates of seedlings and
 juveniles defined the period of population increase and the age of
 succession at which each species reached maximum density and biomass. The
 mortality rate in mature stages determined how long each species persisted
 during succession. An important variation in species replacement occurred
 among study sites. In some sites one species was abundant and the others
 were almost absent, while it was the opposite in other sites. We inferred
 that priority inhibitory effects operated among species during the field
 colonization. Synthesis: Although Trema, Cecropia, and Trichospermum are
 considered typical pioneer trees, these species differed importantly in
 their demographic attributes during succession. The speed at which r
 declined with age of succession indicated the moment at which each species
 reached its maximum density and species replacement sequence during
 succession. However, inter-specific priority inhibitory effects during
 field colonization may also be involved in the chance of colonization and
 replacement between species with similar regeneration strategies.
description: Data were gathered from fourteen 10 x 50 m (500
 m<sup>2</sup>) plots, eleven established in 2000, one in 2002,
 and two in 2004. All plots were established in abandoned cornfields. Due
 to the land-use dynamics in the region, the number of plots was unbalanced
 regarding fallow age. Nonetheless, the initial fallow age range (0.5-17
 years) of the plots represented the most common secondary forest ages in
 the region. Trees of <em>Cecropia peltata</em>,
 <em>Trema micrantha</em>, and <em>Trichospermum
 mexicanum</em> with heights &gt;= 1.5 m were monitored and
 measured in the entire plots every year until 2018. Individuals &lt;
 1.5 m height were monitored and measured in twenty 1 x 2 m subplots in
 five plots, which represented an initial fallow age range of 1.5 to 19
 years. Additionally, in these five plots were sampled the seed rain (12
 seed traps per plot, randomly distributed) and the seed bank (20 soil
 cores - 10 cm diameter, 10 cm depth- per plot, randomly distributed)
 during two years (2002-2004). Finally, in the year period 2017-2018,
 fecundity data was gathered from mature trees (&gt; 5 cm DBH) of
 <em>Cecropia</em> and <em>Trichospermum</em>,
 which were located outside the plots. No fecundity data for
 <em>Trema</em> was collected.  Data were
 introduced into Excel files and regularly curated by a specialized
 technician.         
description: Because databases combine chronosequence and long-term
 data, three plots were lost during the research period due to fires, and
 we had a subset of plots to study seed rain, seed bank and regenerative
 plants (&lt; 150 m hight), in some databases there are some ages of
 succession without data.