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Effects of Drought, Pest Pressure and Light Availability on Seedling Establishment and Growth: Their Role for Distribution of Tree Species across a Tropical Rainfall Gradient.

Gaviria J, Engelbrecht BM - PLoS ONE (2015)

Bottom Line: Tree species distributions associated with rainfall are among the most prominent patterns in tropical forests.Establishment success after one year did not reflect species distribution patterns.Together these processes sort species over longer time frames, and exclude species outside their respective home range.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Ecology, Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, Bayreuth, Germany.

ABSTRACT
Tree species distributions associated with rainfall are among the most prominent patterns in tropical forests. Understanding the mechanisms shaping these patterns is important to project impacts of global climate change on tree distributions and diversity in the tropics. Beside direct effects of water availability, additional factors co-varying with rainfall have been hypothesized to play an important role, including pest pressure and light availability. While low water availability is expected to exclude drought-intolerant wet forest species from drier forests (physiological tolerance hypothesis), high pest pressure or low light availability are hypothesized to exclude dry forest species from wetter forests (pest pressure gradient and light availability hypothesis, respectively). To test these hypotheses at the seed-to-seedling transition, the potentially most critical stage for species discrimination, we conducted a reciprocal transplant experiment combined with a pest exclosure treatment at a wet and a dry forest site in Panama with seeds of 26 species with contrasting origin. Establishment success after one year did not reflect species distribution patterns. However, in the wet forest, wet origin species had a home advantage over dry forest species through higher growth rates. At the same time, drought limited survival of wet origin species in the dry forest, supporting the physiological tolerance hypothesis. Together these processes sort species over longer time frames, and exclude species outside their respective home range. Although we found pronounced effects of pests and some effects of light availability on the seedlings, they did not corroborate the pest pressure nor light availability hypotheses at the seed-to-seedling transition. Our results underline that changes in water availability due to climate change will have direct consequences on tree regeneration and distributions along tropical rainfall gradients, while indirect effects of light and pests are less important.

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Related in: MedlinePlus

Probability of seed germination (A and B), wet season seedling survival (C and D) and dry season survival (E and F) for species with dry or wet origin as affected by moisture (dry vs. wet site), herbivore exposure (control vs. exclosure) and light availability (canopy openness).Panels A, C and E show means and standard errors from the least squares means table [46]. For canopy openness, results of exclosure and control seeds and seedlings were pooled (see also Fig 3). For overall analyses see Table 1, for planned contrasts (post-hoc-tests) see Table 2.
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pone.0143955.g004: Probability of seed germination (A and B), wet season seedling survival (C and D) and dry season survival (E and F) for species with dry or wet origin as affected by moisture (dry vs. wet site), herbivore exposure (control vs. exclosure) and light availability (canopy openness).Panels A, C and E show means and standard errors from the least squares means table [46]. For canopy openness, results of exclosure and control seeds and seedlings were pooled (see also Fig 3). For overall analyses see Table 1, for planned contrasts (post-hoc-tests) see Table 2.

Mentions: Below we first present the results for overall seedling establishment and growth during the study (Fig 3). The establishment success after one year is the cumulative result of germination and survival patterns, which are presented separately (Fig 4), and integrates processes in the wet and the dry season over the course of the experiment (see also Fig 1). To test our main hypotheses, we first focus on species performance under natural pest pressure (i.e. controls) to compare the performance of home vs. foreign species (i.e. origins) within sites and across sites (planned comparisons in Table 2a and 2b). Then we focus on the effects of pest exclusion within sites and across origins (planned comparisons in Table 2c and 2d). Finally, we depict the effects of light. Full results of the three-way interactions, as well as of pairwise interactions and individual factors are summarized in Table 1, and details are given in S3 Table.


Effects of Drought, Pest Pressure and Light Availability on Seedling Establishment and Growth: Their Role for Distribution of Tree Species across a Tropical Rainfall Gradient.

Gaviria J, Engelbrecht BM - PLoS ONE (2015)

Probability of seed germination (A and B), wet season seedling survival (C and D) and dry season survival (E and F) for species with dry or wet origin as affected by moisture (dry vs. wet site), herbivore exposure (control vs. exclosure) and light availability (canopy openness).Panels A, C and E show means and standard errors from the least squares means table [46]. For canopy openness, results of exclosure and control seeds and seedlings were pooled (see also Fig 3). For overall analyses see Table 1, for planned contrasts (post-hoc-tests) see Table 2.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4664389&req=5

pone.0143955.g004: Probability of seed germination (A and B), wet season seedling survival (C and D) and dry season survival (E and F) for species with dry or wet origin as affected by moisture (dry vs. wet site), herbivore exposure (control vs. exclosure) and light availability (canopy openness).Panels A, C and E show means and standard errors from the least squares means table [46]. For canopy openness, results of exclosure and control seeds and seedlings were pooled (see also Fig 3). For overall analyses see Table 1, for planned contrasts (post-hoc-tests) see Table 2.
Mentions: Below we first present the results for overall seedling establishment and growth during the study (Fig 3). The establishment success after one year is the cumulative result of germination and survival patterns, which are presented separately (Fig 4), and integrates processes in the wet and the dry season over the course of the experiment (see also Fig 1). To test our main hypotheses, we first focus on species performance under natural pest pressure (i.e. controls) to compare the performance of home vs. foreign species (i.e. origins) within sites and across sites (planned comparisons in Table 2a and 2b). Then we focus on the effects of pest exclusion within sites and across origins (planned comparisons in Table 2c and 2d). Finally, we depict the effects of light. Full results of the three-way interactions, as well as of pairwise interactions and individual factors are summarized in Table 1, and details are given in S3 Table.

Bottom Line: Tree species distributions associated with rainfall are among the most prominent patterns in tropical forests.Establishment success after one year did not reflect species distribution patterns.Together these processes sort species over longer time frames, and exclude species outside their respective home range.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Ecology, Bayreuth Center of Ecology and Environmental Research (BayCEER), University of Bayreuth, Bayreuth, Germany.

ABSTRACT
Tree species distributions associated with rainfall are among the most prominent patterns in tropical forests. Understanding the mechanisms shaping these patterns is important to project impacts of global climate change on tree distributions and diversity in the tropics. Beside direct effects of water availability, additional factors co-varying with rainfall have been hypothesized to play an important role, including pest pressure and light availability. While low water availability is expected to exclude drought-intolerant wet forest species from drier forests (physiological tolerance hypothesis), high pest pressure or low light availability are hypothesized to exclude dry forest species from wetter forests (pest pressure gradient and light availability hypothesis, respectively). To test these hypotheses at the seed-to-seedling transition, the potentially most critical stage for species discrimination, we conducted a reciprocal transplant experiment combined with a pest exclosure treatment at a wet and a dry forest site in Panama with seeds of 26 species with contrasting origin. Establishment success after one year did not reflect species distribution patterns. However, in the wet forest, wet origin species had a home advantage over dry forest species through higher growth rates. At the same time, drought limited survival of wet origin species in the dry forest, supporting the physiological tolerance hypothesis. Together these processes sort species over longer time frames, and exclude species outside their respective home range. Although we found pronounced effects of pests and some effects of light availability on the seedlings, they did not corroborate the pest pressure nor light availability hypotheses at the seed-to-seedling transition. Our results underline that changes in water availability due to climate change will have direct consequences on tree regeneration and distributions along tropical rainfall gradients, while indirect effects of light and pests are less important.

Show MeSH
Related in: MedlinePlus