Temporal and spatial variability in seedling dynamics: a cross-site comparison in four lowland tropical forests

Metz, Margaret R.; Comita, Liza S.; Chen, Yu‐Yun; Norden, Natalia; Condit, Richard; Hubbell, Stephen P.; Sun, I‐Fang; Noor, Nur Supardi Md.; Wright, S. Joseph

doi:10.1017/s0266467407004695

Cited by 39 publications

(44 citation statements)

References 55 publications

(98 reference statements)

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“…Whether differences in the strength of nonrandom mortality (regardless of its effect on diversity) across size classes are consistent in other forests has yet to be determined. Accordingly, our results help justify initiatives to incorporate the smallest size classes into several large-scale, long-term forest monitoring projects (38)(39)(40), and call for their more widespread inclusion elsewhere. Similar processes are likely to occur in all communities of sessile organisms in which recruitment primarily occurs through dispersed propagules, including marine communities (41).…”

Section: Discussionmentioning

confidence: 57%

Nonrandom, diversifying processes are disproportionately strong in the smallest size classes of a tropical forest

Green

Harms

Connell

2014

Proc. Natl. Acad. Sci. U.S.A.

101

116

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A variety of ecological processes influence diversity and species composition in natural communities. Most of these processes, whether abiotic or biotic, differentially filter individuals from birth to death, thereby altering species' relative abundances. Nonrandom outcomes could accrue throughout ontogeny, or the processes that generate them could be particularly influential at certain stages. One long-standing paradigm in tropical forest ecology holds that patterns of relative abundance among mature trees are largely set by processes operating at the earliest life cycle stages. Several studies confirm filtering processes at some stages, but the longevity of large trees makes a rigorous comparison across size classes impossible without long-term demographic data. Here, we use one of the world's longest-running, plot-based forest dynamics projects to compare nonrandom outcomes across stage classes. We considered a cohort of 7,977 individuals in 186 species that were alive in 1971 and monitored in 13 mortality censuses over 42 y to 2013. Nonrandom mortality with respect to species identity occurred more often in the smaller rather than the larger size classes. Furthermore, observed nonrandom mortality in the smaller size classes had a diversifying influence; species richness of the survivors was up to 30% greater than expected in the two smallest size classes, but not greater than expected in the larger size classes. These results highlight the importance of early life cycle stages in tropical forest community dynamics. More generally, they add to an accumulating body of evidence for the importance of early-stage nonrandom outcomes to community structure in marine and terrestrial environments. diversity | early life-cycle stages | nonrandom | tropical forest P rocesses that operate nonrandomly with respect to species identity contribute to the structure of natural communities (1-3). Evidence from diverse rain forests includes demographic transitions from seeds to seedlings (4, 5), at the seedling (6, 7) and sapling stages (8) and among large trees (9-12). Although the relative contributions of nonrandom processes at each life cycle stage to determining patterns of abundance and diversity in the mature canopy are unknown, one long-standing paradigm is that community assembly is mediated primarily by events occurring from seed dispersal through seedling germination and small-sapling establishment (13-17). However, despite suggestive patterns (6,7,18,19), evidence is lacking for the comparative strength of early-stage dynamics in determining canopy abundance and diversity.Numerous studies demonstrate significant interspecific variation in the susceptibility of tropical tree seedlings to postgermination hazards, including natural enemies (20, 21), adverse climatic or edaphic conditions (22), physical damage (23), and the crowding or shared-enemies effects of con-and heterospecific neighbors (24,25). In other words, the per capita probability of seedling mortality is nonrandom because the probability of death is not t...

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Section: Discussionmentioning

confidence: 57%

Nonrandom, diversifying processes are disproportionately strong in the smallest size classes of a tropical forest

Green

Harms

Connell

2014

Proc. Natl. Acad. Sci. U.S.A.

101

116

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“…One striking finding was that two species, Metrosideros and Cheirodendron, had zero seed limitation, a phenomenon not previously reported for any studies of comparable duration , Norden et al 2009). In other forests, such a phenomenon might be observed after masting years (Metz et al 2008), but the biology of Metrosideros is apparently distinctive in showing this kind of output, each year saturating the landscape with a large number of tiny seeds (Drake 1992). The other species, Cheirodendron, is a ubiquitous midstory tree that produces abundant birddispersed fruits.…”

Section: Strong Importance Of Seed and Establishment Limitation In Lomentioning

confidence: 99%

Seedling recruitment factors in low‐diversity Hawaiian wet forest: towards global comparisons among tropical forests

et al. 2013

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Recruitment limitations determine forest community regeneration patterns. Source limitation and dispersal limitation contribute to overall seed limitation, while environmental conditions and habitat associations influence establishment limitation. Several hypotheses have made contradictory predictions for how the relative importance of these limitations should vary with diversity. However, comparative data have not been available for low‐diversity tropical forests. We quantified recruitment limitations using 2.5 yrs of seed rain and seedling distribution data collected within a 4 ha forest dynamics plot in low‐diversity native‐dominated Hawaiian wet forest. We further quantified seedling irradiance and substrate habitat associations and niche overlap (using Pianka's niche overlap index). Additionally, we compared recruitment limitations and the frequency of seedling habitat associations across forests using the few available published data from sites employing similar field and analytical methods. In Hawaiian wet forest, seed dispersal more strongly limited recruitment than did establishment limitation across species, with 11 of 18 species completely seed limited (i.e., no seeds found). However, the relative importance of limitations varied greatly among species. For the three most abundant species, habitat conditions more strongly limited regeneration than did seed arrival, especially for the dominant canopy species, Metrosideros polymorpha, which was not seed limited. Most species were significantly associated with specific ranges of irradiance and/or substrates. Although habitat associations may indicate niche differentiation, Hawaiian species also showed significant niche overlap. Across the three forests compared, community‐wide mean seed and establishment limitation values were similar, despite wide variation in diversity. However, recruitment limitations differed strongly among species within forests due to species' life‐history differences. While seed limitation in Hawaiian forest was as high as in high‐diversity forests, mechanisms may differ; seed limitation in Hawaii may arise from loss of pollinators and dispersers rather than from a high proportion of rare species as occurs in high‐diversity forests. The strong habitat associations in Hawaiian forest relative to high‐diversity forests supported theoretical expectations that lower species diversity should increase the importance of habitat associations. However, these habitat associations were not linked to niche differentiation in Hawaii. Our findings suggest that high recruitment limitation may facilitate coexistence despite niche overlap in low‐diversity Hawaiian forest.

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“…It is known that processes affecting the seedling stage act as a strong selective filter controlling patterns of recruitment and are thereby influencing the future species composition of the forest (Swaine, 1996;Whitmore, 1996;Metz et al, 2008). Therefore, it is crucial to understand the impact of changed nutrient availability at this stage of the life cycle.…”

Section: Introductionmentioning

confidence: 99%

Performance of Seedlings of a Shade-Tolerant Tropical Tree Species after Moderate Addition of N and P

2015

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Nitrogen deposition to tropical forests is predicted to increase in future in many regions due to agricultural intensification. We conducted a seedling transplantation experiment in a tropical premontane forest in Ecuador with a locally abundant late-successional tree species (Pouteria torta, Sapotaceae) aimed at detecting species-specific responses to moderate N and P addition and to understand how increasing nutrient availability will affect regeneration. From locally collected seeds, 320 seedlings were produced and transplanted to the plots of the Ecuadorian Nutrient Manipulation Experiment (NUMEX) with three treatments (moderate N addition: 50 kg N ha −1 year −1 , moderate P addition: 10 kg P ha −1 year −1 and combined N and P addition) and a control (80 plants per treatment). After 12 months, mortality, relative growth rate, leaf nutrient content and leaf herbivory rate were measured. N and NP addition significantly increased the mortality rate (70 vs. 54% in the control). However, N and P addition also increased the diameter growth rate of the surviving seedlings. N and P addition did not alter foliar nutrient concentrations and leaf N:P ratio, but N addition decreased the leaf C:N ratio and increased SLA. P addition (but not N addition) resulted in higher leaf area loss to herbivore consumption and also shifted carbon allocation to root growth. This fertilization experiment with a common rainforest tree species conducted in old-growth forest shows that already moderate doses of added N and P are affecting seedling performance which most likely will have consequences for the competitive strength in the understory and the recruitment success of P. torta. Simultaneous increases in growth, herbivory and mortality rates make it difficult to assess the species' overall performance and predict how a future increase in nutrient deposition will alter the abundance of this species in the Andean tropical montane forests.

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Temporal and spatial variability in seedling dynamics: a cross-site comparison in four lowland tropical forests

Cited by 39 publications

References 55 publications

Nonrandom, diversifying processes are disproportionately strong in the smallest size classes of a tropical forest

Nonrandom, diversifying processes are disproportionately strong in the smallest size classes of a tropical forest

Seedling recruitment factors in low‐diversity Hawaiian wet forest: towards global comparisons among tropical forests

Performance of Seedlings of a Shade-Tolerant Tropical Tree Species after Moderate Addition of N and P

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