Salinity constrains size inequality and allometry in two contrasting mangrove habitats in the Gulf of Mexico

Abstract

Abstract:The competition for resources increases size inequality in trees, particularly under low abiotic stress. Because mangrove communities are subject to site-specific salinity (and therefore abiotic stress) gradients, these habitats should differ in height–diameter allometry and size inequality. The size inequality (by the Gini Coefficient, G) and maximum potential height (Hmax from a height–diameter asymptotic model) were determined within the mangrove forest of a coastal lagoon in Veracruz, Mexico in 20 0.25-ha plots, 10 in interdistributary basins (IBs, lower salinity) having Avicennia germinans, Laguncularia racemosa and Rhizophora mangle and 10 in mudflats (MFs, higher salinity) dominated by A. germinans. Size inequality was significantly higher in IBs (G = 0.59 ± 0.02 vs. 0.39 ± 0.03). Due to their significant intercorrelation G, total basal area and density were synthesized in one PCA axis accounting for 67% of total variance and inversely correlated with salinity (R = −0.65, P = 0.003). The height–diameter scaling model reached a stable asymptote (Hmax range: 16–21 m; coefficient of variation CV: 7.7) in IBs, suggesting that trees can still increase their diameter after achieving maximum height. In MFs, no stable asymptote was reached (Hmax range: 11–26 m; CV: 32.5), suggesting a lower growth rate of diameter in the MF trees when compared with IB trees.

Morphological plasticity in mangrove trees: salinity-related changes in the allometry of Avicennia germinans

“…Despite the variation in pore-water salinity during the year, it is consistently higher in MFs than in IB. Previous studies present a detailed description of soil parameters and the annual salinity variation of both mangrove geomorphological types, which coincide with the sampling plots used in this study (López-Portillo and Ezcurra 1989;Hernández-Trejo et al 2006;Méndez-Alonzo et al 2012).…”

“…In the case of this study, we worked under the assumption that the forest had not undergone major changes; it has been a biological reserve since the early 1970s, and although it was previously subjected to anthropogenic transformations, the affected areas are located mainly in the inland-borders of the forests, whereas our plots were strategically located close to the lagoon, ensuring no anthropogenic impact reached the sites. From past evidences (Méndez-Alonzo et al 2012), it can be assumed that environmental conditions have been relatively stable for the last 100 years on each plot, that stand structure in La Mancha is most probably the direct result of prevailing micro-scale site conditions, and that the top height at each site accurately represents a community of trees using the available resources at their maximum capacity. We, therefore, consider that their structural properties and allometric relationships are the result of the environmental conditions in which they grow.…”

“…The lagoon has a surface area of 135 ha with 300 ha of mangrove forest fringing the lagoon. The mean annual precipitation is 1,200 mm and the mean annual temperature is 25°C (Méndez-Alonzo et al 2012). Three seasons can be recognized: dry, rainy, and north winds from October to February.…”

Patterns of seed bank and size asymmetry of plant growth across varying sites in the invasive Lantana camara L. (Verbenaceae)

“…The fact that asymmetries of AGR and crown volume (Gini coefficients) were the greatest in the grazed forest (a site with the highest plant density; see Table 2; Osunkoya et al 2012) supports the notion that size asymmetry of growth increases with density in crowded populations (Weiner and Damgaard 2006;Méndez-Alonzo et al 2012). The lack of significant changes in the asymmetry of crown volume and AGR with time of lantana plants on the farm, just as observed for its unusual bimodal size distribution (see Osunkoya et al 2012) is worth commenting upon.…”

“…Information contained in a set of size measurements (height, diameter, and volume/ biomass) for a population of plants can be used to make inferences about past or present competitive environments within that population (Thomas and Weiner 1989;Weiner 1990;Vega and Sadras 2003;Dolezal et al 2009;Metsaranta and Lieffers 2010;Pretzsch and Dieler 2011;Méndez-Alonzo et al 2012). While there is a prevalence of such studies across many plant life forms and ecological groups, including forest and commercially utilized species, equivalent study on invasive plants as a group is scant (but see Arenas et al 2002).…”