Tree growth periodicity in the ever‐wet tropical forest of the Americas

Abstract

The occurrence of annual growth rings in tropical trees—the result of the seasonal activity of vascular cambium—has been explained by seasonal water deficit or flooding periods. However, little is known about the drivers of annual tree‐ring formation under tropical hyper‐humid conditions without clear seasonal dry periods or flooding (ever‐wet conditions). Shelford's law states that the deficit or the excess of environmental resources limits plant growth. Accordingly, we hypothesize that excess soil moisture, a slight seasonal reduction of precipitation and a reduction in light availability determine rhythmic growth in ever‐wet tropical forests. We first assessed the occurrence of rhythmic growth in 14 tree species from the Biogeographic Chocó Region (annual rainfall 7200 mm) using three methods: Radiocarbon (14C) dating (all studied species), tree‐ring synchronization (4 species that have replicates) and automatic dendrometers (two species). Then, we assessed the effect of environmental drivers (rainfall, short‐wave radiation, temperature and soil moisture) on tree growth based on tree ring and dendrometer observations. We present evidence of annual tree‐ring formation in all 14 studied tree species. Depending on the tree species, we observed positive and negative correlations between growth, water availability and light availability. These relationships suggest that both excess or deficit of environmental resources may explain the seasonal pattern of tree growth. Although we cannot differentiate between excess soil water and low light availability by high cloudiness, we suggest that cloudiness frequency could affect tree growth in these forests. Synthesis. We reveal the annual formation of growth rings in the unexplored wetter‐end tropical forests, where seasonal growth depends on either high soil moisture and hypoxia or light limitations by cloudiness and photosynthesis constraints.

Growth Rings in Nine Tree Species on a Neotropical Island with High Precipitation: Coco Island, Costa Rica

“…Thus, excess water in the soil, cloudiness, and low solar radiation between November and March could result in a reduction in photosynthesis, along with seasonal variations in the vascular cambium and other aspects of tree growth [16], leading to the formation of growth rings in seven of the nine species studied on Coco Island. According to Giraldo et al [33], annual formation of growth rings in unexplored tropical forests in rainy areas is governed by seasonal growth that occurs due to high soil moisture and hypoxia, or light limitations due to cloudiness and limitations of photosynthesis.…”

Tropical Trees Will Need to Acclimate to Rising Temperatures—But Can They?

“…Annual tree rings are undoubtably less distinct and less widespread in the tropics than in temperate and boreal zones, but an increasing number of studies have demonstrated that many tropical tree species (i.e., >230 species; refs. [88,113]) do in fact exhibit visible annual growth rings (including in the wettest perhumid tropical forests [114]). Even in the absence of visible annual rings, it is possible to date wood samples and create chronosequences based on high-resolution isotopic measurements and/or radiocarbon dating [115,116].…”

Insights into Growth, Ring Formation and Maximum Ages of Brazil Nut Trees (Bertholletia excelsa) Using 14C Dating and Tree-Ring Analysis

“…Nevertheless, the use of bomb curve radiocarbon measurements to confirm annual ring formation has stimulated a number of recent studies on tropical species (i.e. Giraldo Giraldo et al 2023; Andreu-Hayles et al 2015; Baker et al 2017; Herrera Ramirez et al 2017;). Despite growing interest, however, dendrochronological studies in the tropics still face major challenges relating to the distinctiveness of tree-ring boundaries, the occurrence of missing rings, and the determination of the annual nature of tree-rings (Baker et al 2017; Herrera-Ramirez et al 2017).…”