Pole diameter and wood density are variables commonly used in allometric equations to estimate tree biomass and carbon stocks in tropical forests. The effect of variations in tree water content on pole diameters is often disregarded in allometric equations. This study aimed to determine the effect of rainfall seasonality on tree growth, stem wood and bark water content and to assess the relationship between water content and wood density (dry mass to fresh mass volume ratio) in 120 trees from 28 species in a
Tree wood density and diameter growth rate at breast height (DBH) are variables commonly used in mathematical models to estimate tree biomass and carbon stocks in tropical forests (
Basic wood density (dry mass to fresh volume ratio) can vary among species, tree-to-tree, and even among different parts of the same plant (
Variations in pole water content are mostly related to rainfall seasonality (
Variations in the water content of poles reflect their water-storing capacity - tree capacitance (
In this study we hypothesized that trees grow faster in the wet season and that bark and wood hold less water in the dry season. The aims of this study were: (1) to determine the effect of monthly rainfall on tree growth in diameter and water content of the bark and stem wood; and (2) to assess the relationship between water content and wood density in tree species of a pristine
Data were collected in 2006 at the Tropical Forest Experimental Station (ZF2 reserve - 60° 08′ W, 2° 36′ S) National Institute for Research in the Amazon, State of Amazonas, Brazil. The vegetation is a dense
Climate data were collected using a weather station Li-1401 (Li-Cor, Lincoln, NE, USA) placed at the top of a 40-m tall observatory tower located near the study site (60° 06′ 53″ W, 02° 35′ 21″ S). Air temperature, relative humidity (Humitter 50y, Vaisala Ov, Finlandia) and photosynthetically active radiation (PAR, LI-190SA, Li-Cor, Lincoln, NE, USA) sensors were connected to a datalogger (LI-1400, Li-Cor, Lincoln, NE, USA). Air temperature and relative humidity data were collected at 30-minute intervals and PAR data at intervals of 15 minutes. Rainfall data were collected at 14-day intervals using a conventional pluviometer positioned at the top of the observatory tower. The daily cumulative irradiance (mol m-2 day) was calculated by integrating the instantaneous PAR values over the whole day period. The monthly average of cumulative irradiance was obtained from the daily data.
In the rainy season (April-May) and dry season (August-September) of 2006, core samples of bark and wood (3 to 5 cm in-length and 5.15 mm in diameter) were collected from the tree poles at 1.3 m from the ground surface (
Water content (WC) was obtained as the difference between fresh mass (FM) and dry mass (DM) divided by the fresh mass (
In all 120 sampled trees, tree diameter was measured at monthly intervals from January to December 2006, using dendrometric bands, which had been previously installed, four months before the beginning of this study. To determine the relationship between monthly rainfall (total amount of rainfall over a month) and tree growth, for each month, growth data were pooled across species to obtain the mean monthly growth rate of the trees.
An analysis of variance (ANOVA) under the assumption of a completely randomized design was used for data analysis. Pearson’s coefficients were calculated for the relationship between monthly rainfall and tree growth, water content and tree diameter, and between tree growth and stem water content and wood density. All statistical analyses were performed with the SAEG 9.0 statistical package from the Federal University of Viçosa (Brazil).
In 2006, total annual rainfall was 2448 mm, which was quite close to the historical mean (2420 mm) for central Amazonia (
In most of the tree species (26 out of 28), trees had stem wood water content higher in the rainy season than in the dry season, but several species showed an opposite pattern for the water content of the bark (
During the rainy season, wood water content of the 28 tree species ranged from 25.5% (
The stem wood water contents recorded in this study are within the range found by other researchers (
Contrary to our initial expectations, the bark water content of most trees was either equal or higher in the dry season than in the rainy season (
On a mass basis, the wood has less water content than the bark because of its main cellular components. Although the sapwood contains parenchyma tissue which can easily expand, the xylem conduits are less prone to contraction and expansion. Indeed, the mature xylem can contract and expand involving elastic deformation (reversible change in shape), but with little exchange of water with the adjacent tissue (
Across species there was no correlation between tree growth in diameter and monthly rainfall throughout the year (
Tree growth was faster in some species (
Irrespective of the season, we did not find any significant relationship between tree size, expressed as DBH, and water content (
Water-induced expanding and shrinking of poles pose a major challenge for accurate determination of tree growth in diameter (
Wood density varied among the 28 species studied, with a mean value of 0.75 g cm-3 (
The mean wood density value found in this study is 7% higher than the mean value previously recorded in the Amazon region, about 0.70 g cm-3 (
A negative correlation (
The wood water content of the studied species negatively correlated with wood density (
Although the period examined was short (twelve months), the number of trees we measured (n = 120) and the closeness of the annual rainfall in 2006 to the historical regional mean (2448
The authors thank the Ministry of Science Technology and Innovation (MCTI/INPA), and the Foundation for Research Support of the State of Amazonas (FAPEAM). The Coordination of Improvement of Higher Education Personnel (CAPES) and the National Council for Scientific and Technological Development (CNPq). We also thank the anonymous reviewers for their helpful comments and suggestions.
Water content of wood and bark during the rainy season (black bars) and the dry season (white bars) of 2006. Each bar denotes the mean of several trees within a species. Error bars represents the standard error of the mean. Labels and the number of trees per species are given in
Box plot of the water content of wood (A) and bark (B) across the 28 tree species (120 trees) used in the study, in the dry (August-September ) and rainy season (April-May) of 2006. For panel A:
Relationship between tree growth and monthly rainfall across the 28 studied species. The black diamond indicates a negative value (see text for discussion). Mean tree growth in diameter was 0.17 mm month-1. Each data point represents the mean growth rate of the 120 sampled trees in a given month of 2006.
Relationship between water content of wood (solid circles) and bark (empty squares) and tree diameter measured at 1.3 m (DBH), in the rainy season (A) and dry season (B) of 2006. Each data point represents one tree. For panel A:
Relationship between wood water content and wood density (A) and between tree growth and wood density (B) across the 28 studied species (120 trees). Each data point represents one tree.
Mean ± standard deviation of tree growth in diameter (TGD) and wood density (WD, dry mass to fresh mass volume ratio), and the range of diameter of the sampled trees at 1.3 m height (DBH, cm) of the 28 species used in the study. Species and their labels, the botanical family and number of sampled trees per species (N) are also shown.
Species | Label | Family | N | TGD(mm month-1) | WD(g cm-3) | DBH(cm) |
---|---|---|---|---|---|---|
Bdu | Malpighiaceae | 4 | 0.22 ± 0.07 | 0.62 ± 0.02 | 22.5 - 45.7 | |
Ebi | Vochysiaceae | 3 | 0.12 ± 0.05 | 0.56 ± 0.02 | 12.7 - 19.0 | |
Ebr | Lecythidaceae | 12 | 0.13 ± 0.10 | 0.83 ± 0.01 | 12.0 - 26.0 | |
Eco | Lecythidaceae | 7 | 0.15 ± 0.09 | 0.79 ± 0.01 | 11.1 - 27.0 | |
Egr | Lecythidaceae | 3 | 0.13 ± 0.06 | 0.82 ± 0.03 | 19.1 - 46.1 | |
Epe | Lecythidaceae | 5 | 0.08 ± 0.07 | 0.81 ± 0.02 | 12.0 - 48.3 | |
Esp | Lecythidaceae | 4 | 0.09 ± 0.08 | 0.82 ± 0.02 | 13.1 - 27.0 | |
Gar | Apocynaceae | 4 | 0.10 ± 0.07 | 0.85 ± 0.01 | 12.0 - 35.9 | |
Gau | Lecythidaceae | 3 | 0.07 ± 0.08 | 0.77 ± 0.02 | 15.1 - 20.6 | |
Ila | Fabaceae | 4 | 0.47 ± 0.16 | 0.76 ± 0.03 | 14.1 - 22.5 | |
Lag | Lacistemataceae | 3 | 0.17 ± 0.06 | 0.60 ± 0.02 | 12.5 - 19.0 | |
Lca | Chrysobalanaceae | 3 | 0.20 ± 0.07 | 0.87 ± 0.03 | 28.0 - 37.0 | |
Lmi | Chrysobalanaceae | 5 | 0.13 ± 0.07 | 0.87 ± 0.01 | 14.0 - 34.1 | |
Mit | Lauraceae | 5 | 0.07 ± 0.05 | 0.76 ± 0.02 | 10.1 - 21.3 | |
Msc | Euphorbiaceae | 3 | 0.10 ± 0.07 | 0.89 ± 0.01 | 28.9 - 40.3 | |
Mgy | Sapotaceae | 4 | 0.16 ± 0.10 | 0.71 ± 0.01 | 17.6 - 40.4 | |
Mgu | Olacaceae | 3 | 0.11 ± 0.07 | 0.81 ± 0.03 | 16.1 - 49.8 | |
Pto | Urticaceae | 4 | 0.27 ± 0.09 | 0.42 ± 0.02 | 16.0 - 34.0 | |
Pcl | Sapotaceae | 3 | 0.11 ± 0.04 | 0.78 ± 0.13 | 10.1 - 20.0 | |
Pgu | Sapotaceae | 3 | 0.10 ± 0.05 | 0.89 ± 0.02 | 22.0 - 64.8 | |
Pma | Sapotaceae | 4 | 0.17 ± 0.06 | 0.91 ± 0.02 | 14.2 - 44.0 | |
Psp | Sapotaceae | 3 | 0.13 ± 0.05 | 0.79 ± 0.03 | 13.0 - 19.8 | |
Pap | Burseraceae | 8 | 0.11 ± 0.04 | 0.63 ± 0.01 | 10.0 - 30.0 | |
Phe | Burseraceae | 3 | 0.10 ± 0.09 | 0.58 ± 0.02 | 11.7 - 13.8 | |
Smi | Malvaceae | 4 | 0.47 ± 0.22 | 0.65 ± 0.02 | 21.9 - 46.9 | |
Sto | Fabaceae | 4 | 0.13 ± 0.04 | 0.81 ± 0.02 | 11.0 - 34.1 | |
Tve | Fabaceae | 4 | 0.45 ± 0.12 | 0.56 ± 0.02 | 10.1 - 21.3 | |
Tsy | Malvaceae | 5 | 0.07 ± 0.04 | 0.71 ± 0.02 | 11.0 - 15.0 |