Martin Worbes

How to Measure Growth Dynamics in Tropical Trees a Review

Cambial dormancy and annual rings in tropical trees are induced by annually occurring dry periods or flooding. Growth periodicity is indicated by the leaf fall behaviour and is connected with an annual periodicity of shoot elongation. Changes in stem diameter are measured with a dendrometer or by measurable differences in the electrical resistance of the cambium. Dendrochronological methods applied to carefully prepared samples can serve as proof of the annual periodicity of growth zones. For this purpose the following methods have been used: cambial wounding, radiocarbon dating, pointer year detection and regression analyses of ring width and climate data. Although X-ray densitometry and the analysis of stable isotopes in rings of tropical trees promise to provide interesting climatological information, the use of these methods remains difficult.

One hundred years of tree-ring research in the tropics - a brief history and an outlook to future challenges

Summary Tree-ring analysis in the tropics exists since more than one hundred years. In more than 20 tropical countries and numerous tree species the existence of annual tree-rings is doubtless proven. Rhythmic growth is induced by short drought periods or long lasting inundation, the influence of the photoperiod is questionable. Climatological analyses of tree-ring chronologies show the influence of El Nino on tree growth. Tree-ring based age determinations give maximum ages of not more than 600 years for broad leaf trees in tropical lowlands. Increment estimations by ring-width measurements give reliable results for sustainable management systems in tropical forests.

Phenology and stem-growth periodicity of tree species in Amazonian floodplain forests

To study the impact of the annual long-term flooding (flood-pulse) on seasonal tree development in Amazonian floodplains, the phenology and growth in stem diameter of various tree species with different leaf-change patterns were observed over a period of 2 y. The trees of the functional ecotypes, evergreen, brevi-deciduous, deciduous and stem-succulent showed a periodic behaviour mainly triggered by the flood-pulse. Trees have high increment during the terrestrial phase. Flooding causes a shedding of some or all leaves leading to a cambial dormancy of about 2 mo and the formation of an annual ring. Studies carried out in tropical dry forests verify a strong relationship between the phenological development and the water status of the trees, strongly affected by seasonal drought. The comparison of the phenology and the diameter growth of the corresponding ecotypes in floodplain forest and a semi-deciduous forest in Venezuela shows a displacement of at least 2 mo in the periodicity, except for stem-succulent tree species. For stem-succulent trees it remains unclear which factors influence phenology and stem diameter growth.

On the dynamics, floristic subdivision and geographical distribution of varzea forests in Central Amazonia

Abstract. Within different stands of the white-water inundation forest (varzea forest) in the Central Amazon region, composition, abundance, frequency and basal area of tree species were recorded. Determinations of age and radial growth rates were conducted using dendrochronological methods. Results show significant differences in age, history and species composition between stands as well as different growth strategies among dominant species. Assignment of tree species to growth strategies by means of anatomical and morphological features together with quantitative aspects of vegetational analysis permit the further differentiation of successional stages of varzea forests. General features of successional stages were quantitatively described and compared with forest types from outside the varzea. Many tree species of the varzea forests are widespread in South America, and not limited to floodplains. Their occurrence on sites with distinct dry seasons suggests that they are not specifically adapted to flooding but are tolerant to seasonality in general.

Growth Rings, Increment and Age of Trees in Inundation Forests, Savannas and a Mountain Forest in the Neotropics

Investigations on growth zones of tropical trees were carried out and published since the beginning of our century.In tropical regions with severe annual dry seasons or inundation phases trees form annual rings. This is demonstrated for trees from Central Amazonian inundation forests and the Gran Sabana in Venezuela using a combination of several dendrochronological methods (wood anatomy, radiocarbon dating, ring width measurements).The occurrence of annual rings allows the determination of age and growth rate of trees. The growth rate depends on the growth strategy of the species and the growth conditions. At a given site growth rate shows a weak negative correlation with the specific gravity of the wood of trees from the upper story. Several reported ring width patterns are explained by the vegetation history of different forest stands.

Dating Tropical Trees by Means of ^14C From Bomb Tests

Stem discs of trees from several tropical stands were macro- and micro- scopically investigated. The radiocarbon level of individual increment zones was deter- mined. Time series show concurrence of the 14C level of air and wood during the 14C peak from bomb tests and are compared with series from temperate zones. An annual growth rhythm of trees from Amazonian inundation forests and from the Gran Sabana in Ven- ezuela was demonstrated. The increase of 14C levels by internal carbohydrate transfer from sapwood to heartwood is shown for Quercus costaricensis.

How Old are Tropical Trees? the Persistence of a Myth

The recent report of ancient trees in the Amazon region (Chambers et al. 1998) with a maximum radiocarbon dated age of about 1400 years for the long-living pioneer species Cariniana micrantha is discussed in the light of dendrochronological age determinations from Africa and South America together with the results of indirect age estimations from other sources. There is a tendency in the literature to considerably overestimate the maximum ages of tropical trees. Age determination by the direct counting of annual rings and making estimations for hollow trees by measuring growth rates and diameters result in ages between 400 and 500 years for the largest trunk dimensions, e.g. in Cariniana legalis.

Review of Radiocarbon Data from Atmospheric and Tree Ring Samples for the Period 1945-1997 Ad

A summary of 14C data from atmospheric sampling and measurements on wood from annual tree rings for the period 1945-1997 AD is presented and evaluated. Atmospheric records are characterized by different distributions of bomb-test 14C between the Northem and Southem Hemispheres, latitude dependence, and seasonal fluctuations. Radiocarbon data from tree rings are summarised and plotted against atmospheric records from similar latitudes. In some cases, discrepancies are found. Possible reasons for this include: 1) the use of stored carbohydrate from the previous year, 2) different 14C levels in the air around subcanopy trees due to respiration of CO2, 3) regional and local effects of anthropogenic CO2 and 14C sources, 4) sampling of wood material too close to ring boundaries, and 5) insufficient pretreatment of tree ring sampies for dating. But in cases where trees were carefully selected and the sampies adequately pretreated, radiocarbon data from tree rings show excellent agreement with direct atmospheric sampling records.

Annual tree rings revealed by radiocarbon dating in seasonally flooded forest of the Mapire River, a tributary of the lower Orinoco River, Venezuela

The occurrence of seasonal growth rings in the wood of Campsiandra laurifolia, Acosmiun nitens, Pouteria orinocoensis and Psidium ovatifolium, common species growing in the flooding forest of the Mapire river, was analyzed using wood anatomy and ring- width analysis. The test of the annual ring formation was performed using radiocarbon analysis based on the nuclear weapon effect. All species showed growth rings visible to the naked eye. The ring boundaries in all cases were marked by bands of marginal parenchyma. The index ring-width curves of the four studied species showed a strong relationship with the fluctuation of the water river level during the non flooded months, suggesting that an increase in the water level during these months positively influenced the growth indicating that the rings were formed on an annual basis. The content of radiocarbon in the wood of anatomically predated rings of Campsiandra laurifolia and Pouteria orinocoensis confirm these results. All studied trees are slow growing with less than 2.5 mm annual increment.

Management criteria for Ficus insipida Willd. (Moraceae) in Amazonian white-water floodplain forests defined by tree-ring analysis

Ficus insipida Willd. (Moraceae) is a fast growing tree species of early successional stages in the Amazonian nutrient-rich white-water floodplains (várzea). The species is one of the most economically important low-density wood species in the community-based forest management project in the Mamirauá Sustainable Development Reserve (MSDR) in Central Amazonia, where timber species are managed using a polycyclic selection system with a minimum logging diameter (MLD) of 50 cm and a cutting cycle of 25 years. In this study we analyze the floristic composition, stand structure and forest regeneration of a natural 20 year-old stand at an early successional stage and we model tree growth of diameter, height and volume of F. inspida based on tree-ring analysis to define management criteria. The volume growth model indicates that the preferred period for logging should be at a tree age of 17 years when the current annual volume increment peaks. This age corresponds to a diameter of 55 cm, which would be an appropriate MLD.RésuméFicus insipida Willd. (Moraceae) est une essence à croissance rapide présente dans les premiers stades de succession dans les forêts inondables sur sols riches d’Amazonie («varzea»). Cette essence est l’une des plus importantes essences productrice de bois de faible densité, dans le cadre du projet de gestion forestière communautaire durable de la réserve de Mamiraua, en Amazonie Centrale. Ces forêts sont gérées sur le principe d’un système polycyclique avec récolte des arbres présentant un diamètre minimal de 50 cm et une révolution de 25 ans entre récoltes. La présente étude analyse la composition floristique, la structure des peuplements et la régénération dans une forêt naturelle âgée de 20 ans et issue d’une phase de régénération. Un modèle de croissance en diamètre, hauteur et volume a été adapté à Ficus insipida sur la base d’une analyse de cernes, afin de définir des critères de gestion. Le modèle de croissance en volume indique que l’âge de récolte optimal est d’environ 17 ans, au moment du pic de production courante annuelle. Á cet âge, les arbres atteignent un diamètre de 55 cm, qui constituerait ainsi un diamètre minimal de récolte (DMR) tout à fait approprié.