Jochen Schöngart

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.

A Classification of Major Naturally-Occurring Amazonian Lowland Wetlands

Our estimates indicate that about 30% of the seven million square kilometers that make up the Amazon basin comply with international criteria for wetland definition. Most countries sharing the Amazon basin have signed the Ramsar Convention on Wetlands of International Importance but still lack complete wetland inventories, classification systems, and management plans. Amazonian wetlands vary considerably with respect to hydrology, water and soil fertility, vegetation cover, diversity of plant and animal species, and primary and secondary productivity. They also play important roles in the hydrology and biogeochemical cycles of the basin. Here, we propose a classification system for large Amazonian wetland types based on climatic, hydrological, hydrochemical, and botanical parameters. The classification scheme divides natural wetlands into one group with rather stable water levels and another with oscillating water levels. These groups are subdivided into 14 major wetland types. The types are characterized and their distributions and extents are mapped.

A classification of major natural habitats of Amazonian white-water river floodplains (varzeas)

Most countries sharing the Amazon basin have signed the Ramsar Convention on Wetlands of International Importance but still lack complete wetland inventories, classification systems, and management plans. Amazonian wetlands vary considerably with respect to hydrology, water and soil fertility, vegetation cover, diversity in plant and animal species and primary and secondary productivity. Here, we propose a classification system of major natural habitats of Amazonian white-water river floodplains (várzeas) based on hydrological, water and soil chemistry and biological parameters. The Amazonian várzea is one of the largest Amazonian wetlands. It is exceptionally rich in plant and animal species and plays important roles in landscape history, evolution, hydrology and biogeochemical cycles of the Amazon basin. Most of Amazonia’s rural population lives in or along the várzea, emphasizing the economic importance of its natural resources. Our classification indicates five major systems, which are subdivided into 10 main habitats and up to 40 functional (vegetation) units of which the most important mesohabitats are described. We understand this classification as a dynamic system, as it is open to the inclusion of future research attempts and habitats without affecting the entire classification system. Our classification may be used for scientific purposes, such as comparative studies on biomass, productivity, biogeochemical cycles and biodiversity. Also, because the classification builds on habitat types and/or vegetation and functional units already distinguished by the local population it may be especially useful in guiding intelligent use of várzea habitat for specific management activities, such as agriculture, animal husbandry, forestry, fisheries, and conservation.

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.

Tropical forest warming: looking backwards for more insights

In his balanced and much-needed review on the effects of global warming on tropical rainforests, Richard Corlett [1] discussed gaps in knowledge, research needs and corresponding research methods. However, an important and powerful technique for studying the effects of climate change on tropical forests was not mentioned: the analysis of tree rings.

Recent Amazon climate as background for possible ongoing and future changes of Amazon humid forests

Recent analyses of Amazon runoff and gridded precipitation data suggest an intensification of the hydrological cycle over the past few decades in the following sense: wet season precipitation and peak river runoff (since ∼1980) as well as annual mean precipitation (since ∼1990) have increased, while dry season precipitation and minimum runoff have slightly decreased. There has also been an increase in the frequency of anomalously severe floods and droughts. To provide context for the special issue on Amazonia and its forests in a warming climate we expand here on these analyses. The contrasting recent changes in wet and dry season precipitation have continued and are generally consistent with changes in catchment-level peak and minimum river runoff as well as a positive trend of water vapor inflow into the basin. Consistent with the river records, the increased vapor inflow is concentrated to the wet season. Temperature has been rising by 0.7°C since 1980 with more pronounced warming during dry months. Suggestions for the cause of the observed changes of the hydrological cycle come from patterns in tropical sea surface temperatures (SSTs). Tropical and North Atlantic SSTs have increased rapidly and steadily since 1990, while Pacific SSTs have shifted during the 1990s from a positive Pacific Decadal Oscillation (PDO) phase with warm eastern Pacific temperatures to a negative phase with cold eastern Pacific temperatures. These SST conditions have been shown to be associated with an increase in precipitation over most of the Amazon except the south and southwest. If ongoing changes continue, we expect forests to continue to thrive in those regions where there is an increase in precipitation with the exception of floodplain forests. An increase in flood pulse height and duration could lead to increased mortality at higher levels of the floodplain and, over the long term, to a lateral shift of the zonally stratified floodplain forest communities. Negative effects on forests are mainly expected in the southwest and south, which have become slightly drier and hotter, consistent with tree mortality trends observed at the RAINFOR Amazon forest plot network established in the early 1980s consisting of approximately 150 regularly censused 1ha plots in intact forests located across the whole basin.

Biomass and net primary production of central Amazonian floodplain forests

In this chapter the existing knowledge on biomass in floodplain forests and the compounds that contribute to their net primary production (NPP) are presented and discussed in comparison with data from non-flooded upland (terra firme) forests. Fine litterfall in old-growth floodplain forests are similar to litterfall data from terra firme forests. The few existing estimates of root biomass in nutrient-rich white-water floodplain forests (varzea) indicate lower belowground biomasses in floodplain forests than in terra firme forests due to regular flooding which limits the development of deep roots. Along the chronosequence, C-storage in the aboveground coarse live wood biomass (AGWB) of varzea forests indicates a strong increase during the first 50–80 years of successional development, but afterwards no increase in AGWB can be observed. On the other hand C-sequestration in the AGWB of varzea forests declines more than threefold along the successional gradient. In comparison to terra firme forest, the varzea forests have lower C-stocks, but a higher C-sequestration in the AGWB. The estimated aboveground NPP in young successional stages of the central Amazonian varzea is among the highest NPP known for tropical forests, while the NPP of the late succession in the varzea is in the upper range of the NPP of old-growth forests in the terra firme. The available database for nutrient-poor floodplain forests (igapo) is insufficient to estimate their NPP. Climate-growth relationships of tree-ring chronologies of species from central Amazonian terra firme and floodplain forests indicate opposing signals during El Nino years. During these events large areas of terra firme forests release carbon to the atmosphere due to the warmer and drier climate conditions, while the weakened flood-pulse favours tree growth in the floodplain forests which might therefore sequester parts of the climate-induced carbon emissions of terra firme forests.

A classification of the major habitats of Amazonian black-water river floodplains and a comparison with their white-water counterparts

The Amazon River and its large tributaries are bordered by floodplains covering tens of thousands of square kilometers. Studies on the structure, function, and species composition have allowed a classification of the macrohabitats of Amazonian white-water floodplains, rich in suspended matter and nutrients and of neutral pH (várzea). Here we describe the use of a similar approach to classify the macrohabitats of the black-water floodplains, rich in humic substances, poor in nutrients and acidic (igapó) of the Negro River and its black-water tributaries. With 12 subclasses and 25 macrohabitats, the igapó is less complex than the várzea. Although white-water and black-water rivers are subjected to similar flood regimes, the low sediment load and shallower declivity of the Negro River lead to reduced sedimentation and erosion processes. Differences in nutrient levels between both ecosystems influence species composition, richness, and growth rates of higher plant communities. Species richness is lower in igapó than in várzea, and wood increment and litter production of igapó trees is about half that reported for várzea trees. In addition, igapó lacks highly productive herbaceous plant communities that are common in várzea. The classification of igapó macrohabitats provides a valuable tool for the elaboration of sustainable management strategies and conservation. While many várzea macrohabitats are suitable for small-scale agriculture, animal husbandry, forestry and commercial fisheries, the carrying capacity of igapó is limited and allows only for subsistence-level fishery and agriculture, the capture of ornamental fishes, and ecotourism. We argue that the biota of most igapó macrohabitats is highly sensitive to changes in hydrological cycles as caused by river damming and/or by climate change.

WOOD SPECIFIC GRAVITY OF TREES IN AMAZONIAN WHITE-WATER FORESTS IN RELATION TO FLOODING

Wood specific gravity (SG) was analysed from wood cores of 180 individuals belonging to 58 common upper canopy tree species of late successional white water (varzea) forests in the Mamiraua Sustainable Development Reserve, Central Amazon Basin. We tested for a SG gradient of trees along the flood gradient. Mean SG in the low varzea was 0.62 g cm-3, in the high varzea 0.57 g cm-3. SG tended to increase with height and duration of flooding. In the two species that occurred in both forest types (Hevea spruceana, Tabebuia barbata) SG was significantly lower in the high varzea trees. Therefore, height and duration of flooding seem to be important factors influencing growth and wood properties in varzea trees. In addition, SG variation depended on the core section and to a lesser extent on tree diameter and height. Compared to trees in Amazonian upland ecosystems, SG of the varzea trees was lower than SG in Central and Eastern Amazonian terra firme, but was within the same range reported for Western Amazonian terra firme.

Ecophysiology, Biodiversity and Sustainable Management of Central Amazonian Floodplain Forests: A Synthesis

This synthesis chapter provides an overview of the 23 chapters of this book. With more than 1000 tree species, Amazonian floodplain forests are the most diverse forests of this kind. They occur in different forms and under different hydrological and chemical (water and soil) conditions. Forests in nutrient rich whitewater river floodplains (varzeas) are richer in species, more dynamic, and more productive than those of black- and clearwater rivers. The new species colonization concept explains the relationship between upland and varzea forests. A model of forest succession is provided that indicates the development of different seral stages under different hydrological and sedimentological conditions. Trees react to long-term flooding and water-logging of the soils with many anatomical, morphological, physiological and phonological adaptations, which result in specific life history traits. Seed production, seedling establishment, and sapling survival are of fundamental importance for the regeneration of these forests and their reactions to the frequent set-backs caused by erosion and sedimentation processes. Until now, the use of floodplain forests has been restricted to highly selective timber exploitation, which depletes the stocks of the respective tree species. A management model, based on growth-oriented logging (GOL) is provided here. In this model, the extraction of the logs depends on water levels, the maximums and minimums of which can be predicted using new model based on sea surface water temperatures in the Pacific and the Atlantic Oceans. Such predictions would facilitate the management of the natural resources of the varzea, including management using forestry. When the many riparian forests are included, floodplain forests cover about one third of the Amazonian rain forest area. However, this fact has not been considered in management aspects and climate models for Amazonia. Global climate changes certainly will affect the hydrological cycle in Amazonia. However, we consider the prediction by the Hadley Center of a near “savannization” of the Amazon forest to be without sufficient scientific basis and unhelpful, because it may even accelerate the deforestation of Amazonia. The maintenance of intact wetlands will be very important for the sponge function of the landscape, which acts to retain water and to buffer extremely dry and wet periods. In this context, the floodplain forest is of utmost importance as a refuge for many plant and animal species.