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Artenverbreitung und Bestandesstruktur in amazonischen Várzea-Wäldern und Möglichkeiten der Erfassung von Waldtypen mittels fernerkundlichen Methoden
Abstract
In amazonischen Weißwasser-Überschwemmungswäldern (Várzea) wurden in zwei Untersuchungsräumen auf insgesamt 5 ha Untersuchungsfläche floristische Arten-inventare durchgeführt. Die in der Literatur beschriebenen, für eine Waldtypen-differenzierung verantwortlichen abiotischen Faktoren Überschwemmungshöhe und -dauer, jährliche Sedimentationsraten, Bodentextur und Einstrahlung wurden erfasst. Über synökologische Artengruppierungen wurden verschiedene Waldtypen klassifiziert. Die wesentlichen Ergebnisse der Feldaufnahmen sind: Der von Junk et al. (1989) beschriebene „Flutpuls“ ist der wesentliche Faktor einer Artenzonierung in Várzea-Wäldern. Verschiedene Waldtypen zonieren sich entlang des Flutgradienten. Der Artenreichtum steigt kontinuierlich mit zunehmend topografischer Höhenlage eines Bestandes. Der Flutgradient bedingt zwei floristisch und physiognomisch unterschiedliche Habitate: 1. Die Várzea Baixa, 2. Die Várzea Alta. Sedimentation und Bodentextur sind unmittelbar an den Flutpuls gekoppelt und verändern sich mit fortschreitender Sukzession des Waldes und dem zeitgleich einhergehenden „Höhenwachstum“ der Standorte. Die hohe geomorphologische Dynamik der Várzea bedingt mehrere, parallel zueinander existierende „Mikrohabitate“, in welchen, je nach Stabilität der Umweltbedingungen, allogene oder autogene Sukzessionsabfolgen stattfinden. Várzea Baixa-Wälder durchlaufen, bis zur Entstehung artenreicher „Klimax“-Bestände, weitgehend die von Worbes et al. (1992) vorgestellten Sukzessions-stadien der frühen und späten Primär- und Sekundärgesellschaften. Allogen gesteuerte Sukzession findet dabei im Wesentlichen in frühen Stadien nahe der hochdynamischen Flussufer statt, autogene Sukzession bei „stabileren“ Verhältnissen im Inneren der Wälder sowie im Bereich der Altarme und Dammuferseen. Várzea Alta-Wälder sind in anthropogen „ungestörten“ Gebieten stets artenreiche Schlusswälder, die vermutlich aus Várzea Baixa-Wäldern hervorgehen. Várzea Alta-Wälder sind durch einen Terra Firme-ähnlichen Artenreichtum gekennzeichnet, so dass bisherige Angaben über Artenzahlen der Várzea deutlich nach oben korrigiert werden müssen. In visueller Bildinterpretation von LANDSAT TM-Daten (Kanäle 5,4,3) deuten bereits unterschiedliche Texturen und Spektralbereiche innerhalb des Várzea-Waldes auf unterscheidbare Bestandesstrukturen und verschiedene Waldtypen hin. Mit dem Ziel, diese Waldtypen über fernerkundliche Methoden zu erfassen und ihren Flächenanteil zuverlässig zu quantifizieren, wurden als „scaling up“ - Ebene zwischen Geländeinformation und Satellitendaten Luftbilder von allen Untersuchungsflächen interpretiert. Für jeden Waldtyp wurden die im obersten Kronenraum erkennbaren Bestandesstrukturmerkmale Kronenanzahl, Kronen-flächen, Wuchshöhen und Bestandeslückenanteile erfasst. Mittels LANDSAT TM-Daten wurden schliesslich verschiedene Waldtypen klassifiziert und ihr Flächen-anteil auf insgesamt ca. 5.000 km2 quantifiziert. Die wesentlichen Ergebnisse der Anwendung fernerkundlicher Systeme sind: Alle Bestandesstrukturmerkmale im obersten Kronenraum zeigen eine direkte Abhängigkeit zum Sukzessionsgrad eines Bestandes. Mit fortschreitender Sukzession kommt es zu: -Abnahme der Kronenanzahl, -Zunahme der durchschnittlichen Kronenfläche, -Zunahme der Wuchshöhen, -Zunahme der Stratifizierung, -Zunahme der Bestandeslückenfrequenz. Vier verschiedene Waldtypen zeichnen sich in LANDSAT TM-Daten durch charakteristische Spektraleigenschaften aus und sind klassifizierbar: 1. Primärstadium entlang offener Flussläufe (offene Formation), Várzea Baixa, 2. Primärstadium im Bereich verlandeter Flussarme und Seen (geschlossene Formation oder Chavascal) und Pionierwaldformation (frühes Sekundär-stadium), Várzea Baixa, 3. Späte Sekundär- bis Klimaxformation, Várzea Baixa, 4. Klimaxformation, Várzea Alta. Der Flächenanteil der Waldtypen variiert je Untersuchungsraum, geomorpho-logischer Dynamik und anthropogener Beeinflussung. Die späte Sekundär- bis Klimaxformation der Várzea Baixa nimmt jedoch in beiden in dieser Untersuchung ausgewählten Räumen den größten Flächenanteil in Anspruch, die artenreichen Várzea Alta-Bestände den geringsten Flächenanteil 1. EINLEITUNG .................................................................................. 1 2. ZIELE DER ARBEIT......................................................................... 4 3. RAHMENBEDINGUNGEN UND STAND DER FORSCHUNG ............................................................................... 6 3.1 Die Várzea ...................................................................................... 6 3.2 Verbreitung und Ökologie der Várzeawälder ........................ 8 3.2.1 Abiotische Rahmenbedingungen und Adaptationsmechanismen .......................................................... 8 3.2.2 Artenbestand der Várzeawälder ................................................. 11 3.2.3 Artenzonierung und Sukzessionsdynamik .................................... 13 3.3 Fernerkundung - Stand der Forschung ................................... 15 4. UNTERSUCHUNGSRÄUME ........................................................ 18 4.1 Auswahl der Untersuchungsräume ........................................... 18 4.2 Klima ................................................................................................ 20 4.3 Hydrographie ................................................................................ 21 5. MATERIAL UND METHODEN .................................................... 24 5.1 Feldaufnahmen ............................................................................ 24 5.1.1 Lage und Beschaffenheit der Untersuchungsflächen ................. 24 5.1.2 Messung abiotischer Standortfaktoren ........................................ 27 5.1.2.1 Digitale Geländemodelle ....................................................... 27 5.1.2.2 Sedimentationsmessungen ..................................................... 27 5.1.2.3 Bodentextur ............................................................................. 28 5.1.2.4 Lichtmessungen ...................................................................... 29 5.1.3 Floristische Arteninventare ........................................................... 30 5.1.3.1 Arteninventar * 10 cm BHD ..................................................... 30 5.1.3.2 Arteninventar < 10 cm BHD .................................................... 31 5.1.4 Berechnung bestandesstruktureller Parameter ........................... 31 5.1.4.1 Klassifizierung von Charakterarten nach dem IV-Index .......... 31 5.1.4.2 Bestimmung von Diversität und Gleichverteilung ................... 32 5.1.5 Synökologische Artengruppierungen .......................................... 34 5.1.5.1 Gruppierung der adulten Individuen ...................................... 34 5.1.5.2 Gruppierung des Verjüngungsbestandes ............................... 37 5.2 Fernerkundung .............................................................................. 39 5.2.1 „Scaling up“ durch kleinformatige Luftbilder .............................. 39 5.2.1.1 Aufnahme ............................................................................... 39 5.2.1.2 Aufbereitung ........................................................................... 39 5.2.1.3 Erfassung von Bestandesstrukturdaten ................................... 41 5.2.2 Satellitenbilddaten ...................................................................... 42 5.2.2.1 Visuelle Bildinterpretation unreferenzierter TM-Daten ............ 42 5.2.2.2 Georeferenzierung und radiometrische Transformation ........ 43 5.2.2.3 Unüberwachte Klassifizierung ................................................. 44 5.2.2.4 Überwachte Klassifizierung ..................................................... 45 I. ERGEBNISSE - Teil I: FELDAUFNAHMEN .............................. 47 6. ABIOTISCHE STANDORTFAKTOREN ...................................... 47 6.1 Überflutung .................................................................................... 47 6.1.1 Digitale Geländemodelle ........................................................... 47 6.1.2 Eindimensionale Artengruppierung entlang des Flutgradienten . 50 6.2 Sedimentation ............................................................................... 56 6.3 Korngrößenbeschaffenheit der Bodenprofile ........................ 58 6.4 Einstrahlungsverhältnisse ............................................................. 60
... New sediment deposit can reach 0.3-1 m every year (Junk, 1989; Campbell et al. 1992) so that there is a high nutrient input into the ecosystem which consequently is highly productive (Figure 1B) and extremely dynamic, with strong erosion and new land formations (Figure 1C). Fine-coarse sediments, which are deposited primarily in oxbows with reduced water velocity, worsen the physical soil properties because of the increasing lack of oxygen at the root level (Wittmann, 2002). The monomodal flood pulse of the rivers causes drastic changes in the bioavailability of nutrients, oxygen levels, and concentrations of phytotoxins (Parolin et al. 2004). ...
Amazonian várzea forests are characterized by a high diversity of species and adaptations against extended flooding. Waterlogging and submergence can last up to 210 days per year, with a water column of up to 6-7 m. The present paper gives an insight into the current knowledge of morpho-anatomical, phenological and physiological responses to flooding in várzea trees, into patterns of regeneration and seedling recruitment, and into differences found along the flooding gradient, and between populations of selected species. This knowledge may serve as a basic tool for forest management. The high selective logging already caused a substitution of timber species, with high damages in the remaining stands, calling for rigorous management plans. Since the regular inundation induces the formation of annual rings, and tree growth responds to the prolonged vegetation period with significantly wider ring widths in El Niño years as compared to neutral years, tree ring analysis can be used also for the development of models to predict tree growth and to determine minimum logging diameters and cutting cycles for timber species. Resumen Los bosques de várzea Amazónica se caracterizan por una alta diversidad de especies y adaptaciones a largos periodos de inundación que pueden durar hasta 210 días del año, con una columna de agua excediendo los 6-7 m. La presente publicación presenta una revisión del conocimiento actual sobre las respuestas morfo-anatómicas, fenológicas, y fisiológicas a las inundaciones, y los patrones de regeneración, no sólo a lo largo de la gradiente de inundación, sino además entre poblaciones de las especies. Este conocimiento puede servir de base para instrumentos de manejo forestal sostenible. La alta selección de árboles de corte ya está causando una sustitución de las especies de madera, con alto daño al resto de árboles en pie, lo cual requiere un riguroso plan de manejo. Puesto que las inundaciones regulares inducen a la formación de anillos/aros anuales en los árboles de la zona de inundación, y el ancho de los anillos/aros está correlacionado con el pulso de inundación y con las variables climáticas, y en los años de El Niño el nivel máximo de inundación es significativamente más bajo, el análisis del aro de los árboles puede ser usado también para el desarrollo de modelos para predecir el crecimiento de los árboles y determinar los diámetros mínimos para el corte de los árboles y los ciclos de corte para las especies de madera. Palabras clave: Amazonía, ecofisiología del árbol, establecimiento, gradiente ambiental, productividad, especiación, análisis de anillos del árbol, El Niño. Introduction Amazonian várzea forests are seasonal floodplains with a monomodal, predictable flood-pulse (Junk et al. 1989) and cover approximately 300.000 km 2 along the main rivers in the Amazon basin (Figure 1A). Seasonal precipitation causes periodical inundations of the floodplains along the Amazon River. These periods of extended flooding can last as much as 210 days per year, with a water column of up to 6-7 m. New sediment deposit can reach 0.3-1 m every year (Junk, 1989; Campbell et al. 1992) so that there is a high nutrient input into the ecosystem which consequently is highly productive (Figure 1B) and extremely dynamic, with strong erosion and new land
... Sedimentation on slip-off slopes can reach 0.3-1 m every year (Junk, 1989;Campbell et al., 1992). On undercut slopes, erosion can wash out several hectares of forests during one high-water period (Wittmann, 2001). These unstable conditions result in the parallel existence of several forest types, forming a patchwork of microhabitats (Kalliola et al., 1991;Campbell et al., 1992). ...
Although flooding and the highly dynamic geomorphology influence ecophysiology of trees in Amazonian white-water forests (várzea), information about the extent of these environmental conditions on distribution and richness of tree species is scarce. To better understand dynamic of natural forest succession and the development of different várzea forest types, we inventoried structure and floristic composition of trees ≥10 cm DBH in a total area of 5.24 ha in várzea forests near Tefé and near Manaus, Brazilian Amazon. The forests were of different successional stages and situated on different sites along the flood-level gradient. Topography and average inundation of all inventoried trees was measured with a theodolite. Sedimentation was recorded during the aquatic phase 2000 and the soil texture in each site determined.
... preferrably establishes on longterm flooded sites which are less exposed to sedimentation (1-5 cm of sediment deposit per year, silt fraction of 60%; Wittmann 2001). It may therefore establish below an open canopy formed by Salix humboldtiana (Worbes 1994, Oliveira 1998) where sedimentation rates are lower because upright stems break the flow of water, effecting an active deposition of sediment at the water-vegetation interface (Terborgh and Petren 1991). ...
Cecropia latiloba can be considered to be one of the most efficient colonizers of open areas in the nutrient-rich whitewater floodplains of the Amazon river. Its main strategy to be successful is the high tolerance towards waterlogging and submergence, and the fast vertical growth and reiteration capacity. This, and the tolerance of high irradiation and sediment deposition allow C. latiloba to form large monospecific stands on open sites, and thus the first closed canopy which represents the initial phase of a successional sequence which leads to highly diverse forests. This tree is extremely well adapted to the adverse growth conditions in Amazonian floodplains with prolonged periods of flooding and seedling submergence. The species occurs on the lowest levels in the flooding gradient. Although it belongs to the most often cited species under aspects of taxonomy, species distribution and general descriptions of the ecosystem, little has been published about its ecology. In the present paper the ecological, physiological and phenological characteristics of C. latiloba are described. It is an evergreen species which constantly produces new leaves. With flooding, leaf production is reduced but new leaves are flushed also with prolongued flooding. The peak of flowering and fruiting are in the flooded period. When mature, the fruits are dispersed mainly by water and fish. Seed germination occurs, without dormancy, within 5-13 days after water retreat. In the 7 months before the first flooded period seedlings reach 1 m of height, and height growth increases until 15-20 m are achieved. Photosynthetic assimilation is high, with values of up to 21 mumol CO2 m-2s-1. C. latiloba is a very flood tolerant species, and waterlogged seedlings continuously produce new leaves and adventitious roots.
Amazonian várzea forests are floodplains inundated by nutrient-rich white-water rivers occurring along the Amazon River. They
are regularly flooded for up to 210 days per year by water columns of 10–15 m. Topographic variation results in different
flooding amplitudes and durations along the flooding gradient, where the different tolerance to flooding of different plant
species results in a vegetation zonation. We made a review of literature about the vegetation composition ofvárzea floodplain forests of Brazilian Amazonia along the Amazon River. Twenty-two studies were selected. Basing on the distribution
of inventories which are concentrated in three main areas around the three larger cities Belém, Manaus and Tefé, we classified
the inventories into three regions: (A) Estuary region with flooding regime influenced by daily inundations linked to the
tides; (B) Central Amazonia near Manaus; (C) Western part of Brazilian Amazonia bordering Peru and Colombia, including Tefé
and the “Reserva de Desenvolvimento Sustentável Mamirauá”. Summarizing the analyzed species lists, 36 tree species were registered
in all sampled regions including the estuary. The regions A +C have 63 species in common, region B+C 143, and A+B 50. In the
inventories analyzed here, an increase in species numbers from East to West can be confirmed, but it is difficult to state
whether this is not an artefact due to local sampling. Vertical zonation patterns are difficult to discuss due to the lack
of comparable data. The inventoried areas are small, and there is an urgent need for comparable floristic inventories throughout
the basin. Destruction is spreading rapidly and the traditional use of forests and its resources is changing to a destructive
exploitation that already has changed much of the physiognomy and diversity of this unique ecosystem.
Sediment-rich rivers seasonally flood central Amazonian várzea forests, leading to periodic anoxic conditions in the rhizosphere and requiring morphological and structural adaptations, such as aboveground root systems. We investigated some possible relationships between root types and environmental factors in forest plots covering 3.1 ha of várzea in the Mamirauá Sustainable Development Reserve, Brazil. Digital elevation models of the study sites were obtained; sedimentation and soil texture were investigated to check relationship between position of trees on the flood gradient, soil conditions, and aboveground root systems. Different types of aboveground roots were closely related to flooding duration and habitat dynamics. Species subjected to higher and more prolonged floods tended to produce more aboveground roots than species subjected to lower and shorter inundations. Plank-buttressing species increased with decreasing flood height and/or flood duration, and with increasing growth height and basal area. Habitats inundated for long periods were dominated by species with low growth heights and low basal areas, which formed stilt roots and aerial roots. Root system and sediment deposition showed a close relationship, plank buttressing being more common in sites subjected to lower sediment rates. In the disturbed sites close to the main river channel colonized by pioneer species, the occurrence of buttresses was lower than in less disturbed climax stages. No clear relationship was found between root systems and sediment grain sizes.
So far, timber resources in central Amazonian floodplain forests are managed by selective logging with a felling cycle of
25 years and a diameter cutting limit (DCL) of 50 cm. However, these time and diameter limitations are estimations or legal
restrictions rather than being derived from scientific data. From 14 tree species of nutrient-rich white-water (várzea) and
nutrient-poor black-water (igapó) floodplain forest in central Amazonia wood growth in diameter and volume was modelled using
tree-ring analyses. Cumulative diameter growth curves indicated periods between 15 and 261 years for species to pass over
the DCL of 50 cm. From volume growth models the minimum logging diameter (MLD) was defined as diameter at the age of maximum
current volume increment rates. For the majority of the analysed tree species the MLD was higher than the DCL of 50 cm. Felling
cycles, estimated as the mean passage time through 10 cm diameter classes until reaching the MLD, indicated large variations
from 3 to 53 years between tree species. Tree species which occur in both floodplain system present significantly lower diameter
increment rates in the igapó than in the várzea due to the contrasting nutrient status. The sustainable use of timber resources
in the igapó is, under current management options, not practicable and this ecosystem should be therefore excluded from timber
resource management and permanently protected. The várzea is a dynamic system with highly productive forest ecosystems which
favours the development of an integrated sustainable forest management. However, such a timber resource management must be
species-specific. Based on tree ages, increment rates, volume production and population structure of commercial tree species
the GOL concept (Growth-Oriented Logging) was developed to achieve a higher level of sustainability for the timber resource
management in várzea forests.
Fruits and seeds are released into the water and may be submerged or floating for several days to months – a situation which
normally makes most seeds unviable. Trees are adapted and seeds remain visually sound for >2 months when continuously submerged.
This stands in contrast to the majority of land plants, whose seeds quickly lose viability if submerged for prolonged periods.
On the contrary, seeds of floodplain species kept in air dry or decompose within few days or weeks. Many species have high
nutrient contents as a function of the relation to fish dispersal, just as in upland forests diaspores of species dispersed
by mammals are rich in fat and proteins. However, in Amazonian floodplain trees dispersal syndromes are closely linked to
water, with all necessary adaptations enhancing floatation and attractiveness for fish. High nutrient contents are also advantageous
for the seedling, because a high investment of the parent tree into seed reserves guarantees fast initial growth. This can
be crucial in an environment with a flood amplitude exceeding 10m. Time for seedling establishment in the non flooded terrestrial
period is reduced to few months or weeks. For a fast and well timed establishment, seeds must germinate fast and they need
adequate nutrient reserves.
Trees colonizing Central Amazonian floodplains are subjected to extended periods of waterlogging and submersion surviving up to seven months of flooding per year. Flood is a consequence of changes in water level of ca. 10 m in the largest rivers of the region, and leads to a fast depletion of oxygen in the soil modifying the metabolism of the plants. Flooding tolerance varies between species and ecotypes as well as the biochemical traits and processes allowing the survival and adaptation of plant species. This results in a typical substitution of plant communities in these environments according to the depth of inundation. Amongst the developed metabolic adjustments and growth strategies and adaptations plants may show wood-ring formation, indicating annual growth reduction related to the inundation phase. The reduction of growth is preceded by stomatal closing, degradation of leaf chlorophyll, decrease of photosynthetic rates, carbohydrate translocation, and alteration of the hormonal balance. Floodplain trees develop as well protection mechanisms which can diminish damages caused by the long lasting annual hypoxia or even anoxia. Although the majority of woody plants can support periods of anoxia varying between a few hours to some days, in non-adapted species, irreversible damages can be caused leading to the death of the roots, when longer periods of flooding are imposed. These damages are attributed to the accumulation of toxic end products of the anaerobic metabolism, the loss of metabolic energy or the lack of respiration substrate. All and all the adaptations described at the biochemical level for temperate tree species inhabiting wetland are found in Amazonian floodplain trees; however, they are not enough to explain plant survival. This indicates the existence of novel mechanisms still to be found which together with the fate of the tree species inhabiting Amazonian floodplains in a changing climate are the main challenges faced by wetland scientists in the near future.
Amazonian floodplain forests are classified into nutrient-rich white-water floodplains (várzea) and nutrient-poor black-water
and clear-water floodplains (igapó). Tree species distribution depends on sediment- and nutrient-loads of river waters, on
flood regimes and hydro-geomorphic disturbance. The distribution of the different floodplain forest types is determined by
adaptations of tree species to different levels and periods of flooding, and most habitats and species are strongly zoned
along the flooding gradient. This leads to characteristic successional stages with distinct species composition, diversity,
and forest structure. Amazonian floodplains and especially the várzea is covered by the most-species rich floodplain forest
worldwide. Low flooded forests are floristically distinct from highly-flooded forests, and characterized by intense species
exchange with the surrounding uplands. Highly-flooded forests are characterized by elevated degrees of endemic tree species.
This indicates comparatively stable environmental conditions over large part of the Amazon basin since at least the early
Palaeocene. It is likely that the Amazonian floodplains represented linear refuges for moist-sensitive tree species from the
Amazonian uplands during periods with dryer climatic conditions.
Three pioneer tree species —Salix humboldtiana, Cecropia latiloba, Senna reticulata — form monospecific stands in the Central Amazonian white-water flood plain. In contrast toterra firma forests where species composition is unpredictable even for pioneer species, in Central Amazonianvárzea the occurrence of the main colonizing species seems to be predictable. This predictability is linked to characteristic habitat conditions and the low number of pioneer species. This preference for different habitats is reflected by different germination and early growth, by the structural and physiological characteristics, as well as by the reproductive and morphological adaptations of the three main species. The germination rate was above 90% in all species, and the duration until germination ranged between one day inSalix and 14 days inCecropia. Stem elongation was more than 10 cm per month inSalix andCecropia, and about 50 cm per month inSenna. Wood specific gravity ranged from 0.33 g cm−3 inCecropia to 0.45 g cm−3 inSenna. The annual wood increment increased by 1.20 (Cecropia), 1.23 (Salix) to 2.14 cm per year (Senna). All species produced adventitious roots, lenticels and/or stem hypertrophy. Leaf photosynthesis was between 17 and 20 µmol m−2s−1, and reached a maximum of 30 µmol m−2s−1 inSenna. Flowering and fruiting inSalix occurred throughout the year, whereas inCecropia andSenna they were concentrated in the flooded period.Salix humboldtiana occurs mainly at low sites subjected to long periods of inundation and high sedimentation rates. OnceSalix has formed dense forest stands, sedimentation and water currents are reduced at these sites andCecropia latiloba may take over. This species grows on low to middle elevations in the flooding gradient at sites with lower current and sedimentation rates.Senna reticulata does not tolerate submergence and colonizes habitats that may have strong currents and high sedimentation on higher levels in the flooding gradient.
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