Long-term Forest Dynamics in Peruvian Amazonia
1Jones,T.D., 1Roucoux,K.R., 1Baker,T.R., 2Gosling,W.D., 1,3Honorio,E., 4Lähteenoja,O., 1Lawson,I.T.
1
School of Geography, University of Leeds, Leeds, UK; 2 Department of Earth and Environmental Sciences,
CEPSAR, The Open University, UK; 3Instituto de Investigaciones de la Amazonia Peruana (IIAP), Peru;
4Department of Biology, University of Turku, Finland
1. INTRODUCTION
5. STUDY SITES
The dynamics of tropical forests are changing, with significant implications for the global carbon cycle and regional climate,
The
but monitoring of forests has been undertaken systematically only since the 1970s. We are investigating the potential of
Amazonia, near Iquitos, Loreto, in northern
peat sequences in northwest Amazonia, recently dated and found to accumulate exceptionally rapidly, to provide finely-
Peru. The climate is hot and humid: mean
resolved pollen records that extend the forest history back over several millennia, providing a much-needed long-term
annual temperature: 26˚C; mean annual
perspective. These data will provide insights into the mechanisms driving current changes in tropical forest ecology and
precipitation: 3100 mm [14]. The area is
the sensitivity of these forests to future disturbance and climatic change.
characterised by extensive floodplains,
sites
are
containing
located
seasonally
in
Peruvian
flooded
tropical
forest and aguajales: swamps dominated
2. RATIONALE
by the palm Mauritia flexuosa.
Studies of a network of forest plots across Amazonia [1] show that rates of tree mortality and recruitment [2], growth rates
A recent survey of the area revealed the
[3] (e.g. see figure below) and overall forest biomass [4] have increased over the past three decades. Liana abundance
presence of extensive peat deposits up to
has increased [5], and populations of faster-growing canopy trees are expanding at the expense of slower-growing
5.9 m thick. Peat accumulation rates were
understorey species [6]. Understanding the mechanisms behind these changes is important for predicting their
consequences for biodiversity, the global carbon cycle and the rate of climate change [7].
Mean rate of stem recruitment, stem mortality, and their
between 1.69 and 2.56 mm yr-1, and
Site locations: core site names are in boxes. (Adapted from [15]).
carbon accumulation ranged from 39 to
Three sites with differing characteristics (e.g. ombrotrophic and
85 g C m-2 yr-1 over the past 3000 cal yr
minerotrophic) and demonstrating strong potential for high-resolution
BP. Carbon storage and flux associated
palynological analysis were selected from the aforementioned survey [15]
with
for further study. These are described below:
the
peatlands
may
be
globally
significant [15].
difference (with 95% confidence intervals), determined from 50
1. Quistococha
long-term monitoring plots across South America (1971-2002).
Solid lines = additions; dotted lines = losses; lines with error
bars = difference [3].
•
Mauritia flexuosa palm swamp
•
Nutrient-poor ombrotrophic peatland [16]
•
pH 3.14, conductivity 73.5 µS cm-1
•
5.90 m sediment core obtained; consisting of 4.13 m
peat; remainder grey clay
•
Basal peat horizon previously radiocarbon dated to
2335 cal yr BP [15].
The cause of these changes has generated intense debate as it has implications for whether Amazonian forests are
This aguajale is found adjacent to Lake Quistococha. A
currently acting as a carbon sink and therefore slowing climate change. It has been suggested that the increase in
lake sediment core was retrieved from the lake to allow
biomass in many plots might be explained by recovery from disturbance events prior to monitoring [8]. If correct, simple
Above: Lake Quistococha and adjacent palm
swamp forest.
comparison with the peat cores. Lake gyttja is underlain by
extrapolations from the forest plot data to estimate a regional carbon sink may be sensitive to how well current networks
similar grey clay to that found below the peat in the
sample the full disturbance/recovery mosaic [9]. Even if the current plot network is robust to this bias [10], it is important to
aguajale. A full vegetational succession sequence should
understand whether the regional carbon sink is driven by recovery from disturbance, or increased resource availability
be recorded in the Quistococha peat core, documenting the
[11], in order to predict its long-term trajectory and sensitivity to future fluctuations in climate and disturbance regimes. The
A)
initiation and growth of the palm swamp forest associated
only way to address this directly is to examine the history of currently monitored areas using palaeoecological techniques
with infilling of the lake.
(e.g. [12]).
B)
2. Buena vista
3. RESEARCH OBJECTIVES
•
Seasonally flooded forest
•
Minerotrophic peatland –
This research will investigate the potential of Peruvian peat sequences to
C)
nutrients from flooding
produce pollen records of the local vegetation history over the past 3000 years
•
(focusing in most detail on the last 1000 years). Specifically we aim to:
Above: A) Peat core from the Quistococha
aguajale (3.15-3.65 m depth); B) Transition
into clay beneath the peat in the aguajale
(4.05-4.55 m); C) Lake Quistococha
sediment core – grey clay (6.79-7.39 m).
pH 4.75; conductivity
113.3 µS cm-1
•
1. Characterise the peat sequences using sedimentological analyses to
3.65 m sediment core;
consisting of 3.25 m peat;
establish the nature and timing of peat accumulation;
remainder grey clay
2. Produce pollen and charcoal records spanning the last 1000 years at c.50-
•
year resolution. This will allow greater understanding of succession and
Basal peat horizon
previously dated to
disturbance processes;
1217 cal yr BP [15].
3. Monitor vegetation change; permanent vegetation and carbon monitoring
Above: Vegetation at the seasonally
flooded site, Buena Vista
plots of 0.5 ha have been set up around each coring location to facilitate a
3. San Jorge
detailed floristic inventory at each core site and provide means to monitor
changes in the future. This work complements the existing network of
regional plots [13].
4. Establish the relationship between pollen rain and vegetation by comparing
pollen assemblages in surface samples with floristic inventory data obtained
Above: Forest disturbance in
Peruvian Amazonia (Cecropia
growing along the river bank)
•
Mauritia flexuosa palm swamp and forest
•
Ombrotrophic raised bog
•
pH 2.76; conductivity 171 µS cm-1
•
6.35 m sediment core; consisting of 5.16 m peat; remainder grey
clay
around the core sites.
•
Basal layer of peat previously dated to 2850 cal yrs BP [15]
Above: San Jorge
4. METHODOLOGY
a) Coring of peat and lake sediment
b) Vegetation and the pollen rain
c) Contemporary monitoring
Knowledge
modern
of
the
pollen
rain
• Analysis of pollen and spores to determine vegetation
history and composition of the modern pollen rain;
assemblage is a pre-
• Charcoal analysis to reconstruct fire history;
requisite
• Determination of organic content through loss on ignition;
for
reliable
insights into mineralogy via magnetic susceptibility;
interpretation of fossil
[17].
• Chronological control by correlation of loss on ignition
Pollen traps were set up
profiles with previously dated sequences from the sites
in the plots; they will be
[15]. New radiocarbon dates will also be obtained.
pollen
records
collected
after
Peat and lake sediments were obtained using a Russian
peat corer. A raft was constructed for coring in the centre of
Lake Quistococha.
Pollen trap placed 5 m above
the ground to avoid flooding.
d) Laboratory analysis
and
one
re-set
year
to
supplement information
All trees with diameter at breast height (DBH)
from
>10 cm in the 0.5 ha plots were identified, tagged
samples.
the
surface
and the diameter measured. All stems with DBH
>1 cm were measured in circular plots of 4 m
radius around each pollen trap.
Aguaje palm (Mauritia
flexuosa) pollen (60 µm
diameter)
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