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Work In
Progress: |
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Robyn
J. Burnham |
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Department
of Ecology & Evolutionary Biology |
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and Museum of
Paleontology |
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University
of Michigan |
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Contact Robyn: rburnham@umich.edu |
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Curriculum Vitae and Active Courses Click HERE |
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Overview I am interested in the origin, diversification, and maintenance of
plant diversity in northern South America. I am concerned about conservation
and wise management of ecosystems in tropical areas of the Western
Hemisphere, and I approach those ecosystems with goals of identifying
processes of diversification, specialization, migration, and distribution of
plants. The organisms I study
are climbing plants: vines and lianas.
Rooted at the ground level, but traversing the canopy with the support
of trees, climbers have a unique life style that appears to be sensitive
to small and large perturbations.
Recently I have extended my interests in climbers to North America
under the CLIMBERS project. |
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Academic Research My research is focused on several topics (click one to read more): |
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Paleoecology
and Systematics of Neogene plants from northern South America |
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My interests in
modern forests have focused on a group of plants that are not
phylogenetically allied: the woody climbers, or lianas. Lianas are found in
about 140 families of plants and have probably existed on earth almost as
long as there were trees up which to climb. Lianas are often excluded from
large tree plot censuses (BCI,
Yasuní,
Pasoh, etc.) because of time and funding limitations involved in these
studies. They are often included in smaller area plots but at the diameter
limit of >10cm, a large stem for a liana. So we know relatively
little about tropical liana communities, compared to tropical tree
communities. Lianas contribute roughly 10-35% of the species diversity to
tropical and temperate forests (if we count just the woody species), and
usually less than 10% of the biomass, based on litter fall or stem diameter
estimates. I have worked
primarily in two areas in the neotropics: Yasuní
National Park in eastern Ecuador and Madre de Dios Department / Manu National Park in eastern
Peru. Both areas are reasonably well-protected parks, with adequate access
and biological stations out of which a large group of biologists can work. In Yasuní, the objectives
of my project are: ** provide species lists and identification guides for the
lianas of the park ** provide census information on species that are rarely
encountered ** determine the pattern of ecological and geographic
distribution of liana species in the park: who is the king, who are the
oligarchs, and who are the proletariat? ** how are species added and subtracted from communities by
human impacts: what matters? ** what is the population structure of the dominant species (Machaerium
cuspidatum [Fabaceae] is king) based on analysis of genetic variation
among individuals. I am
currently approaching this using AFLP methods (see
below under Machaerium
project). ** monitor changes over time in forest communities within
Yasuní to assess the ecological impact of the current land use
practices: oil extraction
by multinational companies, including road construction; expansion of indigenous populations
(both Quichua and Huaorani); and scientific and ecotourism study of forested
communities. In Manu, the
project has only just begun: I intend
to duplicate the type of sampling I have undertaken
in Yasuní in order to ask similar questions about this analogous forested
ecosystem. Once the system of plots is complete, I will compare the known
distributions of the various importance classes of lianas (king, oligarchs, and
proletariat) both within Manu and then to Yasuní. Although Manu and Yasuní
represent similar kinds of physiographic settings: base of the eastern Andes,
relatively rich soils, dominated by terra firme habitats, I expect that the
lianas will be highly influenced by the individual dynamics of the two
systems. Manu forest dynamics may be strongly influenced by an highly-active, migrating river, whereas Yasuní may be
more influenced by particularly high turnover. |
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I have used the
following sampling scheme in Yasuní National Park and Manu National Park. Plots are selected based
on prior establishment of one hectare tree inventory
plots (dbh > 10cm) censused and maintained by Nigel Pitman (Yasuní)
or John Terborgh (Manu). Not all of my liana plots have a corresponding tree
plot, but most do. Not all of their tree plots have a corresponding liana
plot. Each one hectare plot is
sampled using five 4 x 100m transects. Total sample area = 0.2 ha. If the
hectare is set up as 100 x 100, then the transect
are located every 16 meters (parallel to one another) within the plot. A few
plots are hectares established as 10 x 1000 m plots, and in these cases my
five transects are lain end to end for the first 500 meters of the hectare. A
sketch of the set up is archived here (as a pdf file). All lianas >
1cm diameter are counted, identified, collected as necessary, and located
within the 10m segment of the transect. Stems are
measured at the widest part of the stem, exclusive of abnormal bulges and
nodes. Each stem is measured only once, so a great deal of following
individual lianas through the forest to determine their point of rooting and
connection to other individuals is involved. Lianas are counted if
they enter the transect anywhere from 0 to 2 m in height, such that some
stems can be rooted outside the 4 x 100m transect. Lianas are not counted if
they are not climbing or dependent on another plant in any way. This
eliminates the possibility of preferential recognition of some distinctive
species over others. It rarely does exclude some reasonably large (up to 2
cm) stems. In addition to the
counting of all liana stems > 1cm diameter, I keep a tally of all
other climbing species less than 1 cm in diameter that I find in the
transects. These tallies are kept on a "every
10 m" basis, such that I start a new list every 10 meters of a transect.
Although these data cannot be considered quantitative because I do not keep a
count of how many stems of an individual species I find every 10 meters, it
adds a good sense of the density of the smallest stems and gives me a
complete species list per plot. All data are compiled
into Excel worksheets on a per hectare basis, recording stem diameter, names,
notes on stem characteristics, and collection status. In recent revisits of plots
in Ecuador, I found that I could relocate almost every stem I had originally
censused (one year previously), in spite of the fact that I do not mark stems
with aluminum tags. |
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Paleoecology and Systematics of Miocene
and Pliocene plants from northern South America I have two on-going projects (click to see info): ________________________________________ |
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We are in the process of getting this
web-ready. For starters take a
look at the work Bonnie has done on the dominant Ficus species (pdf). CLICK |
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In 1995, I was
introduced to the Ecuadorian highlands by vertebrate paleontologist, Rick
Madden. He had discovered a wealth of angiosperm fossil plants interbedded with
Miocene mammalian fossils in several Miocene basins of southern Ecuador. With
an Ecuadorian counterpart, we made a quick trip to the basins of Cuenca,
Nabon, Loja, and Giron so that I could get a first-hand look at the outcrops
and the potential of the plant fossils there. At the time I was skeptical
that I would be interested in any plant fossils that were so young… The fossils were
beautiful, abundant as promised, and I was quickly won over by the
interesting questions provided by the physical context of the fossils. By the
time the intermontane basins of the Ecuadorian Andes were receiving sediments
in their rivers, lakes and swampy areas, the continent had been isolated for
at least 40 million years. The rising Andes and potential migration corridors
provided to Central America during the later part of the Cenozoic call into
question the age of both the extant Andean flora and the northern immigrants
that made their way into Amazonia. Over the past ten years
I have collected plant fossils from three of the Andean basins. Elizabeth Kowalski completed her
dissertation on interpretation of paleoclimate, based on fossil plants from
the Nabon Basin, while I am slowly working on the taxonomic identities of the
80+ species from the Cuenca and Loja Basins. The taxonomy of the Nabon Basin has not been properly
addressed either, at this point.
A preliminary family list is premature at this point, but keep your
browser on this spot — you never know when species identities will fall
into place. At least this I can say: In Cuenca we have found abundant remains
of fossil palms — palmate palms, as usual.
This will help us constrain the temperature to the warmer end of the
spectrum. There we also find abundant specimens of the relatively dry forest
genus, Loxopterygium
(Anacardiaceae). In Loja we find
abundant Tipuana tipu (Burnham, 1995, Amer. J.
Botany), a legume that is today found in subtropical Bolivia and northwestern
Argentina. The only extant member of the genus is widely planted as a street
tree in Southern California! From both Loja and Cuenca we find a large number
of other members of the Fabaceae, with leaf sizes ranging from tiny Acacia/Mimosa-like
leaflets up to larger Pithecellobium and Inga sized leaflets. The identification of
Miocene fossils from South America should not really be so terribly
difficult. They are modern enough that we should find similarities with
extant species, and the flora of South America is increasingly better known
every day. However, the range of possibilities of species that just might
occur at the range of elevation possible at these sites is daunting! We
estimate that elevations could have been from 750 to 2000 meters, a range
that includes all but those species that only like the Amazonian lowlands or
the paramo. The
current loss of habitat from these elevations in South America due to
habitat destruction, development, landslides, and other human-exacerbated
forest loss makes our job just that much harder. As paleobotanists we often
feel removed from issues of conservation but this is a concrete example of
why even the most academic-minded paleobotanist do take note of the current
over-exploitation of natural habitats. Over 1500 fossils have
been collected by our projects in the three Miocene Basins. Roughly 30
localities in each basin have yielded identifiable fossils. This link will lead you to photos of a few
unidentified specimens from the Miocene of Ecuador. Our current guess or more
information accompanies each specimen. If you have a suggestion on the
identity of any of these, let me know! Please note the EPN number for the
fossil you might recognize. These links will lead
you to composite pages of plant morphotypes from the Cuenca Basin of Ecuador.
They are pdf files, so use your browser’s back button to return |
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Population
Structure of a modern Amazonian Liana Dominant: Machaerium cuspidatum |
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During my work in Yasuní
Ecuador, it was clear that one dominant liana could easily be classified as
THE KING. This is Machaerium
cuspidatum, a Fabaceae with single-seeded, winged fruits. Here is a photo of Machaerium
cuspidatum in fruit and flower. |
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One of the things that
intrigued me was that I had actually rarely seen Machaerium cuspidatum in fruit or
flower. The collections in known
herbaria were relatively few, given that M. cuspidatum was the dominant liana, and
often the specimens were sterile (not fruits and flowers). So I started to wonder whether many
of the stems of Machaerium might actually be clones. Lianas certainly do have a high propensity for clonality,
and just how extensive that clonal nature might be was unknown. There have been some very
interesting studies in Mexico on one or two species in which the extent of a
single individual is known by laboriously following that individual
throughout the forest. I was
hoping for something larger-scale and simpler. |
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It seemed like it might
be possible to assess the genetic similarity among ramets using Amplified Fragment
Length Polymorphisms (AFLP from DNA).
With a student assistant from University of Michigan, Mr. Ben Oxender , I made about 95 collections of different stems
all over Yasuní in September of 2002.
I preserved leaf specimens in silica gel (made herbarium collections
of all) and returned the material to Duke University where I extracted DNA
from the samples and ran AFLP analyses on them. The analysis is still underway, but the results are, so
far, indicative of a very widely panmictic population, contrary to what I had
expected. We are still analyzing
the material and data. This did
not come as a total shock because on one of our last days in the field, Ben
and I stumbled upon the Machaerium cuspidatum depicted above and so I could no longer say I had
never seen many fruits. This
specimen happened to be on the 50 ha plot administered by the CTFS system, so
it is certain to attract some attention there. |
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