The plants on the highest mountain in Ecuador
have migrated more than 500 metres to higher altitudes
during the last two centuries. This is determined in a new
study, in which Aarhus University researchers compared
Humboldt’s data from 1802 with current conditions.
-
- The Chimborazo
volcano towers at a height of up to 6,268
metres. In 2012, Danish researchers followed in
Humboldt’s footsteps up the mountainsides to
study how much the plant species had migrated
upslope during the last two centuries. Photo:
Naia Morueta-Holme
Although most of the world’s species diversity is found
in tropical areas, there are very few studies that have
examined whether tropical mountain species are affected by
climate change to the same extent as temperate species. A
new study has now determined that major changes have taken
place during the last two centuries.
By comparing the migration of plant communities on the
Chimborazo volcano in Ecuador with historical data from
1802, Aarhus University researchers found an average upslope
shift of more than 500 metres. The entire vegetation
boundary has moved upwards from 4,600 metres to almost 5,200
metres. The main explanation for this dramatic shift is
climate change over the last 210 years.
-
- In 2012, the
researchers made an updated version of
Humboldt’s Tableau from 1802. The illustration
shows how glaciers, vegetation boundaries and
vegetation zones have changed in the last 210
years. Illustration: Morueta-Holme et al.
In Humboldt’s footsteps
The German scientist Alexander von Humboldt
travelled to South and Central America around the
1800s to map the distribution of plants and to
explore what determines the different vegetation
boundaries. He collected plants over a period of
many years, and his collections led to a better
understanding of the link between climate and
species distributions, which he described in several
works. One of his most noteworthy works was the
Physical Tableau, a cross-section of the Chimborazo
inscribed with the names of the plants he found on
the mountainside.
“Humboldt’s Tableau and the accompanying
descriptions make up the oldest known data set in
the world of vegetation along elevation gradients.
It provided us with a unique opportunity to study
how plant distributions have changed in the tropics
during the last two centuries,” says Professor
Jens-Christian Svenning, Department of Bioscience,
Aarhus University, who is one of the authors of the
study.
In summer 2012, the team of researchers followed
in Humboldt’s footsteps to Chimborazo to map the
current distribution of the plants. The fieldwork
was carried out at an altitude of up to 5,200
metres.
“Right up at 5,185 metres, we found the last
trace of vegetation. A defiant little plant
belonging to the sunflower family and half covered
in snow – in full flower in spite of the cold
conditions, the thin air, and the harsh wind,” says
Naia Morueta-Holme, the lead author of the study.
The fieldwork was carried out in connection with her
PhD studies at the Department of Bioscience, Aarhus
University.
Upward shift of vegetation zones
By comparing the two data sets, it became clear that not
only the vegetation growth limit has moved, but also the
vegetation zones defined by Humboldt. The individual plant
species are now found more than 500 metres upslope than they
were 210 years ago. These changes in the vegetation are more
than expected as a result of today’s warmer climate.
Other studies show that there is now less precipitation
in the area, which has also contributed to the significant
shrinkage of the glaciers covering the top of the volcano.
In addition, the lower parts of the volcano have been
intensively cultivated, and a number of species that were
previously only found in the lowland near agricultural areas
have been introduced by humans.
A combination of human-induced climate change and the
direct impact on the plant communities via cultivation of
the landscape around the volcano helps explain the
large-scale vegetation shift – more than has been
experienced in other regions outside the tropics.
Provides insight into the future
The study shows how historical data sets can be used to
demonstrate the way nature is already shifting in response
to global and local environmental change. This provides
insight into what to expect in the future, when climate
change is forecast to be even more severe than witnessed in
the last two centuries.
“Even though the plants have kept up on average until
now, we see many individual species that are lagging behind,
while others – especially common species that are good at
spreading and living under many different conditions – are
moving upslope. We can thus expect even more drastic changes
in the vegetation in the future, and there are concerns
about how the rare and specialised species will survive –
particularly in the tropics, where most of them grow,”
explains Naia Morueta-Holme.
The results of the study can be used for purposes such as
nature conservation by giving high priority to efforts to
minimise the direct impact of landscape cultivation.
The study is featured in the scientific journal
Proceedings of the National Academy of Sciences USA.