Page 32 - Science

INSIGHTS | PERSPECTIVES | RESILIENCE

ECOLOGY In another study, Poorter et al. (5) exam-
ined recovery rates of 45 Neotropical for-
What makes a terrestrial est sites after clearance from 1500 records
Even
on
spanning the past
years.
this
20
ecosystem resilient? shorter time scale, the authors found strong
and
geographical
in re-
climatic variation
covery rates, with seasonally dry forests ap-
A complex set of biotic and abiotic factors determines pearing to have less resilience than that of
humid tropical lowland forests.
the resilience of an ecosystem Innovative analysis of satellite imagery
is starting to provide another important
data set for determining spatial patterns
By Kathy J. Willis, Elizabeth S. Jeffers, climatic perturbation and is thus often dis- of resilience (6, 7). For example, Seddon et
1,2
2
Carolina Tovar 1 carded; a data record that shows no change al. (6) used monthly Moderate Resolution
is harder to publish. Imaging Spectroradiometer (MODIS) satel-
ith increasing incidence of ex- In recent years, new sources of ecological lite data, taken globally at 5-km resolution
treme climatic events, disease data and algorithms for analyzing resilience between 2000 and 2013, to develop a veg-
outbreaks, and other environ- have begun to provide answers to the three etation sensitivity index that captures the
mental perturbations, conser- questions posed above. These studies have relationship between climatic anomalies
vation of terrestrial ecosystems been carried out in almost every terrestrial and relative variance of the vegetation (see
W that can retain their structure biome (3); here, we focus on those under- the figure, left). This method identifies how
and function despite environmental shocks taken in tropical ecosystems. sensitive different regions of vegetation
has moved rapidly up the international po- have been to climatic variability over the
litical agenda. International environmental WHERE ARE THE MOST RESILIENT past 14 years. In the tropics, more resilient Downloaded from
policies and targets such as the Aichi Biodi- TROPICAL ECOSYSTEMS? areas included the woody savannas of the
versity Targets and the Sustainable Devel- Data sets normally used to examine other Brazilian Cerrado and the drylands of the
opment Goals include conserving resilient ecological phenomena have recently been Sahel. By contrast, vegetation in parts of
ecosystems as a key priority. analyzed to determine both forms of resil- the West Africa and the Amazon basins was
An ecosystem can display resilience in at ience. Cole et al. (4), for example, used data highly sensitive to climatic perturbations.
least two ways: in the ability to resist an en- from fossil pollen records to compare tropi-
vironmental perturbation and not switch to cal forest recovery rates after perturbations WHAT ATTRIBUTES PROVIDE RESILIENCE?
another state, and in how quickly it recovers between and within regions. In a meta- In addition to showing relative patterns of http://science.sciencemag.org/
after the disturbance (1). However, research analysis, they examined 283 forest distur- resilience, these spatial and temporal rec-
into what makes a terrestrial eco- ords provide important data sets
system resilient is complex. Many with which to test the many hypoth-
hypotheses have been proposed, sug- eses relating to resilience (1, 2) and
gesting a suite of possible abiotic and the complexity of the interacting
biotic attributes responsible for resil- biotic and abiotic factors that can
ience (1, 2). Understanding resilience lead to it (2). For example, a key abi-
also requires comparative data sets otic attribute hypothesized to influ- on March 1, 2018
that span both space and time and ence resilience is climate, and there
that address at least three questions: is some evidence emerging to sup-
Where are the most resilient ecosys- port this. In Neotropical dry forests,
tems, what attributes make them the highest rates of above-ground
more resilient than others, and how biomass recovery after clearance oc-
close is an ecosystem to losing its curred in regions with higher local
resilience? rainfall and lower water deficit (the
The first step toward addressing difference between potential evapo-
these questions is to find data sets transpiration and rainfall) (5).
demonstrating that particular eco- Other studies have hypothesized
systems display resilience. Some that the number of times an ecosys-
projects fail at this hurdle. It is of- tem is disturbed, the less resilient it
ten difficult to find data sets span- becomes, as indicated by a slowing
ning a long enough time to record Species richness, as in this West African tropical rain forest, may not down in recovery rates after each
the response of an ecosystem to an always provide resilience to external perturbations (see the figure). subsequent disturbance. However,
environmental perturbation, espe- this relationship does not always
cially in forested ecosystems with trees that bance and recovery events over the past hold true, especially over longer time inter-
have decades-long generation times. Fur- 20,000 years in Central and South Ameri- vals. Cole et al. (4), for example, found the
thermore, the record of a resistant ecosys- can, African, and Asian rain forest blocks. opposite effect in the fossil tropical forest PHOTO: FABIAN PLOCK/ALAMY STOCK PHOTO
tem will display no change despite a known They found substantial spatial differences data sets; the more times a system was dis-
in recovery rates; Central American tropical turbed, the faster it recovered, presumably
rain forests appeared to recover faster from because the vegetation became dominated
1 2
Royal Botanic Gardens, Kew, Richmond TW9 3AB, UK. Oxford
Long-term Ecology Laboratory, Department of Zoology, environmental perturbations than those in by forest species that could tolerate and re-
University of Oxford, Oxford OX1 3PS, UK. Email: k.willis@kew.org South America and Asia. spond quickly to disturbance. The type of
988 2 MARCH 2018 • VOL 359 ISSUE 6379 sciencemag.org SCIENCE
Published by AAAS

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