Current warming and likely future impacts - Climate Change: Biological and Human Aspects - page 292

during glacials to what are now tropical montane species, tropical mountains are
today home to species with a long genetic history and this has contributed to their
high biodiversity. 4 However, in the past the global climate has alternated with glacial-
interglacial cycles from present-day to cooler temperatures. Yet today we are seeing
temperatures going the other way, into warmer times that are unprecedented for the
Quaternary, and this means extinctions that are unprecedented in the Quaternary. So
not only will there be extinctions associated with species at very high latitudes but
we will also lose tropical montane biodiversity.
Of course, species' shifts across landscapes are not just associated with future
climatic warming; we have already discussed (Chapter 4) how species relocated with
past climate change. Notably, this took place to and from refugia where a species (or
species community) survived either a glacial or an interglacial.
One significant concern in all of this is the plight of our nature reserves. These sit
mainly among landscapes that, as has been noted (and will be again), have become
highly fragmented by human use and transformation. This fragmentation impedes
species migration and so means that many nature reserves can be considered to
be ecological islands: an idea that sprang from two North American ecologists,
MacArthur and Wilson, in their Theory of Island Biogeography in 1967. The problem
is that because the climate is changing these island nature reserves are in the wrong
place. Alternatively, they could be considered as being in the right place but not
featuring the communities of species likely to flourish under future climates. Either
way, these nature reserves will not, in a climatically changed future, sustain the species
they have helped conserve in the past. Species will be stranded. So the current places
of refuge will not be sufficient for our present conservation goals in the future. What
is to be done?
One solution could be to ensure that there are ecological corridors to allow species
to migrate. Of course, a highly fragmented landscape tends not to lend itself to such
corridors. In such circumstances it may just be possible to create a sufficient number
of scattered small reserves or mini-communities of species in the landscape. These
might be carefully managed hedgerows, strips of green along motorways, parks (and
especially managed areas within parks) and even clusters of urban gardens. Such areas
may provide stepping stones for some species. Altogether the landscape, though still
fragmented, could feature escape routes. The landscape, with its scatter of mini and
temporary refugia, could be viewed as a matrix. (Although many may associate the
term matrix with mathematics, it actually comes from the Latin meaning a breeding
animal or mother but with particular respect to propagation, and womb. Nonetheless,
this conservation use does chime with its other use to denote a complex assemblage.)
Of course, as part of creating an assemblage of mini-communities of species, many
of these communities will need to be managed to encourage diversity. This is not
just for the obvious goal of maximising biodiversity within the managed ecosystem
(which may in some cases is not be ecologically desired), but within the assemblage
of ecosystems within the reserve, as there are often knock-on effects between ecosys-
tems. Effects can cascade across ecosystems. For example, the presence of fish in a

4

Readers who are not life scientists may care to note that biodiversity does not just relate to the diversity
of different species but also the genetic diversity within a species.