3. Results and discussion
This section presents the most interesting findings concerning
the influence of the plant cover evolution on the green roof thermal
behaviour.
Usually plant layer is considered as a homogeneous layer so that
the entire surface has the same characteristics (level of cover, foliage
density, Leaf Area Index, albedo, etc.). But plant layer on a
green roof is usually composed of different plant species, with
different morphological and physiological characteristics, which
leads indeed to a heterogeneous layer. Even within species, big
differences can be found. For instance, the most used genus for
green roofs, that is Sedum sp, shows large variations between
species. This heterogeneity can affect the whole green roof thermal
behaviour.
In addition, besides the floral diversity the rigor of certain climates
must be added, such as the Mediterranean Continental
climate, with large temperature variations and long periods of
drought, which implies more different plant growth rates in comparison
to other milder climates.