Environmental Engineering Reference
In-Depth Information
reference data on this topic are so limited and variable that it is not possible to
confidently estimate the annual growth of shrubland communities.
14.1 Introduction
Shrublands may represent the most mature local communities and not be able
to “evolve” towards proper forests. In these cases, their presence is mostly due
to very strong limiting (stress) factors, such as long-lasting warm or cold peri-
ods, scarce water availability, nutrient-poor or toxic soils, intensive drainage, etc.
Elsewhere, shrublands represent unsteady steps within a dynamic process, which
may be progressive or retrogressive. In the first case, they issue from the recent
colonization performed by woody species after land abandonment (Corona et al.
2008
; La Mantia et al.
2008
), and their complexity increases along with cover rate
till they become mature forests. In retrogressive succession, in contrast, severe
and/or frequent disturbance (i.e., grazing, burning, cutting, etc.) causes the struc-
tural simplification of pre-existing forest communities. As a consequence, shrub-
lands and open maquis communities may have similar physiognomies even when
they have rather different histories to tell. Thus, a lack of historical information
may bias any trial to assess how plant biomass is likely to change in the future.
On the other hand, as shrub communities often develop when forests degrade, the
knowledge of their carbon stock is relevant in assessing the baseline for negotiat-
ing future agreements with respect to carbon balance.
At present the official data concerning non-forest Italian vegetation do not
match perfectly: in fact, according to the most recent (2005) National Forestry
Inventory (
http://www.sian.it/inventarioforestale/jsp/home.jsp
) shrublands cover
990,916 ha and woodlands 46,678 ha, while following the official data provided
by the National Forestry Inventory carried out in 1985, Corona et al. (
1997
) esti-
mate that altogether Italian shrubby, rupicolous, and riparian plant communi-
ties occupy 2,164,500 ha and have a carbon stock of 26.4 (18-35) Mt. The same
authors also report 256 Mt as the average value of carbon stock in Italian forests
(high forests
+
coppices) and tree plantations.
Beyond these discrepancies, there is no doubt about the important role played
by shrublands in the global carbon stock, as indicated by the Kyoto Protocol
(the “Marrakesh Agreements” explicitly refer to shrub vegetation colonizing
abandoned agricultural land). On the other hand, there are few available studies
concerning the biomass and the net ecosystem exchange capacity of shrublands
(Navarro Cerrillo and Blanco Oyonarte
2006
). This is also true for the most com-
mon woody species (hereinafter abbreviated “WS”) typical to Mediterranean (Us
et al.
1997
) and Italian (Costa and La Mantia
2005
; Corona et al.
2012
) shrub-
lands, and even less information is available concerning biomass assessment at the
community level. This knowledge gap not only depends on the lack of field inves-
tigations focused on the dominant WS but also on the high floristic and structural
variability of shrublands themselves.
