Agriculture Reference
In-Depth Information
3
2
1
0
-1
-2
LowFire
HighFire
LowFire
HighFire
Regional
Local
Fig. 9.13
Net relatedness index (NRI, i.e. standardized form of the mean phylogenetic distance) of
woody species coexisting in communities in contrasted crown fire regimes (LowFire vs. HighFire).
Note that low mean phylogenetic distance implies high net relatedness. At regional scale, “LowFire”
corresponds to mountain communities living in zones that rarely burned, and “HighFire” are
warmanddrycoastalcommunitiessubjecttoahighfrequency of crown fires. At local scale (under the
same climate), “LowFire” corresponds to communities growing in fertile soils while “HighFire”
are communities growing on poor soils where flammability is higher. In comparison with community
null models, HighFire communities show higher NRI than expected by chance (phylogenetic
clustering), which indicates the importance of habitat filtering in shaping fire-prone communities.
(Elaborated from Verdu
´
& Pausas 2007 and Ojeda
et al.
2010.)
distributed in closed-canopy chaparral where postfire resprouting likely limits
seedling recruitment opportunities and obligate seeding populations are distrib-
uted in more open communities (J.E. Keeley unpublished data). Similar environ-
mental selection is suggested by the switching between lignotuberous resprouters
and obligate seeders multiple times in the endemic clade of South African Cape
Podalyrieae tribe of Fabaceae (Boatwright
et al.
2008
).
Conclusions
Fire-prone landscapes began with the origin of land plants, and fire has potentially
been a factor whenever climate and soils combined to create sufficient biomass
and seasonality to generate continuity of available fuels. Thus, trait evolution in
fire-prone plant communities is closely linked to ecosystem processes that contrib-
ute to fire spread. Lightning ignitions vary in abundance and seasonal timing, but
over most (but not all) land surfaces they have been a ready source of ignitions for
