Linking Restoration and Ecological Succession (Springer ... - Inecol

84 Joe Walker and Paul Reddell
4.7 Retrogressive Rainforest Successions: What Lessons
for Restoration?
Recognizing and understanding the widespread occurrence and nature of retrogressive
succession on old soils in the humid tropical is fundamental to successfully
and predictably restoring sustainable and functional forest cover to
these areas.
Activities to restore forest cover in the humid tropics are varied in their
primary purpose. These can range from habitat replacement for rare species
conservation, through to tree establishment for catchment protection or for
plantation forestry. Each purpose is likely to have different objectives in relation
to productivity, species composition, and ecosystem function, as well are
require different implementation methods suited to the purpose, budget, and
local conditions. Where these activities are planned in old landscapes, there
are two broad approaches that can be applied to deal with the implications of
retrogressive succession. These are:
1. Alter the site conditions to ameliorate as far as possible the degraded state
of the disturbed system and restore its pre-disturbance state.
2. Recognize the new system state and set realistic endpoint, composition, and
productivity objectives consistent with this post-disturbance, retrogressed
state.
In some instances, especially where the main impacts of disturbance have
been on site nutrient capital, it may be possible to use a well-planned fertilizer
strategy to recapitalize limiting nutrients into the disturbed area and return it
to a potential state and vegetation type closer to the original. However, this
is often likely to be expensive and resource intensive. Interestingly, the most
limiting nutrient after disturbance in many old landscapes is calcium (Nykvist
1998), which is accumulated in wood and bark and has an essential role in lignin
formation. Treatments to ameliorate the effects of anthropogenically accelerated
retrogression on hydrological characteristics may also be technically possible,
especially to increase surface infiltration, however these are unlikely to be
economically feasible on the broad scale.
A less resource intensive approach that is likely to be more widely applicable
is to recognize the biophysical constraints in the new post-disturbance, system
state and develop endpoint objectives for composition, structure, productivity,
and/or function based on this state. In many areas there may be landscape “analogues”
of the new state, where natural erosion and weathering have progressed
more rapidly in particular landscape locations and where existing plant communities
can be used as models for species composition, structure, productivity,
and function in the restoration process.
4.8 What Do We Need to Know to Restore Old Disturbed Landscapes?
Fundamental to the restoration of old disturbed landscapes is recognition that:
1. Retrogressive succession (in which total nutrient capital declines and hydrologic
functioning changes as systems age) is a normal, long-term, natural
process in old landscapes.