Author: Marcus Bulstrode

Abstract:

River systems around the World are exhibiting ecological collapse largely due to anthropomorphic pressures. The condition of riparian vegetation across most parts of Australia shares a common trend: one of general decline. Australia’s Wet Tropics region experiences high annual rainfall and supports significant levels of biodiversity. Integrated into this landscape are regionally important agricultural industries such as banana, cattle grazing and sugar cane production. The interface between agricultural systems and water drainage networks is the highly important riparian vegetation. Evaluating the long term trend and condition of dynamic riparian vegetation communities is critical in establishing interventions such as erosion and sediment control, contaminant mitigation, and revegetation works.  

The current methods being used to manage the interface between cropping systems and riparian vegetation are deflecting natural vegetation succession and reducing riparian structural resilience. High biomass grasses such as Guinea grass (Panicum maximum), are aggressive colonisers that either directly compete or indirectly causes high mortality levels in native tree seedlings. This is largely due to cropping-system-solutions for their control being inappropriately applied to adjoining natural areas.

Land management system utilising non-selective herbicides sprayed along the riparian interface increase invasive weeds whilst limiting the ability of the natural system to regenerate. These activities can generate a ‘weed-shaped hole’, providing the opportunity for further decline over time. This is particularly the case when the invading species is a ‘transformer’. 

My case study in Australia’s Wet Tropics shows that; when the ability for riparian vegetation to recover is arrested by certain land management practices, system collapse can occur. This collapse is the net result of a cycle of disturbance and invasion. With zero or low tree seedling recruitment, riparian vegetation lacks the capacity for natural regeneration, sufferers from lowered resilience to disturbance, and propagates and perpetuates the need for costly interventions. The inherent checks and balances that initiate self-repair within these systems following disturbance no longer operate, or do they? 

My research indicates that many river systems still exhibit the capacity to regenerate critical ecological functions and their subsequent ecosystem services. When we identify that a natural system is working towards recovery, then logic would suggest, it is in our interest to facilitate this recovery. The current cycle of degradation can be broken through the adoption of relatively small changes in land management practices, such as, when possible, incorporating practices that are sympathetic to natural regeneration through native tree recruitment.