There is evidence that there has been a decline in small and medium floods in the past decade as a result of water use; prolonged drought and potential effects of climate change.
It is likely due to a combination of a number of factors that include water resource development; climate change and shorter term climatic cycles.
Climate change (increased temperatures and decreased rainfall) which has exacerbated the effects of water resource development and altered fire regimes.
Note that the climate as described here is relevant to the time of listing the issue of climate change is addressed under Threats (see Section 7).
Climate Change (decreased rainfall) Water Resource Development Threat Agriculture (grazing) Altered fire regimes Human Disturbance (recreation) Invasive species Stressor Decreased frequency and duration of inundation Increased equency intensity of fires Direct vegetation removal Physical disturbance increased erosion Pigs Horses Weeds Carp Altered seasonality of inundation Ecological Effects Increased competition from invasive species Altered vegetation community composition Decreased vegetation health Increased likelihood of blackwater events Disruption to breeding Critical Component Process Service Component Vegetation (river red gum forests) Service Significant wetland types physical habitat Component Vegetation floodplain marshes) Service Significant wetland types physical habitat Component Native fish Service Threatened species; ecological connectivity Component Wetland birds Service Physical habitat for feeding breeding threatened species Figure 29 Stressor model of the Barmah Forest Ramsar site (after Gross 2003 and Davis and Brock 2008). 6.1 Water resource use Water resource use in the Murray Darling Basin involves large scale water interception; delivery and extraction which has resulted in major changes to the hydrology of the Murray River (Gippel and Blackham 2002 MDBC; 2008) and floodplain wetlands (MDBC; 2007).
Such effects act either directly on the systems or indirectly by reducing their resilience to other environmental factors such as drought; climate change; grazing or introduced species; or by changing the competitive interactions among different species.
Decreased condition of river red gums as a result of decreased frequency and duration of inundation (Bren 1988 Cunningham et al. 2009) Decreased extent of moira grass (Pseudoraphis spinescens) from replacement by Myriophyllum propinquum (due to increased frequency of small floods) and encroachment by river red gums (attributed to a decrease in medium floods) (Bren 1992) Increase in exotic flora species; due to decreased floodplain inundation frequency (Stokes et al. 2010) Decreased breeding numbers and successful fledging events of colonial nesting waterbirds due to a decrease in frequency and extent of moderate floods (Leslie 2001) Impacts to native fish populations with low flow conditions having a negative effect on the spawning and recruitment of native fish; including the reduction in the recruitment of carp gudgeons (Hypseleotris sp.); southern pygmy perch (Nannoperca australis) and golden perch (Macquaria ambigua) but a favourable effect on the spawning and recruitment of pest species such as common carp (Cyprinus carpio) (MDBC 2008) and Increased incidence and intensity of blackwater events due to reduced frequency of inundation; coupled with unseasonal inundation (during warmer months) resulting in very low dissolved oxygen concentrations and fish deaths. 6.2 Climate change The CSIRO Murray Darling Basin Sustainable Yields Project (CSIRO 2008 Chiew et al. 2008) has modelled the effect of climate change and related factors on the water resources in the Murray Darling Basin; including predictions for the TLM Icon Sites.
Under the future climate models; there was a range of potential climate estimates ranging from extreme wet to extreme dry.
Exacerbate effects of water Climate change (increased Long resource development and Certain temperatures and decreased rainfall). term altered fire regimes.
It is likely due to a combination of a number of factors that include water resource development; climate change and shorter term climatic cycles.
It is likely due to a combination of a number of factors that include water resource development; climate change and shorter term climatic cycles.
Climate change (increased temperatures and decreased rainfall) which has exacerbated the effects of water resource development and altered fire regimes.
The three aspects of climate that most directly affect wetland ecology are rainfall (both local and in the catchment); temperature and (to a lesser extent in temperate systems) relative humidity.
Note that the climate as described here is relevant to the time of listing the issue of climate change is addressed under Threats (see Section 7).
Climate Change (decreased rainfall) Water Resource Development Threat Agriculture (grazing) Altered fire regimes Human Disturbance (recreation) Invasive species Stressor Decreased frequency and duration of inundation Increased equency intensity of fires Direct vegetation removal Physical disturbance increased erosion Pigs Horses Weeds Carp Altered seasonality of inundation Ecological Effects Increased competition from invasive species Altered vegetation community composition Decreased vegetation health Increased likelihood of blackwater events Disruption to breeding Critical Component Process Service Component Vegetation (river red gum forests) Service Significant wetland types physical habitat Component Vegetation floodplain marshes) Service Significant wetland types physical habitat Component Native fish Service Threatened species; ecological connectivity Component Wetland birds Service Physical habitat for feeding breeding threatened species Figure 29 Stressor model of the Barmah Forest Ramsar site (after Gross 2003 and Davis and Brock 2008). 6.1 Water resource use Water resource use in the Murray Darling Basin involves large scale water interception; delivery and extraction which has resulted in major changes to the hydrology of the Murray River (Gippel and Blackham 2002 MDBC; 2008) and floodplain wetlands (MDBC; 2007).
Such effects act either directly on the systems or indirectly by reducing their resilience to other environmental factors such as drought; climate change; grazing or introduced species; or by changing the competitive interactions among different species.
Under the future climate models; there was a range of potential climate estimates ranging from extreme wet to extreme dry.
It is likely due to a combination of a number of factors that include water resource development; climate change and shorter term climatic cycles.
Altered fire regimes (increased frequency and intensity of fires); leading to Death of mature river red gums.
Increased risk of destructive wildfire through increased understorey biomass.
This reduction in floodplain and wetland inundation is likely to exacerbate the effects of river regulation already observed at the site with an increase in stress to vegetation and fauna communities. 6.3 Altered fire regimes Although mature river red gum trees can survive low intensity fires (MacNally and Parkinson 2005) saplings are fire sensitive (Dexter 1978).
With decreased inundation; fuel loads in the understorey can increase and result in intensive fires if ignited. 6.4 Invasive species There are over 100 species of introduced flora within the Barmah Forest Ramsar site and weed cover has been described as extensive (DSE 2003b).
Altered fire regimes (increased Adverse changes to forest Medium Current frequency and intensity of fires). structure.
Invasive species (e.g. weeds; carp; Increased risk of destructive Certain Current horses). wildfire through increased understorey biomass.
Altered fire regimes (increased frequency and intensity of fires); leading to Death of mature river red gums.
Increased risk of destructive wildfire through increased understorey biomass.
This reduction in floodplain and wetland inundation is likely to exacerbate the effects of river regulation already observed at the site with an increase in stress to vegetation and fauna communities. 6.3 Altered fire regimes Although mature river red gum trees can survive low intensity fires (MacNally and Parkinson 2005) saplings are fire sensitive (Dexter 1978).
With decreased inundation; fuel loads in the understorey can increase and result in intensive fires if ignited. 6.4 Invasive species There are over 100 species of introduced flora within the Barmah Forest Ramsar site and weed cover has been described as extensive (DSE 2003b).
Altered fire regimes (increased Adverse changes to forest Medium Current frequency and intensity of fires). structure.
Invasive species (e.g. weeds; carp; Increased risk of destructive Certain Current horses). wildfire through increased understorey biomass.
Again; it is unknown whether this is a result of sustained change or the effec of the prolonged drought from to 2010.
The duration; seasonality; frequency and intensity of wetting and drying determines the type of biota that occurs on the floodplain and wetting and drying can provide important cues for flora and fauna in reproductive cycles.

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