European settlement brought with it the loss of the northern grasslands and severe alteration to the natural ecology of woodlands and wetland environs. Changes brought with European settlement included the widespread loss of clumping grasses, clearing for agriculture, the introduction of foreign animals and plants. Other changes include the use of fertilisers, the grazing of domestic animals, the absence of fire (both natural and aboriginal) and changed hydrological cycles. These issues have all had major impacts on the environment. The processes that formed and maintained the environment have been significantly altered to those in which the animals and plants evolved.

Changes have occurred to the environment have included the simplification of ecosystems across much of the landscape, from natural to agricultural ecosystems. The replacement of complex interrelationships with simple linear ones.

It is important to understand that with disturbance an ecosystem and its environment don't cease to exist, but change. Indeed the environment is still going through a process of change, with some species losing the battle to exist, and others flourishing. Primary factors responsible for determining which species flourish and which ones disappear include what parts of the environment have changed and how fast this change occurs. Many species have the ability of some species to adapt their own behaviour to cope with change through learnt behaviour, such as eating introduced plants, some have been able to adapt at a genetic level to change. Unfortunately many species haven't faired so well, with some having already become extinct, many greatly depleted from their natural ranges and others facing an uncertain future. Human intervention can help to tip the balance back in favour of some species.

Primary reasons for the impacts on many species range from the loss of resting, breeding, feeding habitats, to predation by introduced species. Often there is a wholesale change in the balance of the food chain, which means that there is simply not the availability of food to support a species at some part of its life cycle. In many cases a combination of issues.

Animal survival is intrinsically linked to plant life. The diversity of one affects the diversity of the other. For example changes to vegetation affect insect populations, which in turn affect pollination of orchids and other native plants which in turn provided a food source for certain birds. The disappearance of the native orchids has meant the disappearance of this food source. Isolation of remnant native vegetation and the clearing of ancient trees also means that suitable breeding habitat such as tree hollows are affectively lost forever, as they take several hundred years to regenerate.

Invasion by exotic plants or animals cause direct predation, competition for existing food, breeding sites or simply impose stress through terrorising and competition for territories. In many instances there is simply no place left in the environment for native animals or plants introduced species have essentially filled their ecological niches. Many of these introduced species thrive in the absence of natural factors which limit their own breeding, or survival in their own native environments. Examples include the invasion of roadside remnant vegetation by pasture grasses such as Phalaris, which outcompetes native species for light, moisture and nutrients.

Many plant species including grasses, herbs, shrubs and trees are now severely limited in their ranges and also face uncertain futures. In most cases the issues that caused the decline in most species in the northern plains are still operating.

Prior to European settlement there were some species which occurred, in greater numbers, others in lesser numbers. There was a much wider range of species, which occupied the landscape. Kangaroos, Wallabies, Koalas, Echidnas and a range of other species would have been found wandering the grassland/woodland habitats. A range of small marsupials would also have been found in the area that now forms the park. A number of reptiles including the Carpet Python, Lace Monitor, Bearded Dragons, and Bluetongue lizards, Legless Lizards to name a few would have also been common, forming an integral part of a diverse and complex and resilient food chain within the parameters of the environment in which they lived. These species are no longer found in area that forms Cussen Park.

Birds such as Brolgas and some now extinct or endangered birds made the Northern Plains home for their breeding seasons. The park now provides an important refuge for some of these endangered species and many more considered rare, or vulnerable to extinction.

Despite the changes which have occurred to the Northern Plains, the work done by the Tatura community in developing Cussen Park has provided significant habitat for many species.