Which of the approximately seven hundred species of Eucalyptus are you thinking in, to say that they will have negative ecological consequences? How many hectares? What site (climate, soil, original vegetation) are you considering?
Usually, most negative consequences are caused by bad decisions in species-site selection from people. The most usual answer will be to use native species, but things are not so simple, as many times there are no native species that meet
certain needs. For example, some species of eucalyptus are very fast growing under specific site conditions, and no native species can match them or supply the same products.
You don't have to replace it with other plants, because eucalyptus doesn't need a lot of requirements for growing places, you can use an intercropping pattern with other plants side by side
Eucalyptus is one of the species that grows in swampy areas and submerged areas, and if surface water is not available, it consumes groundwater. If I have an old forest of eucalyptus, it is not necessary to replace the species, but to remove old trees that have reached a life cycle that I can cut down. And I start planting other species according to the conditions of the cultivation area. It is preferable to afforestation of drought-resistant species because they do not consume an amount of water. Since the world is heading towards water rationing, it is better to keep eucalyptus away from the afforestation plans.
I can plant acacia trees of all kinds. Parkinson's trees are also good.