An important goal in landscape design is to avoid potentially irreversible ecosystem changes. Such changes have been discussed in the context of thresholds, regime shifts and extinction cascades. Thresholds occur where small changes in one variable result in a large change in another variable. Regime shifts occur when a system 'flips' from one state to another. Extinction cascades occur where the extinction of one species triggers the loss of one or more other species, which in turn leads to further extinctions. Potentially irreversible changes may occur as a result of changes in many variables. Three variables are discussed here: (i) the amount of native vegetation cover; (ii) the structure of native vegetation; and (iii) species composition. Species extinctions may occur more rapidly at particularly low levels of native vegetation cover. However, negative effects may be partly mitigated in heterogeneous landscapes and where the matrix resembles natural vegetation structure. The structure of native vegetation is often related to disturbance regimes. Extinction cascades are more likely to occur following the loss of structural attributes that many species depend upon, such as features typical of old-growth forest or other ecosystem-specific keystone structures. Changes to species composition per se also may result in extinction cascades. This risk is particularly high when entire functional groups or keystone species are lost. Landscape design should attempt to maintain: (i) high levels of natural vegetation cover embedded within a heterogeneous matrix; (ii) structurally characteristic native vegetation, including keystone structures; and (iii) a diversity of species within and across functional groups, including keystone species.