Resistance is the ability for an ecosystem to remain unchanged when being subjected to a disturbance or disturbances. Some ecosystems are better at resisting change than others, and therefore have high resistance.
Resilience is the ability and rate of an ecosystem to recover from a disturbance and return to its pre-disturbed state. Some ecosystems can shift greatly from their previous state and still return to pre-disturbance conditions. The measure for how far an ecosystem can be shifted from its previous state and still return to normal is called its amplitude.
Both resistance and resilience are components of determining ecosystem stability. Both can also occur at the community, population, and individual level. An ecosystem can have high resistance to disturbance, but low resilience, and vice versa. Low resistance can sometimes be advantageous, such as in ecosystems that rely on natural disturbances to temporarily change their conditions in order to remain stable over the long term.
Sources:
“Resistance and resilience of ecosystem metabolism in a flood-prone river system” by Urs Uhelinger http://www.limnology.uni-muenster.de/etc/experieco/lit/respiration/Uehlinger_2000.pdf
“The Stability of Ecosystems” http://www.glyndwr.ac.uk/bartlett/ecology/stability.htm
https://en.wikipedia.org/wiki/Ecological_stability
“Pinus Clausa” by Jennifer Carey http://www.fs.fed.us/database/feis/plants/tree/pincla/all.html
Image: http://www.fs.usda.gov/land/ocala/landmanagement