eventually the plants grown from an inbred seed source may decline in viability, for example when Dawn Redwood (metasequoia glyptostroboides) was first discovered to not be extinct a small seed collection was made from which all the USA population of that tree came from, after a few generations seed viability became very poor, another collection was supposed to have been made in the 1990's to get a broader genetic base to produce trees from to solve that problem. So inbreeding can eventually cause problems down the line, in more ways than fertility. It can lead to increased susceptibility to diseases and a general decline in vigor.
In Western Oregon there are a few scattered populations of Ponderosa Pine, you cannot take a population from one area and plant the seed in another area and have them live to maturity, they will only get to be large enough to be difficult to remove when they die. The populations are inbred and cannot tolerate conditions outside of the area they evolved in. Another good reason to not have any of those horrid trees in you life.
