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| Stones and boulders which have come tumbling down from Twll Du have formed this scree. Some large rocks inaccessible to sheep have masses of vegetation on them. Lichens colonise first on freshly exposed rock surfaces. Later seeds may germinate and mosses may grow where there is sufficient water. As these plants die, their remains decompose and pockets of organic matter develop. In time a complete plant community will spring up. |
