Even though the Azores look very green and sometimes wild, the vegetation has been extremely altered. A great part of it has been wiped out in the past 600 years for its valuable wood (for tools, buildings, boats, fire wood, and so on) and to clear land for agriculture. As a result, it is estimated that more than half of insects on the Graciosa island have disappeared or will become extinct. Many cultivated places (which are traditionally dedicated to pasture or to growing colocasia, potatoes, maize and other crops) have now been abandoned, especially as a result of emigration. Consequently, some invasive plants have filled these deserted and disturbed lands. Hydrangeas are another potential pest, but their threat is less serious. Notwithstanding the fact that hydrangeas were introduced from America or Asia, some locals consider them a symbol of the archipelago and propagate them along roadsides. "Cryptomeria", the Japanese cedar, is a conifer extensively grown for its timber. The two most common of these alien species are "Pittosporum undulatum" and "Hedychium gardnerianum". Reforestation efforts with native laurissilva vegetation have been accomplished successfully in many parts of the Azores.