Consequences of land management practices on willows and higher trophic levels

A broad perspective on the current status of willow populations in Arizona is developed based on a landscape scale view of plant demography in space and a long-term temporal view since the Pleistocene. For germination and establishment, willows need moist mineral soil at higher levels of precipitation than normal for at least 2 years. In Arizona, regeneration may be successful only once or twice in a century even if disturbance creates mineral soils. However, declining disturbance over the landscape has greatly reduced the possibility for willow regeneration. Since the end of the Pleistocene glacial/pluvial period, when conditions in Arizona were probably excellent for willows, gradual drying has resulted in willow species with decreasing population sizes and ranges, with some only in relictual stands. With little or no regeneration and small isolated populations, the biodiversity of insect herbivores and their carnivores supported by willows has inevitably declined, probably by 50 percent of species or more. Simple land management practices could divert the course to local extinction of several willow species in Arizona.