Spanish mistletoe travels

Movement of species as the climate warms is a staple of a lot of ecological research. In the case of plants, the species moves even though the actual organisms don’t. Seeds at the colder limits of the range become more successful. Seeds and plants at the other end of the range, where it’s warmer become less successful as better adapted neighbours move in.

In Europe, this usually means species appear to migrate north, or else up the slopes of hills, where the habitat was previously too cold. One of the most recent examples of this is a study of Viscum album subsp. austriacum, mistletoe, by Regino Zamora and Ana Mellado of the University of Granada. They examined the plant in a Mediterranean pine forest in the Sierra de Baza Natural Park. Like the other plants in the park, it has rising temperatures to contend with – but its lifecycle means it has a few more problems.

Mistletoe is a hemi-parasite. While it can photosynthesize, it still needs a host in order to supply nutrients to the plant. Typically the plant grows on Pinus nigra, Black Pine. However, if it is to move into new territories then it needs a suitable host in the new location. It also needs a way to get there. It does this by having it seeds eaten by birds, or else carried on birds by sticking to them with its sticky fruits. So reproduction is reliant on both suitable hosts and transport.

Zamora and Mellado have found that mistletoe in Andalucia is moving upwards, partly be parasitising a sub-optimal host. Mistletoe in Sierra de Baza is adapted to live on P. nigra but it can make do with P. sylvestris var. nevadensis if it has to. The authors say that what is going on here is that the parasite is reacting faster to warming than its host, and so it is already expanding its range faster than the pines it prefers. It means that some species are interacting much more often than they used to, and this could have effects on both of them as they come into more frequent contact.

For now, it seems that warming it opening up new habitats to mistletoe. But, if temperatures continues to rise, then it might find that its hosts disappear, leaving it with no habitat to grow.