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Apple Trees & Phenological Mismatch

Plant / pollinator mismatch is a growing area of study as scientists examine effects of ongoing anthropogenic climate change in natural ecosystems. Plant phenological mismatch, the missed timing of flowering plants and their pollinators, also has huge implications for agricultural systems and the economics of food systems. Understanding warming’s effects on these systems, therefore, are of great interest to a rapidly expanding human population and the required agricultural yields for feeding the global population. In this vein, researchers in Hungary tested Apple trees (Malus x domestica) at various stages of phenological stage to observe effects on numbers of herbivores, pollinators, and other insects. They found substantial evidence for effects of mismatch but their study is limited and further research is needed for direct impacts to be examined for both natural and agricultural systems.

Phenology is the study of seasonal observable change within organisms and includes features such as changing fur color in mammals, feather production in birds, and migration patterns in many organisms. For deciduous plants, phenological features include foliage color and drop, and the timing of budding, bursting, flowering, fruiting, and leafing. These features have become important markers of a changing climate globally as historic phenology records can be used as further evidence of temperature change.

The timing of phenological features has important implications across ecosystems as flowering plants (angiosperms) form the base of many ecosystems. Flowering plants depend of course on coevolved pollinators for reproduction and growth of populations. A mismatch in timing with pollinators (ie. migrating or emergence) could have drastic effects from the base of the food web upwards including on the numerous organisms that inhabit and form communities on trees.

A Study in Hungary: An Apple Delay…

Researchers in Hungary manipulated the phenology of apple trees to examine the effects on pollinators and the communities of critters that inhabit the trees. The scientists kept one group of apple trees in cold storage (delayed) to delay bud burst and flowering of the apple trees before planting and another group of apple trees in climate controlled greenhouses (advanced) to facilitate the early onset of budding and flowering prior to planting. Both these experimental groups were compared to trees planted outdoors and experiencing seasonal climate.

keeps Pollinators Less Varied

When each of the tree groups were sampled for arthropod abundance (insects, spiders, etc…), they found that the manipulated trees (delayed or advanced) had less biodiversity than the control trees. Overall numbers for each of the groups varied, but the study showed that specialized interactions, such as herbivores or insectivores with limited diets were more susceptible to the altered timing of the trees.

Noble Chafer at work amongst the apple blossoms

One interesting effect not anticipated was that in all trees, pollinator abundance (ie. bees) was similar despite the different timing of flowering. The researchers suggest that a significant diversity of wild bees hedged the erratic timing of phenological mismatch by being able to respond and ensure fruit set. This, however, was noted in turn that the overall pollinator diversity was lower on the manipulated trees compared to the control.

Ok. Wait, What Does This Mean?

The climate induced changes to phenology of both wild plants and agriculturally important crops has important implications that begin to be examined by this study. Mismatch of the timing of flowering for the apple trees in this study, while not showing impacts on fruiting, did show effects on the diversity of pollinators. In many areas around the world, pollinators are already showing signs of mismatch with plants. If commercially important crops flower without enough pollinators, this obviously could lead to lower yields, higher food prices, and global food shortages.

As it relates to natural systems, the earlier onset of budding and flowering can have impacts on those producers on the rest of the ecosystem. For trees reliant on the arrival of migratory birds for dispersal for example, mismatch could mean heavy impacts on producer population growth and all the organisms that depend on them. Studies using historical data on phenology have shown that mismatch in this area is already occurring.

Bohemian waxwing enjoying a berry and unwittingly being part of a coevolved dispersal strategy

TBD

Many of the studies examined on phenological mismatch require further research. Looking back into historical records, such as Henry David Thoreau’s writings on nature or farmer’s almanacs are helpful to set a baseline from which to compare, but they are sparse and obviously don’t offer a global picture. Also of interest is if plants and pollinators will change on smaller scales through plastic responses (ie. behavioral changes to migration times or budding) to reduce mismatch. If this is occurring, not only would it be an interesting area of research, it could reduce a huge potential detriment to global food systems.

Sources and Further Reads:

  • Kőrösi, Á, Markó, V., Kovács-Hostyánszki, A., Somay, L., Varga, Á, Elek, Z., . . . Báldi, A. (2018). Climate-induced phenological shift of apple trees has diverse effects on pollinators, herbivores and natural enemies. PeerJ, 6. doi:10.7717/peerj.5269

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Published by eprileson

I am a historian and writer who wants to bring to light current events through a historical perspective. It is difficult to understand today's current events without having a grasp of what has occurred before. This is a running thread to help keep people informed about the present and remind everyone to not forget their past. Enjoy and please comment!

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