Conclusion

Abstract

Climate change poses a severe threat to the pollination of numerous tree species worldwide. While the effect of climate change has been evaluated in a number of cases in herbaceous plants and their pollinators, less is known about the interactions between trees and pollination and especially climate change extreme events such as flooding, droughts, temperature increase and changes in precipitation particularly in trees growing in tropical regions. Thus, more research is required in wild as well as in cultivated trees in tropical environments. The influence of both elevated temperature and cool temperatures imposed by climate change conditions on pollen physiology of trees, e.g. viability, growth and pollen tube germination are detrimental for the pollination and in some cases hampers fertilization and subsequent fruit set. Most studies have focused on the effect of elevated temperature within economically important tree crops, but there is a need for more research on wild tree pollens, which would provide scientists with a bigger picture to understand the effects climate change conditions. It is also important to focus on the optimal temperatures for pollen germination in less investigated crop species and among well investigated cultivated trees. Tree pollen seasons have been modified by climate change especially by increased temperatures. Numerous investigations have been carried mainly in Europe and North America describing pollen season advancement or delay over several years. However, less is known about this topic in the tropics. It is suggested that phenological events in tropical regions such as pollen season and flowering need to be described and quantified to better understand the effects of climate change impacts. The effects of elevated and cool temperatures also need to be determined for tree pollinators. Very little is known about the effect of temperature on flight, foraging and feeding activity of tree pollinators in tropical environments. Other climate change events such as unusual precipitation need more investigation under tropical environments in relation to pollinator activity. Climate change extreme events such as hurricanes have provided insight about their devastating effect on trees and their pollinators. Hurricanes can completely wipe out a whole pollinator population and then, subsequent recolonization can be achieved by the pollinator dispersal abilities. Recent hurricane events provide unique opportunities for studying pollinator and tree interactions which can provide meticulous information about natural restoration and mitigation after a severe event. Precipitation as rain, hail, and snow has also been modified by climate change conditions. Precipitation often halts pollinator activity and causes devastating effect when falling as hail often causing leaf, flower and fruit abscission and damaging pollinator hives and habitats. This is particularly the case of tropical regions, where precipitation as hail, an unusual event has generated impacts on trees, but its short term and long term effects require more research. Water logging is another climate change impact which has been evaluated in trees, and it is known to hamper pollination if the water level rises above the tree’s reproductive structures. Also, if roots are submerged for prolonged periods without proper aeration, foliage, flowers and fruits are likely to suffer abortion. Climate change imposed drought has caused reproductive issues in trees including flower decay, abscission and in specialized trees like figs it has caused pollinator declines or removal from a particular area. Specialized fruit tree species such as figs are keystone species because numerous vertebrates, such as mammals, birds as well as the whole food-web are dependent upon them. This raises the question about the importance of pollinators for both cultivated and wild environments which occur through plant-pollinator interactions, in this book, tree-pollinator interactions. These interactions have been thoughtfully studied in herbaceous plants in temperate conditions. Less is known about woody angiosperms and their interactions with pollinators particularly in the tropics where thousands of tree species are awaiting to be studied. Three pollinator mismatches have been evaluated in temperate conditions where pollinators e.g. butterflies have been documented to occur later than the flowering event. In the tropics the interplay of numerous pollinators, i.e. increased pollinator diversity could hamper the effects of climate change factors such as precipitation, decreased or increased temperatures, etc. But more research is indeed warranted to fully understand pollinator diversity and tree pollination in tropical regions worldwide. Describing and quantifying the effects of climate change on pollinators and trees is an important step to establish management and conservation measures for mitigating and adapting to climate change conditions. Effective conservation initiatives are required to preserve both wild and cultivated trees and their pollinators. These measures include farm management, water management, incorporating new technologies, using different tree cultivars and genetic resources, or establishing frameworks for tree conservation under climate change conditions. All of these initiatives solve the problem at least partly and could probably lead to provide consistent solutions. Other conservation strategies have focused on pollinators, identifying ways to enhance landscape features, establish pollinator reservoir areas, generating heterogeneous agricultural landscapes, etc. In spite of all conservation measures to mitigate and adapt to climate change conditions, climate change phenomenon needs to be tackled at its source empowered by consumerism, and also industrial, political and economic criteria in today’s globalized world. The change is more about the attitude of we humans towards nature. It is a change in philosophy from a materialistic view, purely based on generation of wealth regardless of the environmental consequences to a higher philosophical view where the natural world is connected to humans. Pollination in the light of climate change is an essential aspect that has motivated numerous researchers worldwide to provide their view and research initiative. It is important to generate awareness about pollination studies worldwide and particularly under climate change conditions. Developing countries require programs to evaluate and determine the effects of climate change, pollinators and trees. This book is sought to contribute by providing the personal view of the authors and by a literature review of the main aspects that pertain to trees and their pollinators.