Veg history answer

Like I mentioned before, here is a post of an answer for my vegetation history class.  The question: Does history matter?  In other words, do we need to know about events in the past to understand the present?
     History matters.  We do need to know about events in the past to understand the present, but even more, we need to understand the past to understand the present, and the future.  Understanding sequences of events that shaped the past or variables that interacted to cause events in the past will help us better understand the present.  
     The diversity of the Amazon rainforest is a pertinent question that involves the understanding of history.  If we can understand what caused the Amazon to become so diverse, then we understand the present condition better and can possibly plan for the future.  Adams and Woodward (1989) assert that diversity is controlled by modern-day net primary productivity.  However, they state in their introduction that, “ differences in species richness between three northern temperate regions, Europe, eastern North America and eastern Asia, can be mainly explained in terms of present-day climate factors … without the need to invoke the historical explanation.”     They conclude that history does not matter, because strikingly similar patterns in the productivity-richness pattern occur on various continents, separated by vast oceans.  Therefore whatever happened in these various places in the past certainly did not make any difference in what we see there now.
     McGlone (1996) has another argument.  He argues that, “A close relationship between climate and species richness is observable only at regional scales and results mainly from the influence of glacial-interglacial climatic cycles in determining the regional species pool.”  In other words, McGlone refutes Adams and Woodward’s hypothesis by saying that it is important what plants existed on each continent in the past, and what happened to those plants as climate changed.  McGlone argues that both the plants you start out with and the type of climatic changes they have to deal with all help to give us our modern-day assemblages.  He also reminds us that, “Ecological and biogeographical processes work continuously through time, and the current situation must reflect past ecologies.”
     Another author who advocates for the past is Retallack (2001).  In his paper, Retallack poses a lofty argument that Cenozoic climate change was driven by the expansion of the grasslands and the co-evolution of grasslands and grazers.  Throughout his paper, Retallack argues that grasslands have the ability to control global climate by being carbon sinks, fertilizers, dehumidifiers, and fire starters.  Besides his point that grasslands are important to climate change, Retallack reinforces the argument that understanding history is important for understanding the present.  An underlying point of his paper is that we need to understand what caused the Cenozoic global cooling that lead to the recent ice ages in order to understand our present situation, and what might happen in the future.  
     Leopold and Denton (1987) use grassland development to make a strong argument that history is important.  They study the development of grasslands in western North America, and the differences between the Great Plains, Rocky Mountains and Columbia Plateaus grasslands through time.  They state that, “The biogeographic, physical, and climatic contrasts of these regions imply that their historical development must have been very different.”  In comparing the evolution of grasslands over the western U.S., they found stark differences between the three regions over time.  Their conclusion: the regions had to have something different happen to them in the past, and that past affected what we see in those areas today.  
     Lastly, Whitlock and Bartlein (1993) show that history matters in the paleoecologic record of the northern Rocky Mountains.  They conclude that vegetation and climate changes in the northern Rockies during the Holocene were due, at least in part, to changes in summer insolation.  Knowing things like this about the past can help us understand why conditions are as they are today.