4 Climate change and forest change

let's talk about how climate change specifically affects forest ecosystems so far we've been talking about the mechanisms of climate change but let's now focus on specific changes that are going to be an interest to us as forest ecologist the western US and many places like it dominate the arid ecosystems our lives our well-being or economic function our mountain forests in California these hold very substantial portion of our annual water supply these ranges are high and close to ocean and they can intercept lot of moisture in addition to reservoir of water these mountain ranges advances not just truth and that situation is true when you look across the world for example and the Alps this is new champion France the mountains themselves important and furthermore merchants loss of snowpack and general reduction precipitation is changing our mountainous forests in particular it's leading to increases in tree mortality what does the future hold for our mountain forests it looks like at minimum wrong hook for lot of change we expect that tree mortality as phenomenon has been increasing across the globe over the last several decades and is expected to increase with continued drawing of the climate one of the more important and active areas of research in forest ecology is to try to anticipate when and where these kinds of tree mortality events will occur one of our key problems is not just that the climate is drawing but periods of drought are also more likely to be associated with higher temperatures that is drought is getting hotter both of those factors can lead to shift from stable ecosystems to conditions that are not sustainable and this is the general description of this where for structural force composition is stable under current climate but increases in temperature and drier climate is likely to cause mortality and we can see the evidence for this when we look across the globe and given that we know we don't know how much change is going to happen we don't know exactly where it's going to happen and those are important questions but we can be fairly certain that it is coming and that it is coming in many places and that gives us something basis something to work with and that's what this great analysis from Millar and Stevenson had pointed out that in many cases where we know that were exceeding the thresholds for sustaining particular community and we know that we're on the hook for mortality and potentially compositional changes where we can anticipate those we can lessen the impacts so as said there is clear role for management cure and it's important for us to look for solutions that will soften the blow so what kind of changes do we anticipate many and North American forests and this is probably going to occur for all North American forests to some degree or another our arid forests are especially vulnerable we have because plants the ability of trees to defend themselves is often influenced by the environment we can expect increased rates of insect and pathogen growth that's the individual organisms themselves and at least for period of time increases in their impacts so it's that's that's true climate will affect both exotic insects like this one which is an East Coast exotic forest pest called hemlock woolly adelgid as well as our native pests and pathogens such as bark beetle in general water stress reduces plants capacity to defend themselves that's very broad generalization but it is essentially one that you can apply in many different places and in particular there is concern that for many pests changes in winter temperatures increases in winter temperatures can range expansions and there's been some great work recently number of different studies that work to anticipate these interactions better but let's talk about what we expect in terms of changes in vegetation there have been some other attempts to model landscape vegetation change and in the West which is as say this arid ecosystem arid region of the world where forests are very important for local economies sustain the natural resource dynamics of the people who live there the natural resource needs and people who live there and what we should anticipate throughout the West and in places like in the world is loss of snowpack Unruh Greta bleah that is likely to lead to disproportionate loss of mountain forests how will we can anticipate some of the changes here and that is an increase in arid land vegetation such as the Great Basin sagebrush type ecosystems so that's what we can anticipate here and there's some attempts at the landscape scale to try to model these dynamics again anticipate where and to what extent we can when it will occur these changes are happening in California and as well it's not just the rest of the West they're happening throughout the West and all kinds of different ecosystems it's different it's where Aryan forests here in southwest and in the arid woody plant communities the Southwest as well such as the Sonoran Desert the last point that I'll make is the tree mortality itself is not always there many beneficial aspects of treatment to treat time creating structure problem is when we have too many trees dying at once and it overwhelms our capacity to manage that and when it diminishes the natural resources