For more than 30 years, Arbor Age magazine has been covering new and innovative products, services, technology and research vital to tree care companies, municipal arborists and utility right-of-way maintenance companies
Issue link: https://read.dmtmag.com/i/166866
phase the plants are in.Bud break,vigor/growth, degree days to predict the occurrence of almost length of the growing period, and the start of any natural event. So what do we do with this fall senescence can all be seen from space at the info? global scale. Over the course of several years, the NDVI can track these seasonal parameters to Using phenology illustrate all sorts of climatic changes.Combining There are several different ways to put phethis data with historical records, we can see that nology to work for you. First, as there are many the spring emergence date for many plant species events that occur at roughly the same number has been occurring sooner in the year than they of growing degree days, you can use the occurwere before 1960.The first oak leaves to appear rence of one, more conspicuous event, to predict in the spring have advanced eight days earlier the occurrence of something less obvious. For than they were 250 years ago, corresponding to example, the emergence of emerald ash borer the rise in global temperature near the end of (EAB) adults goes unnoticed by pretty much the Twentieth Century.Although the NDVI is everyone.They are small, they fly, and they leave a great tool for tracking global changes, it is prithe tree they exited from shortly after they marily a tool for recording what has already come out. So how can we easily know when happened,not predicting when events will occur. new EAB infestations may be possible? If we For that, we turn to a different index. look at their GDD info for their emergence As touched upon earlier, the leaves of oaks dates, we find they come out at about 550 are emerging earlier due to a rise in annual Phenology starts with observations. GDD. Checking a list of other GDD events, temperature.The correlation between ambient we see the black locust (Robinia pseudoacacia) temperature and emergence dates can be predicted by tracking the begin to flower at 548 GDD, so we can surmise that if we see black amount of accumulated heat using growing degree days (GDD).The locust trees in bloom, EAB adults are out and looking for new ash trees concept is fairly simple and intuitive.Take, for example, a tree that would to infest. typically flower in the first week of June during a "normal" year. If we have consistently cool temps in April and May, that flowering time is likely to be later. If we have an abnormally early and warm spring, it can flower sooner. If we have cool temps in April and the first half of May, followed by unseasonably warm temps the last two weeks of May, our tree may flower right on time. It is not the temperature on one particular day that matters, but the accumulation of temperatures over a period of time that makes the difference.That's what is being tracked by the GGD model. How it is calculated is fairly simple as well. First, you start with a base temperature. In most cases, the base temp (or TBase for our equation) is 50 degrees Fahrenheit, because not much plant growth occurs when temps are in the forties, thirties, or colder.Then, on every day you take the high temp (TMax) add the low temp (TMin), and divide by 2 to get an average. Now, subtract our base temp and you have that day's growing degree.The equation looks like this: TMax + TMin - TBase = GDD 2 Say today's high is 75 and the low is 55.Add them together for 130, divide that by 2, for 65, then subtract 50, and we have a growing degree day of 15. If the weather stayed like this for 5 days in a row, we have accumulated 75 GDD. If it stayed like that for 30 straight days, we would have 450 GDD.The GDD number accumulates for the entire growing season, until the temps stay consistently below the base temp, and then reset at the start of the new year.There are several good resources online for checking what events occur at a certain number of growing degree days. Lilacs bloom between 80 and 110 GDD, spruce spider mites hatch at 162 GDD, and the northern catalpas first bloom at 675 GDD.Whether you are in southern Illinois, or northern Michigan, you can track growing www.arborage.com Arbor Age / September 2013 21