As previously noted, that this summer’s drought is pretty exciting to me. Not as, “I hope we get a drought this year!!” It is more like that living in the driest summer in Boston on record gives me the opportunity to watch the trees, shrubs, perennials, etc as the drought intensifies. I’ve been studying the impact and reconstructing drought from tree rings for, well, a while now. Finally, for the first time in my life, I get to live in a severe drought. It has been fascinating.
Before going further on observations, August 2016 was also the warmest August on record in Boston and the number of 90 degree days in this region is on the upper end of those charts. Warming exacerbates drought. So, compounding the lack of rain this summer, increased temperatures might have put eastern Massachusetts in a new realm of drought. Eastern Mass has been in a state of extreme drought for some time.
I’m not going there, however. The trees are showing signs of drought stress. But, some of the trees I’ve talked to over the past decade are now likely saying something like, “Aye, it is a dry summer. But, it has been only about 12-14 months of dry weather. Don’t get me started on the 1960s or the 1660s or the 1630s. We got this.”
So far, this drought has been pretty rough on lawns.
“Lawn” of city park in Maynard, MA, July 24, 2016
But the trees? If you know anything about trees, you know they are tough. They have adapted to conditions like these, but worse. So sure, if you drive around eastern and central Massachusetts, you’ll see browned foliage and pale autumnal colors (that actually began in late July), but you’ll also see that about 90% +/- looks pretty green.
It has been a tough summer. But, it has only been one extremely tough summer. Trees store so much energy that it takes a couple of years to start increasing rates of tree mortality.
Of course, it is more complex than that. Pictures of what appears to be dead trees are turning up on the internet. I’ve seen trees like that, too. What I’ve noticed, however, is that many of these trees were already injured or likely diseased.
As bad as the drought of 2016 has been, it has been like a wolf—the Drought of 2016 is preying on the weak first.
The most leafless and potentially dead trees that I have seen are the elms. It is bad enough that they have to fight Dutch Elm Disease. Now they have to deal with very little water and high temperatures. They’ve been looking pretty sickly, virtually dead, since early to mid August.
But wait, there is more.
The most common mostly leafless or browning trees are those on exposed sites – rock outcrops with shallow soils and the north side of roads and highways (where they get more southern Sun as well as the double-whammy of streets soaking up the Sun’s energy, reflecting it back locally, and releasing it slowly through the evening. The north sides of streets are hot places. Snow melts earlier there, too).
Exposed birches showing signs of drought stress, July & Aug, 2016. Central Mass
The most stressed trees I’ve seen are those along the streets in town. Built environments are tough for trees, especially for those planted in places where they really have no business of being planted. The Norway maples are showing the most significant signs of drought stress in these settings. Some scenes made me think it was late September even though it was mid August’ish. Some Japanese maples are looking pretty crispy, too. Makes me re-think what we should plant in cities and yards.
Norway maple acting like it is autumn. Thanks Drought. Maynard, MA, August 17, 2016
But, it is still much more complex than drought hurting all trees. No doubt most/all trees will have a very narrow 2016 ring, but some species showed signs o stress earlier than others. The yellow tree on the outcrop in the left picture above along is a gray birch. Along Route 2 in central Mass, gray and paper birch were the first to show signs of drought stress.
Perhaps more fascinating to me is how black birch is handling this drought. It is not handling it well. Or, rather, drought is giving this species a whipping.
I’ve been watching two trees on my commute to work. Their progression as the drought has intensified is really fascinating.
Two black birch progressing through intensifying drought. Clockwise: Aug 7, Aug 11, and Aug 30, 2016. Acton, MA
The next species to show observable signs of drought stress was red maple. Rhododendron and dogwood are having observable issues, too, with the dogwood likely also impacted by disease.
Red maple (left) on the north side of a state road and American beech (right). The beech might also be impacted by disease or other local factors. Boxboro, MA, August 6, 2016.
The oaks, in general, are not showing much stress. Funny that, mesophytic species (adapted to more wet conditions) acting more susceptible to drought than more xeric species (adapted to living with less water).
Black oak canopies (left; July 26, 2016) and northern red oak (large, green tree in center of the picture on the right; August 30, 2016). Note: in the picture on the right you can see the stressed black birch featured above. But, do you see the yellow behind the northern red oak? Those are black birch in the forest – not exposed to the road. Understory and canopy black birch in forest conditions are showing drought stress.
Our unpublished tree-ring research indicates black birch to be quite sensitive to drought. 2016 is supporting our finding. The strongest and most consistent limitation of year to year changes in the growth of black birch from 1940 and 2015 is moisture….oh, we have found this before, Table 1 here. Well, our new data from New Hampshire suggests that even in a cooler setting, black birch really needs water.
So, what will happen? What are the ecological impacts? Well, it depends (naturally).
The observer in me is concerned that some of the trees browning in yards and along roads will be cut down even though there is a very good chance that they are not dead yet. As suggested earlier, it will take more than this, the driest summer since the 1870s, to kill a healthy tree.
Tree have to stay in one place and take what is brought to them for their entire lives. So, they store energy for days like these (in the form of “nonstructural carbon”). Literally, this is the opposite of a rainy-day fund. Trees store surplus’ish energy so they can handle dire times, so they can handle defoliation from insects, ice storms, windstorms, etc. Of course, the oaks and pines that suffered defoliation this year through gypsy moths or a disease complex, respectfully, well, they might be on their way out, especially if next year is dry.
…I’ve seen I’ve gone on far too long. Yeah, it has been an exciting summer.
If you’ve made it this far, one last experience from the hands of the Wolf Drought of 2016. We bought a house last summer and this spring I was chomping at the bit to plant all kinds of things so I could watch them go through the seasons and grow. It was the wrong time to put in a new garden. Our town put in water restrictions early in the summer. Two weeks ago, all outdoor watering was banned.
Thinking back to the class that got me into this field, I remember learning about water conservation and graywater. The scene portrayed was always Phoenix, Las Vegas, or Los Angeles. The Wolf Drought of 2016 has brought graywater here, to the Mesic Northeast. Water used to wash fruit and vegetables, water wasted while warming up the shower, for our children’s bath, boiling [food], etc. is now being collected to feed the garden. [This is, admittedly, very privileged. Our lives are not being threatened. We are fortunate.]