Many thanks to Faith Campbell for these guest posts!
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As I pointed out in my previous blog, insects and diseases (native and introduced) have decreased carbon sequestration by live trees on U.S. forest land by 12.83 teragrams carbon per year. This equals ~ 9% of the contiguous states’ total annual forest carbon sequestration. This figure is probably an under estimate (Quirion et al. 2021).
When we consider conifers, the pests currently having the greatest impact are native beetles, especially the mountain pine beetle (Dendroctonus ponderosae) and – in some years and places – southern pine beetle (Dendroctonus frontalis). Still, among the 15 high-damage introduced pests causing a tree mortality rate of 5.53 Terragrams of carbon per year above background level are six pests of conifers: red pine scale (Matsucoccus matsumura), hemlock woolly adelgid (Adelges tsugae), balsam woolly adelgid (Adelges piceae), white pine blister rust (Cronartium ribicola), green spruce aphid (Elatobium abietinum), and Port-Orford cedar root disease (Phytophthora lateralis). Mortality of eastern hemlock (Tsuga canadensis) caused by the hemlock woolly adelgid ranks as one of the four species with the highest elevation in biomass loss as measured by FIA plot data (Fei et al. 2019).
Another study – Mech et al. (2019) – found that of 58 introduced insects attacking conifers, six are causing high impacts. These include the insects listed above plus European spruce sawfly (Gilpinia hercyniae) and larch sawfly (Pristiphora erichsonii). I add larch casebearer (Coleophora laricella) and larch canker (Lachnellula willkommii).
So clearly introduced pests have had serious impacts on conifers … and there is the potential for even wider impacts in the future.
Introduced pests attacking conifers differ from those attacking hardwoods in that the great majority of insets are in the orders Hymenoptera (i.e., sawflies) and Hemiptera (i.e., adelgids, aphids, and scales) rather than Coleoptera (Mech et al. 2019); most were introduced on imported plants rather than on wood; and most were introduced a century ago. (I will write more about introductory pathways in the next blog post.)
The few woodborers that attack conifers (introduced via wood packaging) have so far had limited impact. However, some are spreading toward areas that might be more vulnerable. For example, Orthotomicus erosus can attack native pines and has spread from central California to Arizona. A Eurasian woodwasp, Sirex noctilio, is widespread in the Northeast – in nine states and two provinces. So far it has caused little impact but it probably continues to spread toward the south. There is no official surveillance program so information is scant. No one knows how Sirex will affect the many North American pine species it is known to attack when it reaches regions where they are dominant. These hosts include loblolly (P. taeda) and slash pines (P. elliottii) in the Southeast and lodgepole (P. contorta) and ponderosa pines (P. ponderosa) in the West (Hajek, Haavik and Stephen 2021). Of course, reductions in carbon sequestration are not the only kinds of impacts that matter. Several of the conifers hammered by introduced pests are keystone species in unique ecosystems, so their loss has cascading effects on entire biomes or microhabitats.
The best known example is high elevation forests in the West. Many of these ecosystems have already lost whitebark (P. albicaulis) and limber pines (P. flexilis) to white pine blister rust – losses exacerbated in recent years by the mountain pine beetle. Whitebark and limber pines are considered endangered in Canada (Allison et al. 2021); whitebark pine is a candidate for listing as threatened in the U.S. Another tree of the high-elevation forests – subalpine fir (Abies lasiocarpa) – has also been severely damaged in some areas by the balsam woolly adelgid (BWA). There is an eastern counterpart: mature Fraser fir (Abies fraseri) on high elevation peaks of the central and southern Appalachians has been virtually eliminated by BWA. It is not yet clear whether the dense regeneration will survive or be attacked as the saplings age. Opening of the canopy has led to listing of two endemic species, a lichen and a spider, under the federal Endangered Species Act.
Also in the Appalachians, eastern hemlocks create unique riparian communities that provide habitat for dozens of species – birds, salamanders, fish, and shade-loving plants. Loss of hemlocks to HWA results in changes to water flows and temperatures and open the understory to new plant species.
In Southwest Oregon, half of the total basal area of western white pine (Pinus monticola), 30% of the total basal area of sugar pines (Pinus lambertiana) is comprised of dead trees. This situation results from the combined attacks of WPBR and MPB. Originally trees towering more up to 200 feet high, with dbh of 30 inches, western and sugar pines provided habitat for many species, especially cavity-dwellers (Goheen and Goheen 2014).
What can you do?
Quirion et al. (2021) outline several actions that would help protect the ability of America’s forests to sequester carbon. Concerning native pests, the authors call for improved forest management – with measures tailored to particular species and environmental context. Concerning introduced insects and pathogens, Quirion et al. (2021) echo many others’ call for strengthening international trade policies and phytosanitary standards governing the principal pathways – wood packaging and imported plants. These policies must be supported by enhanced enforcement and early detection tools and strategies and reliable funding for strategic rapid responses to newly detected incursions. I will discuss this in greater detail in my next blog post.
To reduce impacts of pests established on the continent, Quirion et al. (2021) recommend increasing and stabilizing dedicated funding for classical biocontrol, research into technologies such as sterile-insect release and gene drive, and host resistance breeding.
Faith Campbell is president of the Center for Invasive Species Prevention. She has spent 30 years advocating for more effective policies to prevent introduction and spread of tree-killing insects and pathogens. She posts blogs on these issues at www.cisp.us
SOURCES
Allison JD, Marcotte M, Noseworthy M and Ramsfield T (2021) Forest Biosecurity in Canada – An Integrated Multi-Agency Approach. Front. For. Glob. Change 4:700825. doi:
10.3389/ffgc.2021.700825 Frontiers in Forests and Global Change July 2021 | Volume 4 | Article 700825
Fei, S., R.S. Morin, C.M. Oswalt, and A.M. 2019. Biomass losses resulting from insect and disease invasions in United States forests. PNAS Vol. 116 No. 35 pp. 17371-17376
Goheen, E.M. and D.J. Goheen. 2014. Status of Sugar and Western White Pines on Federal Forest Lands in SW OR: Inventory Query and Natural Stand Survey Results. USDA Forest Service Pacific Northwest
Region. SWOFIDSC-14-01 January 2014
Hajek, A. E., L. J. Haavik and F. M. Stephen, eds. 2021. Biology and Ecology of Sirex noctilio in No Am. FHAAST-2019-01. USDA Forest Service, Morgantown, West Virginia.
Mech, A.M., K.A. Thomas, T.D. Marsico, D.A. Herms, C.R. Allen, M.P. Ayres, K.J. K. Gandhi, J.
Gurevitch, N.P. Havill, R.A. Hufbauer, A.M. Liebhold, K.F. Raffa, A.N. Schulz, D.R. Uden, & P.C. Tobin. 2019. Evolutionary history predicts high-impact invasions by herbivorous insects. Ecol Evol. 2019 Nov; 9(21): 12216–12230.
Quirion BR, Domke GM, Walters BF, Lovett GM, Fargione JE, Greenwood L, Serbesoff-King K, Randall JM & Fei S (2021) P&P Disturbances Correlate With Reduced Carbon Sequestration in Forests of the Contiguous US. Front. For. Glob. Change 4:716582. [Volume 4 | Article 716582] doi: 10.3389/ffgc.2021.716582
Personally, I am not in favor of using human-engineered, synthetic biology techniques to solve invasive species problems; there are so many things that could go horribly wrong. Here are a few excerpts from some web pages that I have read that discuss this issue:
How are gene drives dangerous?
Gene drives will permanently alter an entire population. In many cases, there is no going back. If scientists fail to properly anticipate all of the effects and consequences, the impact on a particular ecological habitat — and the world at large — could be dramatic.
Gene drives have been dubbed an “extinction technology” and with good reason: gene drive organisms are created by genetically engineering a living organism with a particular trait, and then modifying the organism’s reproductive system in order to always force the modified gene onto future generations, spreading the trait throughout the entire population.
Although still new and unproven, gene drives have provoked significant alarm among ecologists, biosafety experts, and civil society, many of whom have backed a call for a complete moratorium on the technology. By deliberately harnessing the spread of engineered genes to alter entire populations, gene drives turn on its head the usual imperative to try to contain and prevent engineered genes from contaminating and disrupting ecosystems. The underlying genetic engineering technology is unpredictable and may provoke spread of intended traits. The notion that a species can be removed from an ecosystem without provoking a set of negative impacts on food webs and ecosystem functions is wishful thinking and even taking out a carrier of an unpleasant parasite does not mean the parasite won’t just jump to a different host. Moreover, the implicit power in being able to re-model or delete entire species and ecosystems from the genetic level up is attracting the interest of militarities and agribusiness alike and runs counter to the idea of working with nature to manage conservation and agriculture.
Gene drive accidents are also possible. A lethal gene engineered into a pest species, say, might jump (or, as biologists put it, “horizontally transfer”) into another species that’s a crucial part of an ecosystem.
The possibilities for “weaponizing” gene drives range from suppressing pollinators, which could destroy an entire country’s agriculture system, to giving innocuous insects the ability to carry diseases such as dengue, said MIT political scientist Kenneth Oye, who briefed the bioweapons office.
Gene drive is particularly worrisome because “it’s not just one or two labs that are capable of doing the work,” Oye said — and the “capable” could include do-it-yourself “garage biologists.”
Oye told the Academy panel, “You need to have people probing the security implications [of gene drives] much more effectively” than is now being done.
Researchers can’t possibly account for how every single species — all the countless plants, insects, and as yet undiscovered deep-sea creatures — will be impacted by a change we make to an organism. So unless we develop unique and unprecedented scientific protocols, no matter how much research we do, the decision to use or not use CRISPR gene drives will have to be made without all the evidence.
Michael, I’m not a fan of gene drives either. But in reality, tree breeders use the old-fashioned traditional techniques.. remember after all these years (and funding of cool new technologies).. they just had the proposal for deregulating engineered American Chestnuts when.. last year?
I’ve seen a pattern over the years. Some technology is cool and the research is funded. People get concerned (remember low specific gravity engineering for floppy trees..oops..less lignin). Meanwhile the humble and poorly funded tree breeders (and pathologists and entomologists) continue their work.. and only crop into popular view when… there’s a controversy, e.g https://missoulacurrent.com/outdoors/2019/04/whitebark-pine/.
“Forest Service research ecologist Bob Keane wants to restore whitebark pine in wilderness areas, which account for 45 to 55 percent of the species’ range, because the population throughout the Rocky Mountains has dwindled to where trees no longer produce enough seeds or pollen to make healthy new stands. So focusing on restoration in areas outside wilderness isn’t enough, Keane said.
“But since 2012, the Forest Service has propagated and planted a small percentage of rust-resistant tree seedlings on national forests. Keane argues that seedlings should also be carried into the wilderness, even though it would be an expensive process.
“We as people want to go in and we want to restore it,” Keane said. “Genetic conservation needs a large footprint so you need to include wilderness in the mix.”
And those are boring old-technology rust-resistant seedlings.
Oregon State and I believe the BLM along with the FS has been working on a disease resistant Port Orford cedar, with some success, which I think is a good thing.
Yes, the folks at Dorena Tree Improvement Center in Cottage Grove, I think have been working on it for at least 20 years or so.