Let’s get trees ready to rumble with climate change

[originally posted on www.foreststeward.com on Dec. 17, 2010]

Article reviewed: Forward-Looking Forest Restoration Under Climate Change—Are U.S. Nurseries Ready?

By T.L. Tepe and V.J. Meretsky. Published in Restoration Ecology 2010. Vol. 18 issue 6

The plot line: This is an opinion article, but the authors also did some social science work that provides some data that are presented. They called up state and private nurseries across the country and asked them if they are preparing for or even thinking about climate change with respect to changing the species of seedlings that they offer. Only 20% of the state nurseries said they were thinking about climate change, but most (87%) did offer some seedlings from a fairly broad range that extended beyond their state’s borders. The authors’ answer to their own question, “are U.S. nurseries ready?” seems to be for the most part, “no.” Nurseries are somewhat prepared simply because traditional demands have led them to have species from different climate zones (I would also add that there simply aren’t very many of them so they have to cover wide areas). But this preparedness doesn’t come from specifically planning for future climate scenarios. The authors conclude that in the future, managers will likely want to plant a much wider variety of species than they currently do, and nurseries should prepare for facilitating management responses to climate change by incorporating climate change into their planning.

Relevant quote: “Restoration practitioners considering forward-looking restoration should consider plantings that use a reasonably broad diversity of species to accommodate a range of likely future climates rather than limiting plantings to species suited only to a single predicted future climate.”

Relevance to landowners and stakeholders:

Nurseries are a vital part of the forest management infrastructure, regardless of whether forests are managed intensively for timber or less intensively for other conservation objectives. Seedlings are often planted (“artificial regeneration”) following a disturbance such as a harvest or wildfire in order to establish a cohort of new trees. This article reminds us that the consequences of tree planting are long-term and profound. Trees are long-lived creatures that potentially modify the environment for animals and plants for centuries. A newly established tree (if it survives) is likely to grow in a climatic environment that is different than the one it evolved in. If we take a proactive approach to managing forests to be resilient to climate change, then paying close attention to which species we plant is critical.

Nurseries store and raise the seedlings that are ultimately planted. Without nurseries, we would not have the option of reforesting disturbed areas. While in some cases reforestation may not be needed to meet objectives, in many cases it is the primary way of achieving the goal of quickly establishing a forest following a disturbance such as a severe wildfire. Unfortunately, there appears to be a downward trend in the number of state nurseries. While private nurseries may be able to compensate in terms of meeting short-term demands for seedlings, they are much less likely to be thinking about climate change.

My bottom-line interpretation of relevance for landowners and stakeholders is to support the continuation of state nurseries. We are going to need them. The need seems especially important in southwestern states, where there are apparently hardly any nurseries. When high intensity wildfires occur in dry ponderosa pine forests, burned areas often have no sign of becoming forests again. Planting could help meet the goal of re-establishing forests in these areas, but it can’t happen without the nursery infrastructure in place.

Relevance to managers:

I am not so sure that we can ever expect nurseries to be the driving force behind being better prepared for reforestation needs in the face of climate change. It is managers and regeneration foresters who ultimately drive the demand for seedlings. If they are willing to pay for being more ready for climate change, wouldn’t a nursery then provide them with the type of seedlings they want?

The challenge for managers, however, is dealing with the extreme uncertainty in which seedlings will actually be better adapted to a future climate. The authors make an understated point that it is not just a changing climate but a changing disturbance regime that will shift where tree species will grow in the future.

The authors suggest a hedge-betting approach to dealing with uncertainty. There could be a wide range of species that will be adapted to the future climate. Rather than pick the one species that appears to be the most likely to survive, they suggest using a number of different possibilities based on the likely range of possible future conditions. This is essentially a form of active adaptive management, which I have discussed previously. It also brings up the significant risk of planting species outside of their ranges, which I have discussed previously. Finally, it also brings up how adaptable species might be to climate change just by staying put, which I have also discussed previously.

The bottom line relevance for managers is to take a good look at the seed zone map that is currently used and consider its relevance given the reality of climate change. Here is one for northern California. It was last revised in 1969. Surely this and other seed zone maps are out of date and they more relevance every year that goes by. In the forest that I manage, I have begun small trials where I have planted seedlings from different climatic zones. I have not planted species other than what are locally native, but I have tried to get seedlings from different zones that might be closer to the climate that will occur in my forest in the future. Seedling survival and growth will then be tracked over time. I’ll let you know the results in a couple of decades. Ideally, this will be done on much bigger scales and across large regions (akin to common garden experiments).

A number of websites were given for those interested in learning how climate might change locally. The Nature Conservancy's Climate Wizard looked to be the most interesting, although it doesn't capture the great uncertainty involved with projections.

Critique and/or limitations (there’s always something, no matter how good the article is) for the pedants:

The authors could have done more to recognize the importance of acting with caution when it comes to planting species outside their current zones. Rather than just discuss the planting of new species, they could have also discussed the planting of the same species from different climatic zones. Tree species often cover diverse climates and have high genetic diversity across their entire range.

Using state boundaries as a way to judge if nurseries have broad zones from which they get seeds is not very meaningful because the size and shape of states varies so widely. It would have been more meaningful to actually draw seed source zones around nurseries and see how well these zones overlapped with forest cover across the United States. But this would have obviously been a lot more work… perhaps it can be a future study.