10/5/15

Forest drought mortality

If you want to know more about the hotter droughts mentioned in Colin Mahony’s post a few weeks ago on forest management strategies under climate change mega-disturbances, you might be interested in this recent paper from Allen, Breshears, and McDowell on expectations for forest drought mortality.

Craig D. Allen, David D. Breshears, and Nate G. McDowell 2015. On underestimation of global vulnerability to tree mortality and forest die-off from hotter drought in the Anthropocene. Ecosphere 6:art129. http://dx.doi.org/10.1890/ES15-00203.1

10/2/15

Scouring coastal Alaskan forests : a journey through the past (Part 1)

What does an expanding forest look like?

How hard is it to tell how old a natural forest is?

At what stage during the afforestation of a landscape can we say: “This is a forest.”?

Team #1 at its best.

These are some of the questions I had in mind when I started the 4000-km long road trip to Alaska, with my friend and labmate Ian, also member of the Aitken group, Bean, the famous and beloved Aitkenlab truck, and Jethro the rescued dog toy that has become our mascot over the years.

My goal: reaching the edge of the coastal Sitka spruce forest on the Kodiak Archipelago, and sampling several stands at different distances from the front of expansion. Below is a map showing the Alaskan range of Sitka spruce forest. The arrow indicates the historical route of migration of spruces after the last ice age. Beyond the green line,  You’ll have to look very hard to find any conifer tree, or even any tree taller than you.

Picturekod

Once arrived in Kodiak city, the journey is not over. The forest stands we want to work in require an additional floatplane ride and several miles of dangerous driving on dirtroads. And a dive into welcoming devil’s club bushes.

Spruces from above, loaded with last year’s cone crop. Spot our shadow!

Happy bunny on a flight.

 

On the plus side, the forests are stunning!

Picturekod2

 

There we are, finally. We can start sampling! But wait… sampling what? and how?

Here is what I decided to do:

  1. Find a forest stand (by this I mean a reasonably large continuous undisturbed patch of forest)

    Come on, Ian, look harder

  2. Visually assess the different structural levels (or “cohorts”) of the forest and put them into categories

    cohorts

    The typical cohorts of a mature Sitka spruce stand on the Kodiak archipelago

  3. Randomly select an equal amount of trees (typically 4) per structure level per stand, with a spacing of at least 50m between trees

    DSCN6195

    Ian, we said TREES. Pretty orchids do not fit into the protocol.

  4. From each tree, extract a few needles or bark disk for DNA extraction, and a tree core for age determination.

    A bark sample (there is a thin slice of multiplying cells in there) and a freshly extracted tree core

  5. Go find the next stand

    …before the loggers, if possible (these trees were standing two days earlier).

  6. Somewhere along this iterative process, pick up an additional, valuable team member.
DSCN6636

Hey Sally! Come get bushed with us!

 

I ended up with a slightly structured distribution of stands (Mother Nature wasn’t told about the statistical advantages of spatial uniformity)…

kodiak_sample_map_full

Each pink dot is a sampled stand. (One pink dot might be hiding another)

 

…and occasionally, some fresh fish for dinner (thank you Ian)

Spot the beer… We’re so local.

By matching the age of sampled trees with their genotype across several stands , I will be able to directly monitor the evolution of the genetic makeup of the forest and answer the following questions:

How quickly do newly formed forests accumulate genetic diversity?

How many trees colonised the area, and from where?

Does relatedness among trees increase or decrease as we approach the front of expansion?

 

However, to properly answer these questions, I also need at least one “reference” Sitka spruce population that established a long time ago and can be considered to be in an equilibrium state in terms of genetic structure and diversity. The closest Sitka spruce forest that matches these requirements is on the Kenai Peninsula. That’s where the trip continues! Different landscapes, different challenges, different team, and so, very logically,…. different blogpost.

 

DSCN6538

To be continued…

09/22/15

Hedging against climate change in managed forests

A review paper published last month in Science highlights the threats to temperate forests posed by anthropogenic global warming.  Millar and Stephenson (2015) in particular focus on climate-change-related “hotter droughts”, compound stressors, and “megadisturbances” that can cause the collapse of forest ecosystems and interruption of ecosystem services such as water, biodiversity, and wood products. In light of the ongoing mountain pine beetle epidemic, this is not an abstract future scenario for British Columbian forests and the communities that depend on them.

One of the figures in Millar and Stephenson (2015) is particularly pertinent to the work we do in the Aitken lab. It illustrates two contrasting management approaches: the first, “reactive”, approach aims to maintain ecosystem services at historical levels by protecting the existing ecosystem structure and function; the second, “proactive”, approach accepts lower ecosystem services in order to facilitate a transition to a more resilient ecosystem state. The “reactive” approach is prone to sudden collapse of the ecosystem and its associated ecosystem services, with slow subsequent recovery to a new set of ecosystem services; the “proactive” approach aims to achieve a gradual transition in which ecosystem services are continually available, though at reduced levels. A proactive management approach is obviously desirable, but achieving it in practice will likely prove to be difficult. The proactive forest managers in this illustration chose the right species for the future climate. Would that choice be so obvious in reality?

Figure 4 from Millar and Stephenson (2015), illustrating tradeoffs of reactive vs proactive approaches to managing ecosystem services in the face of climate change

Figure 4 from Millar and Stephenson (2015), illustrating reactive vs proactive approaches to managing ecosystem services in the face of climate change

Informing appropriate reforestation strategies for uncertain future climates is an overarching goal of our research at the Aitken lab. We focus on understanding how existing populations of trees might be adapted to a range of anticipated future climates of their source locations, or of new locations where they may be better adapted.  In the illustration from Millar and Stephenson (2015), a different species is introduced to the ecosystem. The Aitken lab generally investigates a more intermediate approach, in which seedlings from a non-local population of a native tree species are introduced to harvested stands. The same principal applies, however: diversity is the simplest hedge against uncertainty. All the better if the composition—the species and genotypes—of this introduced diversity is well-informed.

Millar, C. I. & Stephenson, N. L. (2015). Temperate forest health in an era of emerging megadisturbance. Science, 349(6250), 823–826.