Resilience & Resistance

Understanding resilience and resistance from an ecological standpoint can be difficult, however the basic definitions for each term are fairly simple:

Resilience-measures how quickly a system recovers from disturbance and returns to a steady state (Glyndwr University 2016)

Resistance-measures how much a system resists change. A system which remains the same in spite of disturbance or changes in, for example, nutrient input, has a high resistance (Glyndwr University 2016)

In terms of wildfire ecology, I think the use of these terms is helpful in managing our natural resources. By understanding a species level of resilience and resistance, we can better predict what their health will be like post and pre disturbance. However, the use of such broad terms in such a widely spanned field may cause confusion, and a universal definition of both terms should be set for natural resource managers so that everyone stays on the same page.

The link I've provided as my source lists some great examples that are pertinent to these terms in relation to wildfires and species' responses.

Source:
Glyndwr University. 2016. Introduction to Ecology: The Stability of Ecosystems. Available from http://www.glyndwr.ac.uk/bartlett/ecology/stability.htm

Australian firebirds and savanna fires

Recent studies have revealed a fascinating fire adaptation in Australian hawks. The Brown Falcon and Black Kite have been directly observed setting fires in Australian savanna by carrying burning material to new areas.

Image source: https://en.wikipedia.org/wiki/Fire_ecology#/media/File:Fire_hawks.jpg

Why do they do this? Fleeing prey such as insects, amphibians, and small mammals are an easy catch for the birds, who wait just in front of the fires to nab them as they leave the burning area. This is an example of a very unique fire adaptation in the animal kingdom.

Australian savanna or grassland is an ecosystem that evolved with fire, and many of the plants there are adapted to fire. Several species of Eucalyptus, for example, exhibit serotiny (fire-dependent seed release), epicormic branching (new growth that comes from tissue protected from fire), and tall crowns with few lower branches.


Image source: http://anpsa.org.au/APOL24/dec01-5.html

Eucalyptus can even encourage fires--the rot-resistant leaves produce a flammable oil which creates a huge fuel load on the ground. Eucalyptus can be very long-lived, but has trouble regenerating if there is a thick understory. The highly flammable leaf litter under these trees can help clear out the understory during a fire, allowing the trees to regenerate, both via serotinous seeds and epicormic branching.

Sources:
http://www.grindtv.com/wildlife/birds-of-prey-are-starting-fires-deliberately-in-australia-study-reveals/
http://wildfiretoday.com/2014/03/03/eucalyptus-and-fire/

Jack Pine: Fire Disturbance

Learning about disturbances in ecology is interesting; fire is considered a natural disturbance and can be very helpful in terms of new growth and species richness in a ecosystem.  Some plants fire to establish, germinate or reproduce. An example of this is. An example of a plant that needs fire to germinate is the jack pine. Found in the eastern United States and Canada the jack pine has pine cones that are so hard and so thick that they need fire to melt the natural “glue” the make that keeps them shut. The pine cones can hang on to trees for rears without opening until a fire comes around to melt the resin that holds them together. The jack pine and other plants the release seeds after a fire have adapted to this for multiple reasons. These reasons include a lack of undergrowth that will compete with them while they are small. Also fire introduces nutrients that plants need to survive into the soil. Although fire can impact and ecosystem in many ways, positively or negatively depending on the species, after a fire it always leaves an ecosystem with room for new growth.

Without disturbances in an ecosystem we would have far less species richness because of this we count on things such as fire, wind, flooding, ect. for species to thrive. Although sometimes us as humans try to bring everything to a balance, what we really should be doing is letting nature take it course. 

https://www.nps.gov/fire/wildland-fire/learning-center/fire-in-depth/different-ecosystems/jack-pine-greatlakes.cfm

Arid Plant Fire Adaptation

Adaptation is the act by which beneficial, heritable traits evolve by natural selection and survivability utilizing the best biologically engineered solution to sustain and avoid an impact. It performs a particular function. A characteristic that is defined a trait as meeting the criteria of adaptation when it could be proven that it was engineered design, passed on to off-spring (heritability), increased the fitness (natural selection), and the trait evolved due to fire (phylogeny).

Buckbrush germination following fire.

For an example the fourwing saltbush (Atriplex canescans) is considered a plant of evolutionary plasticity, making it well suited for survival in early post-fire communities (USFS). This also makes it moderately fire resistant and is a selection for green firebreaks in some regions as it is a semi-evergreen and does not easily ignite.

Fourwing saltbush

Another example is a trait found in many plants like Buckbrush (Ceanothus cuneatus) that is adapted to chaparral fires and is considered a fire recruitment species. The high temperatures of fire are necessary to melt and crack the seed, which have a high germination rate (USDA, 2015).

Buckbrush

What exactly are fire adaptations?

Photo by www.Naturallnorthidaho.com

Fire as a process in an important part of forest ecology. Many plants around the world have characteristics that enable them to better tolerate differing fire regimes and return intervals. Since no two species of plants are alike and the physical properties of fire tend to behave differently in response to different landscapes, the interactions amongst plants and fire are very unique. Because of these dynamics, plant species evolve and adapt in response to fire over time. Collectively we have come to acknowledge these processes as "adaptations". However,  Fire in California's Ecosystems points out a very important point. Because fire as an ecosystem process, has effects at the landscape scale and over many generations of fire events- the fire regime. Species are not actually adapted to fire per se, but to the fire regime. Species persist because they possess advantageous traits that allow them to thrive amongst a particular fire regime ( Sugihara et al., 2006).

Photo by Siobahn Sullivan

Fire effects individual plants directly and even indirectly by changing the adjacent landscape. One of the most resistant and common plant adaptations here in Central Oregon is none other than thick bark. Since low intensity, frequent fires are a natural part of the historic ecosystem in the high desert, many mature ponderosa pine stands have evolved along side and in conjunction with fire due to insulating tissues and self pruning mechanisms. Since prolonged exposure to heat can often damage or even kill an individual, the role of fire in the high desert has produced numerous morphological traits to protect from extreme heat damage during a fire.


Since plants exposed to prolonged extreme temperatures will often suffer loss of foliage and tissue, many plants have evolved to depend on the rapid regeneration of foliage post-fire. In most cases, low-growing shrubs and other hardwoods accustomed to returning fires are able to regenerate quickly due to the varying locations of buds on the plant body. Buds at or below the surface are most often able to survive fires, because they're insulated from the heat by soil. Conversely, individual species who's buds reside at ground level or near the crown of the plant are more likely to suffer critical burning. These sort of mechanisms are most often adventitious amongst fires of varying magnitude and duration.

Photo by WildUtah

Fire adaptation

Fire adaptation is the ability of a species to resist and survive fires. This is accomplished through natural selection that causes the development of adaptive traits that vary between species. There are numerous adaptations that are all very different from one another and all very effective in maintaining biota survival during or following a fire.

Photo courtesy of B.C. Wildfire Management Branch

One example of this is called serotiny, or the ability of a plant to retain seeds in their canopies, releasing them following a fire instead of at seed maturation. This assists a plant in recovering and repopulating following a devastation.  Serotiny doesn't happen exclusively to fire adaptive plants, but is a characteristic of fire adaptation. The most popular example of this seed retention is by some species of pine tree, who hold their seeds high in the trees. The seeds of the pine tree are encased in a hardy cone, like a womb, and sealed with a waxy substance that melts in the presence of fire, releasing the seed to germinate. The needles of a pine tree also have a high moisture concentration, the trunk covered in thick bark, and are "self-pruning", causing them to be more tolerant to surface fire. Lacking branches low to the ground reduces "ladder fuel", which carries fire upwards towards the canopy, causing heavy damage.

Photo by Seb Ruiz

Plants are not the only thing that can be considered fire adapted. Animals can also possess adaptations to fire. It is uncommon for mature animals to be found dead following a fire, mostly because they know where to go to escape fire. Some birds and small mammals can burrow into the soil, which is an excellent insulator against fire, in order to survive a fire. Some species can also benefit from from fire as it can bring prey to easily accessible areas. Herd and small animals can be pushed into open areas and insects flee smokey areas, creating lots of food for some animals and even leads to increasing reproductive rates following fire.

Photo by A. Morris

Works Cited

"Ponderosa Pine." State Symbols USA. Web. 17 Apr. 2016. http://www.statesymbolsusa.org/symbol-official-item/montana/state-tree/ponderosa-pine

Press, The Canadian. "B.C. Wildfire Officials Concerned with 2nd Heat Wave - British Columbia - CBC News." CBCnews. CBC/Radio Canada. Web. 17 Apr. 2016. http://www.cbc.ca/news/canada/british-columbia/b-c-wildfire-officials-concerned-with-2nd-heat-wave-1.2719326

“The Ecology of the Ponderosa Pine Zone.” Ministry of Forests, Lands and Natural Resource Operations, British Columbia. Web. 17 April 2016.

<https://www.for.gov.bc.ca/hfd/pubs/docs/bro/bro60.pdf>

Fire Adapted Species

Fire adapted species possess inherited traits that allow them to enhance their survivorship or fitness during or after a fire. Fire adaptations are derived from a long history of plant species evolving in ecosystems with fire regimes. In order for a trait to be considered a fire adaptation, fire must be the main selective force that allowed that trait to thrive within a species. There are many selective forces that could’ve promoted traits that improve survivorship or fitness in fire, which makes identifying a fire adaptation a difficult process. Today, there are many traits that are generally accepted as fire adaptations and are managed as such.

1.     Thick bark is considered to be a fire adaption because it can prevent the vascular cambium form being damaged. The bark acts like a medium that transfers heat from the fire to the cambium. If the bark is thick, it will take more energy to transfer enough heat to cause damage. This fire adaption will increase survivorship when exposed to low or possibly moderate severity levels of fire. A high severity fire will likely produce enough heat to damage the cambium and engulf the tree. Areas will low to moderate fire intensity regimes will likely select for trees with thicker bark since trees without this trait could have lower survivorship.

2.     Another fire adaptation could be plants with growing points below the soils surface. These plants have the ability to surface low severity fires because the soil acts like an insulator and protects the growing points below the surface. These plants can successfully remain established after a fire. High or moderate intensity fires can heat up the soil to a point of damaging the plant beyond recovery.