Geography 140
Introduction to Physical Geography

Lecture: Biomes Dominated by Shrubs

     C. Scrubland is dominated by a continuous or discontinuous cover of 
        shrubs.
        1. The most extensive scrubland is the Mediterranean scrub. 
           a. This is dominated by a continuous shrub cover, ranging in height 
              from 1-5 m. Very characteristic of these plants is that they 
              have high root-to-shoot ratios.  This means that most of the 
              plant's biomass is underground, in deep and extensive root 
              systems.  A one meter plant might have a 15 meter deep root 
              system!  Not only is the shrub cover continuous, it is normally 
              extremely dense.  It is nearly impossible to hike through, 
              unless you find deer trails or some such!  You do not want to 
              get off the trails here, folks:  If you have a hiking accident, 
              you'll be nearly impossible to find (until your pathetic remains 
              wash down in the winter rains?).  
                i. In California, this stuff is called "chaparral" and some 
                   common species include manzanita, scrub oak (a shrub form 
                   member of the oak genus), ceanothus (sometimes called 
                   mountain lilac because its flowers look like miniature 
                   lilac blooms), mountain laurel, and chamise. 
               ii. In the Mediterranean, it is often called  "maquis" or some 
                   variant on that (such as "macchia" in Italian).  Some 
                   common species include rosemary, rose, scrub oaks, oregano, 
                   thyme (gee, a whole bunch of spices and herbs popular in 
                   cooking). 
              iii. In Australia, this association is dominated by scrub 
                   eucalyptus and is called "mallee scrub."
               iv. In Chile, it's called "matorral."
                v. In the southwestern tip of South Africa, the corresponding 
                   vegetation is called "fynbos."
           b. There may be a discontinuous or grouped understory of herbs 
              (forbs and grasses), which are most evident in breaks in the 
              shrub cover. 
           c. This vegetation is associated with the Mediterranean climate 
              (bet that came as a surprise!), Csa or Csb climates in the 
              Köppen system you learned about in lecture 20.  This means 
              that the plants have to adapt to a climate with a severe summer 
              drought.  One more condition is needed, though, besides the 
              right climate:  Mediterranean scrub normally is confined to the 
              steeper, more unstable slopes, with the most skeletal soil 
              development.  On gentler slopes, grassland or Mediterranean 
              woodland will dominate.  Mediterranean scrub dominates the 
              slopes that "no-one else wants."  Good thing, too, because the 
              presence of Mediterranean scrub stabilizes those slopes and 
              keeps them from washing downslope every winter.  You disturb the 
              scrub and you get mudslides like crazy.

           d. Unfortunately, regular deciduousness is tied to the onset of 
              winter, so that particular xerophytic adaptation isn't helpful. 
              So, these plants rely on these alternative strategies to get 
              through the summer dry season:
                i. They have small or needle-shaped leaves (even some non-
                   conifers) to reduce the area from which water is lost in 
                   transpiration and respiration.
               ii. They often have dense, thick bark (such as the manzanita, 
                   with its almost artificial-looking shiny or matte red 
                   bark), again to cut down on water loss through the stems 
                   and branches.
              iii. The leaves are also dense and tough, or sclerophyllous. 
                   This makes the leaves resistant to decay later, when an 
                   aged leaf falls to the ground.
               iv. The leaves often have aromatic oils in them, usually 
                   variants on terpenes.  These can be used allopathically 
                   against other plant rivals for water or against pests and 
                   herbivores).  These oils also act against a lot of 
                   detritivores, so the leaf litter resists decay and piles up 
                   inexorably as time goes on, a fuel....
           e. This vegetation is adapted to recurrent fire, which is a hazard 
              associated with any climate having a long, hot dry season.  But 
              this relationship with fire goes beyond a simple adaptation to a 
              Mediterranean climate fact of life:  This vegetation is actually 
              dependent on fire for its renewal and reproduction!
                i. Since most of the plants live underground, a fire above 
                   ground isn't going to kill them:  What it does is "prune" 
                   the deadwood and old stems, kind of like what you do when 
                   you prune rose bushes to renew the plants.  So, after a 
                   fire, they stump-sprout vigorously.
               ii. Also, a fire turns all that above-ground biomass into ash 
                   fertilizer and exposes the ground to sunshine:  The ideal 
                   situation for the successful germination of the plants' 
                   seeds.  In fact, some species' seeds can't germinate until 
                   they've been cracked open by the heat of a fire first!  The 
                   reason selection has produced such tough seeds is that 
                   there's no point to germinating under a cover of mature 
                   shrubs, because the shading is so dense and the competition 
                   from the established plants for water is so fierce.  By 
                   waiting until a fire, these seeds' chance of survival is 
                   enhanced by all that sunshine and the fertilizing effect of 
                   the ash.
           f. Here's the kicker:  Since this vegetation actually 
              depends on fire for its reproduction and renewal, it 
              makes sure that fire occurs!  After the first few seasons 
              after a fire, the probability of a fire increases each year, as 
              the fuel level slowly and inexorably builds up.  Even better, 
              not only does the probability of a fire increase, but the 
              magnitude of the fire increases, too, again because of 
              the build up in fuel levels.  So, this is "pyrogenic" 
              vegetation, par excellence.  Remember that:  As time goes 
              on, the probability and the magnitude of a fire increases.
           g. Okay, got all that?  Now, let's add humans to the mix, 
              Homo "sapiens."  For some bird-brained reason, we 
              Americans love to build expensive homes in this stuff!!!
                i. This is just loony.  When you look at the other cultures to 
                   dominate these landscapes, you find they stayed out of the 
                   mountains in the late summer.  
                   a. The Native Californians had dealt with this stuff for 
                      thousands of years and pretty well had the system 
                      figured out:  They didn't put their base camps up in the 
                      mountains and, in fact, they were notorious for setting 
                      it on fire themselves, because they liked the tender 
                      early successional plants that appeared after a fire and 
                      they knew their favored game animals did, too.  The 
                      Spanish governors complained about this quite a bit (one 
                      Spanish governor in fact issued an edict in 1798 
                      forbidding the practice, which everyone promptly 
                      ignored).
                   b. The Spanish culture had come from the Mediterranean and, 
                      again, these folks knew all about Mediterranean scrub 
                      and THEY stayed the heck out of those mountains in the 
                      summer.  In fact, despite Governor de Arrillaga's 
                      pronouncement, a lot of them continued the practice, to 
                      increase forage for their cattle herds.
                   c. Then, in 1848 came the gringos.  The US got the entire 
                      northern frontier of Mexico, including California, after 
                      the Mexican-America War of 1846-48.  The North American 
                      culture had its cultural roots in England, a wet climate 
                      (Cfb, remember?).  That culture had a thing about a home 
                      on the hill with a great view.  I think it had to do 
                      with the military advantage of putting a castle on a 
                      hill to keep an eye on anyone bringing an army in to 
                      attack.  Pretty soon, the home on the hill became 
                      associated with being rich.  Anyone who got rich wanted 
                      to mimic the titled mucky-mucks and build their own 
                      castle on the hill to make a statement that they've 
                      "come up in the world."  This wasn't too disfunctional 
                      in the American East, which is also pretty humid.  The 
                      problem is these people had no cultural experience with 
                      the drier climates of the West, particularly that fire-
                      loving chaparral.
                   d. So, by the 1920s, we had the movie colony putting up 
                      ostentatious nouveaux riches homes in the hills 
                      of Hollywood and Beverly Hills, and pretty soon everyone 
                      was imitating them up and down the State of California.  
                      Plot complication:  The vegetation burns every 3 to 20 
                      years, and the longer it goes without fire the surer and 
                      the worse a fire becomes!!!
                   e. Now, biogeographers and ecologists had suspected how 
                      things work by then, but that knowledge did not get out 
                      to the larger culture very efficiently.  And it wouldn't 
                      have made much impression, anyhow:  The cultural need 
                      for a "home with a view" is an extremely potent one in 
                      American culture.  Gosh, it is so important that people 
                      want "view lots" when they croak!!!  Here you're dead 
                      and you want a view lot?  You have nothing to view it 
                      with, but, darn, you CAN take it with you!  I guess the 
                      theory is your grieving loved ones will get to enjoy the 
                      view when they visit you every week to put flowers on 
                      your grave.  Uhhhh, Anglo-American culture doesn't do 
                      grave visits -- the dominant culture is also into 
                      denying death as well as chaparral fires.  So, this is 
                      just a crazy thing in the American culture.
               ii. Less amusing than the craziness of "homes with a view" 
                   (including your final home) is the social cost of indulging 
                   this environmentally dysfunctional environmental 
                   æsthetic.  
                   a. Chaparral firefighting takes an enormous amount of tax 
                      money.  We have municipal, county, state, and Federal 
                      firefighting agencies, which all coöperate with one 
                      another in mutual aid agreements to stomp out any fire 
                      that gets going in those hills, because of the extremely 
                      expensive homes up there.  Fully 75 percent of the 
                      Federal-level firefighting budget is spent on our five 
                      local counties!  One of the more ironic moments I 
                      remember from the 1993 fires of Malibu and Laguna Hills 
                      was seeing dirt-poor little Yuba City (about half an 
                      hour north of Sacramento on 99) sending fire crews and 
                      equipment to help out.  This is a hidden upward tax 
                      transfer from the usually poorer folk living on the 
                      flats to subsidize the social costs of rich people who 
                      should know better living in an extremely dangerous 
                      natural environment.
                   b. It gets better:  To get a mortgage, you need proof of 
                      fire insurance.  Insurance companies are smarter than to 
                      give fire coverage to people with homes in the most 
                      pyrogenic vegetation on Earth.  So, would-be homeowners 
                      have to turn to the State FAIR Plan. This is an 
                      assigned-risk pool that any insurance company doing 
                      homeowners' policies in California has to participate 
                      in.  They get these fire country policies assigned to 
                      them randomly and they are forced to provide them fire 
                      insurance.  But there's a kick:  These premia have to be 
                      "affordable."  This means that the insurance companies 
                      cannot recover the full risk they're assuming by the 
                      premium money coming from these hillside residences.  
                      So, where do they get the money to subsidize those who 
                      choose to enjoy this crazy pyrogenic lifestyle (for the 
                      private benefit of a view)?  Yep.  From raising fire 
                      insurance rates on everybody else.  This is yet another 
                      hidden upward income transfer in the service of 
                      environmentally suicidal æsthetic values.  
                   c. If people had to pay enough taxes and insurance premia 
                      to cover the risk they are voluntarily assuming, they 
                      probably wouldn't choose to live up there.  Society 
                      subsidizes the cost of living in pyrogenic vegetation, 
                      but allows the benefit of views to be privatized.                     
                   d. Hopefully, public education might also help reduce 
                      people's desires to live up there.
              iii. Chaparral fire hazard, then, is yet another illustration of 
                   the tendency for human society to respond to recurrent low 
                   magnitude events (here, chaparral fire hazard) in such away 
                   as to make itself vulnerable to the rarer, much higher 
                   magnitude event (an extremely hot-burning and fast-moving 
                   conflagration created by years of zealous Smokey the Bear 
                   suppression of any earlier fire).  We shall see this theme 
                   repeated elsewhere in this class, too.
        2. Mediterranean coastal sage is a scrub vegetation closely related to 
           Mediterranean scrub. 
           a. It looks rather similar, with a continuous cover of shrubs from 
              about half a meter to 3 m high.

              

           b. The leaves are also small and sclerophyllous and aromatic with 
              terpene compounds.
           c. In fact, a lot of the genera are the same, only the species 
              varying.
           d. It's also found in the Mediterranean climate, but generally in 
              the Csb and Csbn climates (mild winter, especially in foggy 
              coasts). Coastal sage is found at lower elevations than 
              Mediterranean scrub, though still on usually pretty steep 
              slopes, and it faces the sea.  You don't find it inland:  It's 
              generally within a kilometer or so from the ocean.
           e. The big difference is in how coastal sage deals with getting 
              water during the summer drought of Mediterranean climates:  
              Instead of the deep root system that chaparral plants have, 
              coastal sage plants have dense, shallow root networks to trap 
              fog-drip the moment it falls on the ground below the plants.
        3. Garrigue is also closely related to Mediterranean scrub.  
           a. Unlike Mediterranean scrub (e.g., chaparral or maquis), garrigue 
              is composed of a discontinuous cover of shrubs.
           b. They are smaller than Mediterranean scrub plants:  The shrubs 
              are generally somewhere from 15 cm to 1 m in height.  You may 
              find the occasional small tree or small group of little trees.
           c. The common species in the Mediterranean borderlands include 
              thyme, oregano, lavender, prostrate juniper, and the Kermes oak.
           d. It is associated with the Mediterranean climate (Csa and Csb), 
              but it tends to dominate soils that stunt the shrubs, such as 
              the alkaline soils that form over limestone (which are calcium-
              rich and, so, basic in pH) and serpentine outcrops.
        4. Heath is another scrubland, common in the west coast marine 
           climate.
           a. It is dominated by a continuous cover of low shrubs, largely of 
              the Ericaceae family.
           b. There normally is also a grouped distribution of some low trees 
              and an understory of many forbs, grasses and sedges, mosses, and 
              lichens.
           c. Places you can find heath include Northwest Europe (most 
              famously England, Scotland, and Wales), minor occurrences in the 
              Pacific Northwest, and New Zealand.
           
              

           d. Geotrivia for you:  The word, "heathen," used to describe the 
              old pagans of Europe, meant "heath dweller," as in someone way 
              out in the tules who wouldn't have yet been exposed to 
              Christianity.  The word, "pagan," for that matter, means someone 
              living out in the "pays," French for "countryside" (or boonies).  
              Basically, Dark Ages Christians were calling these rustic people 
              "hillbillies."
     D. Desert is dominated by a very discontinuous low to medium shrub cover 
        (usually half a meter to about 2 m tall). 
        1. The vegetation often shows a random to uniform pattern, as well as 
           a lot of distance between individual plants, which reflects the 
           fierce competition over a scarce and unpredictable water resource.  
           The competition often is conducted through allelopathy, chemical 
           warfare between plants. The shrubs will sometimes group where water 
           is reliably more abundant, as in washes and swales between hills.

        

        2. In some places, such as really unstable sand dunes, desert pavement 
           (closely fitted rock and pebble surface from which all materials 
           finer than gravel have been blown out), and alkali flats, there may 
           be virtually no vegetation at all.

        3. Other life forms are also normally present.
           a. Sometimes, you find a very discontinuous grass cover as a 
              secondary cover in good years.
           b. Very commonly, there is an understory of forbs, which are 
              ephemerals appearing in spring wherever there's enough temporary 
              water.  They go through a frantic growth, flowering, and seed-
              setting process, often in as little as three to six weeks, 
              "hoping" to emerge from seeds to create tons of seeds before the 
              dryness returns.
           c. Sometimes, you even find trees, such as cottonwoods or palms in 
              oases or along a wash.
           d. Very commonly, you will find succulents, such as cacti, which 
              get through dry spells by water storage and protect their water 
              stores with a formidable set of spines and thorns.
        4. Desert vegetation is associated with (duh!) desert climates, both 
           tropical deserts (e.g., our "low desert") and temperate deserts 
           (our "high desert").  These are the BWh (hot desert) and BWk (cold 
           desert) climates in the Köppen system.
           a. BWk is different only in that it gets a cold winter, seeing 
              temperatures often below freezing. 
                i. BWk deserts tend to be located between 30-50° N or S, 
                   inland, behind a mountain produced rainshadow in the 
                   Westerlies belt.
               ii. Examples of BWk deserts include our own Mojave (high 
                   desert); the Basin and Range deserts of eastern Washington 
                   and Oregon, western Colorado; Utah; a lot of Nevada, and 
                   much of N. Arizona and New Mexico; the Patagonian Desert of 
                   Argentina; the Central Asian deserts around and to the 
                   north of the Caspian and Aral seas; and the Gobi Desert of 
                   Mongolia.
           b. BWh deserts are warm to torrid all year round. 
                i. They tend to be located between 15-35° N and S along 
                   the west coasts of the continents, where they are affected 
                   by subsiding air from the Subtropical High and the cold 
                   currents offshore at those latitudes.
               ii. Examples include our low desert (the Colorado Desert of 
                   southeastern California), the Sonoran Desert, much of Baja, 
                   the Atacama Desert of Peru and Chile, the Namib Desert of 
                   southern Africa, the desert of the Australian Outback, and, 
                   of course, the famous Sahara-Arabian-Thar desert system.

              

     E. Tundra is a very low lying vegetation, dominated by a cover of very 
        small shrubs that can be continuous, discontinuous, or grouped in 
        coverage.  The vegetation is very diverse in life forms but very 
        simple in terms of the number of species involved.  Other life forms 
        in tundra, mixed in with tiny shrubs, include grasses and sedges that 
        form tussocks or little mounds, bryophytes (largely mosses), forbs 
        that may be ephemerals or cryptophytes, lichens, and, very bizarrely, 
        tree SPECIES that can only grow as very small SHRUBS (e.g., birches, 
        willows, alders).  If you took their seeds and planted them a thousand 
        kilometers towards the equator, they would grow into respectable trees 
        15 to 30 m high!  

              

        1. Basically, here, any tree seedling that tries to answer its genetic 
           pattern and grow into a regular tree is going to be constrained by 
           the short growing season and the shallow zone of thawed out soil 
           ice, and be pruned back by the extreme windiness of the tundra 
           climate.
        2. Tundra is associated with the ET climate (phone home, Köppen), 
           so we can predict where to find it:
           a. It can be found on the north coast of Alaska and Canada, the 
              west coast of Alaska, the south coast of Iceland, the north 
              coast of Iceland, and the north coast of all of Eurasia.  This 
              is Arctic tundra.
           b. There is also a small amount of it in northern Antarctica and in 
              southernmost South America, as well as the nearby 
              Falklands/Malvinas Islands. This is Antarctic tundra.
           c. It can also be found on many mountains where they stick out 
              above timberline.  This version is called "alpine tundra."

              


So, we've looked at biomes dominated by the shrub life form in this lecture.  
These included scrublands, which are dominated by shrubs usually forming a 
complete ground cover.  Four examples were discussed:  Mediterranean scrub, 
easily the most extensive spatially; Mediterranean coastal sage; heath; and 
garrigue, a more open and not completely continuous version of Mediterranean 
scrub.  Three of these are associated with Mediterranean climate, while the 
fourth (heath) can be found in west coast marine climates.  Desert vegetation 
was the last shrub-dominated biome discussed, and it is characterized by an 
extremely discontinuous (and sometimes locally grouped) shrub cover, 
accompanied by a sparse mix of other life forms.  Not surprisingly, desert 
vegetation is associated with desert climates, both tropical and temperate.  
Equally imaginatively, tundra vegetation is found in tundra climates!  In the 
course of this lecture, I used chaparral to discuss fire hazard and its 
inequitable political economy and the human tendency to respond to recurrent, 
low magnitude hazards in a way that sets humans up to be vulnerable to the 
rarer and much higher magnitude event.


In the next lecture, we'll go over grass-dominated biomes and finish up our 
whirlwind tour of biomes or vegetation associations.

Document and © maintained by Dr. Rodrigue
First placed on web: 11/06/00
Last revised: 07/02/07