Today we are looking at the spatial variations of vegetation that exists in a volcanic landscape.
Our case study is the magnificent landscape of the Tongariro National Park in New Zealand.
This landscape has numerous volcanoes including Mount Tongariro,
Mount Ngaruahoe and Mount Ruapehu.
The first pattern I want to cover is that of altitudinal zonation.
This diagram shows the zones of different forest types found in New Zealand as altitude increases.
At higher altitudes vegetation types are generally shorter and sparser.
Plant life gets shorter and sparser until eventually only ice and snow is found on the bare rocks.
At lower altitudes the climate is generally warmer so the vegetation is characterized by large forest trees.
This is because air cools as it rises so areas of higher altitude have colder temperatures
We call the change of temperature as air rises the Adiabatic Lapse Rate.
Generally average daily temperatures fall about 0.6 degrees for each 100 vertical metres.
Let's take a closer look at the interactions vegetation has with soil,
relief and climate to produce these patterns.
At high altitudes wind speeds have high velocities and the temperatures are cold.
Parent volcanic material dominates.
Further rates of condensation increase as temperatures fall so rainfall also increases with altitude.
Only the hardiest organisms can survive here such as this Moss located at 1650 meters on Mount Ruapehu.
Mountainous areas with steep slopes have high rates of erosion. Any loose material is quickly carried downslope.
Even at this altitude
there are signs that plants are clinging to the bare rock.
Just in the crack here we've got some grass, and there's some very thin soil
that's formed in between the cracks of this volcanic rock.
At an altitude of 1,200 meters soils are thin but are still deeper than they are higher up the mountain.
Here there are numerous species of small plants growing such as Mountain Inaka
Snow Totara
Bog Pine
Tussock grass
Mountain Toatoa
and flowering plants such as the Mountain Daisy. In the summer there's a spectacular display of alpine flowers.
These plants traps silt and ash that have been transported by wind, mountain streams or melting ice
and themselves add organic matter.
They act to further protect the surface from erosion.
Mountain Beech is also found here
However at this altitude their growth is stunted.
The Mountain Beech grows from the 700 meter mark up to the tree line
and can grow up to 15 meters tall.
This is the smallest of the beech species in New Zealand.
Another interesting tree bounty is the conical shaped New Zealand Cedar. (Pähautea)
This tree can be found even at altitudes of 1,200 meters, and they can live as long as 1,000 years.
At around 900 meters beech forest dominates.
Beech trees are evergreen broadleaf trees with small rounded leaves as you can observe here on the forest floor.
Adverse altitude temperatures are still cold, but a much more acceptable and soils are becoming deeper.
Towns such as Waiouru are at a similar altitude to this.
New Zealand has five species of beech tree: The Red Beech,
the Silver Beech,
Black beech, Hard Beech
and Mountain Beech.
At this site we find Mountain Beech and the larger Silver Beech which can grow to 25 meters.
Silver Beech enjoys the cool temperatures and wetter climates that exists at this altitude.
One tree that must be avoided here is the Bushman's Lawyer. Many a hiker has been caught by it's barbs.
(Grunts) Oh, Oh my goodness. Look at that cut. That was done by this.
This evil plant is the Bush Lawyer. Beware of this plant. It will cut you.
You can also find here the Rangiora tree, more affectionately known as the
Bushman's friend. You can imagine from these broad leaves, why many hiker has found it useful.
Mountain cabbage trees
flaxes
Hall's Totara and other species are also found here.
The Red Beech is the largest beech tree that grows to 35 meters, but prefers the warmer temperatures at lower altitudes.
At lower altitudes from sea level to 650 meters podocarp forest dominates.
Podocarps are conifers that are distinguished from pines because they bear small fruit instead of cones.
These forests are stratified with emergent podocarps over 30 meters tall dominating.
Podocarps include some of New Zealand's largest tree species such as the Totara
the Matai or black pine
the Miro or brown pine
the Kahikatea or white pine
the Mairi
and the Rimu
These trees live to be hundreds of years old.
Rimu is the dominant podocarp of the Central North Island forests.
Kahikatea is New Zealand's tallest species
with one tree reputedly to have been up to 68 meters tall.
They prefer swampy soils and is often found growing on the floodplains of rivers.
Many of these trees have epiphytes growing on them. Epiphytes are plants that grow on other plants such as these ones here.
The next layer is the canopy which is trees that grow to about 20 meters.
Examples of this include the Hinau
the Rewarewa
and the Pukatea.
The Pukatea is unique. It is the only New Zealand native that has buttress roots
which is similar to the species that usually frequent tropical rainforest.
Below this is the sub canopy which includes species such as the Mahoe or Whitey Wood
Tree ferns such as the Ponga, Mamuka and Wheke
the Lancewood
Cabbage trees.
Below this is an assortment of small species no taller than 5 meters
such as the Horopito.
The Horopito is a shrub that is also known as Pepperwood because of its reddish leaves,
which when eaten they leave a peppery taste in the mouth.
This little beauty is called the Horopito tree.
You can identify it by its own reddish leaves.
Now, in Maori known as the Horopito and the English name for this is called the pepper wood and the
reason was called this is because when you chew it's got a very peppery taste and quite
frankly it is more like eating a chili. I'll give you a little demonstration here.
All right this one here
is (mumbles with food in mouth) very environmentally friendly but
But um, my goodness!
Now don't swallow this okay, don't do this at home.
Now when you finish this... yuk!
Gosh, I must spit this out.
Many juvenile trees such as the young Miro that you can see here, grow in close proximity to its mother tree are growing in this layer
while waiting for a gap to open up so they can compete for the sunlight.
On the forest floor there are mainly mosses and ferns
such as Hounds Tongue Fern,
the Crown Fern
and Kidney Fern
There is a lot less sunlight penetrating down here
These lowland forests are home to numerous native bird species
including the Kiwi
the Tui
Bellbird
the Kereru or native pigeon
Fantails
the North Island Tomtit
Silver Eyes
and the North Island Robin.
On the flatter land at lower altitudes
erosion rates are much slower and deposition of alluvium by rivers and flood occurs.
Thus soils are often deeper and more fertile than higher up.
In this volcanic environment there may be alternating layers of ash laid down from historic volcanic eruptions.
On the forest floor
there is a thick layer of decaying
plants and animal matter.
We call this humus.
Below that is the topsoil.
You have to dig a lot deeper before you get to the bedrock below.