Forestry & Rangeland Management Lecture Notes

Classifying Forests

Forests occupy about 30% of the earth’s land. About half of that is tropical forest. Make sure to review

your forest biomes for your test. No matter what biome the forest is, we can classify the forest based

on its age

Old growth forests are forests that have not been seriously disturbed by humans or natural disasters for

at least 200 years. They are important reservoirs of biodiversity and have been seriously depleted by

human population growth.

Approximately 40% of the existing

forests on earth are old growth

forests.

These maps are just showing

coverage of old growth forests. If we

looked at total forest coverage, it has

actually increased since 1920 in the

form of 2nd

growth forests and tree

plantations. Currently the US is

growing more wood each year than it

uses.

Second growth forests are forests that have been significantly disturbed by humans or natural disasters.

They have regenerated through secondary succession and are still important ecosystems in harboring

biodiversity. They make up roughly 60% of forests on earth

Tree Plantations are like man-made forests. They are also called tree farms. On these plantations,

growers plant trees of one or two species and then they harvest them all at the same time, then plant

more. These trees are sold and turned into wood products. There are several problems with this. There

is also a lack of biodiversity since it is a monoculture, so the plantations can be very susceptible to pests.

Soil can also be eroded easily when all trees are cut and habitat is destroyed when all the trees are cut.

A benefit of these plantations is that they provide wood products without requiring the logging of old

growth or second growth forests. Many biologists suggest only establishing tree plantations on area

that has already been cleared and rather than clearing forests to plant tree plantations.

Services Provided by forests

There are a number of ecological services provided by forests: Support nutrient cycling

They reduce soil erosion, provide habitats and promote biodiversity. As you read about in The

Omnivore’s Dilemma, forest soils can absorb and retain water. Forests also serve to purify air and water

as they take it in and then release it. Trees absorb carbon and store it while producing oxygen. Finally,

trees can influence local climates through transpiration. As they release water into the atmosphere

from their leaves, this increases the humidity of the air. In tropical rainforests, this is part of a positive

feedback loop that maintains enough moisture in the air for rainforests to exist where they do.

Forests also provide a variety of economic services. They provide fuelwood for heating and cooking,

lumber and pulp for papermaking. Forests can also be used for grazing some livestock (like the farmer

does with the pigs in the Omnivore’s Dilemma). Finally forests provide jobs for the people who harvest

Logging

Logging is the primary activity that disrupts forest

ecosystems. The first thing that a logging

company will do is build a road which exposes soil

to erosion and fragments habitats. These roads

make it easier for invasive species to get into the

forest and cause damage to the ecosystem. Also,

roads provide a point of access for more and more

people (miners, hunters, farmers etc) to get into

this forested area and potentially cause damage.

Once logging companies build the road they will begin taking trees. The traditional method used is

clear-cutting. This method makes good economic sense because it allows the logger to get the most

money out of the land at that time. But there are some

ecological problems with clear-cutting such as extreme

soil erosion, loss of soil nutrients, water pollution in

downhill streams, loss of habitat & loss of biodiversity in

the ecosystem.

Alternative Logging Methods

There are other methods that loggers used that can cause

less environmental damage and thus maintain the

ecosystem in a healthy state for longer. Loggers can

practice selective cutting where only the intermediate or

older trees are cut so that some trees remain to retain the

soil. This is not effective in every forest ecosystem, but can serve to avert much of the environmental

damage caused by clear cutting.

Strip cutting involves clear-cutting only a strip of the

forest at a time, allowing it to regenerate and then

cutting a nearby strip. As you can see in the picture,

this prevents water pollution because trees remain in

the watershed to hold the soil in place.

Role of Fire

Fire is a natural part of many forests and other biomes. In biomes where fires naturally occur

frequently, organisms are adapted to withstand moderate fires and recover quickly. For example in

most forests, fires will burn small trees and grasses and but won’t damage large fire-resistant trees. In

forests, some pine cones will not open to germinate without fire. Fires also restore nutrients to the soil.

Therefore, these biomes need regular fires. If regular fires don’t happen, lots of underbrush will build

up and when there is finally a fire, there will be more fuel, so it will burn hotter and longer. If that

happens, it can even burn the large fire-resistant trees, causing much more damage and making it

harder for the forest to regenerate.

Healthy Forests Initiative

In the 1990’s there were a few large forest fires. In response, congress passed the Healthy Forests

Initiative which was a law that put timber companies in charge of clearing the underbrush of forests. In

return they get to harvest large trees. They would remove the brush manually- they did not have to do

a controlled burn to remove it or undergo any environmental reviews.

There are some problems with this law. It is not based on sound science of forest ecosystems. Since

there are no prescribed burns, there is a greater chance of a large, damaging fire occurring. Studies

have shown that prescribed burns are the most effective way at preventing large damaging fires. Some

of the worst fires in US history have burned through areas that have been cleared rather than burned;

clearing brush is not an effective method to prevent forest fires. Additionally, medium and large sized

trees are the most fire- resistant, so their removal makes the ecosystem less resilient. Their removal

also allows for greater growth of small trees and brush which are more flammable. It also leaves behind

slash (leftovers from the clearing process), which is also highly flammable.

What are Rangelands?

Rangelands are grassland biomes (including chapparal) where animals can roam and graze on grasses

and brush. Sometimes rangelands will be fenced in to form pastures where animals are more

contained. If these lands are not good for farming, grazing animals on these rangelands is a great way to

produce food from them. You are taking plant energy that our bodies cannot process and turning it into

meat, a form that we CAN process, just by having cows or sheep eat the grass.

Threats to Rangelands

Because grass grows from the base, grazing is actually good for

rangeland ecosystems. When an animal eats the top of the

blade of grass it stimulates growth at the base of the plant. In

the right side of the photo you can see an area that has been

moderately grazed and is healthy. Because these ecosystems

have evolved with grazing herbivores, it is possible to have

rangeland that is undergrazed, which reduces its overall

productivity. However, the bigger problem is when there are too many animals grazing in the same area

because they will eat the whole plant and not leave enough of the blade of grass for it to regrow quickly.

When the number of animals exceeds the land’s carrying capacity it is called overgrazing and is shown

to the left of the fence in the photo above.

Some consequences of this overgrazing are that grass cover is reduced & more soil is exposed to

erosion. Soil is also exposed to the trampling of animals which can compact the soil and reduce pore

space. This would reduce the moisture content because there would be less pore space to hold water

and it would ultimately limit the rangeland’s resilience

Sustainable Managements of Rangelands

There are techniques that ranchers can use to continue utilizing rangelands for grazing their animals

without degrading them. The best way to do this is to make sure the carrying capacity of a particular

area is not exceeded. The most widely used method is rotational grazing. Ranchers use portable

fencing to confine their animals to one area for 1 or 2 days. They allow them to graze and then move

them to a new area to repeat the process. They are not returned to the first area until it has a chance to

regenerate.

Ranchers can also preserve particularly vulnerable areas, like riparian zones, by fencing them off

entirely. Animals naturally head towards water, so ranchers can also protect vulnerable areas by placing

watering holes, salt blocks and supplemental feed at different locations to draw the animals away from

natural water sources.

The photos show an example of a destroyed riparian zone on the San Pedro River in Arizona. It was

degraded by overgrazing of cattle, but after banning grazing in that corridor for 10 years, the ecosystem

was restored.

Finally, environmentalists, ranchers and the government can work together to make sure that

rangelands are sustained for the future. In the Southwest, where there is a lot of rangeland, there has

been a lot of pressure to develop these lands as the population has increased. Environmental groups

have paid ranchers to put restrictions on the deeds to their lands (conservation easements). These

would prevent any future owner of the land from developing it further into houses or shopping centers

etc. Local governments can also zone fragile rangeland so that it cannot be developed.