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Destruction of flora by fires

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Wed Aug 10, 2005 8:14 pm Unread post
I witnessed veld fires almost every day whilst in the Kruger in July (15th to 23rd Satara to Shingwedzi)I can only assume that they were created by some careless person as there was no lightning that time of the year. Maybe ciggs? The destruction of the young trees in the park is becoming a problem in that they do not reach maturity before being burnt down beyond recovery which means that the larger mature trees are becoming scarcer in certain areas. Any thoughts?
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Wed Aug 10, 2005 11:55 pm Unread post
I think in some instances I think management endorse destruction of small trees, ie.,some of those are instigators in bush encroachment, though others also form nice parkland stands, that is aesthetically pleasing and all.. Still have point that especially out of season and intense ones can be detrimental.

regards,
w



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Thu Aug 11, 2005 7:49 am Unread post
I doubt they burn part of the park for aestetic reasons wildjohn.



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Fri Aug 12, 2005 7:26 pm Unread post
The park is divided into some 400 burn blocks, and current fire management tries to follow a natural pattern in that all lightning ignited fires are allowed to burn themselves out without human intervention. However man made fires are controlled to a degree (where possible). Fires in general will result in the grazing of that area improving significantly, but the trees take a hammering especially the young ones. This was evident in the northern areas of the park where there are thousands of hectares of young mopani trees, which ,often due to new fires a few seasons later, result in the death of the trees as they are not yet strong enough to withstand the fires.
This is more so in areas where the grass is lush thus resulting in a large biomass which feeds an intensely hot fire.



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Mon Aug 15, 2005 8:18 am Unread post
The strucute of the mopani you refer to as being in shrub form as a result of fire is not entirely due to fire. The soil type and geology also paly a vital role in determining the size and structure of maponi trees.
I do agree though and more and more questions are being raised about it - what is the role of fire in destroying woodlands rather than elephants.




Mon Aug 15, 2005 8:55 am Unread post
I think the fires have a far bigger detrimental impact that the elephants. There are definitely more fires, effecting bigger areas, than what there was 10 years ago - my personal view.
The fires are not only affecting the flora. We saw tortoises on a regular basis a few years ago. Now a tortoise is a rare sighting. :(



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Mon Aug 15, 2005 7:11 pm Unread post
Hi Fever Tree, I never actually said that the Mopani trees asumed a shrub like form because of fires. Re-read my posting.The young trees are not strong enough in many instances to cope with the intensly hot fires. I agree that the form of tree or shrub is due to, amongst others, soil composition. The elephant population is also causing huge destruction to the tree population due to their excessive numbers, and, together with fires, the problem is compounded.



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Tue Aug 16, 2005 8:56 am Unread post
Sorry, I did misread your post. What I have witnessed with mopani, is there amazing ability to coppice after fires, and this then helsp to keep them in the shrub form as well - and of course the elephants prefer it this way, as the browse is at a nice height for them to feed from.



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Sat Sep 24, 2005 10:44 am Unread post
I attended a meeting on Wednesday evening 21/9/05 and we were informed that some 60% of the park in the south has been burnt by fires and some 40% in the north. This can have serious effects as far as grazing and browzing is concerned in the short term. (until it rains) I also wonder how many animals have been injured because of this. Have just heard on the news this morning that twenty elephants have been injured by fires in the Pilanesburg park.



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Tue Sep 27, 2005 7:32 am Unread post
fevertree wrote
What I have witnessed with mopani, is there amazing ability to coppice after fires, and this then helsp to keep them in the shrub form as well - and of course the elephants prefer it this way, as the browse is at a nice height for them to feed from.


At Mapungubwe, it was interesting to see the size and shape of Mopani trees in the areas where the elephants are and where they aren't. Elephants have definitely got something to do with them being short and fat.



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Thu Oct 27, 2005 1:17 am Unread post
Thoughts on the matter?

Well to compound thoughts logically you have to look at life history traits of plants. In disturbance areas you get resprouters and re-seeders.

They show a trade off between allocation of resources at what age they should reproduce, how often, how many seeds, and how long should the parent live.

Long lived sprouters have good regeneration after a disturbance, but poor reproduction

non-sprouters have bad regeneration but produce many seeds

The two types differ in carbon allocation and storage as sprouters store carbon as starch reserves for regrowth. Mopane and acacia species adopt resprouting from an underground starch reserve in the roots called a lignotuber.

This life history trait offers a high survival rate when in a high disturbance environment, but a low recruitment rate of offspring (trade-off).

I have the pleasure of working with the world leading botanist in this particular field and shall try to convey the mechanisms at work (not nearly as good as he does but im all u got :))

In a savanna ecosystem fire naturally would occur every 2-3 years. (fynbos about 10-15). Within the ecosystem there are two main types of consumers, herbivores and fire.

Most herbivores graze/browse below 2/3m high, most fires damage below 2-4m high. This is a problem for seedlings as to become trees they have to escape this danger zone. A zone which has been coined as the 'fire trap'

Trees then employ a strategy to try break free from this fire-trap before being burned down again. As lignotuber sprouters get destroyed and have to grow again from the storage root (ground level) its a tough challenge to grow 3-4 m, out of the fire trap, before being wiped out again. Acacia nigrescense, amoung others employ a pole type growth form. They utilize alot of reserves to send up a single pole stem as fast and as high as possible to try overcome trap. This is visable in the growth form of many resprouter species in fire disturbed savannas.

This is evident at kruger when studying the lignotubers in different burn frequency areas. At frequent or intense burning sites the 'saplings' are still below the fire trap, and pole-like. The dating of the lignotubers though show that these 2m high 'saplings' are infact 30 years old +
Many spend their whole lives as 'saplings'
WJ BOND of UCT called this life history Gullivers as the giant trees were being kept down, trapped by the fire much in the same way as Gulliver was tied down when he arrived on lilliput by the lilliputians. Here acacias are being hindered by the lilliputian fire until they are released. When gulliver was released he stood tall. The same as acacias once they escape the 'fire-trap'

Image
Gilliver (acacia) being restricted by the lilliputians (fire) until release

Image
Note the pole growth form of the tree in the foreground and the trees in the background. In an attempt to escape the fire trap.best picture i could find im sorry but it shows the pole growthform well compared to other acacia areas with the same species more concerned with surviving browsing than fires.

Image
Cage growth form taken in a goat farm where fire has been removed and browsing is done by goats, who eat everything around

Areas of browsing disturbance see many species, such as mopane and acacia opt for a different strategy in life history and architechture. Instead of allocating starch to massive root stores, browser effected species have smaller lignotubers as much carbon is stored in stems. Topkill by browsers is rare in comparison to that of fire. Its safe enough to store carbon above ground. These are not fire resistant but form the cage with short ramified shoots, creating a shrub/bush appearance like above.

Adult trees may look quite similar in appearance but the difference in life history traits to overcome fire/browser traps are obvious.

Shrub form is therefore a result of browser protection strategy as apposed to a fire resultant pole strategy. The "short and fat" mopane bushes definately were as a result of the browsing activity you observed lam, well noted!

of course soil plays a role in growth as nutrient levels effect all living things. Physical composition would play a part in recovery as clay type wetlands may reduce oxygen avaliability for lignotubers which is crucial for respiration and growth. Soil porosity etc and aeration would control recovery periods but pole type lignotubers in waterlogged soils follow regular pole growth patterns after months when the soil becomes oxygenated.

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The destruction of the young trees in the park is becoming a problem in that they do not reach maturity before being burnt down


as for becoming a problem not reaching maturity the sprouters have evolved this life history strategy to cope with regular fires (2-3years) and those periods of irregular fires (sometimes shorter periods sometimes longer). The game they are playing works in this environment as most of the large trees in such disturbed environments are sprouters. Not to worry then Naturesguy some acacia in kruger are 1m tall and 30 years old. They live for most of their life trying to escape the trap and are the tortoise in the race against the hare, a strategy that works for some- acacia and mopane included.

So those are some thoughts. Some from me, but most from personal communication with WJ BOND and JJ MIDGLEY in the field with the UCT Botany department



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Thu Oct 27, 2005 8:26 am Unread post
The problem with a 30 year old, 1 metre tall knobthorn is that from a reproductive point of view it is of no use in the population. It does not have the ability to flower and set seed (the concept of stage of the life history of the plant, not age).
Secondly, what is being over looked and is one of the major criteria in Kruger Parks biodiversity objectives is to also create/protect structural diversity in the plant population. Regular fires and elephants reduce this structural diversity to the shrub from of 2-3 m height. This is not acceptable from the TPC point of view as outlined in Krugers management strategy.



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Tue Nov 01, 2005 12:17 am Unread post
SAHGCA-UCT

A question: Do these two different strategies you described happen within the same species of tree? (As one of your remarks might be (maybe wrongly!) interpreted???) Or do a species of tree keep to one strategy?

*****

It is important to note that the peacefull Savannah scene you sit and watch at dusk, is actually a battle ground!

A Savannah system is formed by the battle between woody plants (trees etc.) and grasses. They are constantly batteling each other for supremacy and controle of resources such as nutrients, water and light.

In the Savannah setup woody plants would always win the battle, if it were not for the two main allies of the grass population nl. herbivores and fire. Naturally occuring fires and herbivore population are important factors in keeping the KNP (and other systems) in a stable state.

For a Savannah system to work, you need quite a lot of 1 meter tall, 30 year old Knobthorns! Otherwise it would quickly turn into a forest or thicket. Then of course - you also need a lot of tall reproducing trees!

It is a matter of (very dynamic) balance!


As for the impact of elephant vs fire:

When it comes to bigger trees, the elephant impact is definatley the bigger! Big trees have the abbility to withstand the impact of fire. (Unless they have been weakend by porcupine etc. or in the case of a very intense fire).

Elephant de-barking of trees is a major mortality factor! Many people tend to think that elephant push over trees as a show of strength, and that is the big reason they impact on the environment. Most damage occurs by de-barking standing trees or pushing trees over to reach the root system. Trees = food!

A damaged tree is a target for secondary attacks by insects, etc. A tree with a part of its bark removed is also much more funerable to fire!



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Tue Nov 01, 2005 8:43 am Unread post
The maintenance of a savanna system is controlled by the differential access to resources by trees and grasses. Grasses being shallow rooted make opportunistic use of early season rainfall which does not penetrate down to tree roots. This gives them a competitive edge over trees and allows them to over crowd and shadow tree seddlings in the grass layer. This also restricts the recruitment of trees into larger size classes. This is exacerbated by fire and herbivores.
Trees are deeper rooted, and are able to initially sprout leaves before the onset of the rainy season because of retained soil moisture. However they are dependent on rainfall reaching the deeper soil layers for continued seasonal growth. Therefore trees need deep penetrating rain in order to prosper. In drought years, grasses actually fare better than trees as the grasses can optimally utilize the low rainfall which penetrates as far as there roots but does not penetrate sufficiently for the trees roots. This plays animportant role in the tree/grass composition of a savanna. If you look at time series photogrpahs, you can see how a savanna at some stages is dominated by trees and shrubs, and a few years later by grasses.

Savannas are therefore far from anything near balance as mentioned in a previous post. It is recognised that flux and heterogeniety are the main factors maintaining savannas. The balance concept has now been rejected by ecologists. Savannas are maintained by disturbance events and differential access to resources on a temporal scale.



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Fri Nov 04, 2005 1:07 am Unread post
It has been shown that the most important controling factors is actually fire and herbivores, rather than resources (not that access to resources does not play a role!). If the maintenace of the Savannah eco-system were based on resources alone, there would not be such problems with bush encrouchment where the ecosystem has been disturbed by humans!

Also. The roots of trees actually compete with those of grasses, even in the top layer of earth! They do grow deeper than those of grasses, but that does not mean that they do not compete at the top!

Some trees, such as Boscia albitrunca (Shepherds-tree / Witgat), is known for their deep roots that actually goes down to the water table. They are not strictly dependant on rain to be able to grow. If those trees were not controled by Herbivore or fire they would dominate!

It is because of these reasons that a healthy burning-regime is such an important management tool in Nature conservation.
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