About 80% of the ecosystem biomass of tropical rainforests occurs as

Question

About 80% of the ecosystem biomass of tropical rainforests occurs as woody tissues of trees, while only about 15% of the organic matter occurs in soil and litter, and about 5% is foliage. As with all forests, the biomass of animals is much less than 1% of that of the total ecosystem. In contrast, temperate forests maintain much larger fractions of their total ecosystem biomass as organic matter of the soil and forest floor. The reason for this difference is the relatively rapid rate of decomposition of dead biomass in the warm and humid environmental conditions of tropical rainforests. Because most of the biomass and nutrient content of tropical rainforests occurs in the biomass of living trees, and because their soils are usually highly infertile and extremely weathered, the fertility of this ecosystem is rapidly degraded after the forest is cleared.

Select Strengthen for the statement that would, if true, most strengthen the argument, and select Weaken for the statement that would, if true, most weaken the argument. Make only two selections, one in each column.

Select  Strengthen  for the statement that would, if true, most strengthen the argument, and select  Weaken  for the statement that would, if true, most weaken the argument. Make only two selections, one in each column.

Fish181 · Answer

At the very least, how do we even figure out the conclusion of this passage? Having a strong grasp of the conclusion may help in discovering the weakener/strengthener.

Sajjad1994 · Answer

Official Explanation

This is a strengthening and weakening question, and therefore it is important that we understand the conclusion of the argument. The conclusion is that  the fertility of this ecosystem is rapidly degraded after the forest is cleared.  What ecosystem? Tropical rainforest. And the passage talks about 80% of ecosystem biomass of tropical rainforest being worried issues, 15% being organic matter, 5% being foliage. Generally it is animals. If biomass contributes to 1%, and it is much higher in the case of temperate forests. And the reason is given to strengthen and weaken.

The option  (D)  says that the least contribution of biomass of forests so this tends to convey that there is little correlation between biomass and soil. And therefore, this adds weight to the logic of the infertility of soil. So this strengthens. And this option  (E)  brings in an alternate explanation and hence weaken the argument.

Danny134 · Answer

Can someone please explain why B is not the correct answer for Strengthen. Thanks in Advance!

Purple_Wizard · Answer

@karishmab @gmatninja - please help here

Purple_Wizard · Answer

chetan2u   GMATNinja  please help with this problem, it looks confusing. I am unable to understand the weakener / strengthener.

Purnank · Answer

GMATNinja  Can you please help in understanding this question?

chetan2u · Answer

The para speaks of biomass, the sum of mass of all organisms in an ecosystem, in different forests.
 Tropical rainforests:  Woody tissue - 80%,  organic matter in soil - 15 %, foliage(leaves etc) - 5% and animal - less than 1%
 Temperate forests:   organic matter in soil  is much higher in proportion. 
  Reason for the difference in organic matter in soil:  relatively rapid rate of decomposition of dead biomass in the warm and humid environmental conditions of tropical rainforests.

Further, the conclusion and reasons given are: Forest trees hold max biomass ( 85%) and soil does not have any nutrient value, so removal of trees from ecosytem will lead to degradation of fertility there.

Next we have to find the strengthener and weakener.
I'll initially look for the options related to tropical rainforests.
The rate of decomposition of biomass in warm and hot climates is one of the major contributors for the clearing of the equatorial forests.....  equatorial forest, so should not be of much use  
The soils of tropical rain forests are found to be poor in mineral content.....  That is what is already stated in the reasoning of conclusion.   
Temperate forests are far more enriched in fertility and wildlife diversity......  Temperate forests, so discard .  
The least contribution to biomass of forests is by the organic matter from soil.....  The fertility of soil would so depend on the external factors, trees here. So, could be a strengthener.  
Most deserts that were once tropical forests are near coastal areas where salt content is very high in the air, affecting the ecosystems fertility....  Gives you another reason, so a weakener.

However, I would say you will have lot of other better questions in forum to practice from.

RiyaJ0032 · Answer

Hello  DmitryFarber !

Could you please help me understanding why option D is given as a strengthener?

It's just telling us that organic matter from soil contributes least to biomass of tropical forest

but how does it tell us that clearing these forest will strip the soil of any nutrients (which is the assumption here) and interfere with the fertility of soil?

If you could share your insights,
Thanks!

If any expert could also help, please do-
 KarishmaB 
 MartyMurray 
 GMATNinja 
 Mannisha

DishaAgarwal12 · Answer

I have not understood the passage at all please help

Bunuel · Answer

Video solution from Experts Global:

https://www.youtube.com/watch?v=bS0e4gl9bII

Dereno · Answer

The passage begins with the explanation of tropical rainforest biomass split up:

80% of biomass = Woody tissues ( actually the huge trees of tropical forests)

15% of the biomass = Soil and litter

5% of the biomass = Foliage.

They bring a new entrant animals , which is LESS THAN 1% of the total ecosystem. What does this mean? The contribution of animals to the biomass ecosystem is negligible and can be discarded.

Next, TEMPERATE FOREST : MAJOR chunk of the the biomass belongs to Soil and forest floor.

Whats the reason for this contradiction:  decomposition rate is HIGH , in the  tropical rainforests.

How can the decomposition rate be high ? As most biomass and nutrient is concentrated in the woody tissues , once logging of trees is done in the tropical rainforest- the major biomass chunk is removed out of the system. Leaving us with 20% of the biomass, which is infertile and can be weathered quickly.

May be due to rain runoff, or due to rapid decay these 20% can be expected to disintegrate soon. So, the CONCLUSION is  IF YOU CLEAR THE Tropical RAINFOREST , the fertility drops down.

We need to find an answer , that strengthens and weakens the Conclusion.

The Options:

1. The rate of decomposition of biomass in warm and hot climates is one of the major contributors for the clearing of the equatorial forests.

Clearing of equatorial or any forest can be attributed to logging, rate of decomposition wild fires etc. so, this cannot be either a strengthener or weakening statement.

2. The soils of tropical rain forests are found to be poor in mineral content. 
 
 Yes, the soils of tropical rainforest can be found to be poor in mineral content. But what have caused the soil to be in such a poor state is what needs to be ascertained.

3. Temperate forests are far more enriched in fertility and wildlife diversity.

Does this option in either way impact the logging of trees in tropical forests and their consequences. Hence, Wrong.

4. The least contribution to biomass of forests is by the organic matter from soil.

This strengthens the view that biomass major contribution is attributed to something else - Woody tissues. If that’s true, then the logging of forest trees in the rainforest region would impact the decline of fertility. Hence, a valid strengthening option.

5. Most deserts that were once tropical forests are near coastal areas where salt content is very high in the air, affecting the ecosystems fertility.

This option mentions the tropical rainforest is usually located near the coastal areas, and the high salt content of the coastal areas is the causative factor for degradation of fertility of tropical rainforests. So, the logging of trees cannot be considered as the cause as mentioned in the conclusion. Hence, weakening option.

About 80% of the ecosystem biomass of tropical rainforests occurs as

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Strengthen	Weaken
		The rate of decomposition of biomass in warm and hot climates is one of the major contributors for the clearing of the equatorial forests.
		The soils of tropical rain forests are found to be poor in mineral content.
		Temperate forests are far more enriched in fertility and wildlife diversity.
		The least contribution to biomass of forests is by the organic matter from soil.
		Most deserts that were once tropical forests are near coastal areas where salt content is very high in the air, affecting the ecosystems fertility.

GMAT Two-part Analysis (TPA) Questions

About 80% of the ecosystem biomass of tropical rainforests occurs as

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