19: Ecosystems - Problems Flashcards
(DSE 2014 IB Q5)
In a study, a plot of land was burnt by fire. After this, the vegetation on this land, classified into herbs and woody plants, was monitored for 8 years. The percentage cover of each type of vegetation is shown in the graph below.
Explain which type of succession is shown in the above case. (2)
Secondary succession,
since it involves the restoration of a community after a major disturbance, which is the fire.
(DSE 2014 IB Q5)
In a study, a plot of land was burnt by fire. After this, the vegetation on this land, classified into herbs and woody plants, was monitored for 8 years. The percentage cover of each type of vegetation is shown in the graph below.
Describe briefly how the dominant community of vegetation changes with time after the fire. (2)
From years 0 to 3, herbs are the dominant vegetation.
From years 3 to 8, woody plants are the dominant vegetation.
(DSE 2014 IB Q5)
In a study, a plot of land was burnt by fire. After this, the vegetation on this land, classified into herbs and woody plants, was monitored for 8 years. The percentage cover of each type of vegetation is shown in the graph below.
Explain the changes in the dominant community of vegetation with time. (4)
Underground vegetative organs and seeds were not damaged in the fire.
Herbs generally germinate and grow faster than woody plants,
hence the percentage cover of herbs increased rapidly at first,
becoming the dominant vegetation in the first three years. As woody plants continue to grow and over-shadow the herbs / out-compete the herbs for light, they replace herbs as the dominant vegetation.
The graph below shows the net carbon dioxide uptake of three plant species (W, X, and Y) at different light intensities.
Explain why species W is the first to colonise a barren area among the three species. (3)
Barren areas often have a high light intensity due to the absence of vegetation.
Species W has the highest net uptake of carbon dioxide at high light intensities.
Therefore, species W has the highest rate of photosynthesis and grows faster than other species to colonise the barren area.
The graph below shows the net carbon dioxide uptake of three plant species (W, X, and Y) at different light intensities.
Suggest one possible reason why species W may not grow well in an area where species Y is dominant. (2)
Species Y may form shade in the area and decrease the light intensity in that area.
The rate of carbon dioxide uptake of species W decreases significantly as light intensity reaching species W decreases. Therefore, the growth rate of species W will decrease.
