Succession: how ecosystems rebuild after a change

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Two sites after a change (model data)

   site	what happened	soil at the start	years until grasses cover half the ground
   lava site	a lava flow covered the land	none	40
   fire site	a fire cleared the forest	soil and ash	4

2. 1.

   Jun compares two sites. Which claim fits the table?

   • The lava site was quicker, because bare rock leaves nothing in the way of the new plants as they spread
   • The two sites took the same time, because both began with no plants on them
   • The fire site was slower, because its soil was lost and had to form again
   • The fire site is secondary succession, and it was quicker because its soil was still there

3. Two sites at the start (model data)

   site	soil depth at the start (cm)	first plants seen
   new lava rock	0	lichens and mosses
   abandoned field	12	annual plants

4. 2.

   Esme compares the sites. Which statement does the table support?

   • The rock began with no soil, so it will recover faster than the field
   • The field began with soil, but the rock has to build its soil first
   • Both sites need people to plant their first species before anything starts
   • The field began with soil, so it has to build soil first, like the rock
6. 3.

   Kira reads the graph. Which plant type has the greatest cover at year 20?

   • Grasses, at 50 percent
   • Shrubs, at 50 percent
   • Trees, at 5 percent
   • Annual plants, at 20 percent
7. 4.

   Milo reads the graph. Between which two years does the tree cover rise the most?

   Use the picture in question 3.

   • Year 50 to year 60, a rise of 20
   • Year 40 to year 50, a rise of 30
   • Year 30 to year 40, a rise of 20
   • Year 20 to year 30, a rise of 15

8. An old field left alone (model data)

   question	answer
   years since farming stopped	8
   ground cover now	grasses cover most; a few shrubs; no trees
   soil	deep

9. 5.

   Pia reads the card. What most likely comes next in this secondary succession?

   • Lichens and mosses begin to build soil on the bare ground
   • Tall trees take over before the shrubs have spread
   • Shrubs spread, and small trees begin to join them
   • Annual plants return as the main cover for good

10. Three sites after a change (model data)

    site	what happened	soil afterward
    cooled lava flow	lava covered the land	none
    fire-cleared forest	a fire cleared the trees	soil and ash
    farm field left alone	farming stopped	soil

11. 6.

    Ren reads the table. Which two sites will show the same kind of succession?

    • The cooled lava flow and the fire-cleared forest, since both were cleared
    • The three sites share one kind of succession
    • The cooled lava flow and the farm field left alone
    • The fire-cleared forest and the farm field left alone

12. Cover on a lava field at year 35 (model data)

    plant type	cover (percent)
    lichens and mosses	15
    grasses	20
    shrubs	45
    trees	5

13. 7.

    Noah reads the table. Which stage is this lava field in?

    • The shrub stage, because shrubs cover the most and trees are just starting
    • The pioneer stage, because lichens and mosses are still the main cover of the ground
    • The grass stage, because grasses must lead before any shrubs appear
    • The tree stage, because any trees mean the trees have come first
14. 8.

    Tala reads the graph. A fire cleared the forest between year 80 and year 100. What starts after the drop?

    • Primary succession, because the cleared forest lost its soil
    • A new forest, once people plant the trees
    • Secondary succession, because the soil stayed behind
    • No change, because a climax community cannot change

15. Share of trees in a climax forest (model data)

    survey	oak (percent)	hickory (percent)	pine (percent)
    year 0	40	35	25
    year 30	38	36	26

16. 9.

    Zee compares two surveys of a climax forest. What do they show?

    • Pine is rising, so the forest is leaving its climax stage and starting again
    • The forest has no equilibrium, because the three shares are not equal
    • The same three trees lead, with small shifts, so the balance is dynamic
    • The shares should not move in a climax forest, so the surveys must be wrong

17. A lava field at year 30 (model data)

    question	answer
    first living things	lichens and mosses
    soil	a thin layer
    grasses	now growing

18. 10.

    Ari reads the card. Why can grasses now replace the pioneers on this lava field?

    • Grasses need people to plant them once the pioneers have gone from the rock
    • Grasses can grow straight on the bare rock, so the soil changed nothing for them
    • The pioneers stay the main plants, and the grasses grow on top of them
    • The pioneers built soil where less hardy, more competitive grasses can grow