aqa biology biodiversity question help!

https://pmt.physicsandmathstutor.com/download/Biology/A-level/Topic-Qs/AQA/4-Genetics-Biodiversity-Classification/Set-C/4.6%20Biodiversity%20within%20a%20community%20QP.pdf
page 19, part a.
mark scheme:
1. Only cleared and abandoned and introduction of non-native species make (significant) difference;
2. Because only (means of) these ± 2 SDs from zero / no change;
3. About same number / 4 to 3 increase or decrease (species) richness/ biodiversity
can someone explain what these points mean

if you look at the graph, each change caused by humans is plotted with a central spot, and a bar either side of the spot to represent the standard deviation. if you look at the spots for "land cleared.." and for "introduction of non-native species", they have a much greater effect since the mean is at least 2 standard deviations far from 0 (which represents no change). This shows that the "land cleared..." causes an increase in species richness whereas the "introduction of non-native species" causes a decrease in species richness. Does this make sense?

thank u for responding! okay i got that land cleared increases species richness and intro of non-native species causes decrease in species richness.
u said that the mean is 2 SDs far from 0, however in the graph looking at the x-axis, the points only go up to 1, so how can any data be 2 SD away from 0? that's what i don't get