Tree plantations are areas where trees are planted for a particular purpose. Some tree plantations increase the supply of wood for construction and fuel. In many plantations, fast-growing, alien tree species are planted. Undergrowth is found in and around plantations, increasing plant biodiversity. Undergrowth is mainly made up of indigenous (native) small plants and shrubs. [Figure 1.1] shows part of a plantation of eucalyptus trees. Bangladesh has many tree plantations as part of a national tree-planting programme. Two fast-growing, alien tree species planted in Bangladesh are acacia, Acacia auriculiformis, and eucalyptus, Eucalyptus camaldulensis. Acacia and eucalyptus are considered to be invasive species as they outcompete indigenous tree species such as sal tree, Shorea robusta, and mango, Mangifera indica. Scientists carried out an investigation into the biodiversity of plant species in the undergrowth in plantations of alien trees compared with the undergrowth in plantations of indigenous trees. The hypothesis that the scientists tested was stated as: The undergrowth in plantations of alien tree species will have a lower biodiversity of plant species than the undergrowth in plantations of indigenous tree species.

Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

1. [1] species of tree or type of tree;
2. [2] any two from: 1 (same) number of/3, plantations for each tree species; 2 (same) size/area of, plot/(sampling)area / 36 m x 36 m / 1296m² ; 3 (same / used a) belt transect (same method in all plots/plantations) ; 4 (same) months / seasons (of the year) or sampling at the same times;
3. [5] any five from: using a belt transect: 1 use of tape / line / string, and quadrat (to create belt transect); 2 selecting a start point for the, transect / placement of tape / line / string or all transects same length, in plots / plantations / repeats ; 3 same (size) quadrat ; 4 sample at /use quadrat at, regular intervals / stated distances along the, tape / line / string / transect or continuous belt transect; collecting data: 5 method to identify each of the plant (species in the quadrat); 6 count / record / note the number of (individuals), each plant species (n) (in each quadrat / at each sampling point) or estimate percentage (%) cover of each plant species (in each quadrat) ; 7 use at least 3 different transects (in each plot) ; 8 named hazard and risk and precaution; e.g. (see table below) hazard: plants / fungi; risk: falling trees / branches; precaution: hard hat; hazard: thorns; risk: ; precaution: gloves/goggles / mask/ long trousers / PPE; hazard: irritant/allergy infection (spores); risk: ; precaution: antihistamines / cover skin / first aid equipment; hazard: (named) animal(s) parasite; risk: bites / infection / attack / stings / allergy; precaution: antivenom / antihistamine / trained, professionals / medics, available / insect repellent/gloves / goggles / mask /PPE / cover skin; hazard: plantation terrain; risk: trip hazard; precaution: correct footwear / watch where you are walking / use walking sticks; hazard: ; risk: getting lost; precaution: work in group / maps / use GPS/guide; hazard: poachers; risk: being attacked / shot; precaution: trained, professionals/ medics, available
4. [1] any one from: (does not support) 1. acacia and mango have the same means or acacia and mango have similar, D values / index or mango and invasive species have overlapping, D values / index / means +/- SD ; (does support / partially support) 2. sal tree has the highest, D value / index / mean or sal tree has greater, D values / Index / mean, than both alien species;
5. [2] concentration / mg cm⁻³ | volume of stock solution / cm³ | volume of (distilled) water / cm³; 7.5 | 37.5 | 12.5; 2.5 | 12.5 | 37.5;
6. [3] 1 correct processes and correct figures; 2 (correct) answer to 3 significant figures; ecf if mp1 is incorrect 3 decrease / minus (number) ;
7. [3] any three from: improvement | impact; 1 More, intermediate / smaller values / intervals appropriate examples accepted | better idea of the, trend / pattern / effect ; 2 exclude anomalous results | improve reliability; 3 repeat reading for 2.5/5.0/7.5 mg cm⁻³ (any of these 3 might be anomalous) | check the anomaly / improve reliability; 4 repeat investigation at least twice or repeat with more marigolds | better idea of trend / improve reliability / reduce effect of anomalies ; 5 (calculate) standard error / standard deviation / confidence intervals / statistical analysis | check for significance (difference between the means) / checking accuracy ; 6 use marigold clones | exclude genetic effects / improve validity; 7 use Vernier calliper | more precise measurements; 8 measure the mass of all the roots | improve reliability;
8. [2] any two from: 1 (same) mass of soil; 2 sample from same depth ; 3 sampled at the same time; 4 sample from same, distance from roots / position in the pot ;