14 5 Forests are important habitats. (a) The effect of cutting down trees on the number of bird species observed in two different forest habitats was investigated. (i) Give two biotic factors, other than cutting down trees, that could affect the number of bird species observed in a forest. 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(ii) Some of the results of the investigation are shown in the table. Forest Number of bird species in areas of the forest where no trees are cut down Number of bird species in areas of the forest where some trees are cut down A 35 19 B 16 10 Calculate the Chi-squared value (χ2) for forest B using the formula shown. 2 2 ( ) O E χ E − = ∑ (3) Answer .............................................................. Turn over 15 (iii) The table gives some critical values for the Chi-squared test. Probability level Critical value 0.05 3.84 0.01 6.64 0.001 10.83 The Chi-squared value for forest A is 4.74. Deduce the effect of some trees being cut down on the number of species of birds in these two forests. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 16 (b) Many forests are exploited by humans. (i) Describe how forests can be managed as a sustainable resource. 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(ii) Explain the impact of cutting down trees on climate change. (4) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 5 = 13 marks)