3.2. FRBandsamplingdepthลึก FRB สุ่มตัวอย่างมีขนาดเล็กมากในป่า boreal กว่าในร้อน หรือแจ่ม (p < 0.001) (ตาราง 4), และมีความสัมพันธ์ในเชิงบวกอย่างมีนัยสำคัญระหว่าง FRB รวมและความลึกในป่าเขตร้อน และซึ่งการสุ่มตัวอย่าง (r2 = 0.48, p < 0.001, N = 73 และ r2 = 0.52, p < 0.001, N = 173, respec tively) ประเมิน FRB extrapolated สำหรับทั้ง rooting ลึกโดยใช้สมการ (1) ได้ 526±321gm−2, 775±474gm−2 และ m−2 518 g ± 776 ในป่า boreal แจ่ม และเฉพาะ ตามลำดับ (ตาราง 5) ค่าเหล่านี้ได้ 26 – 67% สูงกว่าผู้ตามเดิมสุ่มตัวอย่างความลึก ความแตกต่างการ statis-tically อย่างมีนัยสำคัญ (p < 0.001 ตาราง 5)3.3. ContributionofunderstoreyvegetationrootstototalFRBThe proportion of the total FRB extrapolated for the whole sam- pling depth attributable to the understorey vegetation roots was assessed with data covering 74 temperate and 59 boreal forest stands. Tropical forests could not be included because there were no data available for the analyses. The proportion tended to be higher in the boreal forests (0.31±0.26) than in the temperate forests (0.20±0.29), and higher in the needleleaf forests (0.29±0.28, N = 101) than in the broadleaf forests (0.13 ± 0.25, N = 32), but the differences were not statistically significant (p > 0.05). There were relatively more forest stands without any understorey vegetation in the temperate (40 out of 74) and broadleaf forests (22 out of 32) than in the boreal (4 out of 59) or needleleaf forests (25 out of 101). No significant relationships (p > 0.05) were found between FRB of trees as a proportion of total FRB and tree stand basal area (m2 ha−1), tree stand density (treesha−1) or stand age (data not shown).3.4. Tree,understoreyandtotalFRBinthebiomesThe mean FRB of trees calculated using the original sampling depth did not differ between the temperate and boreal forests (p > 0.05), whereas it was significantly higher in the broadleaf than in the needleleaf forests (p=0.05) (Tables 5 and 6). These differ- ences disappeared when the mean FRB of trees by biome was calculated for the whole rooting depth (p > 0.05) (Tables 5 and 6).There were no significant differences in the mean understorey FRB between the temperate and boreal forests or between the broadleaf and needleleaf forests (Tables 5 and 6).The mean total FRB (trees + understorey) did not differ signifi- cantly between the biomes in the non-extrapolated original data (p > 0.05), but the extrapolated values for the whole rooting depth differed significantly between biomes (p<0.05) (Tables 5 and 6), being higher in the tropical and temperate forests than in the boreal forests (Tukey HSD test, p < 0.01). There were no significant differences (p > 0.05) in the mean total FRB biomass between the broadleaf forests and needleleaf forests or between the evergreen and deciduous tropical forests (Tables 5 and 6).3.5. RelationshipsbetweenFRBandstandandenvironmental characteristicsWe started by exploring the relationships between the eight tree stand and environmental variables by means of PCA ordination. Of the environmental variables, latitude, temperature and annual precipitation had the highest scores on the first ordination axis and only elevation on the second axis (Fig. 2), while among the tree stand variables stand density and basal area had the highest scores on the second axis and the needleleaf and broadleaf forests were located at opposite ends of the first axis.
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