Richness
Neither short- nor long-term exclusion had an effect on the number of arthropod MOTUs detected using COI. The GLMM including all study farms and oaks (N = 72) showed no differences between treatments (𝜒2 = 4.675; p = 0.097) (Figure 3, top left panel A), although the number of MOTUs found in the one-year exclosures was slightly higher than under the other trees. Analysing only the 3 farms with control and experimental one-year exclosures (N = 48), there were differences by Treatment (𝜒2 = 5.218; p = 0.022), but not by Farm (𝜒2 = 3.959; p = 0.138). Post hoc analysis, however, showed no significant differences between control and short-term exclosure trees within the same farm (Figure 3, top left panel B).
Contrary to COI, 16S detected significant differences in arthropod richness at the MOTU level. The GLMM including all trees (N = 72) showed that there were differences between treatments (𝜒2 = 15.302; p < 0.001), and post hoc analysis showed that the number of MOTUs was significantly higher under one-year-exclusion trees than under control trees (estimate = -0.364; T = -3.868; p < 0.001). However, there was no difference in richness between the arthropod communities found at long-term exclosures and control trees (Figure 3, top right panel A), nor between short- and long-term exclosures. When looking at just the 3 farms with control and experimental one-year exclosures (N = 48), there were differences both between treatments (𝜒2 = 16.116; p < 0.001) and between farms (𝜒2 = 26.603; p < 0.001). Post hoc analysis showed that the number of 16S MOTUs was greater in one-year exclusion trees than in controls in all three farms (Figure 3, top right panel B).
At Family level, we found significant differences between treatments considering all study trees (𝜒2 = 7.425; p = 0.024; N = 72). Post hoc analysis showed that arthropod Family richness was higher beneath one-year-exclusion trees than beneath the controls (estimate = -2.700; T = -2.542; p = 0.035), but not at ten-years-exclusion farms (estimate = -2.596; T = -1.853; p = 0.161) (Figure 4A). Considering only the one-year exclosures and the control trees, both Treatment (𝜒2 = 7.844; p = 0.005) and Farm (𝜒2 = 13.380; p = 0.001) had significant effects on Family richness. However, post hoc analysis showed only marginal significance differences within farms (Figure 4B).
At the Order level, we found no differences between treatments when taking all trees into consideration (𝜒2 = 1.363; p = 0.506). At the farms with only control and one-year-exclusion trees, significant differences were found among farms (𝜒2 = 11.132; p = 0.003), but not among Treatments (𝜒2 = 1.105; p = 0.305).