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).