Plant diversity enhances moth diversity in an intensive forest management experiment

Abstract

Intensive forest management (IFM) promises to help satisfy increasing global demand for wood but may come at the cost of local reductions to forest biodiversity. IFM often reduces early seral plant diversity as a result of efforts to eliminate plant competition with crop trees. If diversity is a function of bottom-up drivers, theory predicts that specialists at lower trophic levels (e.g., insect herbivores) should be particularly sensitive to reductions in plant diversity. We conducted a stand-level experiment to test bottom-up controls on moth community structure, as mediated by degrees of forest management intensity. Using a dataset of 12,003 moths representing 316 moth species, moth richness decreased only slightly, if at all, as herbicide intensity increased (P = 0.062); the moderate treatment, which is most commonly applied in the northwestern USA, was estimated to have 4.72 (±2.14 SE, P = 0.039) fewer species than the control. Structural equation modeling revealed strong support for an effect of herbicide on plant abundance, which influenced plant species richness and subsequently moth species richness. Moth species richness was associated with plant species richness and followed a power law function (z = 0.42, P = 0.006), which is surprisingly consistent with a recent large-scale experiment in agricultural systems, and provides support for bottom-up drivers of moth community structure. Moth abundance was not influenced by the direct effects of silvicultural herbicide treatments. Site-level effects and variation in pre-harvest vegetation communities resulted in residual broadleaf and herbaceous vegetation in even the most intensive treatment. Even at low densities, these residual deciduous and herbaceous plants supported higher than expected moth abundance and richness. We conclude that forest management practices that retain early seral vegetation diversity are the most likely to conserve moth communities.

Relationship between moth (night active Lepidoptera) diversity and vegetation characteristics in southern Sweden

“…Similar results have also been obtained in some previous studies (e.g. Axmacher et al 2009;Root et al 2017), but there are also reports of opposite patterns (Axmacher et al 2004). From a theoretical perspective, given that the larval stages of almost all moth species feed on one or a few particular vascular plant taxa, such a relationship should be expected, but the relationship may be compromised by the high mobility of the imagos and the ability of many moth species to feed on more than one host plant.…”

Conservation and production responses vary by disturbance intensity in a long‐term forest management experiment

“…Further, we consider a toxicity effect to be unlikely given results from other studies that indicate how quickly herbicides are absorbed by plant tissues (Newton et al 1984, Lautenschlager and Sullivan 2004). Results for other taxa (including invertebrates) and processes (decomposition and soil productivity) from the study support this conclusion (Root et al 2016, Frey 2018). Although effects on the plant community do not appear to have caused long‐term changes in the avian community, we emphasize that a diverse and well‐developed shrub layer is an important ecosystem service itself and that treatments may have eliminated some plant species from individual sites.…”

Herbicides and herbivory interact to drive plant community and crop‐tree establishment

“…, Root et al. ). We randomly selected experimental blocks from a broader suite of harvest units that were available in the initial year of the study (2009).…”