Response of saproxylic insect communities to logging history, tree species, stage of decay, and wood posture in the central Nearctic boreal forest

Saproxylic insect assemblages are essential functional components of forest ecosystems that can be affected by forest management.We used a split-plot ANOVA design to analyze differences in selected saproxylic insects（all arthropod orders and dipteran and parasitic hymenopteran families） emerging from dead wood of sites with different logging histories（horse-logged,mechanically-logged and unlogged）,tree species（Populus and Picea）,stage of decay（early-and late-decay stages） and posture（standing and downed logs） in the boreal forest of central Canada.No clear effects of logging history were seen for the studied taxa; however,interaction between logging history and other dead wood features was apparent.Cecidomyiidae consistently emerged more from Populus than from Picea dead wood.Most of the studied saproxylic families were more abundant in late-decay than in early-decay wood.Dipterans of the Cecidomyiidae,Ceratopogonidae,Empididae,Mycetophilidae and Sciaridae families,and hymenopterans of the Diapriidae and Ichneumonidae families were significantly more abundant in downed than in standing dead wood.In contrast,Mymaridae was most abundant in standing dead wood.Our study provides evidence that some insects at high taxonomic levels respond differently to dead wood quality,and this could inform future management strategies in the boreal forest for the conservation of saproxylic fauna and their ecological functions.

The saproxylic beetle assemblage associated with different host trees in Southwest China

Dead wood is a habitat for many insects and other small animals, some of which may be rare or endangered and in need of effective protection. In this paper, saproxylic beetle assemblages associated with different host trees in the subtropical forests in southwestern China were investigated. A total of 277 species （1 439 specimens） in 36 beetle families were collected from 117 dead wood samples, of which 101 samples were identified and respectively belonged to 12 tree genera. The number of saproxylic beetle species varied greatly among logs of different tree genera, with the highest diversity on logs of Juglans. Generally, broad-leaved trees had a higher richness and abundance of saproxylic species than coniferous trees. Cluster analysis revealed that assemblages from broad-leaved tree genera were generally similar （except for Betula） and assemblages from coniferous trees formed another distinct cluster. The subsequent indicator analysis proposed that there are different characteristic species for different cluster groups of host tree genera. In our study, log diameter has no positive influence on beetle species density. Conversely, comparisons of individual-based rarefaction curves suggested that beetle species richness was highest in the small diameter class both in coniferous and broad-leaved tree genera. With increased wood decay, proportion of habitat specialists （saproxylic beetles living on one tree genus） decreased, whereas proportion of habitat generalists （living on more than three tree genera） increased. The beetle species density was found to be higher in early stages, and decreased in later stages as well. A negative influence of altitude on saproxylic beetle species richness and abundance was detected. It was indicated that different tree genera and altitudes possibly display cross effects in modulating the altitudinal distribution and host preference of the beetles.

Diversity of beetle species and functional traits along gradients of deadwood suggests weak environmental filtering

Background: Gradients in local environmental characteristics may favour the abundance of species with particular traits, while other species decline, or favour species with different traits at the same time, without an increase in average species abundances. Therefore, we asked: do variations in species and traits differ along gradients of deadwood variables? Do species abundance and trait occurrence change with species richness within or between functional groups? Thus, we analysed the beetle assemblages of five forest sites located in Italy, along the Apennines mountains.Methods: From 2012 to 2018 we sampled beetles and five deadwood types in 193 plots to characterise the deadwood gradient: standing dead trees, snags, dead downed trees, coarse woody debris, and stumps. We modelled beetle species relative abundances and trophic traits occurrences against the deadwood variables using joint species distribution models.Results: Out of 462 species, only 77 showed significant responses to at least one deadwood type, with a weak mean response across species. Trophic groups showed mostly negative responses to deadwood variables. Species abundance increased with species richness among sites only for phytophagous and saproxylophagous. Trait occurrence did not increase with species richness among sites, except for phytophagous and saproxylophagous.However, trait occurrence changed significantly with species richness of several trophic groups within some sites.We found that increases in species richness do not result in decreases in species abundance of a given trophic group, but rather null or positive relationships were found suggesting low interspecific competition.Conclusions: Our findings suggest that in Mediterranean mountain forests there is still room for increasing the level of naturalness, at least for what concerns deadwood management. On one side, our findings suggest that competition for deadwood substrates is still low, on the other side they indicate that increasing deadwood volume and types to improve overall beetle richness may increase also beetle abundances.

Diversity of click beetles in managed nonnative coniferous and native beech stands: Consequences of changes in the structural and species composition of tree stands in Central Europe

The natural composition of forests has undergone significant changes over recent centuries.A closer-to-natural tree species composition has long been perceived as key to a high biodiversity.We investigated the impact on communities of click beetles(Elateridae)caused by changes in the tree species composition of spruce monocultures compared to reference sites of recently unmanaged natural beech forests.To collect data,passive interception traps were distributed within managed spruce stands of different age classes and natural beech forests of various developmental stages.The beetle species richness was slightly but not significantly higher in the beech forests.The saproxylic species group was significantly more common in the spruce stands,whereas the group of nonsaproxylic species was significantly more abundant in the beech stands.In the commercial stands,the significantly highest species richness was in the clearings(0–10-year-old stands),and at this forest age class,the vast majority of the beetle species occurred in the spruce stands.In the developmental stages of the natural forest,a slightly higher beetle richness was found at the disintegration stage.The study results suggested that different tree species compositions and stand structures affect the communities of click beetles and substantially change their species composition and thus their response to external influences.Therefore,management of stands using diverse silvicultural systems is recommended for creating diverse ecological niches in forests.

Experimental evidence on biodiversity impacts of variable retention forestry,prescribed burning,and deadwood manipulation in Fennoscandia

Intensive forest management has been applied in most Fennoscandian forests for a period of almost one felling rotation.This paradigm has produced even-aged and even-structured forests of different successional stages that cover about 90%of forest land.At the same time,wildfires have been nearly eliminated in most of the Fennoscandian nature.Consequently,hundreds of species are red-listed because of forest management.To support these species,forest management requires improvements.Variable retention forestry and habitat restoration have been suggested to mitigate negative effects of forest management on biodiversity,and these have been practiced to some extent during the past few decades.Here,we review experimental results on the effects of variable retention and two restoration measures(prescribed burning and artificial addition of coarse woody debris)on different species groups in Fennoscandia.Our key findings are as follows:(i)Many species respond positively to felling within a few years,apparently due to released and often ephemeral resources,such as fresh residue and stumps.Species associated with shady conditions are negatively impacted,but any retention supports many of these,and their species composition remains almost unaffected with 50-70%retention of the initial tree volume.(ii)These effects remain detectable for at least 10-30 years or,according to some studies,nearly 100 years,e.g.,in polypore fungi.(iii)Initial effects of prescribed burning on most species groups(apart from pyrophiles)are negative,but within 10-15 years post-fire sites begin to support many rare and threatened deadwood-dependent species.Epiphytic lichens,however,remain negatively affected.(iv)Artificial addition of deadwood(mostly high stumps)supports a wide spectrum of deadwood-dependent species,but the species composition differs from that of naturally died trees.(v)Moisture and micro-habitat variation are crucial for forest species at harvested sites,at least in forests dominated by Norway spruce.We conclude that felling method as such is of little importance for threatened forest species,although retention mitigates many negative effects.These species require microclimatic continuity,and maintenance and active increase of legacies,such as deadwood of different qualities(species,downed/standing,snag/log/stump,decay stage),very old trees,and tree species mixtures.

Wildfire yields a distinct turnover of the beetle community in a semi-natural pine forest in northern Sweden

Background:Fires have been an important natural disturbance and pervasive evolutionary force in the boreal biome.Yet,fire suppression has made forest fires rare in the managed landscapes in Fennoscandia,causing significant habitat loss for saproxylic species such as polypores and insects.To better understand how the beetle community changes(species turnover)after a wildfire in a landscape with intense fire suppression,we monitored beetles with flight intercept traps the first 3 years as well as 12 years after a large wildfire in a national park in northern Sweden(a control/unburnt area was set up for the last year of sampling).Results:Species composition changed significantly among all studied years with a continuous turnover of species following the wildfire.The indicator species analysis showed that year 1 post-fire was mostly associated with cambium consumers and also the pyrophilous species Batrisodes hubenthali.Year 2 was the most abundant and species-rich year,with Tomicus piniperda as the most important indicator species.The indicator species year 3 were mostly secondary successional species,fungivores,and predators and were characterized by lower species diversity.Year 12 had higher diversity compared with year 3 but lower species richness and abundance.A control area was established during year 12 post-fire,and our analyses showed that the control area and burned area differed in species composition suggesting that the beetle community needs longer than 12 years to recover even after a lowintensive ground fire.Conclusion:The wildfire area hosted several red-listed and fire-dependent species suggesting that after a century of landscape-level fire suppression in a semi-natural area,the reintroduction of fire benefits rare and pyrophilous species and still impacts species composition after 12 years.This study implies that fire has long-lasting effects on high latitudes and that prescribed burning has the potential to benefit biodiversity over decades in these landscapes while also highlighting the value of considering the whole species community and not only monitoring abundance and richness to assess biodiversity after management actions.