Forest Management Intensity Affects Aquatic Communities in Artificial Tree Holes

Abstract

Forest management could potentially affect organisms in all forest habitats. However, aquatic communities in water-filled tree-holes may be especially sensitive because of small population sizes, the risk of drought and potential dispersal limitation. We set up artificial tree holes in forest stands subject to different management intensities in two regions in Germany and assessed the influence of local environmental properties (tree-hole opening type, tree diameter, water volume and water temperature) as well as regional drivers (forest management intensity, tree-hole density) on tree-hole insect communities (not considering other organisms such as nematodes or rotifers), detritus content, oxygen and nutrient concentrations. In addition, we compared data from artificial tree holes with data from natural tree holes in the same area to evaluate the methodological approach of using tree-hole analogues. We found that forest management had strong effects on communities in artificial tree holes in both regions and across the season. Abundance and species richness declined, community composition shifted and detritus content declined with increasing forest management intensity. Environmental variables, such as tree-hole density and tree diameter partly explained these changes. However, dispersal limitation, indicated by effects of tree-hole density, generally showed rather weak impacts on communities. Artificial tree holes had higher water temperatures (on average 2°C higher) and oxygen concentrations (on average 25% higher) than natural tree holes. The abundance of organisms was higher but species richness was lower in artificial tree holes. Community composition differed between artificial and natural tree holes. Negative management effects were detectable in both tree-hole systems, despite their abiotic and biotic differences. Our results indicate that forest management has substantial and pervasive effects on tree-hole communities and may alter their structure and functioning. We furthermore conclude that artificial tree-hole analogues represent a useful experimental alternative to test effects of changes in forest management on natural communities.

Using sentinel prey to assess predation pressure from terrestrial predators in water-filled tree holes

“…We recorded a higher species richness of insect larvae in water-fi lled tree holes and a higher percentage predation by arthropods in the core zone than in the buffer zone. This indicates that insect larvae in water-fi lled tree holes are negatively affected by management as is reported in previous studies (Gossner et al, 2016;Petermann et al, 2016;Petermann et al, 2020). Arthropod predators might be less abundant in the buffer zone due to lower resource availability.…”

Management of ecosystems alters vector dynamics and haemosporidian infections

“…Thus, the negative effect of increased leaf litter depth on culicid abundance is likely related to the effect that a higher productivity does not per se lead to a higher abundance, but rather to a higher species richness 77 . In relation to management intensity and those species that reproduce exclusively in tree holes – both abundance and species richness are negatively affected by increased intensity 78,79 . There was also a negative effect of leaf litter depth on infection rate.…”

Direct and indirect effects of forest management on tree-hole inhabiting aquatic organisms and their functional traits

“…Humans have strongly modified forest ecosystems worldwide and this has caused a dramatic loss in biodiversity across spatial scales (Sala et al, 2000;Newbold et al, 2015). A recent metaanalysis (Paillet et al, 2010) and several subsequent individual studies (Wells et al, 2011;Gossner et al, 2014;Petermann et al, 2016;Elek et al, 2018) have shown that an intensified management of forests may negatively affect various groups of animals and plants. However, different aspects of forest management may vary in intensity and direction of their effects.…”