Forest management intensity affects aquatic communities in artificial tree holes

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.Fil: Petermann, Jana S.. University of Salzburg; Austria. Berlin-Brandenburg Institute of Advanced Biodiversity Research; AlemaniaFil: Rohland, Anja. Friedrich Schiller University; AlemaniaFil: Sichardt, Nora. Friedrich Schiller University; AlemaniaFil: Lade, Peggy. Friedrich Schiller University; AlemaniaFil: Guidetti, Brenda Yamile. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Friedrich Schiller University; AlemaniaFil: Weisser, Wolfgang W.. Friedrich Schiller University; Alemania. Technische Universität München; AlemaniaFil: Gossner, Martin M.. Friedrich Schiller University; Alemania. Technische Universität München; Alemani

Data from: Effects of management on aquatic tree-hole communities in temperate forests are mediated by detritus amount and water chemistry

1. Arthropod communities in water-filled tree-holes may be sensitive to impacts of forest management, for example via changes in environmental conditions such as resource input. 2. We hypothesized that increasing forest management intensity negatively affects arthropod abundance and richness and shifts community composition and trophic structure of tree-hole communities. We predicted that this shift is caused by reduced habitat and resource availability at the forest stand scale as well as reduced tree-hole size, detritus amount and changed water chemistry at the tree-hole scale. 3. We mapped 910 water-filled tree-holes in two regions in Germany and studied 199 tree-hole inhabiting arthropod communities. 4. We found that increasing forest management intensity indeed significantly reduced arthropod abundance and richness in water-filled tree-holes. The most important indirect effects of management intensity on tree-hole community structure were the reduced amounts of detritus for the tree-hole inhabiting organisms and changed water chemistry at the tree-hole scale, both of which seem to act as a habitat filter. Although habitat availability at the forest stand scale decreased with increasing management intensity, this unexpectedly increased local arthropod abundance in individual tree-holes. However, regional species richness in tree-holes significantly decreased with increasing management intensity, most likely due to decreased habitat diversity. We did not find that the management-driven increase in plant diversity at the forest stand scale affected communities of individual tree-holes, for example via resource availability for adults. 5. Our results suggest that management of temperate forests has to target a number of factors at different scales to conserve diverse arthropod communities in water-filled tree holes

PLoS ONE / Forest management intensity affects aquatic communities in artificial tree holes

Jana S. Petermann, Anja Rohland, Nora Sichardt, Peggy Lade, Brenda Guidetti, Wolfgang W. Weisser, Martin M. Gossner(VLID)191345

Petermann16_artificial tree holes

Petermann16_artificial tree hole

Insect communities in water-filled tree holes

collected in the fiel

Mixed model results for abundance and richness.

<p>Mixed model results for abundance and richness.</p

Effect of forest management intensity on difference in detritus volume.

<p>Difference in volume of detritus in the artificial tree holes was calculated between the start of the experiment and harvesting time (June or September). Values above zero represent a net gain, below zero a net loss of detritus from the tree hole. Data are from the Hainich region (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0155549#pone.0155549.s010" target="_blank">S4 Table</a>) from June (closed symbols and solid lines) or from September (open symbols and dashed line). Symbols represent means per plot, error bars show ±SE. Forest management intensity was calculated according to Kahl and Bauhus [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0155549#pone.0155549.ref030" target="_blank">30</a>]. For results of statistical analyses see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0155549#pone.0155549.s010" target="_blank">S4 Table</a>.</p

Comparison of macroinvertebrate communities of artificial and natural tree holes in the two regions in June.

<p>A) abundance (square-root transformed), B) species richness and C), D) composition. Artificial holes are depicted by black bars and symbols, natural holes by grey bars and symbols. Average water volume differed between artificial and natural tree holes (artificial tree holes had larger average volume). However, the differences in abundance and richness between artificial and natural tree holes were still significant after fitting water volume as a covariate (for results of statistical analyses see text). Raw abundance and species richness (i.e. not adjusted for differences in volume) are shown here. The low overlap between artificial and natural communities in the composition plots (C, D) shows that community composition differed between artificial and natural tree holes in both regions. Only taxa with more than five occurrences per region across both tree-hole types were used for the nonmetric multidimensional scaling (NMDS) plots in C and D. Stress = 0.17, n = 214 for Alb, stress = 0.21, n = 124, for Hainich. Please note that experimental set-up and the volume of artificial tree holes also varied between the two regions, so they cannot be compared directly.</p

Experimental design.

<p>In the two regions (Alb and Hainich), we set up six artificial tree holes in each of 29 and 24 plots, respectively. In the Alb, three of the holes in each plot had openings at the side, three at the top. In the Hainich, all tree holes had top openings. Tree holes were installed in April. In the Alb, all tree holes were collected in June, in the Hainich, three were harvested in June, three remained until September. Tree holes in the Alb had a maximum volume of 10l, in the Hainich a substantially lower maximum volume of 600ml. For further information on tree-hole characteristics and measurements in the two regions, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0155549#pone.0155549.s007" target="_blank">S1 Table</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0155549#pone.0155549.s002" target="_blank">S2 Fig</a>. Table numbers in the figure refer to tables with the respective statistical analyses for the data sets: <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0155549#pone.0155549.t001" target="_blank">Table 1A and 1B</a> for data sets involving June data in the Alb and June and September data in the Hainich, respectively, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0155549#pone.0155549.s008" target="_blank">S2 Table</a> for June data (and additional environmental variables) in the Hainich. Grey areas depict forests, white areas non-forest habitats. Maps reprinted with permission from Landesamt für Geoinformation und Landentwicklung Baden-Württemberg (17.03.2016, Az.: 2851.2-D/7537 <a href="http://www.lgl-bw.de" target="_blank">www.lgl-bw.de</a>) for the Alb and from GeoBasisDE / TLVermGeo (2016) for the Hainich.</p

Insect community composition.

<p>Nonmetric multidimensional scaling (NMDS) plot showing the composition of insect communities in artificial tree holes in the two regions in June: A) Alb, B) Hainich. Red symbols in A represent artificial holes with a side opening, symbols in black are artificial tree holes with a top opening. The size of the symbols represents the density of natural tree holes in the respective plots. Forest management intensity affected community composition in the Alb and in the Hainich as shown by the arrow drawn by fitting forest management intensity <i>post hoc</i> and indicating tree holes in plots with high and low forest management. Opening type and tree-hole density had an effect on community composition in the Alb only (shown by the clustering of similar symbols). For results of statistical analyses, see text. Only taxa with more than five occurrences per region across both tree-hole types were used for the plots. Stress = 0.16, n = 137 for Alb, stress = 0.19, n = 134, for Hainich.</p