Chestnut (
Biodiversity conservation is a fundamental objective of sustainable forest management (
Forest management influences the abundance and diversity of beetle (Coleoptera) communities, which have important ecological functions, being prey or predators themselves, but also pollinators, herbivores and decomposers (
The EU Habitats Directive and Natura 2000 network recognize the importance of the chestnut stands (habitat 9260, Annex I), managed both as high forests and plantations, for biodiversity conservation (
The prevalence of coppice stands over high stands is significant and related to the rapid growth rates and short rotation periods of chestnut, but also to the high vitality of stumps and resilience to stress factors, such as fires and diseases. Several authors have investigated the changes in biodiversity of different taxonomic groups in coppice stands (
Here we assess how different management types influence the α-diversity of beetles in chestnut forest stands in the Aspromonte National Park (Apennines, southern Italy). Specifically, we used the Coleoptera community and saproxylic beetles as ecological indicators. Three management options were considered: (i) young and (ii) mature coppice stands, and (iii) traditional fruit orchard. In addition, considering the ecological, environmental and cultural importance of the traditional fruit orchards in the Italian and European landscape (
The study was carried out in three different agroforestry systems dominated by chestnut: (i) young (YC, 2 years old) and (ii) mature (MC, 11 years old) coppice stands located in Santo Stefano in Aspromonte (38° 10′ 48.798″ N. 15° 47′ 03.51″ E); and (iii) traditional fruit orchard (TO, older than 80 years) located in Cardeto d’Aspromonte (38° 03′ 36.66″ N. 15° 46′ 53.82″ E).
The stands occur on similar ecological and environmental conditions, on the borders of the Aspromonte National Park (Calabrian Apennines -
The climate is temperate, typical of Mediterranean mountainous environments. Mean annual temperature is about 8 °C, while average minimum and maximum monthly temperatures are 0.5 °C (the coldest month) and 16 °C (the warmest month), respectively. Average total annual precipitation is 1200 mm, mainly occurring over the winter season (Meteorological station of Gambarie d’Aspromonte, 1187 m a.s.l.). Summer aridity is almost absent as frequent orographic precipitation occurs, due to the exposure to the moist air deriving from the Tyrrhenian sea.
Each analyzed management type extends on about 12 ha. A total of 60 sampling plots (20 per each management type) were established and located at a regular distance of 50 m to each other, following a systematic aligned grid (
Within each management type (YC, MC and TO), three randomly selected circular plots were established for dendrometric measurements. The following parameters were recorded: diameter at breast height (DBH), canopy cover (through visual estimation), and total tree height. Veteran trees (orchard) have been identified by applying the criteria of the above-mentioned Ministerial Decree 23/10/2014. Tree volumes were calculated
The collection of Coleoptera was carried out using window flight traps (WFTs). At the center of each sampling plot, one WFT was positioned at a height of 2 m above the ground (
Systematics and nomenclature followed
Collected saproxylic and non saproxylic species were grouped according to the prevalent trophic categories, defined as follows: (i) xylophagus (organisms feeding exclusively or largely from wood); (ii) saproxylophagus (organisms feeding exclusively or largely from fungus-infected wood); (iii) mycophagous (organisms feeding exclusively or largely on fungi); (iv) mycetobiontic (organisms feeding on carpophores of large
Regarding the IUCN risk categories, the sampled saproxylic beetles follows the Italian Red List (
At a plot level, we quantified the abundance (
In this study, univariate indices were calculated combining the number of species and their abundance. Particularly, we calculated the following four diversity indices: (i) the Shannon Index, taking into account the number of individuals, as well as the number of taxa (
with
(iii) the Equitability index (also known as Pielou’s evenness), which measures the evenness of individual distribution among taxa and is calculated as the ratio between the Shannon diversity index and the logarithm of the number of taxa; (iv) the Dominance index (= 1-Simpson index), that ranges from 0 (all taxa are equally present) to 1 (one taxon completely dominates the community -
with
The MHs were surveyed only in the traditional fruit orchard, and not considered for the two coppice stands, since they were characterized by high tree density with small stem diameters. These young structural features and the associated development stage do not allow the formation of MHs, which are usually linked to the presence of mature and veteran trees (
A set of 47 MHs, according to
For each univariate index, the confidence intervals were calculated through a bootstrap procedure (
In order to assess the significance, the PERMANOVA statistical test (Permutational Analysis of Variance) was applied, which considers the values of similarities without any assumption about the data distribution (
The number of trees per hectare was 23.360 for YC and 5814 for MC. In TO, 125 trees per hectare were recorded (
We collected 6282 specimens, belonging to 259 species. A total of 53 beetle families were detected. Among the sampled beetles, 34.3% were saproxylics, namely 3783 specimens belonging to 89 species and 53 families of Coleoptera (Tab. S1 in Supplementary material).
In TO 2986 individuals were collected, whereas 2255 in YC and 1041 in MC. Considering the number of sampled species, 164 different species were found in YC, 111 in MC and 145 in TO. Furthermore, 43 of these species occurred in all the three agroforestry systems.
The most abundant species were
In
In general, the diversity indices analyzed were always higher for all beetle communities than for the saproxylic community only, with the exception of the dominance index. This difference was strongly evident for the Margalef and Shannon index, since the number of individuals characterizing all beetle communities was higher than for the saproxylics (34.3%). This difference was less evident in the equitability index, for which an evenness distribution of individuals was observed, both considering saproxylic and non-saproxylic species in three agroforestry systems. Finally, the dominance index had higher values in saproxylics than in all beetle communities, as in this component the Nitidulidae completely dominated the community.
Both for all beetle communities and for the saproxylics only, the diversity indices were always significantly lower in TO than in YC and MC, with the exception of the dominance index, which was significantly higher in TO than in YC and MC (
For the Margaleff index, no significant differences were found between YC and TO, both considering all beetle communities and the saproxylics only, probably due to the high abundance of some species (
A total of 495 MHs was counted, with an average of 41.2 ± 6.4 ha-1. In
Several MHs were absent (
Those MHs appearing on cavities and tree injures were the most numerous (8 and 7 MHs per tree, respectively). The analysis of variance showed significant differences in the number of MHs per tree among the different MH forms (F[6, 133]= 52.47, p<0.001). In particular, we observed three groups of MHs (group 1: Cavities, Tree injures; group 2: Crown deadwood, Epiphytic and Epixylic, Excrescens; group 3: Fresh exudates); no significant differences within groups were detected, while they occurred between the three groups. However, considering the second group, the number of “Excrescens” was not significantly different from that of “Fresh exudates”. Fig. S1 in Supplementary material reports those pairs of MH forms significantly differing between each other after Tukey’s test.
Cleridae, Scraptiidae, Tenebrionidae and Throscidae were positively and significantly correlated with the “Cavities”, representing 70% of the insect families. Only a few insect families (
About the 59% of the families (
The Anthicidae and Bruchidae were positively correlated with all MH forms, except for the “Excrescens”, for which the correlations were negative. The Elateridae were negatively correlated with all MH forms, while the Oedemiridae were the only family positively correlated with all MH forms. Finally, several families revealed a random distribution (
The α-diversity of Coleoptera communities and saproxylic beetles was relatively high, in terms of species richness. The different management types had an impact on α-diversity, confirming our first hypothesis. In fact, a lower number of species was found in MC (111 beetle species) than in YC and TO (164 and 145, respectively). Tree density in MC was the highest among the tested management types, which, in combination with the associated structural traits (
In MC all the trophic categories were uniformly present in terms of species and abundance (
Among the various ecological parameters that influenced differences among sylvicultural systems (YC, MC, TO - 43 beetle species in total), in terms of diversity and abundance of species, available solar radiation represents a discrimination element between coppice stands and the fruit orchard (
Differences in solar radiation below the canopy occurred also between YC and MC, the latter being characterized by denser canopy cover, determining microclimatic conditions that allowed a more diversified beetle community.
In TO we found about 41 MHs per ha, occurring on large trees. It is important to note that, although few MH forms were present in TO, they had a high frequency on each tree. The presence of large trees and the density of tree-related MHs significantly influenced the abundance of the different families of Coleoptera, suggesting a high variability between species that feed on deadwood or other substrates (
Saproxylic beetles represented 34.3% of the whole beetle community and provided information on species diversity of the whole beetle community, confirming our third hypothesis. Among saproxylics, 22 out of 89 species are included in IUCN Red Lists (Tab. S1 in Supplementary material). In particular, for the vulnerable category,
Beetle community compositions differed among the three management methods, suggesting that a matrix of chestnut agroforestry systems should be used to improve conditions for biodiversity in this rural landscape (
Landscapes with high density of veteran trees and high diversity of associated fauna should be preserved for conservation purposes (
Beetle communities proved to be excellent bioindicators in chestnut agroforestry systems of the fragmented Mediterranean landscape in southern Italy. Forest management strategies should be oriented to diversify the territorial mosaic as much as possible, ensuring the presence of suitable habitats for keeping the populations of organisms in balance. The occurrence of MHs in managed chestnut agroforestry systems represents a valid ecological indicator for conservation purposes.
In this territorial matrix, mature orchards play a key role in the preservation of saproxylic and non-saproxylic beetle communities. Coppicing (YC, MC) and orchard management (TO) may add to natural disturbances, determining the rotation periods and creating landscape heterogeneity, thus influencing the biological cycle of beetle communities. In this sense, considering both spatial turnover and species richness of beetles allows a more comprehensive assessment of the processes contributing to species diversity than considering species richness only.
Our results highlighted that, in chestnut agroforestry systems, Coleoptera communities (particularly saproxylics) may help direct management practices aiming at biodiversity conservation. Restoring structural heterogeneity through flexible management strategies, considering the rural matrix, as well as structures and processes that would occur in the absence of human impact, may prevent excess loss of biodiversity in chestnut agroforestry systems. With this aim, further studies warrant to investigate chestnut coppices converted into high forests and abandoned coppices.
The authors thank the specialists of the various taxonomic groups: Paolo Audisio (Nitidulidae); Alessandro Bruno Biscaccianti (Alexiidae, Biphylidae, Cerylonidae, Dascillidae, Dermestidae, Erotylidae, Eucemidae, Laemophloeidae, Lathridiidae, Lucanidae, Mycetophagidae, Salpingidae, Scirtidae, Sphindidae, Tenebrionidae, Trogossitidae); Enzo Colonnelli (Anthribidae, Attelabidae, Brentidae, Curculionidae); Gianluca Magnani (Buprestidae); Massimo Faccoli (Curculionidae, Scolytinae); Fabrizio Fanti (Cantharidae, Lampyridae); Emanuele Piattella (Scarabaeidae); Giuseppe Platia (Elateridae); Roberto Poggi (Staphylinidae Pselaphinae); Pierpaolo Rapuzzi (Cerambycidae,
Location of the study area in Southern Apennines (Italy); black dots represent the location of the sampling plots, for each investigated area, where window flight traps were positioned. (A-A1): young coppice (YC); (B-B1): mature coppice (MC); (C-C1): traditional fruit orchard (TO); (D): window flight trap positioned in each sampling plot.
Number of species for each trophic category in the three agroforestry systems. (MB): mycetobiontic; (MY): mycophagous; (NI): commensal; (PR): predator; (SF): sap-feeder; (SX): saproxylophagous; (UN): unknown; (XY): xylophagous.
Median values and related variability of the diversity indices for young coppice (YC), mature coppice (MC) and traditional orchard (TO), both for all beetle communities and for the saproxylics only.
Number of MHs per tree for each MH form. The horizontal line indicates the median values; in the box, the lower limit corresponds to the value of the first quartile (Q1) of the distribution and the upper limit to the third quartile (Q3); the vertical lines (whiskers) delimit the intervals in which the lower values of Q1 (in the lower part) and the greater values of Q2 (in the upper part) are positioned. Outliers are reported as asterisks. Boxes with different letters indicate significant differences in the number of MHs between different MH forms (p<0.05).
Correlation coefficients (r) between the abundance of each family of saproxylic insects and the MHs forms.
A graphical representation of chestnut agroforestry systems and rural matrix considered fundamental for preserving saproxylic and non-saproxylic insects (drawings: G. Parisi; photo of
Type, definition and description of the MHs recorded in TO (from
Form | Group | MH form |
---|---|---|
Cavities l.s. | Woodpecker breeding cavities | Small woodpecker breeding cavity; Medium-sized woodpecker breeding cavity; Large woodpecker breeding cavity; Woodpecker “flute” (breeding cavity string) |
Rot holes | Trunk base rot hole; Trunk rot hole; Semi-open trunk rot hole; Chimney trunk base rot hole; Chimney trunk rot hole; Hollow branch | |
Insect galleries and bore holes;Concavities | Insect galleries and bore holes. Dendrotelm (phytotelmata, water-filled hole); Woodpecker foraging excavation; Trunk bark-lined concavity | |
Tree injuries and exposed wood | Exposed sapwood only | Bark loss; Fire scar; Bark shelter; Bark pocket |
Exposed sapwood and heartwood | Stem breakage; Limb breakage (heartwood exposed); Crack; Lightning scar; Fork split at the intersection | |
Crown deadwood | Crown deadwood | Dead branches; Dead top; Remaining broken limb |
Excrescences | Twig tangles | Epicormic shoots |
Burrs and cankers | Burr; Canker | |
Fruiting bodies of saproxylic fungi and slime moulds | Perennial fungal fruiting bodies (life span > 1y) Ephemeral fungal fruiting bodies and slime moulds | Perennial polypore; Annual polypore, Pulpy agaric, Pyrenomycete, Myxomycete |
Epiphytic, epixylic and parasitic structures | Epiphytic or parasitic crypto- and phanerogams | Bryophytes; Foliose and fruticose lichens; Ivy and lianas; Ferns; Mistletoe |
Nests | Vertebrate nest; Invertebrate nest | |
Microsoils | Bark microsoil; Crown microsoil | |
Fresh exudates | Fresh exudates | Sap run; Heavy resinosis |
Mean values (± standard deviation) of the main dendrometric parameters for the three management types. (Trees): number of trees; (DBH): diameter at breast height; (Ht): tree height; (G): basal area; (V): volume.
Silviculturalsystem | Trees(N ha-1) | DBH(cm) | Ht(m) | G(m2 ha-1) | V(m3 ha-1) |
---|---|---|---|---|---|
YC | 23360 ± 2700 | 3.36 ± 0.95 | 2.2 ± 0.75 | 20.7 ± 3.2 | 28.8 ± 3.4 |
MC | 5814 ± 904 | 9.0 ± 2.3 | 7.7 ± 1.3 | 36.6 ± 4.1 | 168.31 ± 21.5 |
TO | 125 ± 15 | 74.7 ± 10.1 | 15.8 ± 1.9 | 54.81 ± 3.9 | 409.22 ± 30.7 |
Statistical parameters obtained from the PERMANOVA. The average values of the diversity indices are reported for young coppice (YC), mature coppice (MC) and the traditional fruit orchard (TO). Different letters indicate significant differences among the three agroforestry systems.
Group | Index | F-value | P-level | YC | MC | TO |
---|---|---|---|---|---|---|
Saproxylics | Shannon | 154.48 | <0.001 | 1.912 a | 2.450 b | 1.138 c |
Margaleff | 20.75 | 0.002 | 6.522 a | 8.721 b | 6.075 a | |
Equitability | 47.33 | <0.001 | 0.508 a | 0.598 a | 0.294 b | |
Dominance | 235.62 | -0.001 | 0.242 a | 0.167 b | 0.469 c | |
Whole community | Shannon | 82.31 | <0.001 | 3.063 a | 3.285 a | 2.182 b |
Margaleff | 26.37 | 0.001 | 15.830 a | 20.200 b | 17.870 a | |
Equitability | 59.27 | <0.001 | 0.650 a | 0.650 a | 0.439 b | |
Dominance | 93.62 | <0.001 | 0.101 a | 0.075 a | 0.280 b |
Fig. S1 - Differences of means for the occurring forms of MHs after Tukey test.
Tab. S1 - List of species of Coleoptera and number of specimens collected from young coppice (YC), mature coppice (MC) and traditional fruit orchard (TO).