Invertebrate Biodiversity Survey Results - Polyculture Study June/July 2017

June/July 2017 results

By Christopher Kirby-Lambert – 03/04/2018

For May 2017 Results see here

A sample of invertebrates from the gardens

1. Survey Timing and Conditions

Field survey was carried out on the 29th of June (Perennial polyculture trial garden) and the 2nd of July (Market Garden). Both plots were surveyed in the morning between approximately 09.00 and 11.00. Conditions were warm, sunny and calm on the 29th of June and warm sunny and breezy on the 2nd of July.

2. Survey Plots

2.1. Market Garden

The Market Garden is a well-established and relatively complex plot supporting a range of habitats. Roughly 2/3 of the plot area is given over to agriculture. Half of this is polyculture beds used to grow a variety of vegetable crops. The other half is a forest garden. The market garden has been divided into three sub-plots for the purposes of sampling:

Sub-plot 1 - Forest Garden: Young planted fruit trees over a mix of native grass and herb species similar to that found in the Permaculture beds. There were some more mature trees providing shade in places but much of the sub-plot was open. During the June/July survey visit this plot supported a range of flowering plants providing abundant nectar sources for pollinators.

Sub-plot 2 - Polyculture beds: Rows of cultivated ground for a variety of vegetables. The plots supported a range of vegetable species as well as non-food plants, many of which were flowering and provided ample nectar sources. There are numerous wooden growth supports present in the plots which were noticeably being utilised by dead-wood nesting bees and wasps. Between plot rows there are grassy pathways with fringes of native flora. A pond is present at the edge of the area and is surrounded by a patch of coarse grassland with a significant herb component and numerous flowering plants. Overall, the flora in the non-cultivated areas is closest to that observed in woodland glades and rides nearby.

Sub-plot 3 - Scrub:  An area of relatively dense scrub and small trees containing a mix of species but dominated by Prunus sp. and Malus sp.. There is also a large Poplar (Populus sp) shading much of the area. The understory, where scrub was not so dense as to shade it out, was composed of grasses and woodland herbs. There is a damp area due to run-off from the neighbouring road that has been planted with Yellow Flag (Iris pseudacorus) and reed (Phragmites australis), although this is still in its infancy. Deadwood is fairly limited in this sub-plot.

2.2. Perennial polyculture trial garden

Photo by Christopher Kirby-Lambert

A recently acquired plot of land composed of coarse, unimproved grassland with scattered Rose (Rosa sp.) bushes surrounded by a well established hedge dominated by Elm (Ulmus sp.) and Hawthorn (Cratageus sp.). A large mature Walnut is present in the corner of the plot. Previous management was by goat grazing. Since acquisition of the plot a reasonably sized pond has been dug, but not yet filled, and several polyculture beds have been created. This plot was divided into two sub-plots for the purposes of sampling:

Sub-plot 4 – Grassland: This is currently a homogenous area supporting coarse unimproved grassland with a relatively limited herb component. Scattered low rose (Rosa sp.) scrub was present across the sub-plot. The plot showed a much greater abundance of nectar sources during the June/July survey and several species of flowering plant occurred relatively densely throughout the sub-plot.

Sub-plot 5 – Hedgerow: The sub-plot was surrounded on three sides by a large, mature, hedge. The principal tree species present were Elm (Ulmus sp.) and Hawthorn (Cratageus sp.). There were also significant components of smaller shrubs, predominantly bramble (Rubus sp.), blackthorn (Prunus spinosa) and rose (Rosa sp.). Although deadwood was present it was generally sparse and of small diameter.

Sub-plot 6 – New polyculture plot: Newly dug polyculture beds which, at the time of the June/July survey were almost entirely unvegetated. The tracks between beds as well as their margins did however support a range of ruderal plant species, many of which were flowering. The edges of the sub-plot, where it bordered sub-plot 4 were also flower rich and floristically diverse.

3. Target Groups

1. Coleoptera (beetles): This encompasses a vast range of species with widely differing ecologies, however, the basic ecological niches of many groups are well established and they have been relatively well studied in Europe. In addition the group as a whole is well known to the surveyor and many species are likely to be identifiable to species. In practice the most frequently encountered beetle group in the survey plots by a wide margin were leaf beetles (Chrysomelidae). These species are invariably phytophagous (plant-eating), feeding on living plant tissue. They are often specific to certain plant species or families and so are generally ecologically informative. Weevils (Curculionoidea) were also collected in some numbers and have similar ecological niches. Other groups of beetles collected include saproxylic species that depend on deadwood resources for larval development and tend to feed on pollen from flowers and predatory species.
2. Hemiptera; Heteroptera (true bugs): Another group that has been relatively well studied in Europe and is relatively well known to the surveyor. The Heteroptera include a wide range of families with varying ecologies. Most of those encountered were predominantly phytophagous and ranged from generalists to specialists on particular plant species.
3. Hymenoptera; Aculeata: The aculeates include bees (Apoidea), ants (Formicidae) and a number of wasp families, all groups that are well known to the surveyor. Ants are ground or tree nesting and mostly predatory (although some European species will eat seeds). Bees feed on nectar (as adults) and pollen (as larvae) so are entirely dependent on flower resources for food. They nest variously in dead wood, bare ground and soil, and moss (many species are cuckoos, stealing the nests of the host species). Wasps are predatory and nest in a similar range of habitats as bees.
4. Diptera (true flies); larger Brachycera and Syrphidae: Select groups of flies were recorded. These groups were limited to those that are known to the surveyor and may be ecologically informative in the current survey.

4. Survey Methodology

The field survey methodology utilises a number of widely used collection techniques that, in combination, collect species from most groups present on a site. The use of these techniques is dictated by the habitats present on each plot and roughly follows Natural England’s Common Standards Monitoring (CSM) guidelines1. These guidelines are intended for use in monitoring the quality of Sites of Special Scientific Interest (SSSI’s) in the UK. See Table 1 for a breakdown of the survey methods used on each sub-plot. The total survey time devoted to each sub-plot was the same.

4.1. Field survey techniques

Sweep netting

A lightweight folding circular aluminium frame 40 centimetres in diameter was fitted with a net bag supplied for sweep-netting by GB Nets and attached to an extending lightweight aluminium handle. Net strokes were reasonably rapid, and penetrated as far into the vegetation as possible without the stroke being seriously slowed by its resistance. A maximum of fifty sweeps (counted as single strokes of the net) was taken before examining the catch. The sample was initially examined in the net, noting or capturing large, fast-moving or readily identified species. The remaining net contents were then emptied onto a white tray, and the material in the tray examined for smaller and slower animals. 10 minutes of survey time was devoted to sweep-netting per sub-plot.

Targeted netting

Large, active, species, especially those prone to visiting flowers, resting on leaves, or with regularly visited and recognisable nests, are often most effectively recorded by netting individual animals. This is particularly effective for solitary bees and wasps, but also for some groups of flies. When utilised 30 minutes survey time per sub-plot was devoted exclusively to it. On those occasions, the net used for sweep-netting was employed

Vegetation beating

Samples were taken from tree and shrub foliage, ivy, and dense, tall herbaceous vegetation by holding a net under the foliage and tapping the branches or stems above sharply several times with a stout stick. The sweep net currently in use was most often employed for this purpose. For high vegetation and larger branches, a net with a lightweight folding frame 55 centimetres in diameter and a long bag was also used. This net has the advantage that substantial amounts of foliage can be inserted, or a substantial length of tall vegetation placed next to the net, before sampling. Material was initially examined in the net, then emptied onto a white tray for further sorting. When utilised 30 minutes survey time per sub-plot was devoted exclusively to it.

Active search

Features of significance to invertebrates which are not sampled, or not necessarily adequately sampled, by sweeping, beating or suction sampling were investigated by close examination and hand searching. Attention was particularly paid to: accumulations of plant litter; dead wood; the ground beneath wood, stones and other debris; fungal fruiting bodies; tree trunks; the undersides of plant rosettes; and bare wet ground. When utilised 30 minutes survey time per sub-plot was devoted exclusively to it.

Table 1. Distribution of sampling effort across plots. X denotes that the technique was used in the sub-plot in question.
	Market Garden			Perennial Polyculture Trial Garden
	Sub-plot 1	Sub-plot 2	Sub-plot 3	Sub-plot 4	Sub-plot 5	Sub-plot 6
Sweep-netting (10 mins)	X	X	X	X	X	X
Targeted netting (30 mins)	X	X		X		X
Beating (30 mins)			X		X
Active search (30 mins)	X	X	X	X	X	X
Total survey time	70 mins	70 mins	70 mins	70 mins	70 mins	70 mins

4.2. Lab methodology

Voucher specimens of all encountered species in the aforementioned target groups were collected and retained. Specimens were collected using a pooter, or individual tubes in the case of larger individuals, before being asphyxiated using ethyl acetate. Collection of specimens was limited to the minimum required to ensure a reasonable chance of identification. Specimens were stored in plastic boxes layered between tissue paper and frozen to preserve them until lab examination could occur.

All collected specimens were examined in the lab using a 7-45x magnification binocular microscope. Attempts at identification have been made using a combination of relevant reference books, scientific papers and web-based resources. Whilst the aim of the identification process is to reach a confident species level determination, in practice this has not yet been possible for many species. Most species have been determined to at least genus level, and identifiably different species within a genus have been differentiated numerically, e.g. Bombus sp. 1 and Bombus sp. 2, when species level determination has yet to be achieved. This methodology means that there is the potential to underestimate diversity by missing cryptic species that are near identical in outward appearance to others in the same genus. The identification process will be an ongoing endeavour and specimens will be re-visited periodically in an attempt to identify, with a reasonable level of confidence, the exact species present on the plots. All collected specimens are either glued onto card or directly pinned and labelled for future reference.

See June /July 2017 Sheet in bottom left corner  

6. Notes on June-July results

The June-July survey recorded a total of 237 species in 45 families from the targeted groups.

The most species rich of the target groups were the Coleoptera with 107 recorded species in 22 families. The Chrysomelidae (leaf beetles) were again the most diverse group of beetles recorded with a total of 20 species. Other relatively species rich groups were the Curculionidae (true weevils) with 14 species; the Coccinellidae (ladybirds) with 14 species and the Cerambycidae (longhorn beetles) with 11 species. The Curculionidae feed on living plant tissue, the Coccinellidae are predominantly predatory whilst the Cerambycidae are saproxylic (dead wood feeders) as larvae and feed on nectar and pollen as adults. All of the remaining families of beetle were represented by 10 or fewer species. These families are a mix of phytophagous (live plant), saproxylic (dead wood) and carnivorous feeders.

The aculeate Hymenoptera were the second most speciose group with a total of 69 recorded species, a noticeable increase on the number recorded in May. The most species rich family during the June/July visit were the Halictidae (furrow bees), with 14 recorded species. Species from the families Colletidae (9 spp.), Megachilidae (9 spp.), Andrenidae (8 spp.), Crabronidae (8 spp.) and Formicidae (8 spp.) make up the majority of the remaining Hymenopteran recorded during the June/July survey. The furrow bees (Halictidae) are all ground nesting species. The Colletidae recorded were all members of the genus Hylaeus which includes burrow and deadwood/plant nesting species. The mason bees (Megachilidae) nest in either dead wood or walls whilst Mining bees (Andrenidae) are entirely ground nesting, generally in open, exposed soil or sand. The Apidae were also still relatively diverse (7 spp.) and composed of a mix of ground nesting and cavity nesting species. All the remaining families were represented by 1-3 species.

Only 26 species of Heteropteran bug were recorded during the June/July survey. shield bugs (Pentatomidae), 10 spp., were the most species rich groups of bugs recorded. The Pentatomidae predominantly feed on sap from plant stems The ground bugs (Lygaeidae), 4 spp.,. The Coreidae (4 spp.), Rhopalidae (3 spp.), Nabidae (2 spp.), Scutelleridae (2 spp.) and Alydidae (1 spp.) were all significantly less diverse but included species that were abundant on both plots.

6.1 Plot 1 - Market Garden

Sub-plot 1 – Forest Garden

• Highest species richness of any sub-plot (75 spp.)
• Reasonably diverse Coleoptera (26 spp.)
• High diversity of Hymenoptera (26 spp.)
• Diverse flora and structure - rough grassland, tall herbs, young trees, shrubs
• Reasonable diversity of nectar feeding Hymenoptera (pollinators) due to abundant nectar sources

Sub-plot 2 – Polyculture beds

• Lower species richness than Forest Garden (67 spp.)
• More intensive food production than forest garden means that structural and floristic diversity is lower
• Both planted and wild plants in polyculture beds provide a good nectar source when in flower
• Reasonably diverse Coleoptera (24 spp.)
• Abundant nectar feeding bees (24 spp.) which act as pollinators
• Wooden growth supports provide nesting sites for wood nesting bees and wasps, particularly mason bees in the genus Osmia

Sub-plot 3 – Scrub

• Predominantly homogenous young shrubs and trees with one or two more mature trees
• Low species richness (35 spp.)
• Dominated by Coleoptera (17 spp.) but few (5 spp.) saproxylic species present

6.2 Plot 2 - Experimental Polyculture

Sub-plot 4 – Grassland

• Relatively simple in structure, being predominantly rough, previously goat-grazed, grassland with scattered low shrubby bushes
• High species richness (78 spp.) 
• Numerous patches of flowers attract nectar feeding bees (17 spp.)
• Most of the remaining species are phytophagous (22 spp.), feeding on either leaves or seeds

Sub-plot 5 – Hedgerow

• Lowest target group species richness of sampled sub-plots (33 spp.)
• Dominated by Coleoptera (18 spp.), of which half (9 spp.) are saproxylic for at least part of their life cycle
• Mature hedgerows with mature elm and blackthorn predominant
• Some deadwood present providing habitat for saproxylic species

Sub-plot 6 – New Polyculture plot

• Highest diversity of sample sub-plots (91 spp.)
• Most diverse group are the Coleoptera (49 spp.)
• Very diverse Aculeate Hymenopteran fauna (30 spp.), including 22 spp. Of pollinating bee
• Abundant ruderal plants in disturbed ground
• Floristically diverse marginal vegetation attracted many nectar and pollen feeders

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