Friday, 9 March 2018

Invertebrate Biodiversity Survey Results - Polyculture Study 2017

May 2017 results
By Christopher Kirby-Lambert – 27/02/2018

You can find photos from Chris's May Survey here

A sample of invertebrates from the gardens- Photos by Chris Kirby-Lambert  

1. Survey Timing and Conditions
Field survey was carried out on the 2nd (Market Garden) and 3rd (Perennial polyculture trial garden) of May 2017. Both plots were surveyed in the morning between approximately 09.00 and 11.00. Conditions during both surveys were warm, sunny and calm.

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.
Sub-plot 2 - Polyculture beds: Rows of cultivated ground for a variety of vegetables. The plots were still straw over bare soil during the May visit. 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, dominated by red dead-nettle (Lamium purpureum). 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 Walnut - Juglans regia 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

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 plot. The most frequent flowering plant in the sub-plot during the May survey was a speedwell (Veronica sp.) which occurred in localised but dense patches throughout the sub-plot.
Sub-plot 5 – Hedgerow: The 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.
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.

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.

5. Results

6. Notes on May results

The May survey recorded a total of 179 species in 33 families from the targeted groups.

The most species rich of the target groups were the Coleoptera with 94 recorded species in 19 families. The Chrysomelidae (leaf beetles) were by some margin the most diverse group of beetles recorded with a total of 29 species. Other relatively species rich groups were the Curculionidae (true weevils) with 17 species and the Apionidae (seed weevils) with 11 species. All three of these groups feed on living plant tissue. All of the remaining 16 families of beetle were represented by fewer than 10 species. These families are a mix of phytophagous (live plant), saproxylic (dead wood) and carnivorous feeders. The Coccinellidae (ladybirds) are perhaps worthy of mention here too; 9 species were recorded, several of which were abundant throughout. Many species of ladybird are significant and voracious predators of aphids and can noticeably limit their population. In the context of the current study, focussed as it is on food production, the observation of large populations of a number of species may be of relevance.

The aculeate Hymenoptera were the second most speciose group with a total of 44 recorded species. The most species rich family were the Formicidae (ants), with 12 recorded species. The ants were most diverse in areas with woody vegetation such as bushes and trees and it seems that more than half of the species recorded are associated with such habitats. Species from the families Apidae (9 spp.), Halictidae (9 spp.) and Megachilidae (7 spp.) make up the majority of the bee species recorded during the May survey. The Apidae recorded consisted of a mix of species that nest in burrows in exposed ground (Eucera spp., Amegilla spp. and Melecta spp.), species that nest in hollow plant stems (Ceratina spp.) and species that nest colonially in burrows or moss (Bombus spp.). The furrow bees (Halictidae) are all ground nesting species whilst the mason bees (Megachilidae) nest in either dead wood or walls. Mining bees (Andrenidae) were less diverse in terms of species richness (4 spp.) but one species of mining bee (currently labelled Andrena sp. 3) was the most numerically abundant bee species recorded during the May survey.

37 species of Heteropteran bug were recorded during the survey. The ground bugs (Lygaeidae), 13 spp., and shield bugs (Pentatomidae), 11 spp., were the most species rich groups of bugs recorded. The Lygaeidae feed largely on seeds whilst the Pentatomidae predominantly feed on sap from plant stems. The Coreidae (6 spp.) Nabidae (3 spp.) and Rhopalidae (3 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 (79 spp.)
  • Coleoptera are by far the most diverse group (52 spp.)
  • High diversity of phytophagous Coleoptera (30 spp.) due to diverse food plants
  • 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
  • Significantly lower species richness than Forest Garden (47 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
  • Abundant nectar feeding bees (14 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
  • Lowest target group species richness of sampled sub-plots (32 spp.)
  • Predominantly homogenous young shrubs and trees with one or two more mature trees
  • Some flowering shrubs present early in the year provide a decent source of nectar and pollen, providing food for a range of invertebrate species
  • Phytophagous species predominate (16 spp.)
6.2 Plot 2 - Experimental Polyculture

Sub-plot 4 – Grassland
  • Relatively high species richness (54 spp.)
  • Relatively simple in structure, being predominantly rough, previously goat-grazed, grassland with scattered low shrubby bushes
  • Patches of Veronica sp. attract numerous nectar feeding bees (14 spp.)
  • Most of the remaining species are phytophagous (22 spp.), feeding on either leaves or seeds
Sub-plot 5 – Hedgerow
  • Relatively low species richness (40 spp.)
  • Mature hedgerows with mature elm and blackthorn predominant
  • Blackthorn provides good nectar source early in year
  • Some deadwood present providing habitat for saproxylic species
  • Relatively diverse ant fauna (7 spp.), made up of mostly tree nesting species

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