An intensive tree planting programme began in 1998 with new areas of woodland being created each year as well as specimen tree planting in landscape projects and avenues of trees created and extended. The table below shows numbers of different tree sizes planted since 1998.
Specimen tree – trees planted as heavy standards in part of a landscape project on campus
Standard tree – trees varying in girth from 6-18cm
Whips – bare rooted, young trees with a single stem, not greater than 1m in height.
The varieties of trees being planted have reflected the trees existing at different locations throughout the campus and most of these are native to Ireland or have become naturalized. The following table gives an example of some of the species mixes being used.
Nos of Insect and mite species feeding on trees
Not all of the species in the table are native, some are naturalized and contribute greatly to a rich and diverse habitat in a woodland setting. Species selection is an important consideration in the creation of wildlife habitats as some species support more wildlife than others. Oak for example supports in excess of 420 species of insects and mites, whereas sycamore only supports in the region of 43 and yew only 6 . Different species support different wildlife and it is widely accepted that non-native trees directly support fewer types of insects and are therefore less valuable from a biodiversity viewpoint.
The mixture of mature woodlands and newly planted woodlands makes for a very rich habitat for wildlife. Newly planted areas create corridors and links between areas which may have been isolated, making them more valuable for wildlife cover.
Macro-invertebrate Richness of Tree species
The richness of insect fauna each species supports largely correlates to the time a species has been present and established (i.e., native, naturalized or recently introduced). Further, the abundance or scarcity (isolation) of a given species influences the diversity of invertebrate fauna (Southwood 1961). The biogeography of a region or country is also a factor which in part, determines invertebrate richness of a species – Ireland been an island off a larger island, has a relatively depauperate richness from neighbouring Britain and lower still compared to mainland Europe.
Southwood (1961) depicts differences in richness of fauna which native and non-native trees host with countries where the corresponding taxa are native or introduced. Native species represent a comparatively diverse fauna (i.e., Quercus robur, Q. petraea, Salix spp., Betula spp., Alnus glutinosa, etc.) to introduced species such as Tilia x europaea, Q. ilex and Sycamore.
Leaf form, plant size, local abundance and habitat heterogeneity are important variables for insect diversity for plant species (Kennedy and Southwood, 1984).
Insects which complete part of or all of their life cycle on different trees comprise a variety of guilds depending on how resources of each are utilised. These guilds include; grazers, leaf miners, sap feeders and gall formers as well as pollinators.
Woodlands provide breeding and nesting habitat for a variety of pollinators. Important features include: pools, puddles, ditches, springs, seepages and water-filled rot holes, which provide habitats for hoverflies and other pollinators. Deadwood and old trees provide habitat for flies and beetles with ‘saproxylic’ larvae, for aerial-nesting bees and wasps, and for hibernating insects.
Old rodent holes and dense vegetation are used for nesting by bumblebees.
The richness and composition of taxa varies between different trees including native and non-nate, introduced species.
Tree Layer: Native Species
– Willow (Salix spp.) host the greatest number of phytophagous taxa of all native species. Data from Kennedy and Southwood, 1984 in a re-analysis of the insect fauna associated with different trees in Britain noted this genre with the highest associated phytophagous species. The most diverse groups include Lepidoptera (moths, butterflies, etc.), Hymenoptera and Symphyta (bees, wasps, ants and sawflies) as well as Coleoptera (beetles).
– Many bees and wasps nectar on catkins in late March –April while later in the wasps forage on the large quantities of nectar and pollen produced by these species for protein and energy sources also from sources of honey dew left over by copious aphid larvae.
Willows will support up to 450 invertebrate species (UK) particularly where epiphytic plants have colonised the bark. There is also a high diversity of birds which forage on invertebrates and associated larvae.
– Oaks (Quercus spp.) host the second highest number of phytophagous taxa found on Sessile and Pedunculate Oak which include Lepidoptera, Hymenoptera and Symphyta and Coleoptera (beetles). The species richness in an Irish context is likely to be reduced and differ locally.
– Birch (Betula spp.) are also affiliated with a high species richness of taxa with over 300 insects supported by both native species of the group in Britain (Kennedy and Southwood, 1984).
– Alder (Alnus glutinosa) also in the Betulaceae family hosts a high proportion grazers, in particular. Catkins provide an early source of nectar for bees. Several moth species including the Alder Kitten (Furcula bicuspis), Pebble Hooktip (Drepana falcataria), the Autumnal (Epirrita autumnata) and the Blue Bordered Carpet Moth (Plemyria rubiginata) complete larval stages of their life cycle are supported by Alder (Ref: Moths Ireland – Accessed April 2019). Leaves provide resources for Cranefly, caddisfly and stonefly larvae (when shed into water).
– Other native species including Elm (Ulmus spp.) – (124 species), Poplar (Populus spp.) – (189 species) and Scots Pine (Pinus sylvestris) – (172 species) are also relatively speciose in terms of phytophagous species (Kennedy and Southwood, 1984).
– Ash (Fraxinus excelsior) is associated with relatively few invertebrates (68 species). Although, the Forest Research Council (mainland Britain) indicates a substantially higher diversity of 240 species. Mature Ash is synonymous with Hoverfly of which 72 species were recorded (mainland Britain). Deadwood and organic matter were critical factors for determining presence of hoverflies in plantation woodland. A myriad of Moths such as species use Ash as a food resource the Barred-toothed Striped (Trichopteryx polycommata), Coronet (Craniophora ligustri) and the Centre-barred Sallow (Atethmia centrago) (Ref: Moths Ireland – Accessed April 2019).
– Sycamore (Acer pseudoplatanus) hosts a relatively low insects diversity (43 species) (Kennedy and Southwood, 1984). The introduced species to Britain and Ireland host 12 Aphid spp. in the UK – a number of which are widespread throughout Europe. This is an early flowering tree (late April/early May), bees ‘apparently’ love the light green pollen it displays for bees. Aphids provide prey and foraging opportunity of other invertebrates/bugs. A number of moth larvae pupate on Sycamore such as the Sycamore moth (Acronicta aceris), Ashy Button (Acleris sparsana) and maple prominent (Ptilodon cucullina) (Ref: Moths Ireland – Accessed April 2019). Hoverflies and ladybirds are attracted to aphids which graze on fresh growth.
– Lime (Tilia x europaea): Flowers in June/ early July and is pollinated by bees and a myriad of insects. However, opinion regarding the benefit of Lime to honeybees is debatable (i.e., among beekeepers). Aphids gorge on new growth and harbour a drizzling honeydew which attracts bees (from June to early July). The value of Lime species in Britain is most likely greater where two native species of Tilia occur. 12 leaf miners are recorded on Tilia spp.
– Beech (Fagus sylvatica): insect fauna is likely to be lower than in the native range of this species which was introduced to Ireland in the 18th century where few specific phytophagous species are likely to have immigrated from its native range.
A number of Arthropod species of moths, weevils and gall mites were recorded on leaves of Beech in a woodland study in southern Scotland (Dennis, 1997).
– Horse Chestnut (Aesculus hippocastanum): attracts pollinators including bees which pollinate the flowers (even if they are hermaphrodite) during April/May.
– Field Maple (Acer campestre): 16 Aphid species in the UK (note tree is not commonly plated in Ireland so diversity of aphid species on Field Maple here is questionable).
Planting for succession:
Ensuring tree cover for future generations is an important aspect of the replanting programme in UCD. At Woodview wood there are some magnificent Beech and Copper Beech which are mature/over mature. These trees will be succeeded by young beeches which have been recently planted in the area with a view to the future tree cover and replicating what exists in the area. This is an approach commonly adopted throughout the campus and is carried out through an annual planting programme.
Trees are planted every year in a planned and phased programme in an attempt to redress the balance of the age profile of the trees on campus. At present there is a large gap in the age of the trees planted on the original estates and what has been planted since the University developed at Belfield.