Changes in soil invertebrate decomposer communities during regeneration of Scots Pine within the Abernethy Forest Reserve, Scotland

Abstract

Plans currently exist to extend the range of native woodland within the Scottish Highlands. The effects of such an expansion on birds, mammals and above ground invertebrates have been previously been investigated, but little consideration has been given to soil invertebrates. This research looks at effects of Scots pine (Pinus sylvestris) regeneration on the meso- and macro- soil invertebrate communities.
Within the Abernethy Forest Reserve (the largest remaining tract of native Scots pine woodland within the UK) mature woodland (pine-dominated) and moorland (Calluna vulgaris-dominated) sites were chosen on the three soil types present; an iron podzol, humus-iron podzol and peat. Three intermediate regeneration sites, upon two of the soil types, were also selected based on tree density and diameter at breast height (dbh). Together these sites formed two transects representing succession from moorland to mature woodland on the two soil types. At each site soil invertebrates were collected to a depth of 0.1 in and pitfall traps set. Litter bags were placed at the woodland and moorland sites to examine invertebrate succession during Pinus and Calluna litter decomposition. All invertebrates were identified to order and oribatid mites identified further using the morphospecies technique. The influences of soil type, depth, season and tree age on invertebrate communities were analysed using TWINSPAN and CANOCO.
Results suggested that differences were present in invertebrate abundance and community structure between the two soil types, with more variation occurring along the peat transect than podzol transect. A number of oribatid morphospecies showed differences in density between transect sites and indicator species were present which separated the younger regenerating sites form older woodland. CANOCO analysis demonstrated that this was primarily due to changes in soil pH and temperature.
In litter bags, Calluna showed significantly greater colonisation compared with Pinus at all sites and woodland litter bags supported a greater diversity of invertebrates than comparable moorland bags. Calluna litter is more complex than Pinus and may therefore provide a greater number of niches for invertebrates and shelter from prey. Differences between sites may be due to the presence of species adapted to utilising both litter types at the woodland end of the transect. In general concentrations of N and P significantly influenced the community composition within litter bags (pc0.05), but there were no significant relationships with other macronutrients.
This work has shown that there are differences in the invertebrate community composition during the regeneration of Scots pine and decomposition of litter, however it is currently unclear whether these changes are truly successional.