The aim of this study was to evaluate some of the physical and bioeconomic potentials of a silvopastoral agroforestry system with focus on the Henfaes Silvopastoral Systems Experimental Farm (SSEF) of Bangor University, North Wales.
The study reviewed research studies written on the SSEF from 1992 to 2012; assessed changes in pasture species composition and abundance since establishment; developed allometric equations for the estimation of aboveground biomass (AGB), carbon (C) stock and carbon dioxide (CO2) emission potentials of red alder (Alnus rubra Bong); studied the effect of tree/solar radiation on pasture productivity and quality; and conducted bioeconomic analysis to compare treeless pasture/livestock, forestry, and agroforestry scenarios.
Review of the research studies show that as far as can be determined 66 research studies were conducted on ecosystem services of the UK’s Silvopastoral National Network Experiment (SNNE) and temperate Europe during the period 1992 - 2012. These papers were sourced mainly from the Henfaes SSEF, the UK’s SNNE, other UK and, other European research sites. The studied ecosystem services dealt with provisioning services (40%), regulating services (13%), and supporting services (47%). The scientific domains addressed include timber or wood-fuel potential (20%), pasture/livestock management (20%), biodiversity (20%), carbon sequestration (13%), water management (15%), and soils (12%).
The response of pasture species to thinning varied. The percentage composition by weight of the sown species declined, while that of the grass weeds and the forb weeds increased slightly one year after thinning (2013 – 2014) compared to the adjacent open pastures. The change was not statistically significant. The understory pasture species composition, abundance and diversity changed significantly 20 years (1992 – 2012) after the establishment of the Silvopastoral National Network Experiment at Henfaes. Generally, pasture on the three red alder blocks was found to be largely grass weeds (46-48%) followed by forbs or broadleaf weeds while the sown species declined significantly.
In 2012, 20 years after field planting, the mean AGB were found to vary from 130 kg tree-1 (26 Mg ha-1) to 246 kg tree-1 (49 Mg ha-1) in poor form and good form red alder trees, respectively, based on a stocking density of 200 stems ha-1. Mean C stock was 65 kg C tree-1 (13 Mg C ha-1) in poor form trees and 123 kg C tree-1 (25 Mg C ha-1) in good form trees. Mean CO2 potential was 237 kg CO2 tree-1 (48 Mg CO2 ha-1) in poor form trees and 450 kg CO2 tree-1 (90 Mg CO2 ha-1) in good form trees.
Pasture productivity increased significantly with increasing solar transmission, and with increasing distance from each grazing exclusion cage to the nearest alder tree. Concentration and availability of CP, ADF, NDF and ME were greater in the with-leaves than in the without-leaves growing seasons in response to variation of photoperiod (the duration of sunshine/day length) in the United Kingdom.
The bioeconomic analysis considered three land-use plausible scenarios (‘forestry’, ‘pasture / livestock’ and ‘agroforestry’) and found that, in the absence of grants/subsidies, none were viable. However, application of grants/subsidies, at the baseline assumptions, revealed that forestry was the most viable option with the highest net present value and annual equivalent value, followed by pasture/livestock and agroforestry options.