The carbon storage benefits of agroforestry and farm woodlands

352 Pages·2014·14.72 MB·English

CRANFIELD UNIVERSITY
Matthew A. Upson
THE CARBON STORAGE BENEFITS OF AGROFORESTRY AND
FARM WOODLANDS
SCHOOL OF APPLIED SCIENCES
Doctor of Philosophy
2011 2014
Academic Year: -
Supervisor:
Dr. Paul Burgess
2014
July

CRANFIELD UNIVERSITY
Matthew A. Upson
THE CARBON STORAGE BENEFITS OF AGROFORESTRY
AND FARM WOODLANDS
School of Applied Sciences
This thesis is submitted in partial fulfilment of the requirements for the degree of
Doctor of philosophy.
Doctor of Philosophy
2011 2014
Academic Year -
Supervisor:
Dr. Paul Burgess
2014
July
©CranfieldUniversity,July2014.Allrightsreserved.Nopartofthispublicationmaybe
reproducedwithoutthewrittenpermissionofthecopyrightholder.
Matthew A. Upson: The carbon storage benefits of agroforestry and farm woodlands, ©
2014
Cranfield University, July . All rights reserved. No part of this publication
may be reproduced without the written permission of the copyright holder.
v

ABSTRACT
Plantingtreesonagriculturallandeitherasfarmwoodlandsoragroforestry(trees
integratedwithfarming)isoneoptionforreducingthelevelofatmosphericcarbon
dioxide. Trees store carbon as biomass, and may increase carbon storage in the
ground.
A review of the literature outlined uncertainty relating to changes in carbon
storage after planting trees on agricultural land. The aim of this thesis is to deter-
minetheimpactoftreeplantingonarableandpasturelandintermsofaboveand
belowground carbon storage and thereby address these uncertainties, and assess
the implications for the Woodland Carbon Code: a voluntary standard for carbon
storage in UK woodlands.
Measurementsofsoilorganiccarbontoadepthof1.5mweretakenattwofield
sites in Bedfordshire in the UK: a 19 year old silvoarable trial, and a 14 year old
silvopasture and farm woodland. On average 60% and 40% of the soil carbon (rel-
ative to 1.5 m) was found beneath 0.2 and 0.4 m in depth respectively. Whilst tree
planting in the arable system showed gains in soil organic carbon (12.4 t C ha−1
at 0–40 cm), tree planting in the pasture was associated with losses of soil organic
carbon (6.1–13.4 t C ha−1 at 0–10 cm). Evidence from a nearby mature grazed
woodland indicate that these losses may be recovered. No differences associated
with tree planting were found to the full 1.5 m, though this may be due to a lack
of statistical power.
Measurements of above and belowground biomass, and the root distribution of
19 year old poplar (Populus spp.) trees (at the silvoarable trial) and ash (Fraxinus
excelsior)treesrangingfrom7to21years(atseveralfieldsitesacrossBedfordshire)
were made, involving the destructive harvest of 48 trees. These measurements
suggest that Forestry Commission yield tables overestimate yield for poplar trees
growninasilvoarablesystem.Anallometricrelationshipfordeterminingashtree
biomass from diameter measurements was established.
ThebiophysicalmodelYield-SAFEwasupdatedtotakeintoaccountrootgrowth,
and was parameterised using field measurements. It was successfully used to
describe existing tree growth at two sites, and was then used to predict future
biomass carbon storage at the silvoarable trial.
Measurements indicate that losses in soil carbon at relatively shallow depths
can offset a large proportion of the carbon stored in tree biomass, but assessing
changes on a site by site basis may be prohibitively expensive for schemes such as
the Woodland Carbon Code.
keywords
:
Agroforestry, Soil organic carbon, Woodland Carbon Code, Soil carbon fractiona-
tion, Yield tables, Modelling, Carbon storage
vii

A philosopher, which is what I am supposed to be,
is a sort of intellectual yokel who gapes and
stares at what sensible people take for granted,
a person who cannot get rid of the feeling that
the barest facts of everyday life are unbelievably
odd. As Aristotle put it: the beginning of
philosophy is wonder.
1915 1973
— Alan Wilson Watts ( - )