Thesis (MSc (Forest and Wood Science))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: This study investigated the use of carbon isotopes as a potential measure for water
availability and drought stress in Pinus radiata in the Western and Southern Cape,
South Africa. An understanding of water availability and its variation in space is
fundamental to the implementation of increasingly site-specific management regimes
that have the potential to greatly improve productivity across sites in the region.
Fifteen plantation compartments situated on water shedding sites were identified
where good weather data existed and a water balance model could be run. In
addition, late wood samples were analysed from four co-dominant trees in the same
stand to determine the δ13C values of five tree rings, each representing a specific
growth year before first thinning. Detailed water balances were constructed for each
trial site and drought stress indicators (a) relative canopy conductance (after Granier
et al., 2000) and (b) the ratio of actual to potential evapotranspiration (supply /
demand ratio), were related to δ13C values in latewood.
Maximum available soil water ranged from 52 to 313 mm across trial sites. The water
balance model used adequately described soil water availability throughout each
growing season and indicated that stand stress due to the lack of available soil water
mainly occurred during the summer months of the study period (November to April).
The supply / demand ratio for this period as well as the relative canopy conductance
proved to be good measures of drought stress. The six-month supply demand ratio
(calculated for the period November to April) ranged from 0.04 to nearly 1 (winter
rainfall zone) and 0.35 to 1 (all-year rainfall zone) and were strongly related to δ13C values (p < 0.001; r2 = 0.7822).
It appears that using δ13C values, it may be possible to classify sites into three water
availability classes. This classification may assist in the implementation of intensive
silvicultural operations on an increasingly site-specific basis. Where sites are
enriched with water from lateral flow or upslope positions, δ13C may be the only
reliable technique to quantify soil water availability. / AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die gebruik van koolstof isotope as 'n moontlike maatstaf
vir die beskikbaarheid van water en droogtestremming in Pinus radiata in die Wes-en
Suid-Kaap, Suid-Afrika. 'n Begrip van die beskikbaarheid van water en die ruimtelike
variasie daarvan is fundamenteel vir die implementering van groeiplek-spesifieke
bestuur sisteem wat die potensiaal het om baie verbeterde produktiwiteit oor persele
in die streek teweeg te bring.
Vyftien plantasievakke, geleë op waterskeidingsterreine is geïdentifiseer waar goeie
weer data bestaan en 'n water balans model uitgevoer kon word. Daarmee saam is
laathout monsters vanuit vier ko-dominante bome in dieselfde kompartement
geanaliseer en die δ13C waardes van laathout in vyf jaarringe bepaal wat elk 'n
spesifieke jaar van groei voor die eerste dunning verteenwoordig. Gedetailleerde
water balanse is vir elke proef perseel bereken en aanwysers van
droogtestremming, nl.: (a) relatiewe kroon geleiding (na Granier et al., 2000) en (b)
die verhouding van die werklike teenoor potensiële evapotranspirasie (vraag /
aanbod verhouding) is gekorreleer met 13C waardes in laat hout.
Die maksimum hoeveelheid water beskikbaar op die verskeie proefpersele wissel
van 52 tot 313 mm. Die water balans model wat gebruik is beskryf die beskikbare
grondwater met genoegsame akkuraatheid. vir die hele groeiseisoen. Die model dui
ook aan dat die kompartemente droogtestremming as gevolg van die gebrek aan
beskikbare grond water ervaar gedurende die somer maande van die studie tydperk
(November tot April). Die vraag / aanbod verhouding vir hierdie tydperk, asook die
relatiewe kroon geleiding is geskik om as maatstawwe van droogtestremming
gebruik te word. Die vraag / aanbod verhouding (bereken vir die tydperk November
tot April) het gewissel van 0,04 tot byna 1 (Winter reënval gebied) en 0,35 tot 1 (die
heel jaar reënval sone) en is sterk verwant aan 13C waardes (p <0,001; r2 =
0,7822).
Dit blyk dat met die gebruik van δ13C waardes, dit moontlik kan wees om
kompartemente te klassifiseer in drie klasse van water beskikbaarheid. Hierdie
klassifikasie kan help met die implementering van intensiewe boskultuur
bedrywighede op 'n meer vak-spesifieke basis. Waar vakkeverryk is met water vanuit
laterale vloei of hoër liggende posisies, mag δ13C dalk die enigste betroubare
tegniek wees om die beskikbaarheid van water te kwantifiseer.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6588 |
| Date | 03 1900 |
| Creators | Fischer, Phillip Murray |
| Contributors | Jarmain, Caren, University of Stellenbosch. Faculty of AgriSciences. Dept. of Forest and Wood Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 108 p. : ill., maps |
| Rights | University of Stellenbosch |
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