Mangrove vegetation structure dynamics and regeneration

 

Thesis Philosophiae Doctor Scientiarum

 

Farid Dahdouh-GuebaS


 

A note on the identification of mangroves from aerial photography in Kenya and Sri Lanka.

 

Dahdouh-Guebas, F.1, A. Verheyden1, L.P Jayatissa2 & N. Koedam1.

 

1 Laboratory of General Botany and Nature Management, Mangrove Management Group, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium.

2 Department of Botany, University of Ruhuna, Matara, Sri Lanka.

 

Abstract

 

This note consists of an amendment of the interpretation keys of all study sites in Kenya and Sri Lanka, in which the plasticity of image attributes is assessed and a ‘compromise key’ is drafted.

 

Keywords : mangrove, mapping, remote sensing, aerial photography, Kenya, Sri Lanka.

 


  For publication purposes transformed as follows (incl. On-line Supplementary Material) :


Capacity building in tropical coastal resource monitoring in developing countries : a re-appreciation of the oldest remote sensing method.

Dahdouh-Guebas, F.1,2, A. Verheyden2, L.P. Jayatissa3, J.G. Kairo4 and N. Koedam2.

(1) Biocomplexity Research Team, c/o (2) Laboratory of General Botany and Nature Management, Mangrove Management Group, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium.

(3) Department of Botany, University of Ruhuna, Matara, Sri Lanka.

(4) Kenya Marine and Fisheries Research Institute, PO Box 81651, Mombasa, Kenya.

 

Abstract

Long-term decadal retrospectivity in spatio-temporal imagery analyses can only be carried out using aerial photographs, which are still the most detailed remotely sensed data available.  Visual interpretation of such imagery is most efficient and inexpensive in the light of ecosystem monitoring research in developing countries, which are often unable to cope with the development or the cost of acquisition of commercial space-borne imaging (e.g. IKONOS, Quickbird).  In this light, the present paper explicitly analyses the methodological use of image attributes of air-borne imagery from mangrove forests, and investigates the consistency and constraints of mangrove image attributes in visually interpreted air-borne imagery.  Six image attributes are analysed, and their application is illustrated using various mangrove sites in Kenya and Sri Lanka.  Comparison of identification keys reveals that minor attributes such as ‘ecological position’ are informative, and that image attributes for a particular species or genus apparently are less plastic and wider applicable than formerly assumed.  Emphasis of compulsory fieldwork is made, and constraints related to reflection and interference, amongst others, is discussed.

 

Keywords : mangrove, aerial photography, image attributes, capacity building, Third World.

 

Published in International Journal of Sustainable Development and World Ecology (in press).

 

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On-line supplementary material :

 

Table 2.  Entire set of identification keys.  Keys for the identification of vegetation in mangroves of Mida Creek (a) and Gazi Bay (b) in Kenya, and Rekawa (c), Galle (d) and Pambala (e) in Sri Lanka.  Note that the identification tag should always be considered as a vegetation assemblage dominated by a certain species, rather than as a pure stand.  The vegetation map resulting from the key for Gazi can be consulted in Dahdouh-Guebas et al. (2004a), that for Mida in Kairo et al. (2002), and that for Galle in Dahdouh-Guebas et al. (2000).  Maps for Rekawa and Pambala are available, but were originally based on a simplified form the keys (Verheyden et al., 2002).  The compromis key based on the keys below is given in the paper.

 

(a) MIDA (03°20’ S - 39°59’ E)

Tonality

Texture

Structure

Size

Shape

Shade

Position
Identification

white

plain

plain

variable

variable

none

none

sand

light grey

coarse grain

discontinuous canopy

large-sized crowns

variable

intermediate to dark

water side

Avicennia marina

 

coarse grain

discontinuous canopy or continuous canopy with crowns hard to distinguish

small-sized crowns

variable

light

landward side

 

Avicennia marina

intermediate grey

fine grain

continuous canopy

crowns not visible separately

often lower than surrounding vegetation

circular canopy

light to dark

often landward side

 

Ceriops tagal

dark grey

fine grain

continuous canopy

crowns not visible separately

often large-sized aggregating crowns and sometimes clearly higher than surrounding vegetation

variable

intermediate to dark shade

often bordering water

wide spatial range

 

Rhizophora mucronata

primarily dark grey, but mixed with light and intermediate grey

coarse grain

dense but often with a discontinuous canopy

variable

variable

variable

variable

Mixed stand with Rhizophora mucronata and Ceriops tagal co-dominant


 

(b) GAZI (04°25’S - 39°30’ E)

Tonality

Texture

Structure

Size

Shape

Shade

Position
Identification

white

plain or irregular

plain or irregular

rather large

variable

none

variable

sand

 

irregular

irregular

variable

variable

variable

often clearly man-made

infrastructure

(tracks, constructions)

 

coarse grain and/or blurred

discontinuous canopy

regular

star-shaped crown

light shade

sparse and regular distribution landward

Cocos nucifera (coconut)

light grey

coarse grain

discontinuous canopy

very large crowns, often higher than surrounding vegetation

variable

surrounding vegetation may be shaded intermediate to dark

water side

Avicennia marina

 

fine grain

discontinuous canopy or continuous canopy with crowns hard to distinguish

small-sized crowns

variable

light

landward side

Avicennia marina

 

variable

often discontinuous canopy

variable, but in case of trees often larger than mangroves

variable

none (herbaceous layer), dark (often for trees) or variable

landward side or outside reach of mangrove vegetation

terrestrial vegetation

dark grey

fine grain and blurred

continuous canopy

crowns not separately visible

small-sized crowns, lower than surrounding vegetation

circular canopy

light

landward side or mid-mangrove

Ceriops tagal

 

coarse grain

‘peluche’ texture

discontinuous canopy

regular

circular canopy

intermediate to dark

amongst terrestrial vegetation

sparse and regular distribution

Mangifera indica (mango)

 

coarse grain

discontinuous canopy

very large crowns

variable

dark

always at water side

large-sized canopy

Sonneratia alba

very dark grey

or black

fine or coarse grain

continuous canopy with crowns hard to distinguish

often large-sized aggregating crowns

variable

intermediate to dark

often at water side

wide spatial range

Rhizophora mucronata


 

(c) REKAWA (06°03’ N - 80°50’ E)

Tonality

Texture

Structure

Size

Shape

Shade

Position
Identification

white

blurred

discontinuous canopy

regular

star-shaped crown

light shade

landward

Cocos nucifera

white

blurred

discontinuous canopy

variable

variable

variable

variable

Avicennia spp.

light grey

fine grain

crowns can be distinguished

small-sized crowns

circular

light to intermediate

variable

Aegiceras corniculatum

intermediate grey

coarse grain

crowns hard to distinguish

small-sized crowns

circular

light to intermediate

landward

Lumnitzera racemosa

dark grey

coarse grain

‘cauliflower’ texture

continuous canopy

large-sized crowns

variable

variable

often bordering water

Rhizophora mucronata

black

blurred

crowns not distinguishable

variable

circular

variable

variable

Ceriops tagal


 

(d) GALLE (06°01’N - 80°13’ E)

Tonality

Texture

Structure

Size

Shape

Shade

Position
Identification

white

irregular

irregular

variable

variable

variable

often clearly man-made

infrastructure

(tracks, constructions)

 

blurred

discontinuous canopy

regular

star-shaped crown

light shade

sparse and regular distribution when planted, rather spread randomly in neglected plantations

Cocos nucifera (coconut)

 

blurred

irregular

small-sized crowns

no typical shape

no shadow-side

variable

Clerodendron inerme

 

fine grain

discontinuous canopy

variable

variable

intermediate to dark

medium to dark

Excoecaria agallocha

light grey

fine grain

discontinuous canopy

variable

variable

intermediate to dark

not spatially bound

Excoecaria agallocha

 

coarse grain

discontinuous canopy

never very large

circular

variable

not spatially bound

Bruguiera spp.

intermediate grey

coarse grain

discontinuous canopy

never very large

circular

variable

not spatially bound

Bruguiera spp.

 

coarse grain

discontinuous canopy

medium to large-sized aggregating crowns, but not higher than surrounding vegetation

variable

dark

often at water side

Rhizophora apiculata

 

‘cauliflower’ texture

continuous canopy with no separately visible crowns

medium to large-sized aggregating crowns, but not higher than surrounding vegetation

variable

dark

often as islands in a water body

wide spatial range

Rhizophora apiculata

dark grey

‘cauliflower’ texture

continuous canopy with no separately visible crowns

medium to large-sized aggregating crowns, but not higher than surrounding vegetation

variable

dark

often as islands in a water body

wide spatial range

Rhizophora apiculata

 

coarse grain

discontinuous canopy

medium to large-sized aggregating crowns, but not higher than surrounding vegetation

variable

dark

often at water side

wide spatial range

Rhizophora apiculata


 

(e) PAMBALA (07°30’ N - 80°00’ E)

Tonality

Texture

Structure

Size

Shape

Shade

Position
Identification

white

plain or irregular

plain or irregular

rather large

variable and complex shape

none

none

sand or grassy plain

 

blurred

discontinuous canopy

regular

star-shaped crown

light

sparse and regular distribution

Cocos nucifera (coconut)

light grey

coarse grain

discontinuous canopy

often larger than surrounding vegetation

circular

dark

land or water side

Avicennia spp.

 

blurred

discontinuous canopy

variable

variable

variable

not spatially bound

Excoecaria agallocha

intermediate grey

very fine grain

continuous canopy with many crowns hardly distinguishable

very small crowns

circular

none

landward side

Lumnitzera racemosa

 

coarse grain

and /or blurred

crowns hard to distinguish

medium to large, but never very large

circular

variable

none

Bruguiera spp.

Xylocarpus spp.

 

plain or blurred

none or regular

small

circular

none

none

Acrostichum aureum

 

plain or blurred

none or regular

small

variable

none

at water side

Acrostichum aureum

or Acanthus ilicifolius

dark grey

coarse

continuous canopy

crowns separately visible or not so, often higher than surrounding vegetation

medium to large aggregating crowns

variable

dark

often at water side

wide spatial range

Rhizophora spp.

 

 

References

Year formats as in full paper.

 

Dahdouh-Guebas, F., A. Verheyden, W. De Genst, S. Hettiarachchi & N. Koedam, 2000bFour decade vegetation dynamics in Sri Lankan mangroves as detected from sequential aerial photography : a case study in Galle.  Bulletin of Marine Science 67(2): 741-759.

Dahdouh-Guebas, F., I. Van Pottelbergh, J.G. Kairo, S. Cannicci & N. Koedam, 2004bHuman-impacted mangroves in Gazi (Kenya): predicting future vegetation based on retrospective remote sensing, social surveys, and distribution of trees.  Marine Ecology Progress Series 272: 77-92.

Kairo, J.G., F. Dahdouh-Guebas, P.O. Gwada, C. Ochieng & N. Koedam, 2002aRegeneration status of mangrove forests in Mida Creek, Kenya : a compromised or secured future ?  Ambio 31(7/8): 562-568.

Verheyden, A., F. Dahdouh-Guebas, K. Thomaes, W. De Genst, S. Hettiarachchi & N. Koedam, 2002High resolution vegetation data for mangrove research as obtained from aerial photography.  In : F. Dahdouh-Guebas (ed.), Remote sensing and GIS in the sustainable management of tropical coastal ecosystems, Environment, Development and Sustainability 4(2): 113-133.

 

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