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MonitoringTropical Rain Forest Mictoclimate

JanetE, Nichol

Abstract TheStudy Area 's original tropical rain forest cover has largely The study area comprisesthe central portion of Singaporeis- been removed, leaving only a total of 2700 hectares, or 5 Iand containing the CatchmentArea Nature Reservesand is percent of the island, under primary and secondary forest. bounded on all sides by major trunk roads (Figure 1)' This This area in the center of the island is protected as water area totals 60 sq km of forest,reservoirs, and some urban catchment and nature reservesin spite of intense pressure and suburban development (Figure 2). The most serious en- for development. croachmentinto the forestedarea is from golf courses,from The paper investigates the application of Landsat TM bungalow style residential developmentin the southeast,and thermal data to surface temperature mapping in the vicinity from an expressway,constructed in the mid-1980s,which of Singapore's forested central catchment area as an indica- has effectively divided Singapore'smain primary rain forest, tion of the relative degree of disturbance to the original rain- Nature Reserve,from the rest of the Central forest microclimate. This will assistin the designation of CatchmentArea. The latter is largely 70- to BO-yearsucces- priority consewation status to areas which remain structur- sion secondaryforest, though significant areasof mature for- ally and microclimatically viable as primary rain forest. est, including Nee Soon Swamp in the northeast,remain' Apparent temperatures were coftected for emissivity dif- Terrain is locally steep,and elevationsof over 160 m are ferences of different land-cover types. Pixel data were then found in Bukit Timah Nature Reserve,which is classedas input into a vector GIs and overlaid with existing coverages Hill DipterocarpForest. representing High Forest, Water, Urban Areas, and Elevation Concern has been expressedabout the future regenera- in order to examine the thermol charocteristics of each land- tion statusof this reservedue to its small size and isolated cover type. Distinct spatial variations in thermal characteris- state,though this is difficult to assessdue to the longevity of tics are observed to corrcspond to land-cover differences and rain forest trees in comparison with the rate of environmen- to parameters of forest conservation value. tal changes. The study area is a mixture of lowland and hill diptero- Introduction carp forest,and secondaryforest (Corlett, 19BB),of which the gronpr Shorea,Hopea, Dipterocarpus,and Dryobanalopsare The differential spatial distribution of sreen biomass in Sin- "microclimatic welllepresented. These forest generarequire cool and humid gaporegives rise to highly contrasting condi- conditions for successfulregeneration. Trials have shown tions which can readily be observedon daytime LandsatTM humidity must be above 95 percent to keep dip- thermal imagery, and can be related to other variablessuch that relative terocarp seedsviable with over 20 percent moisture content as topography,land cover, and population concentrations. (Sasaki,1980) because seed deterioiation depends on mois- The accuracyof the satellite derived data is, however, ture content and temperature.Tamari (f gzo) found that the affectedby the complexity of interactionsbetween electro- maximum temperaturetolerances for seedviability in species magnetic radiation and the earth surfaceand atmosphere of and Hopea were 34oCand 35"C,respectively, while within the field of view of the sensor.The most important Shorea the optimum temperaturefor germination of Hopea halferi interactions are the absorptionand emittancepropeities of was between 25'C and 30'C. When the forest at Bukit Timah water vapour and other atmosphericconstituents and differ- was replacedby secondaryforest and golf courses,tempera- ential emissivity (e) of land-covertypes, tures increasedand humidities and soil moisture were re- Thus, although satellite derived radiance values can duced (Hill, 1966),thus exceedingthe tolerancelevels for readily be converted to Apparent Temperature(Black Body tree regeneration. Equivalent Temperature)using Planck's law (Malaret ef 41., Whitmore's observation(rsa+) of the death of B0 Shorea 1985),this usually underestimatesSurface Temperature (Ts) curtsii trees at SenalingInas, , in 1977 following a if correctionsfor e are not carried out. The resulting Ts, dry period also suggeststhe importance of maintaining a hu- moreover, can only be consideredaccurate in clear, dry at- mid microclimate, and Richards (t952) notes the requirement mospheres,and a further correction using atmosphericdata for a moist atmosphereat critical growth phasesof rain for- should be made if absolutetemperatures are required. The est plants, such as germination or flowering. presentsl.udy assumed that atmbsphericwaterjapor was Aoki ef a|. (1.s78),working in PasohForest Reserve, Ma- uniform over the study site. Becauseemissivity differences laysia, approximately 200 km north of Singapore,show 8:45 are not significant for vegetatedsurfaces, correction was only Ru to be the approximatethermal crossovertime between carried out for broad land-cover classes. The main oblective of the study was to evaluateLandsat TM thermal data for monitoring the distribution of tempera- PhotogrammetricEngineering & RemoteSensing, tures in and around Singapore'sRain ForestNature Reserves, Vol. 61,No. 9, September1995, pp. 1159-1165. including analysis of the interior forest microclimate. oo9}jt't 1.2I S5l6109-1 1 59$3.00/0 Division of Geography, NanyangTechnological University, @ 1395 American Society for Photogrammetry 469 , Singapore1025. ald Remote Sensing

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tukit Timah

0t23km Sourco, LANDSA"I'IM, 24.5.89 Figure2. Landcover in and aroundthe CentralCatch- ment Area. Figure1. ThematicMapper thermal waveband of Singa- pore lsland (coolestareas with darkertone).

pixel data, is usually a point measurement, and not spatially averaged. temperatures above the canopy and at ground level. The time of the overpasswas 2 hours later (10:40Ru solar time) and air temperatures in Singapore (mean value for six air bases) EnelgyBudget had reached 30"C, with minimum and maximum values for Spatial variations in canopy temperature may be examined that day of 25.5"Cand 32.2'C, respectively.Thus, land-cover with reference to the energy balance for a plant canopy related differences in surface temperature should be evident. (Equation 1) for which the physical and biological storage The date of image aquisition, 24May 1989, corresponds components(G) can be considerednegligible during daytime to the end of the February to May period which has the low- (Oke,1987): i.e., est rainfall and highest sunshine amounts. Climate data at (1) Macritchie Reservoir(Singapore Meteorological Service, Qn:LE+H+G L990) indicate a warm dry period during the eight days prior where Qn is the net all wave radiation flux, LE is the latent to image aquisition, with a total of only B mm (mean heat flux, and H is the sensible heat flux. rainfall for May is 173 mm). On the six individual monthly Horizontal temperaturevariations in a closed canopy for- days prior to 24 May,24-hourly mean temperaturesin Singa- est are, thus, related to the amount of net radiation (Qn) and pore mean values for the month (27.3'C),and mean exceeded the partition between H and LE.The partitioning depends ielative humidity was lower than the monthly mean value of both on moisture availability and on the heat regulating 86.6 percent. On 24 May, 10.4 hours of sunshine,the highest mechanism of leavesby stomatal closure,generally referred for month, were recorded;relative humidity reachedan the to as canopy resistance(Rb). This is likely to be greaterdur- exceptional low of 55 percent, and these warm and dry con- ing moisture stress.Under normal conditions, if Rb is small, ditions culminated in a thunderstorm during the night of 24- canopy temperatureis closely coupled to air temperature 25 May. Because24 May also recorded the highest wind (Oke, 1987),as surplus canopy heat is used for evapotran- speedsfor the month (2.4 m sec-1,with a monthly mean of spiration, thus maintaining a balancebetween biomassand 1.3 m sec-'), optimum atmosphericconditions prevailed for air temperature. evaptranspirationand, thus, latent heat loss from the forest In such conditions, mature closed canopy forest may be canopy. expected to be cooler than immature forest with an open canopy due to a high leaf areaindex and efficient water up- Thelmportance ofthe Rain Forest Canopy and the take from a well develooedroot svstem in a mature soil. thus Significanceof Forest Canopy Temperatute. promoting LE.However,^in conditions of soil moisture stress, The relevanceof satellite derived Ts for studies of forest mi- an increasein Rb is likely to result in increasedcanopy tem- croclimate depends largely on the relationship between tem- peraturesfor all forest types. If wind speedsalso happen to perature at the canopy and that within the forest. Satellite be low, both types of convectiveheat loss are restricted,re- derived temperaturescorrespond to SurfaceTemperature sulting in a lower relationship between canopy and air tem- which, in a forest zone, is representedby the temperatureat perature, the top of the canopy. However, the relationship between re- During occasionaldry periods in Singapore,the average motely sensedcanopy and air temperaturesis diffrcult to monthly potential evapotranspiration may exceed monthly demonstrate empirically because air temperature, unlike rainfall (Ho, cited in Rahman, 1992). The climatic conditions

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TABLE1. INFRAREDEMrssrvrry ESTMATES USED color composite image as a vector overlay. The digitized pol- ygons were then rasterized, and the 3o-metre pixels were re- Forest (primary rain forest and high secondary forest) 0.98* to the emissivity value for the Water surfaces (mainly catchment reservoirs) 0.98 coded according (Table 1). Although the spa- Suburban areas (grass and dispersed residential areas) 0.95 corresponding land-cover class Urban areas (densely built sites) 0.92 tial reiolution of Landsat's thermal waveband is 120 metres, the data are replicated to give the same pixel size as the visi- (Compiled and interpolatedfrom Curran (t985), Nichol (f ss+), and ble wavebands [so m). The recoded layer representing emis- freld data) sivity could thus be ratioed on a pixel-by-pixel basis with *Curran gives a value of e : 0.99 for closed canopy forest.The pres- Apparent Temperature (To) (Nichol, 1994)1 to produce Ts as ent author found values of e : 0.97 for secondaryforest canopv in follows (Oke, rOBT): Singaporeusing radiancevalues ftom a Wahl Heat Spy radiometer and Tsvalues from a set of contactthermistors attached to ieaf sur- eoTsn:oTon (2) facesand a data logger.Thus, in the absenceof an accuratemap of forest type, the value s : 0.98 is used here to representforest (both where o is the Stefan Bolzmann's Constant''z primaryand secondary)in lhe studyarea. A range of Ts values for the study area, of between 19.5"C and e5.s"C. was obtained. Because the obiective was to estimate spatial tempera- of image acquisition suggest that soil moisture at the time ture structures, absolute temperatures were not required' and enough to explain some of the observed may have been low atmospheric correction was not carried out3. Therefore, as- temperature. spatial variations in canopy suming constant atmospheric conditions over the study area, relative temperature accuracy depends on the noise equiva- Leafand Air Temperatures lent temperature difference for TM6, which is 0'5'C (Wukelic In tropical rain forest, onlv 1 to 3 percent of solar radiation et o.1.,1989). reach;s the ground. The chnopy effectively regulates temper- atures within the forest, preventing extremes of heating and DataAnalysis cooling which would be disastrous to tropical rain forest spe- Tswas compared with other types of thematic data in a vec- cies which have evolved in a stable environment. By day, tor cIS by converting the Tv data to vector format. In order temperatures are highest where leaf area is greatest due to ra- to simplify the raster data for conversionto a polygon_cover- diative absorption (Oke, 19SZ). In mature tropical rain forests age,the image was subsampledby a factor of 4 in both the X where trees are virtually unbranched below the canopy, this and y directions to remove the pixel replication of tvto data, means that the highest leaf biomass, and thus the highest air and was smoothedusing a modal filter' After transformation temperatures, are at the top of the canopy. Air temperatures to the same coordinatesystem as other map digitized data, at other levels appear to be related to this, as shown by sev- the coveragewas synonymouswith an isotherm map, having eral investigators of tropical forest microclimate (Aoki ef o1., homogeneousacross each poly- 'l.g65i temperaturecharacteristics 1978; Baillie , 1974; Baynton et al., Shuttleworth ef o1., gon- (Figure3). 19841. Aoki et aI. (Ls78) found maximum air temperature Four individual polygon coverages,representing High mid-morning at the canopy (a7 m), but six metres above and Forest.Water (CatchmentReservoirs), Urban Areas, and Con- below it, temperatures were approximately 4"C lower and tours, were each overlaid with the temperaturedata in order gradually decreased to ground level. to produce attribute tables summarizing the thermal charac- Baynton et ol. (1965), working in Columbian rain forest, teristics of each thematic land-cover type. Modeling of given discovered a rapid downward heat flux diurnally as warming rangesof temperaturefor the different land characteristics of the canopy occurs after sunrise, with simultaneous air was accomplishedby querying acrossoverlays either in an temperature changes at all levels. interactive plotting mode or by downloading data to a Because relative humidity in the forest is also known to spreadsheetpackage for output in graphic format; for exam- follow the temperature curve (Shuttleworth, 1sB5), canopy p1e,Figure 4 gives the breakdown on an areal basis of forest, temperature would appear to be a useful indicator of forest microclimate. 'This correction is not equivalent to increasing the spatial resolution As well as indicating temperature and humidity condi- to 3o metres because Apparent Temperature represents an average tions within the forest, Ts is an important parameter in itself over a sround surface of 120 metres, However, there is an enhanced because it represents the actual temperatures of plants and spatialind spectral accuracy within each 120-m pixel. The_degree of animals at the surface, whereas air temperature is more con- enhance-eni depends on the relative amounts of each land-cover servatively behaved (Luvall and Holbo, 1991). type within each^pixel and the extent to which Ts is related to these (Nichol, 1s94). CalculationofSurface Tempetatute (Ts). ?Equation 2 is an approximate method in that it fails to take ac- The source of surface temperature data was a 24 May 1989 only count of the wavelength dependence of emissivity. However, at the Landsat TM image whose ihermal band at 10.4 to f Z.S pm wavelength of the sensor, this would account for only approximately (Figure has a spatial resolution of L20 metres 1). 0.3'C difference in Ts. Radiance values were converted to apparent temperature using a quadratic conversion (Malaret et 01., 1985). Emissiv- :rEstimation of the atmospheric effect was made from field data col- correction was canied out for the broad land-cover cate- ity lected over extensive areas of calm water in the Strait of Singapore (forest, gories only water, urban, and suburban) because and inland water bodies (e = 1.0 is assumed). In Singapore these are emissivity differences between different vegetation types at known to vary by less than l"C between anniversary dates. A differ- the wavelength of the sensor are negligible (Luvall and ence of 11"C between satellite derived and actual Sea Surface Tem- Holbo, 1989). The correction was done by screen digitizing perature is indicated. Values of Ts discussed and presented here are the distinct broad land-cover categories (Figure 2) on a false ihus thought to be on the order of 11'C below actual Ts.

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Cent.€l Catchment Anea COOLEST.BELOI,I 20.5" C I eerow ao.s o"q. ffi

ffi eo.s ro a:-o oeg MODERATE.20,5_20.9.C

E a:.r ro ae-s oes WARM.21"C 8 ABOVE ffi az.o ro ze-s oeg r

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I [] reovr :a.o oeq.

'T= l' ffitr q -\ l:+jt \ o !l ---1 NorlhA Figure Figure3. SurfaceTemperature polygons representing ar- 5. Foresttemperature extremes. Coolest and warmestareas correspond to 1 standarddeviation above eas in and aroundthe CentralCatchment Area. and belowmean temperature.

water. and urban temoeratures in the land-cover units corte- sponding to Figure 2,-and Figure 5 shows polygons repre- Resultsand Discussion A comparisonbetween Figures 2 and 3 indicates a close spa- senting forest temperature extremes (values of one standard tial correspondencebetween surfacetemperature and land- deviation above and below mean temperature). cover type. The dependenceof Ts on biomasswas testedby In order to visualize the forest canopy temperatures correlatingthe TM6 emissivity correctedimage data with a more effectively, a digital elevation model was created by vegetationindex image using a random sample of 2000 pix- digitizing map contours and spot heights, thus generating els excluding water surfaces(Figure 7)4.A Spearman'sRank further coverages representing slope and aspect. The eleva- Correlation Coefficientof o.z4 was obtained before em- tion data were compared with canopy temperatures in for- [0.64 issivity correction),suggesting a close,negative relationship ested areas by querying across vector GIS overlays between temperatureand biomass.Notably, the coolest areas corresponding to slope, aspect, and temperature in an inter- correspondto forest,with water bodies being slightly active plotting mode. This produced quantitative data on the warmer. Thesetwo land-covertypes comprise the majority of relation between cool and warm temperature polygons and Iand within the nature reservesboundary (Figure 2). their slope and aspect in relation to sun angle (Table 2). The Beneration of surfaces viewed from opposite angles with re- spect to solar azimuth at the time and date of image aquisi- Spatialand Topological Effects tion (58') permitted visualization of the relationships (Figure Figure 5 indicates a substantialinterior forest microclimate, 6). correspondingin all casesto mature secondaryand primary rain forest. These coolestareas are buffered in most instances by a broad belt of slightly warmer forest or water body. Cool interior forest polygons were surrounded by slightly warmer

700 forest polygons rather than non-forest,and this suggeststhe importance of the buffer for preservationof the forest micro- 600 climate and thus to the integrity of the primary rain forest ecosystem. 500 Topographically,the Central CatchmentArea is divided into northern and southern sectionsby the central lowland 400 containing the Pierce Reservoirs.Additionally, a combination

300 of reservoir and golf course developmenthas split the forest cover into these two sections,although the cooler tempera- 200 tures are maintained acrossthis lowland area due to the sim- ilarly cool temperatureof the water body. loo The loss of the cool forest microclimate generally in ar- +-]- kx 19.5 21.5 23.5 25.5 27.5 29.5 31.5 33.5 35.5 4TM2was used as the veeetation index because a closer relationship Temperature ("C! between this and biomaJs was observed than for the Normalized Dif- ference Vegetation Index. This is due to the latter's dependence on Figure4. Surfacetemperature by land-covertype. high soil rdflectance in visible wavelengths. Within the humid trop- ics, soil is rarely exposed, making the index less effective.

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TneLe2. OotvttsnnrAsPEcr oF Cool nno Wnnv PoLvcot\s (% AREA)

All slopes(>5% slope) CooIpolys Warm polys (Total NE facing (sunny) 4'l- 62 area, 8.82 km'z) SW facing (shady) 59 38 (Total area, 8.26 km'z) 100 100

Steepslopes (>25% slope) (Total 4.24 km'?) NE facing 31 JO area, SW facing 69 42 (Total area, 3.94 km'?) 100 100

NB. Tota} forestedarea, includingboth sloping and flat ground :24.76kmz

(Fig- eas to the south of the Pierce Reservoirs,appears to be due CatchmentArea by a narrow ridge of high temperature to the loss of the protective forest buffer - to golf coursesin ures 3 and B). Thii is severaldegrees higher than that of the the northeastand south, and to Ministry of Defenceinstalla- surrounding forest environment and is due to a 70-metre- tions around Upper Pierce Reservoirto the northwest - thus wide expreisway. Figure B shows that the emissivity-correc- creating an edge effect in most of this region. The warmer tion proiess both shirpens the edge definition spatially and, of temperaturedifference. Even such temperaturesdo not appear to be due to the lower maturity , incre'asesthe magnitude (and thus lower biomass)of the forest itself becausemuch of a narrow break in canopy may constitute a serious threat to this area resemblesprimary rain forest, containing many Dip- the forest microclimate becauseit createsan edge effect terocarp species. whereby warmer and drier air mal penetrateconsiderable Although the preservationof the cool forest microcli- distancesinto the forest.It is evident (Figure 6) that only the mate may depend on meso-scalefactors, i.e., the need for a steep southwest facing slope of the reservecorresponds to wide buffer of one kilometre or more, certain temperature the coolesttemPeratures. characteristicscan be detectedat the micro-scale.Small in- Figure 4 indicates that both forest and water p-ossessa tenuptions in the forest canopy can be detectedas points or similar-,narrow range of temperature,between 20"C and ridgei of higher temperature.For example, it is clear that mi- 23'C, with modal vilues at approximately 21'C' Urban areas, croclimatically, Bukit Timah Nature Reserveis distinctly on the other hand, exhibit a wider range of temperatures,be- separatedfrom the rest of the nature reservesin the Central tween 29oCand 35'C. Temperaturegradients correspond closely with the boundariesof urban areas(compare Figures z and 3), and those acrossa forest-urbanboundary may be very steep,such that the location of high forest' 70 metres acrossan expressway,appears to have little influence on temperaturei in the urban area.(In fact, Luvall ef 41.(1990) found the temperaturetransition between a burned areaand a tree island to be as small as 15 metres),The steepnessof temperaturegradients across land-cover boundaries is to be expectedin Singapore,as in the humid tropics generally, due to Iow wind speeds.

Topog3aphicEffects According to Equation 1, variations in net radiation (Qn) as' for examfle, du-eto topographic differences,could also ex- 'plain variationsin canopytemperature. Of a total of zs kmt of forestedarea' approximately two- thirds has a significant slope of more than 5 percent. One- third comprisesslopes over 25 percent, and this is approximitely equally divided between northeastfacing and southwestfaCing-(sunny and shady) aspects,respectively'-at the date and time of image aquisition. Table 2 examinesthe aspectdistribution of cool and warm polygons; those below ffi waru,above 21 c 2O.5'Cand above21'C. [1111]uooennre' 20.s-21 c The data suggestsome aspect-relatedinfluences on can- because69 pe-rcentof cool polygons.on S coot:berow 20.5 c opy temperatures, ste"epslopes (above25 percent slope) are southwest facing, and-only Sr percent faCethe sunny northeastaspect (see also Figure ti). R ii*ilut, though less marked, pattern is obtained Figure6. Forestcanopy temperature: southwest aspect wfien all slopes,including those below 25 percent, are also correspondingto 238o(opposite of solarazimuth at time considered.fhus, aspectmay be a significant factor among of imageaquisition). others such as relative position and forest structure which influence canopy temPerature'

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o. ooo *]'1

o c :E tro D G o o Norlh 0 o 'l o --l-'*/

65 R=0.74 N=1999 \, Figure7. Correlationbetween Vegetation Index (TM2) and {'tt''jarr

!\Jt i SurfaceTemperature. L''

^@ ffiNll'.-f"^l-^ The influence of aspectin relation to sun azimuth on the growth of tropical rain forest has not been documented,be- -SlY-facing causeaspect is mainly a diurnal (and not seasonal)influence - at low latitudes. In fact, the seasonalrange of temperature FORESTCAN0PY TEMPERATURE: cooiest areas < 20.5C and humidity at all levels in tropical rain forest is very small Figure9. Forestcanopy compared to the daily range.The results suggestthat aspect temperatureshowing aspect of coolestareas. does influence the daily march of temperaturewithin the for- est, and these aspect-reiateddiurnal ef?ectsmay have a signif- icant impact on forest composition and structure when aggregatedon an annual basis. be compensatedat the opposite time of year when solar azi- For example,the southwestfacing (shady) slope of Bukit muth is southward becausemonsoon weather with high Timah (Figure (foregroundJ) Nature Reserve 3 and Figure 6 is cloudinesspredominates at that time. below one standard deviation of mean temoeraturein soite During dry spells or when the forest is under stress,the of its peripherallocation with respect lh-e to interior areasof characteristicallycool and moist rain forest habitat may be forest, and cooler other parts than of the reserve.The cooler more stableon southwest facing slopes.In fact, the dominant temperatureof this slope, which is probably due to the tree in the reserve,Shorea curtsii, which prefers drv sites. morning lag in solar radiation of the canopy, is not likely to doesnot occur on this slooe.

SoilMoisturc Effects Two cool polygons of significant size, 69 and 59 ha., respec- tively, do not correspondto either interior forest or shady as- pect. These are both flat and low lying areas:a primary swamp forest at Nee Soon Swamp, and a late successionsec- ondary forest south of Pierce Reservoir(A on Figure 6). In the latter case,Ministry of Defenceinstallations have ,6 isolated - the site from continuouslv cool areasof forest and water body. Both these areascorrespond to marshy ground which P supplies residual soil moisture for free evapotranspiration from the forest canopy accompaniedby latent heai loss. E Conclusion Satellite derived estimatesof forest canopy temperaturesug- gest that the climate of interior locations in the forest may be cooler than that of peripheral regions,that aspect-related 60 120 1BO 240 J00 temperaturedifferences may be present in tropical rain for- Distonce (meiers) est, and that soil o Corected (3Om) + Uncmected (12Om) moisture availabilitv mav influence forest climate through increasingthe proportionof latent heat loss Figure8. Profileacross expressway showing efFect of from the forest canopy. pixelsize and emissivitycorrection. Although Singapore'sforested nature reservesare rela- tively small, little is yet known about their detailed struc-

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ture, composition, and regeneration status. Thus, although tures, thermal response numbers, and evapotranspiration using the study has identified three factors which appear to influ- an aircraft based thermal sensor, Piofogrommetfic Engineering & ence forest climate, their precise role and relative importance Remote Sen.sing,10(13):1 3s3-1a01. cannot be defined without also considering the influence of Luvall, f.C., and H.R. Holbo, 1991. Thermal remote sensing methods forest structure. Visual comparison with a preliminary map in landscape ecology, Quantitative Methods in Landscape Ecol- (M.G. and R.H. Gardner, editors), Springer-Verlag, of forest structure (Wong, 1993) suggests that, within closed ogy Turner New York, 386 p. canopy forest, forest structure appears to be less related to D. Fabian Lozano, P. Anuta, and C.D. canopy temperature than the three factors of aspect, soil Malaret, E., L.A. Bartolucci, McGillen, 1985. Thematic Mapper data quality anaiysis, Pllofo- moisture, and location. This accords with the findings of Lu- grammetric Engineeri ng & Remote Sensing, 51lS)t1,4O7-1416. vall et o1. [19S0), who found that in Costa Rican rain forest Nichol, 1994. A GIS based approach to microclimate monitoring structural characteristics, namely, basal area and density, t.8., in Singapore's high rise housing estates, Photogrammetric Engi- were less related to forest canopy thermal response than neering & Remote Sensing, 60(1O):1,225-1,232. were environmental factors. Oke, T.R., 1987. Boundary Layer Climotes, Second Edition, Methuen, Although a wide range of Ts values were observed across 435 p. different land-cover types, temperature differences within Rahman, A., 1992. Soils of Singapore, The Singapore Study: Physical forest were confined to a narrow ranse between 20 and 23'C Adjustments in a Changing Landscope (A. Gupta and J. Pitts, ed- such that values beyond one standar"ddeviation of mean itors), Singapore University Press, Singapore,423 p. (warmest temperature and coolest areas) may differ by less Richards, P.W., 1952. The Tropicol Rain Forest, Cambridge Univer- than 1'C. The fact that such small temperature differences sity Press,Cambridge, U.K., a50 p. appear to be significant with regard to environmental factors Sasaki, S., 1980. Storage and germination of Dipterocarp seeds,Mo- of slope, aspect, relative location, and soil moisture indicates laysian Forester, 43:290-308. the sensitivity of the forest microclimate. However, it also Shuttleworth, W., 1985. Daily variations of temperature and demonstrates the importance of utilizing accurate emissivity humidity within and above Amazonian forest, Weather, 4o:1o2- and atmospheric estimates if absolute quantitative analyses 108. of tropical rain forest climate are to be undertaken from sat- Shuttleworth, W., J.H.C.Gash, C.R. Loyd, C.J.Moore, f. Roberts, A.O. ellite olatforms. Marques Filho, G. Fisch, V.P. Silva Filho, M.N.C. Ribeiro, L.B. In view of the fragility of rain forest species in relation Molion, L.D.A. Sa, C.A. Nobre, O.M.R. Cabral, S.R. Patel, and to forest microclimate and also in the context of current fears f.C. Moraes, 198a. Eddy correlation measurements of energy par- of tropical rain forest destruction and global climate change, tition for Amazonian forcsI, Quorterly lournol of Royal Meteoro- "l satellite-based thermography accompanied by cts modeling I ogi co I So c i ety, 7 1.O:^l 43-1.'162. appears to offer a viable means of monitoring the rain forest Singapore Meteorological Service, 1,990.Monthly Abstract of Meteor- Singapore. environment and estimating spatial aspects of the forest en- ologicol Observations Including Upper Air Data, ergy budget in conjunction with ground-based surveys. Tamari, C., 1976. Phenology and Seed Storage Trials of Dipterccarps, Forest Research Institute Pamphlet No. 69, Forestry Department, Kuala Lumpur. Malaysia. Refelences Whitmore, T.C., 1S84. Tropical Roin Forests of the Far Eosf, Second Edition, Oxford Science Publications, U.K., 352p. Aoki, M., K. Yabuki, and H. Koyama, 1975. Micrometeorology and Wong, Y.K., 1993. ?he Forests and Tree Populations, Report of the assessment of primary production of a tropical rain forest in Nature Reserves Survey, Phase 1, Singapore National Parks West Malaysia, lournal of Agricultural Meteorology, 31(3):115- Singapore.216 p. L24. Board. Wukelic, G.E., D.E. Gibbons, L.M. Martucci, and H.P. Foote, 1989. Baillie, I.C., 1976. Further studies of drought in Sarawak, Singapore Radiometric calibration of LANDSAT Thematic Mapper thermal Iournal of Tropical Geography, 43:2O-29. band, Renrote Sen.srngof Environntent, 28:339-347. Baynton, H.W., H.L. Hamilton, P.E. Sherr, and J.J.B.Worth, 1965. 1 1993; revised and accepted 4 1994: revised 14 Temperature structure in and above tropical rain forest, Quor- {Received fuly 1994) terly lournal of Royal Mete orological Society, 91.:225-232. June Corlett, R.T., 1988. Bukit Timah; the history and significance of a small rain forest reserve, Environntental Conservation,1,5(1,):37- |anet Nichol 44. /anet Nichol is currently a Senior Lecturer in Curran, P., 1985. Principles of Remote Sensing, Longman, U.K.,282 the Division of Geography,Nanyang Technologi- p. cal University,Singapore. She has a background Hill, R.D., 1966. Micro-climatic observations at Bukit Timah Forest in RemoteSensing from the University of Colo- Reserve, Singapore, The Malayan Forester, 29(2):78-86. rado (M.A.) and Aston University'sRemote Luvall, J.C.,and H.R. Holbo, 1989. Measurenents of short term ther- Sensing Unit (Ph.D.). Subsequently, she spent six years as a mal responses of coniferous lbrest canopies using thermal university lecturer in Kano, northern Nigeria. As a biogeogra- scanner data, fiemole Sensing of Environment,2711-10. pher and environmentalist, she has carried out a range of Luvall, f.C., D. Liebermann, M. Liebermann, G.S. Hartshorn, and R. consultancy work, including fuel wood surveys in west Af- Peralta, 1990. Estimation of tropical rain forest canopy tempera- rica and coastal resource management in The Philippines.

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