| Monsoon evergreen broad-leaved forest is a typical zonal vegetation in low subtropical China. It is rich in biodiversity and contains high productivity. Continuous gradient observation of the evergreen broad-leaved forest microclimate in Maofeng mountain had been running in 2010. At the same time, conventional meteorological observation was carrying out at an open area outside forest for contrast. Temporal and spatial variation of microclimate factors of the evergreen broad-leaved forest in Maofeng mountain was analyzed. Analysis of microclimate difference among inside and outside the forest and Guangzhou City was also contained in this paper.(1) Diurnal variation of air temperature showed cosine curves. Valley value appeared at 7:00 and 6:00 in the dry and the rainy season, respectively, and peak value appeared both at about 15:00. Mean air temperature in the dry season was lower than that in the rainy season, while diurnal coefficient of variation (CV) of air temperature in the dry season was greater than that in the rainy season. Monthly variation of daily mean air temperature showed normal distribution, and lowest in January highest in July and August. Air temperature in different spatial position referred to canopy had the following relation: above canopy > under canopy > within canopy. Air temperature within canopy was both 0.2℃lower than that above and under canopy in the dry season, 0.2℃and 0.1℃in the rainy season, respectively.(2) Diurnal variation of air relative humidity (RH) showed sine curves. Peak value appeared at 7:00 and 6:00 in the dry and the rainy season, respectively, and valley value appeared both at 15:00. RH mean in the dry season was less than that in the rainy season, while diurnal CV of RH in the dry season was greater than that in the rainy season. Mean RH were lowest in November and December and highest in April. RH in different spatial position referred to canopy had the following relation: within canopy > under canopy > above canopy, and diurnal CV above canopy was the maximum while under canopy was the minimum. Air relative humidity within canopy was 1.0% and 0.5% greater than that above canopy and under canopy in the dry season, respectively, 1.4% and 0.2% in the rainy season. (3) Diurnal variation of air vapor pressure showed cosine curves and W-shaped curves in the dry and the rainy season, respectively. Peak and valley value appeared at 7:00 and 16:00 in the dry season; peak value appeared at 6:00 and 19:00 and peak value appeared at 12:00 in the rainy season. Mean air vapor pressure in the dry season was lower than that in the rainy season, while diurnal CV in the dry season was greater than that in the rainy season. Monthly variation of air vapor pressure mean showed normal distribution, and lowest in December highest in July. Air vapor pressure in different spatial position referred to canopy had the following relation: under canopy > within canopy > above canopy, and diurnal CV above canopy was greater than that within and under canopy. Vapor pressure difference of different spatial position referred to canopy was infinitesimally small in the dry season, vapor pressure within canopy was 0.01kPa greater than that above canopy and 0.01kPa lower than that under canopy in the rainy season.(4) Air temperature inside forest was lower than that outside forest at day time and opposite at night which indicated that forest had the function lowering temperature at day time and heat preservation function at night. Monthly air temperature difference between inside and outside forest was low. Daily average air temperature inside forest was greater than that outside forest in the dry season and opposite in the rainy season. Air temperature difference between inside and outside at day time in the dry season was lower than that in the rainy season, and opposite at night. Urban heat island effect was significant in Guangzhou City, and annual average air temperature in Guangzhou City was 2.5℃higher than that in Maofeng mountain.(5) RH inside forest was greater than that outside forest at day time and opposite at night which indicated that forest had moisture preservation function at day time. Annual averaged RH inside forest was lower than that outside forest. Daily RH amplitude inside forest was less than that outside forest. Annual averaged RH in Guangzhou City was 5.47% lower than that in Maofeng mountain.(6) Diurnal variation of wind speed above canopy showed a wave-shaped curve, and U-shaped curves within and under canopy. Mean wind speed in the dry season was greater than that in the rainy season, while diurnal CV of wind speed in the dry season was less than that in the rainy season. Wind speed in different spatial position referred to canopy had the following relation: above canopy > within canopy > under canopy, and diurnal CV within canopy was the maximum. Monthly variation of wind speed in difference spatial position referred to canopy was different.(7) Diurnal variation of soil temperature at -5cm depth showed cosine curves, and there was no significant variation at -20cm or -40cm depth. Mean soil temperature in the dry season was lower than in that the rainy season, and opposite of diurnal CV. Soil temperature increased with the increment of depth in the dry season, and opposite in the rainy season. Monthly variation of soil temperature showed normal distribution, and lowest in January highest in July. Soil temperature outside forest was greater than that inside forest. Day by day variation of daily mean soil temperature difference inside forest was lower than that outside forest, especially at -5cm depth. Variation of soil temperature during first half of the year was greater than that during second half of the year, and opposite of mean.(8) Daily mean soil moisture content in the dry season was less than that in the rainy season. Daily mean at -15cm was less than that at -30cm in the dry season, and opposite in the rainy season. Diurnal variation of CV was in accordance with that of daily mean. Monthly variation of soil moisture content showed normal distribution, and lowest in November highest in June.(9) Air temperature, air relative humidity, soil temperature (at -5cm and -20cm depth) between inside (at 3m depth) and outside forest had significant linear regression relation.(10) Diurnal variation of global radiation (K↓), reflected radiation (K↑) and net radiation (Rn) can all be represented by single-peak curves. Atmospheric inverse-radiation (L↓) and forest long-wave radiation (L↑) showed cosine curves, effective long-wave radiation (Ln) undulated. Each gross radiation except Ln in the rainy season was greater than that in the dry season. Annual gross K↓of the evergreen broad-leaved forest in Maofeng Mountain was 4201.22 MJ?m-2, of which Rn, K↑and Ln accounted for 63%, 11%, and 26%, respectively. The ratio of each solar radiation components to K↓was Rn >> Ln > K↑in both the dry season and the rainy season. In the dry season the ratio of Rn to K↓was less than that in the rainy season while the ratio of K↑and Ln to K↓both showed an opposite seasonal pattern. Diurnal variation of the ratio of Rn to K↓showed an inverted U-shaped curve which was lower in the early morning and at dusk, higher during the daytime. And the ratio of K↑and Ln to K↓were both higher in the early morning and at dusk and lower during the daytime whose diurnal variation showed U-shaped curves. In 0.5h scale, there exists the best positive linear correlation between Rn and K↓.(11) Daily mean photosynthetically active radiation (PAR) above canopy (PARa) in the dry season was less than that in the rainy season, and PAR under canopy (PARb) showed an opposite seasonal pattern. CV of PARa was less than PARb in both the dry and the rainy season. Diurnal variation of PARa showed a typical single-peak curve, and that of PARb was similar but with a weak double-peak appearing at noon. Appearance of PAR transmissivity peak was in accordance with that of K↓on the whole, especially in the rainy season. Monthly variation of the ratio of PARb to PARa showed乀-shaped curve. PARa and PARb had significant linear regression relation on day scale. PARa and K↓had significant linear regression on day and month scale. Linear regression relation between PARb and K↓was only significant on day scale.(12) Amplitude of soil heat flux increased with the increment of soil depth. Diurnal variation of soil heat flux at -5cm and -10cm depth showed single-peak curves, and diurnal undulation of soil heat flux at -15cm and -20cm depth were very low. Soil heat flux at -5cm and -10cm depth was positive value which indicated the energy transmitted from air to soil in day time, and opposite at night. Diurnal CV of soil heat flux in the dry season was less than that in the rainy season, upper layer greater than lower layer. Soil was the heat source in the dry season and heat sink in the rainy season. The linear regression relation between soil heat flux at -5cm and Rn was significant on 0.5h scale.(13) Factor analysis result of meteorology factors demonstrated that the major factors dominating the forest ecological environment was heat factor, water factor and light factor. |
PDF Full Text Request