Effects of topography and historical disturbance on canopy height structure of tropical forests in Menglun, Xishuangbanna, China.

With the combination of airborne Lidar and panchromatic images in 1981 and 2021, we investigated the canopy height structure of tropical forests in Menglun sub-reserve in the Xishuangbanna National Nature Reserve of Yunnan Province, and analyzed its relationship with environmental factors by using multiple regression tree (MRT) method. The results showed that forests in the Menglun sub-reserve could be clustered into seven types based on canopy height structures, with tropical rainforest, monsoon evergreen broad-leaved forest, secondary forest, and flood plain forest as the main types. The potential solar radiation, altitude, terrain profile curvature, slope and the brightness value of imageries in 1981 and 2021 were main factors that drove the classification. The tropical seasonal rainforest dominated by Pometia pinnata occupied the largest area in valley and low-land. The monsoon evergreen broad-leaved forest dominated by Castanopsis echinocarpa mainly distributed in the ridge and disturbed areas. The secondary forests had homogeneous canopy surface, which was significantly different from the primary forests. The activities of swidden agriculture about three decades ago had legacy impacts on the physiognomy of secondary forests.

Effects of tsaoko (Fructus tsaoko) cultivating on tree diversity and canopy structure in the habitats of eastern hoolock gibbon (Hoolock leuconedys).

In this study, the quadrat method was used to study the effects of tsaoko (Fructus tsaoko) plantation on tree diversity and canopy structure of two natural habitats of eastern hoolock gibbon (Hoolock leuconedys): Nankang (characterized by extensive tsaoko plantation) and Banchang (relatively well reserved and without tsaoko plantation). Totally, 102 tree species from 25 families and 16 woody liana species from 10 families were recorded in Nankang, whereas 108 tree species from 30 families and 17 woody liana species from 12 families were recorded in Banchang. Although the tree species between two habitats is different, both habitats are characterized by enriched food resources for eastern hoolock gibbons, sharing similar dominant plant families. Due to tsaoko plantation, tree density proportion and diversity of forest layerⅠ (>20 m) in Nankang were both significantly decreased, but the tree density of layerⅡ (10-20 m) increased. Likewise, in conjunction with these behavioral observations, we also address potential impacts of tsaoko plantation on the behavior of eastern hoolock gibbon.

Ranging behavior of eastern hoolock gibbon (Hoolock leuconedys) in a northern montane forest in Gaoligongshan, Yunnan, China.

Generally, food abundance and distribution exert important influence on primate ranging behavior. Hoolock gibbons (genus Hoolock) live in lowland and montane forests in India, Bangladesh, Myanmar and China. All information about hoolock gibbons comes from studies on western hoolock gibbons (Hoolock hoolock) living in lowland forest. Between August 2010 and September 2011, we studied the ranging behavior of one habituated group of eastern hoolock gibbon (H. leuconedys) living in a seasonal montane forest in Gaoligongshan, Yunnan, China. Results show that the study group did not increase foraging effort, calculated in this study as the daily path length, when fruit was less available. Instead, the gibbons fed more on leaves and decreased traveling to conserve energy. They relied heavily on a single food species in most study months which was patchily distributed within their total (14-month) home range, and during most months they used only a small portion of their total home range. In order to find enough food, the group shifted its monthly home range according to the seasonal availability of food species. To satisfy their annual food requirements, they occupied a total home range of 93 ha. The absence of neighboring groups of gibbons and the presence of tsaoko cardamom (Amomum tsaoko) plantations may also have influenced the ranging behavior of the group. Further long-term studies of neighboring groups living in intact forests are required to assess these effects.

Seasonal variation of diet and time budget of Eastern hoolock gibbons (Hoolock leuconedys) living in a northern montane forest.

Most gibbons dwell in the tropical forests of Southeastern Asia, but eastern hoolock gibbons (Hoolock leuconedys) survive in high montane forest ranging from 1,600 to 2,700 m a.s.l. in Gaoligongshan (>24°30'N), Yunnan, China. To assess the behavioral adaptations of hoolock gibbons to the montane forest, we related temperature and food availability within the habitat to the seasonal behavioral patterns of a family group and a solitary female between August 2010 and September 2011 in Nankang, Gaoligongshan National Nature Reserve. The maximum temperature was 29.2 °C and the minimum temperature was -0.3 °C during the period. The monthly mean temperature was <10 °C between December and February, making Nankang the coldest gibbon habitat reported so far. Nonfig fruit and fig availability declined to nearly zero in cold months. The family group increased resting and decreased travel and social behaviors when the monthly mean temperature was low. Compared with other gibbon populations, the hoolock gibbons spent proportionally less time feeding on figs and other fruit than other gibbon populations except Nomascus concolor and Symphalangus syndactylus. Only 36 species of plants provided nonfig fruit or figs, which is less than the number of fruit species consumed by any other gibbon population observed during a similar period of time (about 1 year). Hoolock gibbons shifted their diet to leaves and increased feeding time when fruit was not available. We conclude that diet flexibility and an energy-conserving strategy during the cold season when fruit is scarce have enabled the hoolock gibbons to survive in a northern montane forest.