Leaf area index and net primary productivity along subtropical to alpine gradients in the Tibetan Plateau

Aim Our aims were to quantify climatic and soil controls on net primary productivity (NPP) and leaf area index (LAI) along subtropical to alpine gradients where the vegetation remains relatively undisturbed, and investigate whether NPP and LAI converge towards threshold‐like logistic patterns associated with climatic and soil variables that would help us to verify and parameterize process models for predicting future ecosystem behaviour under global environmental change. Location Field data were collected from 22 sites along the Tibetan Alpine Vegetation Transects (TAVT) during 1999–2000. The TAVT included the altitudinal transect on the eastern slope of the Gongga Mountains in the Eastern Tibetan Plateau, with altitudes from 1900 m to 3700 m, and the longitudinal‐latitudinal transect in the Central Tibetan Plateau, of approximately 1000 km length and 40 km width. Methods LAI was measured as the product of foliage biomass multiplied by the ratio of specific leaf area. NPP in forests and shrub communities was estimated as the sum of increases in standing crops of live vegetation using recent stem growth rate and leaf lifespan. NPP in grasslands was estimated from the above‐ground maximum live biomass. We measured the soil organic carbon (C) and total and available nitrogen (N) contents and their pool sizes by conventional methods. Mean temperatures for the year, January and July and annual precipitation were estimated from available meteorological stations by interpolation or simulation. The threshold‐like logistic function was used to model the relationships of LAI and NPP with climatic and soil variables. Results Geographically, NPP and LAI both significantly decreased with increasing latitude (P < 0.02), but increased with increasing longitude (P < 0.01). Altitudinal trends in NPP and LAI showed different patterns. NPP generally decreased with increasing altitude in a linear relationship (r² = 0.73, P < 0.001), whereas LAI showed a negative quadratic relationship with altitude (r² = 0.58, P < 0.001). Temperature and precipitation, singly or in combination, explained 60–68% of the NPP variation with logistic relationships, while the soil organic C and total N variables explained only 21–46% of the variation with simple linear regressions of log‐transformed data. LAI showed significant logistic relationships with both climatic and soil variables, but the data from alpine spruce‐fir sites diverged greatly from the modelled patterns associated with temperature and precipitation. Soil organic C storage had the strongest correlation with LAI (r² = 0.68, P < 0.001). Main conclusions In response to climatic gradients along the TAVT, LAI and NPP across diverse vegetation types converged towards threshold‐like logistic patterns consistent with the general distribution patterns of live biomass both above‐ground and below‐ground found in our earlier studies. Our analysis further revealed that climatic factors strongly limited the NPP variations along the TAVT because the precipitation gradient characterized not only the vegetation distribution but also the soil N conditions of the natural ecosystems. LAI generally increased with increasing precipitation and was well correlated with soil organic C and total N variables. The interaction between LAI growth and soil N availability would appear to have important implications for ecosystem structure and function of alpine spruce‐fir forests. Convergence towards logistic patterns in dry matter production of plants in the TAVT suggests that alpine plant growth would increase in a nonlinear response to global warming.     

Estimation of large herbivore densities in the tropical forests of southern India using distance sampling

Food habits of tigers Panthera tigris in terms of prey abundance were studied in the semi-arid deciduous forests of Ranthambhore National Park, western India, between November 2000 and April 2001. Wild prey availability was assessed by line transects ( n =8) and prey selection by the tigers was determined from analysis of scats ( n =109). Compared to some other parts of the country, prey abundance was found to be high at 96.65 animals km⁻². Chital Axis axis was the most abundant wild prey in the study area, followed by common langur Presbytis entellus , sambar Cervus unicolor , nilgai Boselaphus tragocamelus , wild pig Sus scrofa and chinkara Gazella bennetti. Chital ( c. 31%) and sambar ( c . 47%) constituted the bulk of the tigers' diet and were preferred prey. Nilgai and chinkara contributed minimally to the tigers' diet ( c . 5–7% and <1%, respectively) and were used less than their availability. Domestic livestock made up 10–12% of the tigers' diet. The average weight of an animal consumed was between 107 and 114 kg reflecting a preference for large prey. The analysis reveals that parts of Ranthambhore have high prey abundance, thus making it important for long-term tiger conservation. Despite the high prey abundance, tigers were still considerably dependent on domestic livestock, posing challenges for the park management to resolve potential areas of conflict.     

Estimating seasonal density of blue sheep (<Emphasis Type="Italic">Pseudois nayaur</Emphasis>) in the Helan Mountain region using distance sampling methods

The monitoring of animal populations is necessary to conserve and manage the rare or harvest species and to understand the population change over several years. We used distance sampling methods to estimate seasonal density of blue sheep in a 2,740 km² area of Helan Mountain region by walking along 32 transect lines from winter 2003 to autumn 2005. In all, 367–780 blue sheep were observed in 91–143 groups in the surveys during the seasons. Observed mean group size ranged from 3.42 to 8.35 individuals; encounter rate, the number of groups detected per kilometre, varied from 0.19 to 0.30 during the seasons. A hazard rate key function with cosine series expansion and a half-normal key function with either cosine or simple polynomial series expansion were the best fitting models based on the lowest value of Akaike’s information criterion (AIC). Density estimates varied between 3.627 sheep per square kilometre in spring 2004 and 4.635 per square kilometre in summer 2005. There were no detectable differences in estimated density among seasons (P = 0.887). The estimated density of blue sheep was negatively correlated with the total number of deaths (P < 0.05), number of sub-adult males’ deaths (P < 0.05), number of sub-adult females’ deaths (P < 0.05), and number of male lambs’ deaths (P < 0.05). We concluded that distance sampling surveys should be used to monitor long-term population trends to provide the best quantitative estimates of blue sheep populations in the Helan Mountains region.     

How Reliable are Density Estimates for Diurnal Primates?

Primate population assessments provide the basis for comparative studies and are necessary prerequisites in determining conservation status. The most widely used assessment method is line transect sampling, which generates systematic data quickly and comparatively inexpensively. In contrast, the presumably most reliable method is long-term monitoring of known groups, which is both slow and costly. To assess the reliability of various analytical methods, we compared group and population densities for white-handed gibbons (Hylobates lar carpenteri) and Phayre’s leaf monkeys (Trachypithecus phayrei crepusculus) derived from transect walks with those from long-term group follows at Phu Khieo Wildlife Sanctuary, Thailand. Our assistants and we regularly walked a 4-km transect over 30 mo (480 km total), resulting in 155 gibbon sightings and 125 leaf monkey sightings. We then estimated densities via 1) DISTANCE and 2) the Kelker method based on perpendicular distances (PD) or animal-to-observer distances (AOD). We compared the 3 estimates to values based on known home ranges (95% kernels), accounting for home range overlap, combined with group size data. Analyses of line transect data consistently overestimated group densities for both species, while underestimating group size for leaf monkeys. Quality of results varied according to the group size and spread of each species. However, we found, in accordance with previous studies, that values derived via AOD (or its derivations) matched most closely with population estimates based on home range data.     

Assessment of the woody vegetation of Ol Choro Oiroua, Masai Mara, Kenya

The woody vegetation of the Ol Choro Oiroua Wildlife Management and Conservation area was surveyed. The species present, their size and the vertical distribution of their canopy were recorded. These parameters were then used to determine the percentage cover of woody vegetation at different heights, and the potential productivity of the trees and shrubs in terms of the available browse material. The survey data were converted to Browse Tree Equivalents, Leaf Dry Mass and a Canopy Sub-habitat Index, using the Browse Estimate from the Canopy Volume (B ecvol ) program. These parameters were next used to assess and predict the potential production of available browse material. The assessment established permanent observation plots for browse productivity estimates, and to serve as a basis for monitoring the encroachment or decline of woody species in the region.     

Diverging shrub and tree growth from the Polar to the Mediterranean biomes across the European continent

Climate warming is expected to enhance productivity and growth of woody plants, particularly in temperature‐limited environments at the northernmost or uppermost limits of their distribution. However, this warming is spatially uneven and temporally variable, and the rise in temperatures differently affects biomes and growth forms. Here, applying a dendroecological approach with generalized additive mixed models, we analysed how the growth of shrubby junipers and coexisting trees (larch and pine species) responds to rising temperatures along a 5000‐km latitudinal range including sites from the Polar, Alpine to the Mediterranean biomes. We hypothesize that, being more coupled to ground microclimate, junipers will be less influenced by atmospheric conditions and will less respond to the post‐1950 climate warming than coexisting standing trees. Unexpectedly, shrub and tree growth forms revealed divergent growth trends in all the three biomes, with juniper performing better than trees at Mediterranean than at Polar and Alpine sites. The post‐1980s decline of tree growth in Mediterranean sites might be induced by drought stress amplified by climate warming and did not affect junipers. We conclude that different but coexisting long‐living growth forms can respond differently to the same climate factor and that, even in temperature‐limited area, other drivers like the duration of snow cover might locally play a fundamental role on woody plants growth across Europe.     

Monkey Abundance and Social Structure in Two High-Elevation Forest Reserves in the Udzungwa Mountains of Tanzania

The effects of human activity on population and social structure are a pantropical concern for primate conservation. We compare census data and social group counts from two forests in the Udzungwa Mountains, Tanzania. The main aim is to relate differences within and between the forests to current theory on the effect of human disturbance on primate abundance and group size. The survey reveals the presence of the restricted-range red colobus, Procolobus gordonorum, in New Dabaga/Ulangambi Forest Reserve (NDUFR). The primate community of NDUFR is impoverished compared to that in Ndundulu forest. Red colobus and black-and-white colobus (Colobus angolensis palliatus) abundance and group size are lowest in NDUFR. Fission-fusion of red colobus social groups may be occurring in previously logged areas of both forests. Our observations are consistent with current theory on the effect of habitat degradation and hunting on primates, but the relative effects of the 2 factors could not be differentiated. We pooled the results with previous data to show that abundance of red colobus in the Udzungwa Mountains is lowest at high elevations. Low red colobus group sizes appear to be related to human activity rather than elevation. Black-and-white colobus and Sykes monkeys (Cercopithecus mitis) show no relationship with elevation. Future studies will require more detailed information on vegetation, diet and ranging patterns to interpret fully intraspecific variation in population demography and social structure in the Udzungwa Mountains.     

Effects of an Experimental Increase of Temperature and Drought on the Photosynthetic Performance of Two Ericaceous Shrub Species Along a North–South European Gradient

Plant ecophysiological changes in response to climatic change may be different in northern and southern European countries because different abiotic factors constrain plant physiological activity. We studied the effects of experimental warming and drought on the photosynthetic performance of two ericaceous shrubs (Erica multiflora and Calluna vulgaris) along a European gradient of temperature and precipitation (UK, Denmark, The Netherlands, and Spain). At each site, a passive warming treatment was applied during the night throughout the whole year, whereas the drought treatment excluded rain events over 6–10 weeks during the growing season. We measured leaf gas exchange, chlorophyll a fluorescence, and leaf carbon isotope ratio (¹³C) during the growing seasons of 1999 and 2000. Leaf net photosynthetic rates clearly followed a gradient from northern to southern countries in agreement with the geographical gradient in water availability. Accordingly, there was a strong correlation between net photosynthetic rates and the accumulated rainfall over the growing season. Droughted plants showed lower leaf gas exchange rates than control plants in the four sites. Interestingly, although leaf photosynthetic rates decreased along the precipitation gradient and in response to drought treatment, droughted plants were able to maintain higher leaf photosynthetic rates than control plants in relation to the accumulated rainfall over the months previous to the measurements. Droughted plants also showed higher values of potential photochemical efficiency (F _v/F _m) in relation to controls, mainly at midday. The warming treatment did not affect significantly any of the studied instantaneous ecophysiological variables..