Summer Vegetation Growth Research Articles

Spatiotemporal variations of vegetation cover on the Chinese Loess Plateau (1981–2006): Impacts of climate changes and human activities

Spatiotemporal variations of Chinese Loess Plateau vegetation cover during 1981-2006 have been investigated using GIMMS and SPOT VGT NDVI data and the cause of vegetation cover changes has been analyzed, considering the climate changes and human activities. Vegetation cover changes on the Loess Plateau have experienced four stages as follows: (1) vegetation cover showed a continued increasing phase during 1981-1989; (2) vegetation cover changes came into a relative steady phase with small fluctuations during 1990-1998; (3) vegetation cover declined rapidly during 1999-2001; and (4) vegetation cover increased rapidly during 2002-2006. The vegetation cover changes of the Loess Plateau show a notable spatial difference. The vegetation cover has obviously increased in the Inner Mongolia and Ningxia plain along the Yellow River and the ecological rehabilitated region of Ordos Plateau, however the vegetation cover evidently decreased in the hilly and gully areas of Loess Plateau, Liupan Mountains region and the northern hillside of Qinling Mountains. The response of NDVI to climate changes varied with different vegetation types. NDVI of sandy land vegetation, grassland and cultivated land show a significant increasing trend, but forest shows a decreasing trend. The results obtained in this study show that the spatiotemporal variations of vegetation cover are the outcome of climate changes and human activities. Temperature is a control factor of the seasonal change of vegetation growth. The increased temperature makes soil drier and unfavors vegetation growth in summer, but it favors vegetation growth in spring and autumn because of a longer growing period. There is a significant correlation between vegetation cover and precipitation and thus, the change in precipitation is an important factor for vegetation variation. The improved agricultural production has resulted in an increase of NDVI in the farmland, and the implementation of large-scale vegetation construction has led to some beneficial effect in ecology.

Why lemmings have indoor plumbing in summer

The faeces and urine of microtine rodents are visible in ultraviolet light, and diurnal raptors, such as European kestrels (Falco tinnunculus) and rough-legged buzzards (Buteo lagopus), have the ability to see in ultraviolet light. It has been reported that in Fennoscandia, these raptors use this ability to concentrate their hunting activity in spring on areas where microtines are abundant. We hypothesized that in arctic tundra areas in summer, intense avian predation pressure and short vegetation should select for microtine behaviour that would minimize their exposure to these raptors. We dug up 62 collared lemming (Dicrostonyx groenlandicus) burrows in the Canadian Arctic and all had underground latrines. Latrines are not hidden underground in winter, when lemmings live under the snow, build nests above ground, and defecate above ground, nor does this occur in microtine species living in temperate areas, where summer vegetation growth is greater. Thus, high predation risk may influence not only where prey forage but also where they defecate.

Relationship between climatic factors and the dry matter production of swards of different composition at two altitudes

AbstractThe growth of a timothy sward, a timothy/white clover mixture and a multi‐grass/white clover mixture were compared and related to climatic factors at two sites of different altitudes.Temperature and radiation had a greater effect on sward growth than did species composition or management. If the reproductive and vegetative growth periods were studied separately, then more than 90% of the variation in yield could be explained by temperature and radiation. During spring reproductive growth, yields per unit increment of temperature or radiation were 2–3 times higher than during summer vegetative growth. Spring growth was affected more by temperature than by radiation and the lower yields at the higher altitude were also related to lower temperatures.

Foraging dynamics of muskoxen in Peary Land, northern Greenland

Muskoxen Ovibos moschatus in northern Greenland (79‐83°N) are at the northern limit of their distribution and exist under seasonal extremes dominated by nearly 10 months of winter, much of which is without sunlight. The period of summer vegetative growth is less than two months. In the Kap København area (82°30′N), diversity of plant species is low (76 species of vascular plants) and forage biomass in major vegetation types in summer varies from over 40 g m‐2 in sedge‐dominated fens to ≤5 g m‐2 in polar barrens. Nonetheless, 90‐95% of the ice‐free area consists of barren ground or sparcely vegetated polar desert. During summer, muskoxen apparently foraged opportunistically to maximize intake, with sedges the major food item in fens while willows were the major dietary component when on willow‐dominated slopes. Quality of summer forage was high during its early phenological stages, with 21‐28% crude protein and 60‐75% in vitro digestibility. Microhistological analysis of winter feces indicated dominance by graminoids. Muskoxen spent > 50% of their daily activity feeding, which fits a cline of increasing feeding time with increasing latitude in summer. Increased feeding times at high latitudes appears to be a function of both reduced forage biomass and need to maximize forage intake during the brief summer period when forage quality is high. Movement rates in summer while foraging were inversely related to available forage biomass. Seasonal activity of muskoxen peaks during the rutting period (July‐September) and then declines gradually through early winter to a low in late winter (March‐April).