We sought to quantify changes in tree species composition, forest structure and aboveground forest biomass (AGB) over 76 years (1930-2006) in the deciduous Black Rock Forest in southeastern New York, USA. We used data from periodic forest inventories, published floras and a set of eight long-term plots, along with species-specific allometric equations to estimate AGB and carbon content. Between the early 1930s and 2000, three species were extirpated from the forest (American elm (Ulmus americana L.), paper birch (Betula papyrifera Marsh.) and black spruce (Picea mariana (nigra) (Mill.) BSP)) and seven species invaded the forest (non-natives tree-of-heaven (Ailanthus altissima (Mill.) Swingle) and white poplar (Populus alba L.) and native, generally southerly distributed, southern catalpa (Catalpa bignonioides Walt.), cockspur hawthorn (Crataegus crus-galli L.), red mulberry (Morus rubra L.), eastern cottonwood (Populus deltoides Bartr.) and slippery elm (Ulmus rubra Muhl.)). Forest canopy was dominated by red oak and chestnut oak, but the understory tree community changed substantially from mixed oak-maple to red maple-black birch. Density decreased from an average of 1500 to 735 trees ha(-1), whereas basal area doubled from less than 15 m(2) ha(-1) to almost 30 m(2) ha(-1) by 2000. Forest-wide mean AGB from inventory data increased from about 71 Mg ha(-1) in 1930 to about 145 Mg ha(-1) in 1985, and mean AGB on the long-term plots increased from 75 Mg ha(-1) in 1936 to 218 Mg ha(-1) in 1998. Over 76 years, red oak (Quercus rubra L.) canopy trees stored carbon at about twice the rate of similar-sized canopy trees of other species. However, there has been a significant loss of live tree biomass as a result of canopy tree mortality since 1999. Important constraints on long-term biomass increment have included insect outbreaks and droughts.
La reproduction et le taux de rcnouvellement des populations de phacochores ont eto otudics dans le pörimetre de lütte antitsetso de Nagupande (Rhodosie) et compares avcc d'autres observations effectuees en Afrique du Sud et avec cclles existant dans la litterature.A Nagupande le rut sc situe en mal et la mise-bas en octobrc ou novembre. L'allaitement du re 3 a 4 mois, mais n'a probablement qu'une importance rlduite apres les 8*9 premieres scmaines. La maturite sexuelle intervicnt a la fin de la premiere annce chez les fcmcllcs ct a la fin de la seconde chez les males. Le taux de fcconditc s'clcvait a Nagupande a 72 % des fcmcllcs adultcs ct la moyenne des jcuncs par portccs ctait dc 3,76. En tenant compte de ccs proportions et de la mortalite fcrtale on a pu calculer un potentiel rcproductif maximum a la conception de 316 jeuncs pour 100 femellcs adultes. Dans la memo region la mortalitc juvenile ctait de 70 a 80 % contrc plus dc 95 % pour une population en dcclin et moins de 60 % pour unc autre en pleine expansion.La relation entre la pcriode de reproduction ct le cycle des saisons cst examinee, ainsi que la signification de la maturation sexuelle plus lentc des males dans cette espcce monogame oü le nombre des femelles reproductriccs est equivalent ä celui des males feconds.
These three lakes of the Aare Valley in Switzerland have been subjected to increasingly intense fisheries exploitation in recent decades. Fishing intensities have been roughly comparable in the three lakes in any particular year. Attempts at introducing non-native species have been made in all lakes but none of the attempts have had appreciable effect. Nutrient loading, due to domestic wastes predominantly, has been much greater with the downstream Bielersee than the upper two lakes, and somewhat greater in the Thunersee than the highest lake, Brienzersee. But even the latter is now showing symptoms of nutrient stress, in that populations of indicator phytoplankters have recently erupted.Ecological effects ascribed to the fishery include a marked reduction in stocks of Arctic char due to angling and pelagic coregonines due to commercial gillnetting. The latter taxa have recently shown pronounced fluctuations in year-class abundance. An energetic hatchery program has mitigated exploitation effects to some extent.Total stocks of fishes have increased due to eutrophication with initial increases in all fish taxa, except perhaps Arctic char. The cyprinids, percids, and esocids have increased in the Bielersee to a far greater extent than the salmonids with a result that the latter are now contributing smaller proportions of the catches. The cyprinids have little economic value and their burgeoning stocks are creating ecological and economic problems in the Bielersee as well as many other Swiss lakes. The cyprinids apparently cannot be effectively controlled by piscivores such as esocids, even where the latter are assisted by a hatchery program.
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