نتایج جستجو برای: density of forbs

تعداد نتایج: 21193008  

2007
Elizabeth A. Allen Robert S. Nowak

As pinyon–juniper (specifically, Pinus monophylla and Juniperus osteosperma) woodlands in the western United States increase in distribution and density, understory growth declines and the occurrence of crown fires increases, leaving mountainsides open to both soil erosion and invasion by exotic species. We examined if the loss in understory cover that occurred with increasing tree cover was re...

2012
S. M. Kulpa E. A. Leger E. K. Espeland E. M. Goergen

As wildland fire frequency increases around the globe, a better understanding of the patterns of plant community recovery in burned landscapes is needed to improve rehabilitation efforts. We measured establishment of seeded species, colonization of Bromus tectorum and other nonnative annual plants, and recovery of nonseeded native species in topographically distinct areas within five fires that...

پایان نامه :دانشگاه تربیت معلم - تهران - دانشکده زبانهای خارجی 1386

چکیده ندارد.

2014
Philipp von Gillhaussen Uwe Rascher Nicolai D. Jablonowski Christine Plückers Carl Beierkuhnlein Vicky M. Temperton

Priority effects occur when species that arrive first in a habitat significantly affect the establishment, growth, or reproduction of species arriving later and thus affect functioning of communities. However, we know little about how the timing of arrival of functionally different species may alter structure and function during assembly. Even less is known about how plant density might interac...

Journal: :مرتع و آبخیزداری 0
سیده زهره میردیلمی شناخت مهم ترین تغییر در مؤلفه های کمّی و کیفی پوشش گیاهی بر اثر قرق مراتع دشت کالپوش با استفاده از آنالیز چندمتغیره اسماعیل شیدایی کرکج دانشجوی دکتری علوم مرتع، دانشگاه علوم کشاورزی و منابع طبیعی گرگان موسی اکبرلو دانشیار گروه مرتع داری دانشگاه علوم کشاورزی و منابع طبیعی گرگان

considering the importance of vegetation changes and awareness of its destruction or improvement trends in programming and its proper managing of utilization, this study was conducted in order to survey the effects of grazing on the qualitative and quantitative components of vegetation (including life form, growth form, palatability class, plant families and species diversity) and recognition t...

The study was conducted to determine the plants preference by goats grazing at Central Darfur State, Sudan in 2016. The objective was to identify desirable plants that would assist in range rehabilitation. Five mature female goats were used to determine diet selection using the bite count technique. The total number of bites from each plant species was recorded and the selected diet and prefere...

پایان نامه :0 1391

در این پژوهش به بررسی اثر افزایش ترافیک بر روی تعداد تصادفات پرداخته شده است. به این منظور 30 تقاطع در شهر تهران بطور تصادفی انتخاب گردید و تعداد تصادفات ماهیانه در این تقاطعات در طول سالهای 89-90 از سازمان کنترل ترافیک شهر تهران استخراج گردید و با استفاده از مدل داده های تابلویی و نرم افزار eviews مدل خطی و درجه دوم تخمین زده شد و در نهایت این نتیجه حاصل شد که تقاطعات پر ترافیک تر تعداد تصادفا...

2009
C. E. Sartor L. Marone

Annual forbs form short-term persistent soil seed banks whereas perennial grasses form mostly transient ones in the central Monte desert. A conceptual framework predicts that annual forb seeds will have primary dormancy, whereas perennial grasses will have low dormancy levels. We assessed whether the dormancy traits of four annual forb species and five perennial grass species can account for th...

1976
KAREN R. HICKMAN DAVID C. HARTNETT ROBERT C. COCHRAN CLENTON E. OWENSBY

A 6-year study was conducted in tallgrass prairie to assess the effects of grazing management (cattle stocking densities and grazing systems) on plant community composition and diversity. Treatments included sites grazed season-long (May to October) at 3 stocking densities (3.8, 2.8, and 1.8 hectares per animal unit), ungrazed control sites, and sites under a late-season rest rotation grazing s...

2012
Yingxin Huang Xueyong Zhao Daowei Zhou Hongxiang Zhang Wei Zheng

We compared the phenotypic plasticity of two early successional forbs of nutrient-poor mobile dunes (Agriophyllum squarrosum and Corispermum macrocarpum) and two later successional forbs (weeds) of stabilized, higher nutrient dunes and cropland (Chenopodium acuminatum and Salsola collina) to variations in environmental factors. A controlled (including soil nutrients, water, and population densi...

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