Professor Howlick's questionnaire asked each student to name every other student with whom they had drank with during the past two months. Kerry Sobiski, his assistant, sent emails for the online survey to each person named by students in the first sample. The same question was asked in this online survey. Ms. Sobiski next sent emails for the online survey to everyone named as a drinking partner in the second sample and so on until she had emailed ten different waves of online surveys. She then drew up a list of all students who drank with anyone else who answered the online survey, and used it as a sample for a study on drinking networks on campus. What kind of sampling was Ms. Sobiski using?
A) snowball sampling
B) quota sampling
C) accidental sampling
D) cluster sampling

Snowball sampling

Explanation: Snowball sampling also called chain referral sampling occurs when a research participants request the assistance of other participants for a test or study. It is used where potential participants are hard to find. In snowball sampling a researcher picks the first few samples and either recruits them or asks them to recommend other subjects they know who fit the description of samples needed. This referral technique goes on and on, increasing the size of the respondent population like a snowball rolling down a hill until the researcher has sufficient data to analyze. It's called snowball sampling because once you have the ball rolling, it picks up more “snow” along the way and becomes larger and larger. As evident in the above question Kerry Sobiski employed the assistant of students to recommend other students they have drank with in the past two month, this assistant cascaded further until sufficient enough data was gardered. Without doubt this sampling method is the snowball sampling method.

the first one is d and the second a

clearcutting reproduces a new even-aged stand by completely removing the mature stand.

clearcutting as a silvicultural treatment has several characteristics:

it causes a sudden environmental change

it removes the seed source from the regeneration area

the configuration of the clearcut may affect seed dispersal

it begins a new rotation

it will eliminate some pests that require forest cover

overall, it temporarily removes the forest cover, transforming the forest community and environment.

clearcutting followed by artificial (seeded or planted) regeneration has several advantages:

we can avoid delay in restocking the site

we can introduce a selected species, seed source, and genotype

we can control arrangement and spacing

we can achieve uniformity in the new stand

we can overcome the problems associated with securing sufficient natural regeneration.

the shelterwood method involves the removal of most of the mature stand at the end of the rotation, but a portion of the mature stand is left standing.   the shelterwood method serves three basic purposes:

to prepare the stand for production of abundant seed

to modify the environment in a way that promotes germination and survival of the selected species

to build up the amount and size of advance regeneration to ensure the prompt restocking of the new stand following overstory removal.

the shelterwood method involves a sequence of 3 cuttings:

preparatory cuttings: make the seed trees more vigorous and set the stage for regeneration. see our thinning page for more information.

establishment/seed cuttings: open up enough vacant growing space to allow establishment of the new regeneration.

removal cuttings: uncover the new crop to allow it to fill the growing space.

the residual trees in the shelterwood must:

be sturdy and windfirm

be able to survive exposure

flower and reproduce seed

be the best trees of the mature stand

keep in mind that the shelter trees must not occupy the entire site.   a void must be created in order to make room for the new regeneration. the amount of shelter to leave will depend on the following factors:

species characteristics (seeding and shelter requirements)

the number of cuttings in the cutting sequence (1, 2, or 3)

landowner objectives

the size of the area to be regenerated

the final removal harvest level required to be profitable

the shelter must be removed before it impedes the growth of the new stand or threatens its survival.