How has human use of trees had both a positive and negative impact?

The humans have impacted the biodiversity in both positive and negative way. Due to urbanization, there is regular cutting down of trees which results in the decreased biodiversity and increased level of greenhouse gases due to deforestation. These are the negative impact of human use of trees.

The positive impact includes due to the cultivation of trees by the humans in order to harvest fruits, nuts and other products results in the increased in the population of these specific trees. The use of genetic engineering has also resulted in increased biodiversity of plant species.  

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.