Climatology and Ecology of /who/
/who/'s climate cause
/who/'s climate can be roughly divided into 2 major regions - Mediterranean climates (Csb specifically - this will be important later) in the south, and oceanic climates (Cfb) in the north. This is in part because /who/ is influenced by two different currents, originating from the drift (parallel to latitude) current that should reach shore around the southern /who/-/uuu/ border in its northernmost. Here, the current splits into two (as they tend to do) - a warm current going northward, and a cold current going southward. A major concept to note is that as a rule of thumb, warm currents bring warmth and moisture to the shore, while cold ones don't (thus making the shore drier). Another one is that the ocean moderates climate, which means land closer to the sea will have a more mild climate. In contrast, land further away has a more drastic temperature range - a concept known as continentality.
For the north, the warm temperate current results in a mild, wet climate across the year - warm summer (below 22°C on monthly average), mild winter (above freezing on monthly average), and always raining (including occasional storm and overcast summer day). This is further amplified by the /rrat/ highland to the east. You might know this as orographic lifting. Basically, (wet) wind cools down when travelling upward alongside mountain slopes, which reduces its ability to hold water, as such most of its moisture will be released in the form of rain and snow. As such, the oceanic half of /who/ will be fairly rainy most of the time.
The south, on the other hand, has the unusual weather pattern of dry summer and wet winter - see Geodiode's page for a more detailed explanation of its mechanism. As the dry season (low rainfall) coincides with the hot season (high water evaporation), this results in an exceedingly dry summer, which plays a major role in its biome.
In the more inland eastern highland, the increase in elevation and distance to the ocean can lead to a lower temperature, as well as a more drastic temperature range (see above for the cause), which might put the inland into the highland/cold variant of the two climate zones - humid continental climate (Df_) for the north, and dry-summer continental climate (Ds_) for the south.
/who/'s biome
In general, the biome of a given place (barring human intervention) is determined by a combination of temperature, precipitation (how much water reaches the land), and evapotranspiration ratio (how much of said water is lost before it can be absorbed by the ecosystem). Someone actually compiled these three factors into a single graph: Holdridge life zones system. In most cases of /vtwbg/, we won't have the exact numbers to determine the exact position of any given place, but the important part of the triangle is that it shows how the biome will change if you change one or more of the factors contributing to the biome.
For oceanic climate, the ample rainfall and mild weather mean evapotranspiration ratio will be low (<1), which when combined with the mild temperature range gives us moist forest, wet forest, and rainforest. All these three are considered temperate forests, with the rainforest belonging to its own subcategory of temperate rainforest (yes, it's a thing).
One thing to note about forests is that trees can be roughly divided into two sets of twos - broadleaf or conifers, and evergreen or deciduous. Broadleafs are more common in warm, wet climates and conifers cold, arid climates, while evergreens are more common in warm, wet climates and deciduous in cold, arid climates. For /who/'s oceanic climate, its forests will likely be a mixture of primarily deciduous broadleaf (evergreen broadleaf are most prominent in rainforest) and evergreen conifers (deciduous conifer is mostly limited to extremely cold climates, like subarctic bordering tundra climate), with the ratio dependent on local species distribution and temperature. For temperate rainforest, the additional moisture means "simpler" plants like mosses and ferns, as well as evergreen broadleafs, can thrive here, creating a noticeably different biome from the relatively dry temperate mixed forest.
For Mediterranean climate, /who/'s higher latitude means it is relatively cold and wet. This means the environment, while still too dry for most broadleafs, can still support the growth of evergreen conifer trees. Of course, the summer drought means they often take on additional adaptations to reduce water loss like waxy leaves, but contrary to the arid shrubland of Csa, Csb is home to temperate conifer forests, the most famous of which being the Northern California coastal forests, home to some of the tallest trees in the world.
One thing to note is that biomes, in particular forests, can maintain themselves to a certain degree. This means that in nature, they tend to be spread a bit further away from what their climate entails... which brings us to civilisation, fittingly enough. For better or worse, human civilisation has become a force of nature in itself, and its effect is the most noticeable when it comes to biomes. Trees, in addition to being useful material by themselves, also often grown in climates that happen to be suitable for other plants that are useful for humans. As such, many areas in oceanic climates have since been deforested for farmland, cities, and grazing grounds.