Question: When are maples usually tapped?
About the article "Maple syrup", section "Production".

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Maple syrup production is centred in northeastern North America; however, given the correct weather conditions, it can be made wherever suitable species of maple trees grow.
A maple syrup production farm is called a "sugarbush" or "sugarwood".
Sap is often boiled in a "sugar house" (also known as a "sugar shack," "sugar shanty," or "cabane à sucre"), a building louvered at the top to vent the steam from the boiling sap.
Maples are usually tapped beginning at 30 to 40 years of age.
Each tree can support between one and three taps, depending on its trunk diameter.
The average maple tree will produce of sap per season, up to per day.
This is roughly equal to 7% of its total sap.
Seasons last for four to eight weeks, depending on the weather.
During the day, starch stored in the roots for the winter rises through the trunk as sugary sap, allowing it to be tapped.
Sap is not tapped at night because the temperature drop inhibits sap flow, although taps are typically left in place overnight.
Some producers also tap in autumn, though this practice is less common than spring tapping.
Maples can continue to be tapped for sap until they are over 100 years old.
Located down the path from Maples Unit, Maples Showers are most frequently used by Maples and Mariners.
Six showers are located in Maples Showers with warm water. 
Sugar bush refers to a forest stand which is exploited for maple syrup.
The tree canopy is dominated by sugar maple or black maple.
Other tree species, if present, form only a small fraction of the total tree cover.
In the Canadian provinces of Ontario, Quebec and Nova Scotia, and in some New England states, many sugar bushes have a sugar shack where maple syrup can be bought or sampled.
The maples are tapped for their maple sap in early spring, whenever the weather has warmed so that day-time temperatures are above freezing — — while night-time temperatures remain below freezing.
Typically there will be snow cover on the ground during the tapping period.
The tapping period ends when the supply of maple sap ceases, as when night-time temperatures begin to be above freezing.
After the tapping period, some maple sugar bushes experience a profusion of spring wildflowers which take advantage of unobstructed sunlight before the maple leaves emerge.
In summer, a healthy maple sugar bush is luxuriant and shady.
Autumn leaves are colorful, especially on the sugar maples. 
Snakebark maples are maples belong to the taxonomic section "Acer" sect.
"Macrantha".
The section includes 18–21 species, and is restricted to eastern Asia (the eastern Himalaya east to Japan) with the exception of one species in eastern North America.
The various species of snakebark maples are most easily distinguished from other maples by their distinctive bark, smooth (at least on young trees), and usually patterned with vertical dark green to greenish-brown stripes alternating with stripes of light green, pinkish or white, sometimes with a bluish tone.
Other characters include stalked buds with just one pair of scales, and flowers on arching to pendulous racemes.
The samaras are small, and often numerous.
They are small deciduous trees, typically 5–15 m tall, rarely to 20 m tall, fast-growing when young but soon slowing down with age, and often short-lived; they typically occur as understorey trees in mountain forests, often along streamsides.
Species:  "Acer capillipes" - Kyushu Maple, Red Snakebark Maple  "Acer caudatifolium"  "Acer crataegifolium" - Hawthorn-leaf Maple  "Acer davidii" (syn.
"A. grosseri, A. hersii, A. laisuense") - Père David's Maple, Hers's Maple  "Acer forrestii"   "Acer laxiflorum"   "Acer maximowiczii" - Maximowicz's Snakebark Maple   "Acer metcalfii"   "Acer micranthum"   "Acer morifolium"   "Acer morrisonense" (syn.
"A. rubescens")  "Acer pectinatum" (syn.
"A. taronense")  "Acer pensylvanicum" - Striped Maple, the only non-Asian species  "Acer rufinerve" - Redvein Maple  "Acer sikkimense" (syn.
"A. hookeri")  "Acer tschonoskii" (syn.
"A. komarovii")  "Acer tegmentosum"   "Acer wardii"  Some have good fall color with tones of reds and orange, while others tend toward a pale yellow which is less impressive.
All are relatively hardy compared to many other species of maples, and many are widely cultivated as ornamental trees for their bark.
Several cultivars and hybrids have been developed in cultivation. 
In the lumber industry "Acer rubrum" is considered a soft maple.
The wood is close grained and as such it is similar to that of "A. saccharum", but its texture is softer, less dense, and has a poorer figure and machining qualities.
High grades of wood from the red maple can nonetheless be substituted for hard maple, particularly when it comes to making furniture.
As a soft maple, the wood tends to shrink more during the drying process than with the hard maples.
Red maple is also used for the production of maple syrup, though the hard maples "Acer saccharum" (sugar maple) and "Acer nigrum" (black maple) are more commonly utilized.
One study compared the sap and syrup from the sugar maple with those of the red maple, as well as those of the "Acer saccharinum" (silver maple), "Acer negundo" (boxelder), and "Acer platanoides" (Norway maple), and all were found to be equal in sweetness, flavor, and quality.
However, the buds of red maple and other soft maples emerge much earlier in the spring than the sugar maple, and after sprouting chemical makeup of the sap changes, imparting an undesirable flavor to the syrup.
This being the case, red maple can only be tapped for syrup before the buds emerge, making the season very short.
Red maple is a medium quality firewood, possessing lower heat energy, nominally 5.4 MJ/m³ (18.7 million BTU (mbtu) per cord), than other hardwoods such as Ash: 7 MJ/m³ (24 mbtu/cord), Oak: 7 MJ/m³ (24 mbtu/cord), or Birch: 5.8 MJ/m³ (20 mbtu/cord).
Red Maple make vibrant and colorful Bonsai, and have year around attractive features for display.