疏剪真的有必要做嗎?? thinning pruning

Thinning pruning 翻譯為疏剪、打薄修剪等等

看到Urban Tree Foundation基金會這篇文章，看到心有戚戚焉~
以下重點整理~

疏剪是選擇性去除活枝來降低樹冠密度。在某些地區，疏剪是成熟樹木修剪最常使用的修剪方法。適當的打薄不會改變樹的整體大小，但讓樹冠變薄變輕、可以暫時讓風通過樹冠，減低風阻。並暫時增加地面的陽光穿透量。有時候，則是針對結構具有缺陷的枝條，降低末端的重量，減少折損的機會。圖片上左半部的樹冠便是經過疏剪處理。

習慣進行疏剪的樹木擁有者與管理者認為，這是應該做的，也許他們比較喜歡稀薄樹冠的外觀，或該地區傳統習慣如此。觀測上，與鮮少實施打薄修剪地區相比，因為暴風雨相關的折損量並沒有比較多。除了防颱之外，整棵樹的疏剪主要是一種美學實踐，只能維持很短的時間。

操作時，應該以結構修剪為第一優先，減少缺陷部位負荷。若行有餘力，還未超過最大修剪限制量，則可以繼續疏剪，修出漂亮美觀的樹型。

<疏剪注意事項>
不幸的是，許多人常在不必要時進行疏剪，或者誤解或不當疏剪。很少或甚至並未從樹梢的末端剪除，而從樹冠部內部去除分枝，這通常形成獅子尾巴(lion tail )、或過度修剪(overthinnig)，反而成為結構的弱點。

也許因為疏剪作業容易在地面上產生大堆的樹枝，感覺修剪人員有在做事，客戶比較願意付錢，因此造就了偏好大量修剪的風氣。
(小編 : 甚至聽說有市政府以修剪的枝條量作為計價酬勞@@)

http://treewalker-arborist.blogspot.tw/…/thinning-pruning.h…

資料來源: Urban Tree Foundation

http://www.urbantree.org/thinning.shtml

原文:

Thinning is the selective removal of live branches to reduce crown density. The center and left portion of the tree to the right has been thinned. Thinning, of various types, is the most commonly-practiced method of pruning on mature trees in some regions. Thinning allows wind to pass through or into the pruned section of the crown, which can temporarily improve durability in a storm or sunlight penetration to the ground. Perhaps the best use of crown thinning in the landscape is to reduce mechanical stress on selected limbs from gravity, wind, ice, or snow on branches with structural defects such as cracks, cavities, and hollows, and on codominant, overextended, or long branches. Click here to see the reponse to thinning.

Trees are thinned in many regions because tree owners and arborists believe this is what should be done to trees, or they like the appearance of a thinned crown, or it's a traditional method of pruning in the region. Regions of the world where thinning is rarely practiced do not appear to experience more storm-related tree damage than regions where thinning is common. Thinning is conducted on large or small trees for a number of other reasons. Although entire-tree thinning can be useful, structural pruning should be considered before the entire crown is thinned. In fact, structural pruning is probably the best way to thin. A practical approach would be to structurally prune to reduce defects, then thin to shape and balance to the desired crown aesthetics if maximum pruning dose has not been exceeded. Other than to avoid storm damage, entire-tree thinning of landscape trees is mostly an aesthetic practice that lasts only a short time.

Thinning removes branches from the end portion of limbs. Pruning cuts to thin the crown of a large tree typically range in size from one to four inches in diameter. For purposes of reducing damage from wind, cuts smaller than about one inch in diameter appears to be less effective. However, small cuts of one-quarter to one-half-inch in diameter can be used to thin small ornamental trees such as Japanese maple (Acer palmatum), crabapples (Malus spp.), and citrus (Citrus spp.) for aesthetics and other reasons. Proper thinning does not change the overall size of the tree.

Thinning precautions
Unfortunately, many people prune when it is not necessary, or they misapply or misunderstand thinning, and subscribe to the practice of only removing branches from the interior of the crown. This is often referred to as lions-tailing, overlifting, overthinning, stripping out the interior, or cleaning out. Little or nothing is removed from the ends of the limbs, and this is a mistake. Lions-tailing causes structural weakness. Maybe it is done because it is easy to generate large piles of brush on the ground. It sometimes seems like people that perform this are charging the unaware customer by the pound because of the enormous amount of brush on the ground.