Pruning high-value Douglas-fir can reduce dwarf mistletoe severity and increase longevity in Central Oregon
Pruning high-value Douglas-fir can reduce dwarf mistletoe severity and increase longevity in Central Oregon
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DOI：
10.1016/j.foreco.2016.07.014
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发表时间：
2016-11
影响因子：
3.7
通讯作者：
H. Maffei;G. Filip;N. Grulke;B. Oblinger;E. Margolis;K. Chadwick
中科院分区：
文献类型：
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作者：
H. Maffei;G. Filip;N. Grulke;B. Oblinger;E. Margolis;K. Chadwick
中大型道格拉斯冷杉(Pseudotsuga menzieseiivar.)在14年的时间里，对被矮生槲寄生(Arceuthobium Doutarsii)轻至中度感染的门泽西(Menziesii)进行了分析，以评估机械修剪是否能在不显著影响树木活力的情况下根除槲寄生(或至少延缓严重感染的发生)，并由此推断出寿命。通过比较修剪后的树木(n=173)和未修剪的树木(n=555)：(1)修剪后14年无明显感染的树木的百分比，(2)修剪后14年的丛枝材积等级(BVR)，以及(3)修剪后14年后BVR的增加率，来评估修剪对槲寄生侵染严重程度的即刻和长期修剪效果。生命力/寿命(与未经修剪的树木相比)用6个指标进行评估：(1)树木存活率，(2)严重侵染的发展，(3)死顶的发展，(4)树轮宽度指数，(5)高分辨率多光谱图像的归一化差异植被指数(NDVI)，(6)活冠比(LCR)和生长量。在修剪后的14年里，24%的修剪后的树木仍然没有槲寄生。修剪最有可能成功地根除轻微感染树(BVR 1或2)上的槲寄生，而不会感染邻居。修剪显著降低了修剪后树木的平均BVR。然而，随后的平均强化速率(每十年1.3-1.5BVR)没有受到影响，这意味着一次修剪为∼提供了14年的感染水平进展的喘息时间。修剪后感染强度在显性和共显性树木上比在中间或受抑制的树木上慢。应在修剪后的14年内对通过修剪根除槲寄生的成功和后续修剪的必要性进行评估，以便开发出可检测的扫帚。根据六个指标，丛林扫帚的叶子对树木的长期生命力贡献很小，因为拆除似乎对可用于树木生长和维护的资源影响不大。在严重修剪的树木中，修剪后数年树轮宽度减小，但随后几年以较大的年轮宽度补偿。修剪树的NDVI和LCR增量均显著高于对照树，而严重侵染和/或枯梢的发生率显著高于对照树(5倍和3倍)。如果可能，应评估树木活力的多个指标。即使没有移除所有的槲寄生，修剪也是值得的，因为槲寄生的生长会延迟。去除扫帚的影响似乎很小，修剪后的树冠具有更大的NDVI值。
Mid- to very large-sized Douglas-fir (Pseudotsuga menzieseiivar. menziesii) that were lightly- to moderately-infected by dwarf mistletoe (Arceuthobium douglasii) were analyzed over a 14-year period to evaluate whether mechanical pruning could eradicate mistletoe (or at least delay the onset of severe infection) without significantly affecting tree vitality and by inference, longevity. Immediate and long-term pruning effects on mistletoe infection severity were assessed by comparing pruned trees (n= 173) to unpruned trees (n= 55) with respect to: (1) percentage of trees with no visible infections 14 years post-pruning, (2) Broom Volume Rating (BVR), and (3) rate of BVR increase 14 years post-pruning. Vitality/longevity (compared with unpruned trees) was assessed using six indicators: (1) tree survival, (2) the development of severe infections, (3) the development of dead tops, (4) tree-ring width indices, (5) Normalized Difference Vegetation Index (NDVI) from high-resolution multi-spectral imagery, and (6) live-crown ratio (LCR) and increment. Twenty-four percent of the pruned trees remained free of mistletoe 14 years post-pruning. Pruning is most likely to successfully eradicate mistletoe in lightly infected trees (BVR 1 or 2) without infected neighbors. Pruning significantly decreased mean BVR in the pruned versus the unpruned trees. However, the subsequent average rate of intensification (1.3–1.5 BVR per decade) was not affected, implying that a single pruning provides ∼14 years respite in the progression of infection levels. Post-pruning infection intensification was slower on dominant and co-dominants than on intermediate or suppressed trees. The success of mistletoe eradication via pruning and need for follow-up pruning should be evaluated no sooner than 14 years after pruning to allow for the development of detectable brooms. Based on six indicators, foliage from witches brooms contribute little to long-term tree vitality since removal appears to have little effect on resources available for tree growth and maintenance. In the severely pruned trees, tree-ring width was reduced for several years post-pruning, but then compensated with larger ring width in later years. Both NDVI and LCR increment were significantly higher for the pruned trees than the control trees, while the development of severe infections and/or dead tops was significantly (5× and 3×) higher for the controls. If possible, multiple indicators of tree vitality should be evaluated. Pruning can be worthwhile even if all the mistletoe is not removed, because mistletoe intensification is delayed. The impact of removing the brooms seems to be minimal, and post-pruning crowns had greater NDVI values.