HAVO Montane Ohia Diameter and Cavity Data 2017

We quantified the availability of breeding habitat of the endangered Hawaii Akepa (Loxops coccineus). The species is thought to nest excusively in natural cavities within mature ohia (Metrosideros polymorpha) trees but birds commonly occur in short stature trees that presumably do not have any natural cavities because of their polyploidal (many-branched) structure. To test this hypothesis we searched for cavities in trees where akepa forage and we measured diameter of each stem of each tree examined. The habitat is in montane areas of Hawaii Volcanoes National Park on Mauna Loa volcano.We surveyed 57 plots, 49 in montane woodland and 8 in closed-canopy forest. Six tree cavities were detected in the 214 sampled trees: five cavities were found in 38 trees sampled in closed canopy forest (8.9/ha) and only one cavity was found in 176 trees sampled in montane woodland (0.29/ha). Tree diameters in the forest ranged from 10 cm to 128 cm diameter at breast height (DBH), while those in the woodland were much smaller ranging from 10 cm to a maximum DBH of 54 cm. Most trees in the closed-canopy forest were monopodial (87%, mean number of stems per tree = 1.16, SE = 0.07) with only five of the 38 trees having multiple stems at DBH height. In contrast, most trees in the woodland were sympodial (61%, mean number of stems per tree = 2.11, SE = 0.11) where 108 of the 176 trees had multiple stems. This data release includes two CSV files: the ohia measurements and locations.本研究量化了濒危物种夏威夷管舌雀（Hawaii Akepa，学名Loxops coccineus）的繁殖栖息地可获得性。该物种被认为仅在成熟奥希亚树（Metrosideros polymorpha）的天然树洞中筑巢，但观测到该鸟类常栖息于矮生树木中，这类树木因具有多分枝的结构，推测不存在天然树洞。为验证这一假说，我们在夏威夷管舌雀觅食的树木中搜寻树洞，并测量了每株被测树木所有茎干的直径。研究区域位于冒纳罗亚火山上的夏威夷火山国家公园山地生境中。我们共布设57个调查样地：49个位于山地疏林，8个位于郁闭林。在214株被测树木中共发现6处树洞：其中在郁闭林的38株被测树木中发现5处，密度为8.9处/公顷；山地疏林的176株被测树木中仅发现1处，密度为0.29处/公顷。郁闭林内树木的胸径（Diameter at Breast Height, DBH）范围为10 cm至128 cm，而山地疏林的树木胸径则小得多，范围为10 cm至最大54 cm。郁闭林中多数树木为单轴分枝（87%，单株平均茎干数=1.16，标准误SE=0.07），38株树木中仅5株在胸径高度处具有多茎干。与之相反，山地疏林中多数树木为合轴分枝（61%，单株平均茎干数=2.11，标准误SE=0.11），176株树木中有108株具有多茎干。本数据集包含两个CSV格式文件，分别为奥希亚树测量数据与样地位置数据。