Long-term log decay experiments at the Andrews Experimental Forest, 1985 to 2185

These data are collected from six sites within the H. J. Experimental Forest and are part of a 200-year experiment on the decomposition of logs in a terrestrial environment. The taxa being examined in the experiment are Douglas-fir, western hemlock, western redcedar, and Pacific silver fir. The data start in 1985 and are periodically updated as samples are taken. The last collection of data is planned in 2185. Periodically logs are sampled by measuring their diameters and lengths as well as bark cover and the fraction of their length in contact with the ground. Cross-sections are removed with a chainsaw and dissected with a table saw or other means to determine the density of bark and wood samples. These samples systematically sample each cross-section and can be used to reconstruct the spatial pattern of decomposition. Subsamples are ground and nutrient concentrations are determined to calculate nutrient stores. Twenty one data tables are associated with this study. A general description of the logs (length, diameters, bark cover) is found in td01401 and can be used to estimate how the log has fragmented over time. The areal extent of tissue types (outer bark, inner bark, sapwood, and heartwood) and zones of rotten wood from cross-sections is documented in td01418 and td01419. The position of the pith in each cross-section, a useful indicator of volume loss, is documented in td01420. The density (dry mass/green volume) of samples is documented in td01403 and based on the weights of individual samples (td01404) as well as their dimensions (td01405). The arrangement of samples into transects (top to bottom, left to right) within the cross-sections is documented in td01406. To help explain why some samples may be more dense than others, the area of the sample cross-section covered by knots is documented in td01407 (knots are more decay resistant and of greater density than wood). The radial thickness of inner and outer bark of the undecayed logs is documented in td01409, and can be used to estimate the original thickness of these tissues once extensive decomposition occurs. Given that the outer bark can be quite irregular in shape, water displacement was used to determine the volume of this tissue; these data are documented in td01415. The location of the logs at the six sites is stored in td01413, with distances, slope, and bearing from a series of surveyed posts noted. The cell wall chemistry of samples has been analyzed using the proximate method described by Ryan et al. (td01408) and Van Soest (td01412). The number and type of insect galleries present on logs for the first three years is documented in td01410. The number and species of fungal sporocarps growing on logs in the autumn for the first eight years is documented in td01414. Concentrations of nutrient elements such as nitrogen, phosphorus, calcium, and potassium of dried, ground samples of inner and outer bark, sapwood, and heartwood, as well as fungal sporocarps and insects is stored in td01411. Parameters for regression models derived from these data that describe the temporal pattern of decomposition is stored in td01421.

本数据集采集自H.J.实验林（H. J. Experimental Forest）内的六个样地，属于一项为期200年的陆地环境原木分解实验的组成部分。本实验的研究对象为花旗松（Douglas-fir）、西部铁杉（western hemlock）、西部红雪松（western redcedar）以及太平洋银冷杉（Pacific silver fir）。

数据采集始于1985年，随样品采集工作定期更新，最后一次数据采集计划于2185年完成。研究人员定期对原木开展采样工作，测量其直径、长度、树皮覆盖度以及与地面接触的长度占比。使用链锯（chainsaw）截取原木横切面，再通过台锯（table saw）或其他方式对横切面进行拆解，以测定树皮与木材样品的密度。对每个横切面进行系统采样，所得数据可用于重构原木分解过程的空间格局。将子样品研磨后测定其养分浓度，进而计算养分储量。

本研究共关联21个数据表：
1. td01401记录了原木的基础信息（长度、直径、树皮覆盖度），可用于估算原木随时间的碎裂情况；
2. td01418与td01419记录了横切面中各类组织（外树皮、内树皮、边材、心材）的面积占比，以及腐木区域的分布情况；
3. td01420记录了每个横切面中髓心的位置，该指标可有效反映原木的体积损失程度；
4. td01403记录了样品的密度（干质量/鲜体积，dry mass/green volume），该数据基于单一样品的重量（td01404）及其尺寸（td01405）计算得到；
5. td01406记录了横切面内样品的布设方式（从上至下、从左至右）；
6. 为解释部分样品密度更高的原因，td01407记录了样品横切面中木节（knots）的覆盖面积——木节比普通木材更抗腐烂且密度更高；
7. td01409记录了未分解原木内、外树皮的径向厚度，可用于估算发生大规模分解后该类组织的原始厚度。鉴于外树皮形态极不规则，研究人员采用排水法（water displacement）测定该组织的体积，相关数据记录于td01415；
8. td01413存储了六个样地中原木的位置信息，同时记录了各原木与一系列测量标杆之间的距离、坡度与方位角；
9. 样品的细胞壁化学组成采用Ryan等人（td01408）与Van Soest（td01412）提出的近似分析法（proximate method）进行测定；
10. td01410记录了原木前三年出现的虫道（insect galleries）的数量与类型；
11. td01414记录了原木前八年秋季生长的真菌子实体（fungal sporocarps）的数量与物种信息；
12. td01411存储了烘干研磨后的内、外树皮，边材、心材，以及真菌子实体和昆虫样品中氮、磷、钙、钾等营养元素的浓度；
13. td01421存储了基于本数据集推导得到的回归模型参数，这些模型用于描述原木分解的时间动态格局。