Doctoral Dissertation Research: Engineering Effects of Scale Insects on Forest Dynamics in Fragmented Tropical Montane Oak Forests of Veracruz, Mexico

人类造成的景观变化，包括热带森林砍伐，可以引发复杂的退化过程。这项研究考察了热带森林的破碎化如何影响一种昆虫，对植物和动物以及当地人民的生计产生重大影响。墨西哥东北部的大片常绿山地橡树林已被转为放牧。如今的森林分布在零星的牧场和集约化的农业用地中。在这些森林中观察到的一种地方性蚧虫密度的增加被假设为这种人为破碎化的结果。在过去的几十年里，随着碎裂的进行，温度可能已经变暖，促进了这种昆虫的繁殖力和更高的侵染水平。这项研究考察了这些昆虫的丰度是否对它们赖以为生的树木的生长和繁殖产生了重大影响，从而对这些森林碎片的潜在再生产生了重大影响。树木年轮分析将用于重建森林破碎化和昆虫侵扰的时间，因为这些事件在树木年轮记录中留下了不同的模式。通过比较不同密度蚧虫的树木年轮生长和释放事件的时间，可以考察初始破碎化、虫害和森林更新潜力之间的协同作用。这种蚧虫还产蜜露，这是通常直接以植物花蜜为食的昆虫和鸟类的丰富碳水化合物来源。更丰富的蜜露可能会引起鸟类多样性的变化，以及吸引这种食物资源的其他昆虫的类型和数量的变化。鸟类和昆虫对蜜露含量高低的树木的调查将揭示碎片化如何对营养组织和生物多样性产生意想不到的工程效应。野外植被取样和卫星遥感将用于绘制单个森林斑块内和不同海拔和坡度的尺度虫害分布图。这将有助于深入了解当地森林斑块小气候和更大规模的气候控制如何影响昆虫密度和未来森林动态。本研究中的蚧虫可以被定义为一个生态系统工程师，一个创造、改变或维持栖息地的物种。这项研究从生态系统工程对平衡和可预测性的强调转向了一个为工程师提供非线性动力学和权衡的视角。如果破碎化催化了目前规模的虫害水平，如果虫害对森林恢复有害，那么森林状态可以被描述为一种“锁定”，即一旦破碎化开始，就会导致衰退。最近的研究表明，森林破碎化、干扰和物种相互作用之间的协同作用可能会放大破碎化的初始影响。因此，这项研究试图通过发展更多有关森林破碎化如何展开的背景和实地证据，为这些森林的可持续利用和保护提供信息。蜜露养蜂也将被引入到研究区域附近的一个社区。蚧虫的蜜露可用作蜜蜂的饲料。世界上一些最重要的蜂蜜（新西兰、德国）来自蚧虫。通过建立蜂箱，该项目还希望能激发人们对生计的兴趣，从而减少对放牧的依赖，放牧是造成森林破碎化的主要原因。

Landscape change caused by humans, including tropical deforestation, can set off complex degradation processes. This research examines how the fragmentation of a tropical forest can affect an insect, with significant consequences for the plants and animals, in addition to the livelihoods of local people. Large areas of evergreen montane oak forest in northeastern Mexico have been converted for grazing. Present-day forests reside in a patchy matrix of pasture and more intensive agricultural land uses. Observed increases in the densities of an endemic scale insect in these forests are hypothesized to be a consequence of this anthropogenic fragmentation. As fragmentation has proceeded over the past decades, temperatures may have warmed, promoting greater fecundity in this insect and higher infestation levels. This research examines whether greater abundances of these insects has had large impacts on the growth and reproduction of the trees upon which it feeds, and consequently, on the potential regeneration of these forest fragments. Tree ring analyses will be used to reconstruct the timing of forest fragmentation and insect infestation, given that these events leave distinct patterns in the tree ring record. By comparing the timing of tree ring growth and release events among trees with varying densities of scale insects, the synergisms among initial fragmentation, insect infestation, and the potential for forest regeneration can be examined. This scale insect also produces honeydew, a rich source of carbohydrates for insects and birds that might ordinarily feed directly on plant nectar. Greater abundances of honeydew may initiate changes in bird diversity and in the types and numbers of other insects attracted to this food resource. Avian and insect surveys on trees with high and low levels of honeydew will convey how fragmentation may also have an unanticipated engineering effect on trophic organization and biodiversity. Field vegetation sampling and satellite remote sensing will be used to map the distribution of scale insect infestation within individual forest patches and across different elevations and slope aspects. This will facilitate insight into how local forest patch microclimates and larger scale climatic controls shape insect densities and future forest dynamics.The scale insect in this study can be conceptualized as an ecosystem engineer, a species that creates, modifies or maintains habitats. This study steers away from ecosystem engineering's emphasis on balance and predictability toward a perspective that incorporates non-linear dynamics and tradeoffs for the engineer. If fragmentation has catalyzed current scale insect infestation levels, and if infestation is detrimental to forest recovery, forest state can be characterized as a "lock-in" whereby decline is canalized once fragmentation begins. Recent studies suggest that synergisms among forest fragmentation, disturbance, and species interactions may magnify the initial impacts of fragmentation. Thus this research seeks to inform the sustainable use and conservation of these forests by developing more contextual, field-based evidence of how forest fragmentation unfolds. Honeydew beekeeping will also be introduced to a community neighboring the study area. Honeydew from scale insects can be used as forage for honeybees. Some of the foremost honeys in the world (New Zealand, Germany) come from scale insects. By setting up a hive, this project also hopes to catalyze interest in a livelihood that could lessen dependence upon livestock grazing, the primary contributor to forest fragmentation.