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，可能会引发复杂的退化过程。这项研究考察了热带森林的碎片化如何影响昆虫，对植物和动物以及当地人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改为放牧。今天的森林居住在牧场和更集约的农业土地利用的拼凑矩阵中。据推测，在这些森林中观察到的地方性介壳虫密度的增加是这种人为碎片化的结果。在过去的几十年里，随着碎片化的进行，气温可能已经变暖，促进了这种昆虫更多的繁殖力和更高的感染水平。这项研究调查了这些昆虫数量的增加是否对其赖以生存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巨大影响。年轮分析将用于重建森林碎片化和虫害发生的时间，因为这些事件在年轮记录中留下了不同的模式。通过比较不同密度的介壳虫树木的年轮生长和释放事件的时间，可以检验初始碎片化、虫害和森林更新潜力之间的协同作用。这种介壳虫还会产生蜜露，这是通常直接以植物花蜜为食的昆虫和鸟类的一种丰富的碳水化合物来源。更多的蜜露可能会引起鸟类多样性以及被这种食物来源吸引的其他昆虫的类型和数量的变化。对蜜露含量高和低的树木进行的鸟类和昆虫调查将表明，碎片化可能还会对营养组织和生物多样性产生意想不到的工程影响。将利用实地植被采样和卫星遥感绘制出不同海拔和坡度的不同林区内以及不同坡度的虫害分布图。这将有助于深入了解当地森林斑块的小气候和更大规模的气候控制如何影响昆虫密度和未来的森林动态。这项研究中的介壳虫可以被概念化为生态系统工程师，一种创造、修改或维护栖息地的物种。这项研究偏离了生态系统工程对平衡性和可预测性的强调，转向了一种结合了非线性动力学和工程师权衡的观点。如果碎片化催化了当前的害虫侵扰水平，并且如果侵染不利于森林恢复，森林状态可以被描述为“锁定”，一旦碎片化开始，衰退就被渠化了。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，这项研究试图通过开发更具背景的、基于实地的证据来揭示森林碎片化是如何展开的，从而为这些森林的可持续利用和保护提供信息。还将在研究区附近的一个社区推广蜜露养蜂。从介壳虫中提取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)来自介壳虫。通过建立一个蜂巢，该项目还希望促进人们对生计的兴趣，从而减少对牲畜放牧的依赖，牲畜放牧是森林碎片化的主要原因。

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.