Termite diversity is resilient to land-use change

Cocoa is an important crop for Ghana’s economy, contributing 25% of Gross Domestic Product (GDP). The crop, however, is mainly cultivated on forest-derived soils and is a major cause of land-use change. Termites are an important biological component of tropical ecosystems providing numerous ecosystem services. Previous studies have indicated that termites are sensitive to forest disturbance and decrease in richness and abundance across land-use intensification gradients, with consequences for the essential services that they provide. Native shade trees are often used to improve cocoa cultivation and may reduce the detrimental effects of land-use change on some aspects of biodiversity. The aim of this study was therefore to explore how termites respond to land-use change along a shade-tree gradient in Kakum National Park and surrounding cocoa farms in Ghana (from forest at 80% tree cover to cocoa with no shade cover, to the extreme of cultivated arable crop land). It was predicted that termite richness and abundance would decrease with decreasing shade cover, and with increasing distance from the forest edge. Thirty-four species from 29 genera were sampled, with Ancistrotermes crucifer being found in all the locations (47% of all encounters). Species richness and abundance differed marginally across the land-use gradient, as well as the distance from the forest edge, however, species richness did not show any significance with distance. All the same, termite communities were robust to the disturbance. Our findings suggest that though site influenced species richness and abundance, cocoa trees can play a crucial role in maintaining biodiversity and environmental quality in an agricultural landscape by providing a habitat for forest species that are not found in pastures or farm fields. However, we caution that the relatively low forest baseline of existing forest diversity may inflate the value of cocoa land, with those forests no longer representing undisturbed natural habitats: this highlights that shifting baselines may need to be accounted for when interpreting findings in the Anthropocene.

Methods
Termites were sampled along a single belt transect at each site using the standardized transect method as described by Jones and Eggleton (2000). Transects were 100 m long and 2 m wide, divided into 20 sections of 5 x 2 m each. Transects were geo-referenced, with GPS coordinates taken at the beginning and the end of each transect. One person-hour of sampling effort per section was used to search for and collect termites from the soil (12 pits of approximately 12 cm x 12 cm x 10 cm (depth) were dug per section), accumulations of litter and humus at the base of trees, the inside of dead wood, tree stumps, soil within and beneath very rotten logs, subterranean nests, mounds, runways on vegetation and arboreal nests up to a height of 2 m above ground level. Termites were searched for within each transect section, and samples were collected for each encounter and placed in separate vials. When possible, termite samples for each encounter consisted of two to three soldiers and five to seven workers: in total, seven to ten individuals. Termites were placed in vials filled with 70 @ ethanol and labelled according to the section of the transect they were collected.

可可（Cocoa）是加纳经济的重要支柱作物，贡献了该国国内生产总值（Gross Domestic Product，GDP）的25%。然而，该作物主要种植于森林衍生土壤之上，同时也是土地利用变化（land-use change）的主要诱因之一。
白蚁（Termite）是热带生态系统的重要生物组成部分，能够提供多种生态系统服务（ecosystem services）。既往研究表明，白蚁对森林干扰较为敏感，其物种丰富度（species richness）与多度（abundance）会随土地利用强度梯度提升而下降，进而影响其提供的关键生态系统服务。
本土遮荫树常被用于改善可可种植条件，可缓解土地利用变化对生物多样性部分维度的不利影响。
因此，本研究旨在探究加纳卡库姆国家公园（Kakum National Park）及其周边可可农场的遮荫树梯度（shade-tree gradient）下，白蚁对土地利用变化的响应模式，覆盖范围从80%树木覆盖率的森林，到无遮荫的可可种植园，乃至极端的耕地。研究假设：随着遮荫覆盖率降低、距林缘（forest edge）距离增加，白蚁的物种丰富度与多度均会下降。
本次研究共采集到隶属于29个属的34个物种，其中十字拱白蚁（Ancistrotermes crucifer）在所有样点均有发现，占总遇见次数的47%。尽管物种丰富度与多度在土地利用梯度及距林缘距离上仅存在微弱差异，且物种丰富度与距离并无显著相关性，但总体而言，白蚁群落对干扰具备较强的耐受性。
本研究结果表明，尽管样地条件会影响物种丰富度与多度，但可可树可通过为牧场或农田中不存在的森林物种提供栖息地，在农业景观中维持生物多样性与环境质量方面发挥关键作用。不过，我们需注意：现有森林的多样性本底值相对较低，可能会高估可可种植地的生态价值，而这些森林已不再属于未受干扰的自然栖息地——这凸显出在人类世（Anthropocene）解读研究结果时，需考虑基线偏移（shifting baselines）的影响。

方法
本研究采用Jones与Eggleton（2000）描述的标准化样带法（standardized transect method），在每个样地沿单一带状样带（belt transect）开展白蚁采样。样带长100米、宽2米，被划分为20个5×2米的样段。所有样带均进行地理标记，在每个样带的起点与终点记录全球定位系统（Global Positioning System，GPS）坐标。每个样段投入1人·小时的采样工作量，搜索并采集土壤（每个样段挖掘约12个尺寸为12cm×12cm×10cm（深度）的土坑）、树木基部的枯落物与腐殖质堆积处、枯木内部、树桩、高度腐烂原木内部及下方土壤、地下巢穴、蚁丘、植被上的蚁道以及距地面最高2米的树栖巢穴（arboreal nests）中的白蚁。在每个样带样段内开展白蚁搜索，对每一次遇见的白蚁样本单独分装至样品瓶中。若条件允许，每份样本采集2至3头兵蚁与5至7头工蚁，总计7至10头个体。将白蚁置于装有70%乙醇的样品瓶中，并根据其采集所在的样带样段进行标记。