The comparison of matched historical and repeat photograph pairs provides an important tool to assess historical trends in vegetation and landscape change. An analysis of repeat photographs is invaluable for ground-truthing and augmenting an understanding of trajectories of vegetation change derived from other methods such as aerial photographs, remote sensing and models. In this article, we comment on some of the methodological strengths as well as limitations associated with using historical photographs to understand vegetation change. Strengths include the long time period covered by some images and the level of detail contained in the photographs. Limitations relate to the patchy and potentially biased temporal and spatial coverage of a region. We suggest ways to overcome these limitations while also addressing the important issue of how best to interpret changes observed between two repeat photographs. We suggest that researchers should be open to a wide range of interpretations that may draw on climate models, ecological theory, other historical sources, and the evidence available in the images themselves. Historical photographs, where available, nevertheless provide an indispensable record of change in the landscape useful for anticipating future changes.

匹配的历史照片和重复照片对的比较提供了评估植被和景观变化的历史趋势的重要工具。重复照片的分析对于地面修真和增加对从其他方法（例如航空照片，遥感和模型）得出的植被变化轨迹的了解非常宝贵。在本文中，我们评论了一些方法上的优势以及与使用历史照片来了解植被变化相关的局限性。优势包括一些图像所覆盖的长时间以及照片中包含的细节水平。局限性涉及区域的斑驳且可能有偏差的时间和空间覆盖范围。我们提出了克服这些限制的方法，同时解决了如何最好地解释两次重复照片之间观察到的变化这一重要问题。我们建议研究人员应该对广泛的解释持开放态度，这些解释可以利用气候模型，生态理论，其他历史资料以及图像本身中可用的证据。尽管如此，历史照片仍然提供了不可或缺的景观变化记录，可用于预测未来的变化。