Vegetation Patterns of a New England Sand Plain in Montague MA 1993-1995

For details on methods and results, please see the published paper (Motzkin, G., D. Foster, A. Allen, J. Harrod and R. D. Boone. 1996. Controlling site to evaluate history: vegetation patterns of a New England sand plain. Ecological Monographs 66: 345-365). The Abstract from the paper is reproduced below. "The widespread and long-lasting impact of human activity on natural eco-systems indicates that land-use history must be treated as an integral aspect of ecological study and a critical component of conservation planning. The New England landscape has undergone a complete transformation as forests were converted to agriculture in the 18th and 19th centuries followed by succession to woodland as a result of widespread agricultural abandonment. Despite the prevalence of human impacts, the effect and longevity of land-use practices on modern forest conditions are poorly understood. In the present study of pitch pine - scrub oak vegetation on a sand plain in the Connecticut Valley of Massachusetts, we address the following questions: (1) what is the relative importance of human and natural disturbance and environmental factors in controlling vegetation composition, structure, and landscape patterns; (2) what are the mechanisms underlying human impacts on vegetation, and what is the duration of these impacts; and (3) what are the implications of land-use history for the interpretation and conservation of these communities? Sand plain vegetation was selected for investigation because the homogeneity of site conditions facilitates the interpretation of land-use and natural disturbance impacts, and because the uncommon vegetation and constituent species are priorities for conservation efforts. "Paleoecological data suggest that pre-European fires were common on the study area, perhaps ignited by a large regional Indian population. The area was noted historically as an extensive pine plain and was used for wood products from the 18th to the mid-19th century. Eighty-two percent of the area was subsequently plowed for agriculture before being abandoned in the early 20th century. "Soil analyses confirm the homogeneity of site conditions and suggest that land uses (plowing, woodlot/pasture) were determined according to ownership pattern rather than site factors. Previously cultivated parcels have distinct Ap (plow horizons) 15 - 33 cm deep, whereas uncultivated parcels have A horizons 3 - 10 cm in depth. Soil physical and chemical characteristics are similar among land uses and modern vegetation types. "Aerial photographs document a dramatic transformation in plant cover over the last 50 yr. In 1939, the vegetation was grassland or shrub-heath (49%), open-canopy forest (29%), and scrub-oak shrublands (15%). In 1985, 73% of the study area was forested with pitch pine (40%), hardwood (12%), or mixed stands (21%), 9% was in open-canopy stands, and 3% was covered by grass or shrubs. "Vegetation/land-use relations are striking. Pitch pine occurs almost exclusively (97%) on former plowed sites, whereas scrub oak stands occur preferentially (89%) on sites that have not been plowed. Land use explains the greatest variation in modern vegetation as well as the distribution and abundance of many taxa. Fire has been common across the study area but has influenced vegetation largely within patterns resulting from prior land use. Land-use patterns and factors controlling vegetation composition and structure are broadly paralleled at similar sites elsewhere in the Connecticut Valley. "The study indicates that conservation biologists interested in preserving species, communities, and landscape patterns on sand plains in the northeastern United States need to incorporate a dynamic perspective of biological systems that includes the overriding impact of prior land use. In order to appreciate, study, and display these land-use and vegetation patterns it is essential to conserve the mosaic of assemblages and historical uses within a landscape setting."

有关研究方法与结果的详细信息，请参阅已发表的论文（Motzkin G、Foster D、Allen A、Harrod J、Boone R D，1996年。《调控生境以解析历史：新英格兰砂质平原的植被格局》，《生态学专论》（Ecological Monographs），66卷：345-365页）。

人类活动对自然生态系统的广泛且持久的影响表明，土地利用历史必须被视为生态学研究的核心组成部分，以及保护规划的关键要素。新英格兰地区的景观已发生彻底转变：18至19世纪，森林被开垦为农田，随后因农业活动大范围弃耕，植被经演替重新形成林地。尽管人类活动的影响无处不在，但土地利用方式对现代森林现状的作用及其持续时长，目前仍鲜有研究明晰。本研究针对马萨诸塞州（Massachusetts）康涅狄格河谷（Connecticut Valley）一处砂质平原上的脂松（pitch pine）-灌丛栎（scrub oak）植被展开，旨在解答以下问题：(1) 在调控植被组成、结构与景观格局的过程中，人类干扰、自然干扰与环境因素的相对重要性如何；(2) 人类活动影响植被的潜在机制是什么，以及这些影响的持续时长；(3) 土地利用历史对这类群落的解读与保护工作有何启示？

选择砂质平原植被作为研究对象，一是因为其生境条件具有同质性，便于解析土地利用与自然干扰的影响；二是因为该区域的特殊植被及其组成物种是保护工作的重点关注对象。

古生态学（paleoecological）数据显示，在欧洲殖民者到来之前，研究区域内野火频发，其火源可能源自当地大量的印第安原住民活动。历史上，该区域被称为广阔的松木平原，18世纪至19世纪中期被用于木材生产。随后，区域内82%的土地被开垦为农田，直至20世纪早期才被弃耕。

土壤分析证实了生境条件的同质性，同时表明土地利用方式（耕作、林地/牧场）由土地所有权格局决定，而非生境因素。此前被开垦的地块拥有厚度15-33厘米的典型Ap层（犁底层，Ap horizon），而未开垦地块的A层（A horizon）厚度仅为3-10厘米。不同土地利用方式与现代植被类型的土壤理化性质并无显著差异。

航空影像记录了过去50年间植被覆盖的剧烈变化：1939年，研究区域的植被类型为草地或灌丛荒原（49%）、疏林（29%）以及灌丛栎灌丛（15%）；到1985年，73%的区域为林地，其中脂松纯林占40%、硬阔林占12%、混交林占21%，9%为疏林，剩余3%为草地或灌丛。

植被与土地利用的关联特征十分显著。脂松几乎仅（97%）分布于此前被开垦的地块，而灌丛栎林则优先（89%）出现在未开垦的地块。土地利用方式是解释现代植被格局、以及多数类群分布与多度差异的最主要因素。尽管研究区域内野火频发，但其对植被的影响基本限定在前期土地利用所塑造的格局框架之内。康涅狄格河谷其他类似生境中，土地利用模式与调控植被组成及结构的因素，均与本研究区域大体一致。

本研究表明，若保护生物学家希望保护美国东北部砂质平原上的物种、群落与景观格局，就需要纳入生物系统的动态视角，其中需涵盖前期土地利用所产生的主导性影响。若要理解、研究并呈现这类土地利用与植被格局，就必须在景观尺度上保护群落组合与历史利用方式的镶嵌结构。