Maine's Ecological Reserve system provides an important baseline for monitoring changes in ecosystem composition and function in a relatively unmanaged landscape setting. Ecological reserves are areas where timber harvesting and other forms of resource extraction are prohibited, and where natural disturbances may proceed without significant human influence. Since 2002, the Maine Natural Areas Program and The Nature Conservancy have been conducting a continuous forest inventory in Maine's ecological reserves and encouraging the use of inventory data in research projects.

With steep climatic gradients over short distances, montane ecosystems provide exceptional opportunities to study ecological responses to climate and other environmental changes. Here we present a summary and synthesis of 10 years of research on this theme in a protected area in southern Québec, Canada (Parc National du Mont Mégantic), with ecological conditions closely similar to the northern Appalachians. During the ∼150 years since European settlement, anthropogenic disturbance has reduced the abundance of certain taxa (e.g., Picea [spruce]), while favoring other taxa that thrive during succession (e.g., Betula [birch], Acer [maple]). In more recent decades, climate warming (∼0.21 °C per decade) appears to have prompted upward elevational range shifts for many plant species, although such responses lag behind changes in climate itself. Experimental studies with seeds and seedlings of Acer saccharum (Sugar Maple) suggest that upward range expansion might be constrained by non-climatic factors such as belowground properties and seed predators, while escape from insect herbivores might actually accelerate range expansion. Similar studies with understory plants have not revealed clear evidence of non-climatic constraints on range limits, although some preliminary data presented here suggest a possible role of a lack of microsites with rich, moist soil at high elevation. Current studies focus on the lower elevational range limits of species restricted to mountaintops, such as certain lichens. Vegetation and flowering phenology are also sensitive to climate, and we have found that earlier springs are associated with decreased potential gene flow across populations at different elevations; ongoing studies will determine how differential sensitivity of herbs vs. trees might influence the duration of a high light period in spring in the understory. Overall, we have found clear signals of plant responses to long-term anthropogenic disturbances and recent climatic warming, but considerable uncertainty remains about how climatic and non-climatic factors will interact to determine the future of this montane ecosystem.

New York's Adirondack alpine zone harbors many rare vascular plants threatened by climate change, atmospheric deposition, and damage from recreational use. Here, we report on the results of population monitoring at 6-year intervals of 15 alpine areas. We sampled 366, 360, and 369 randomly placed plots in 2006–2007, 2013, and 2018–2019, respectively. Ten species were found in at least 5% of the plots, with Trichophorum cespitosum (Deer's Hair Club Sedge; 60% of plots) and Huperzia appressa (Mountain Firmoss; 42%) most frequent. Of these 10 species, 5 showed significant increases in density over time and 3 had no significant change in density. The 5 species showing increases also had densities positively correlated with metrics of current or former physical disturbance, such as exposure to western slopes and proximity to hiking trails. These data suggest many rare alpine plants are maintaining population levels; environmental heterogeneity and hiker education in the alpine zone may be contributing to this pattern.

Research at sentinel research sites focuses on long-term ecological monitoring related to global environmental changes. Despite the value of sentinel research sites during the Anthropocene, the factors that drive their development, success, and sustainability are not clear. Here we study the history of Whiteface Mountain, NY—a sentinel research site in global environmental change research. We review the origins of Whiteface Mountain as a research site, its contributions to forest ecosystem science, and the factors that contributed to the location's development, success, and sustainability. We identified 6 key characteristics that contributed to the success of Whiteface Mountain as a sentinel research site: (a) accumulation of high-quality long-term data, (b) features representative of a broad area, (c) availability of appropriate infrastructure and staffing, (d) sustained governmental and community support, (e) active communication and outreach programs, and (f) dedicated leadership. These characteristics provide a roadmap for the successful development and sustainable operation of sentinel research sites in global environmental change research.

Climate change in mountains can vary with elevation, but there is a paucity of long-term climatological datasets for examination of elevational patterns. In the Northeast, there are 2 robust datasets from the highest peak, Mount Washington Summit and Pinkham Notch, NH. We examined trends for temperature, snow, and other derived climate indicators for the period of 1930s through 2018. Results reveal changing climate conditions, consistent in direction of change, including warming temperatures, changing winters, and extended growing seasons. Differences occur with weaker winter warming on the summit, and snow-related indicators providing unclear results for wind-influenced upper elevations. Recommendations for distributed monitoring, particularly for snow metrics, are encouraged for an improved understanding of the complex climate-change response on the mountains in the Northeast.

Understanding climate change and air pollution impacts on the northeastern region's restricted alpine ecosystems is complex. Reduced in size and spatial distribution post deglaciation, these alpine ecosystems survived the Hypsithermal warming period with less change than lower-elevation ecosystems. They are low for their latitude and below physiologically limited treeline. More-recent data support and expand on earlier researchers' hypotheses that wind and moisture, not temperature, explains the continued existence of alpine ecosystems in the Northeast. Shifts in species composition and abundance may occur, but frequency of free troposphere exposure, wind, clouds, and rime-icing events, and related topographic, aspect, and microhabitat may maintain resistance to major alpine-treeline ecotone boundary shifts in this century. Under scenarios assuming high levels of emission of greenhouse gases, future predictions become less clear.

Nature-based tourism is an important economic industry for Maine, with winter tourism especially vulnerable to climate change. Perceptions of risk due to climate change can influence stakeholder decisions to respond (adapt or mitigate) to climate change. We used phenomenology to study how nature-based tourism stakeholders perceive their risk to climate change and how they are responding. We conducted 20 semi-structured stakeholder interviews in Western Maine. We analyzed interviews using interpretive phenomenological analysis. A key theme was that of uncertainty of the causes of climate change, impacts to the region, and whether or not experienced environmental changes were related to climate change. Participants showed a need for information about climate change specific to the study region to facilitate the adoption of more strategies to bolster the adaptive capacity of the destination.

High-elevation habitats are a limited yet critical component of the northeastern landscape that provide important habitat and climate change adaptation values. This study examines the extent, conservation status, condition, and ecological values of high-elevation areas (defined as greater than 823 m [2700 ft] in elevation) in New England and New York. We identified a total of 765 distinct areas at least 4 ha (10 ac) in size. We assessed these areas for their level of conservation, the extent of development and recent timber harvesting, and 14 ecological values. We developed a quantitative scoring system that allowed us to rank areas for their conservation value and identify the most significant unconserved areas. While 86% of high-elevation land across the region has some form of conservation protection, significant areas remain unconserved, particularly in the Western Mountains region of Maine. We discuss the importance of additional high-elevation conservation to regional climate-change adaptation and the potential for mountains to serve as climate change refugia.

Permanent, fishless, alpine and subalpine ponds are extremely rare in New England, and amphibians occupying these ponds are unique bioindicators of environmental change because they are subject to different ecological pressures compared with lowland populations. Further, alpine and montane ecosystems are expected to undergo rapid change in the coming decades. Therefore, uncoupling the interacting effects of temperature, precipitation, and ice-out on breeding efforts may identify specific ecological mechanisms driving reproduction of amphibians. The reproductive phenology of amphibians in climatically extreme alpine environments in the eastern United States is historically under-reported and remains poorly understood. To evaluate the reproductive phenology of amphibians near the upper extreme of their vertical distribution in the White Mountains, NH, we digitally recorded amphibian calls between 2010 and 2020 at 3 permanent, fishless ponds: Hermit Lake (1180 m), Eagle Lake (1278 m), and Lakes of the Clouds (1546 m). Our study revealed dynamic changes in species assemblages and provides the first report of Hyla versicolor (Gray Tree Frog) in a subalpine context (at Hermit Lake). We analyzed the calling phenology of the earliest breeding North American anuran, Rana sylvatica (Wood Frog), and found differences in calling phenology among the 3 ponds and temporary changes in calling phenology correlated with interpolated daily weather parameters. We stress the need for further research to understand both short- and long-term, weather-driven reproductive dynamics in amphibian phenology in high mountains and their corresponding demographic effects.

Winters in northeastern North America have warmed faster than summers, with impacts on ecosystems and society. Global climate models (GCMs) indicate that winters will continue to warm and lose snow in the future, but uncertainty remains regarding the magnitude of warming. Here, we project future trends in winter indicators under lower and higher climate-warming scenarios based on emission levels across northeastern North America at a fine spatial scale (1/16°) relevant to climate-related decision making. Under both climate scenarios, winters continue to warm with coincident increases in days above freezing, decreases in days with snow cover, and fewer nights below freezing. Deep snowpacks become increasingly short-lived, decreasing from a historical baseline of 2 months of subnivium habitat to <1 month under the warmer, higher-emissions climate scenario. Warmer winter temperatures allow invasive pests such as Adelges tsugae (Hemlock Woolly Adelgid) and Dendroctonus frontalis (Southern Pine Beetle) to expand their range northward due to reduced overwinter mortality. The higher elevations remain more resilient to winter warming compared to more southerly and coastal regions. Decreases in natural snowpack and warmer temperatures point toward a need for adaptation and mitigation in the multi-million-dollar winter-recreation and forest-management economies.