Demographic responses of tree communities relative to recent environmental change in northeastern mountain forests
Recent environmental changes have been associated with plant species shifts in many ecosystems. Montane spruce-fir forests in the northeastern United States are expected to be vulnerable to rapid environmental changes. These forest communities are important sources of timber and support regionally unique species assemblages. Recent studies suggest that climatic changes are already affecting three foundational tree species of this region: sugar maple (Acer saccharum), red spruce (Picea rubens), and balsam fir (Abies balsamea). To determine spatial and temporal trends in climate and forest vegetation change we sampled 83 forest plots on 12 mountains in New York, Vermont, New Hampshire, and Maine. By linking regional climate trends with spatial climate data from our research sites we calculated potential elevational shifts in temperature envelopes during the last 50 years. We studied relative distributions of dominant tree species size classes along climatic (elevational) gradients to see if they suggest upslope shifts consistent with recent climate change. We hypothesized that smaller size classes of trees would be at relatively higher elevations compared to larger size classes suggesting an upslope shift.
We found that maximum and minimum annual average temperature envelopes may have shifted upslope by as much as 100 and 312 meters respectively over the last 50 years. However, vegetation surveys suggest that sugar maple and red spruce saplings are at relatively lower elevations than larger size classes (105 and 81 meters respectively). Balsam fir distributions appear stable across elevation gradients in the Northeast. Further examination of other environmental variables suggests that the increasing pH of rainwater and forest management history of low elevation sites may partially explain why some saplings are occupying lower elevations. Recent climatic change may not yet be able to overwhelm other important factors affecting trees species spatial distributions at these scales or distributional responses may lag behind changing climate. These results highlight the importance of considering multiple interacting factors in the face of ongoing climatic changes in the northeastern United States.
Mabadiliko ya idadi ya watu katika jamii za miti kuhusiana na mabadiliko ya hivi karibuni ya mazingira katika misitu ya milimani ya kaskazini mashariki Mabadiliko ya hivi karibuni ya mazingira yamehusishwa na mabadiliko ya spishi za mimea katika mifumo mingi ya ikolojia. Misitu ya miti ya spruce ya mlimani katika kaskazini-mashariki mwa Marekani inatarajiwa kuwa dhaifu kwa mabadiliko ya haraka ya mazingira. Jamii hizo za misitu ni vyanzo muhimu vya mbao na hutegemeza makundi ya spishi za kipekee za eneo hilo. Uchunguzi wa hivi karibuni unaonyesha kwamba mabadiliko ya hali ya hewa tayari yanaathiri aina tatu za miti ya msingi katika eneo hilo: maple ya sukari (Acer saccharum), spruce nyekundu (Picea rubens), na balsam fir (Abies balsamea). Ili kuamua mwenendo wa nafasi na muda katika mabadiliko ya hali ya hewa na mimea ya misitu, tulichukua sampuli za misitu 83 kwenye milima 12 huko New York, Vermont, New Hampshire na Maine. Kwa kuunganisha mwenendo wa hali ya hewa ya kikanda na data ya hali ya hewa ya nafasi kutoka kwa maeneo yetu ya utafiti, tulihesabu mabadiliko ya uwezekano wa mwinuko katika vifuniko vya joto katika miaka 50 iliyopita. "Tumechunguza usambazaji wa jamaa wa aina za miti inayoongoza ya ukubwa wa madarasa pamoja na gradients ya hali ya hewa (upande wa juu) ili kuona kama zinaonyesha mabadiliko ya mwinuko wa mwinuko unaopatana na mabadiliko ya hali ya hewa ya hivi karibuni. """ Kwa mfano, kuna uwezekano kwamba miti ya ukubwa mdogo itakuwa katika maeneo ya juu zaidi kuliko miti ya ukubwa mkubwa, na hivyo kuathiri ukuaji wa miti. "Kama ilivyoelezwa hapo juu, ""kiwango cha juu na cha chini cha joto la wastani wa kila mwaka inaweza kuwa imehama mwinuko kwa mita 100 na 312 kwa mtiririko huo katika miaka 50 iliyopita.""" Hata hivyo, uchunguzi wa mimea unaonyesha kwamba miti ya maple ya sukari na ya spruce nyekundu iko katika urefu wa chini kuliko makundi makubwa ya ukubwa (mita 105 na 81 kwa mtiririko huo). Usambazaji wa msonobari wa balsamu unaonekana kuwa thabiti katika mteremko wa urefu kaskazini mashariki. Uchunguzi zaidi wa vigezo vingine vya mazingira unaonyesha kuwa kuongezeka kwa pH ya maji ya mvua na historia ya usimamizi wa misitu ya maeneo ya chini ya urefu inaweza kuelezea kwa nini miche fulani inashikilia urefu wa chini. Mabadiliko ya hali ya hewa ya hivi karibuni yanaweza kuwa bado hayawezi kuzidisha mambo mengine muhimu yanayoathiri usambazaji wa nafasi ya spishi za miti katika mizani hii au majibu ya usambazaji yanaweza kushindwa na mabadiliko ya hali ya hewa. Matokeo haya yanaonyesha umuhimu wa kuzingatia mambo mengi yanayohusiana katika hali ya hewa ya kaskazini mashariki mwa Marekani.